International Journal o f
Extracellular Vesicles Tune the Immune System in Renal
Disease: A Focus on Systemic Lupus Erythematosus,
Antiphospholipid Syndrome, Thrombotic Microangiopathy
Martina Mazzariol, Giovanni Camussi and Maria Felice Brizzi *
Citation: Mazzariol, M.; Camussi, G.;
Brizzi, M.F. Extracellular Vesicles
Tune the Immune System in Renal
Disease: A Focus on Systemic Lupus
Microangiopathy and ANCAVasculitis.
Int. J. Mol. Sci. 2021, 22,
Academic Editor: Leonora Balaj
Received: 29 March 2021
Accepted: 16 April 2021
Published: 18 April 2021
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Department of Medical Sciences, University of Turin, Corso Dogliotti 14, 10126 Turin, Italy;
email@example.com (M.M.); firstname.lastname@example.org (G.C.)
- Correspondence: email@example.com; Tel.: +39-01-1670-6653
Abstract: Extracellular vesicles (EV) are microparticles released in biological fluids by different cell
types, both in physiological and pathological conditions. Owing to their ability to carry and transfer
biomolecules, EV are mediators of cell-to-cell communication and are involved in the pathogenesis
of several diseases. The ability of EV to modulate the immune system, the coagulation cascade, the
angiogenetic process, and to drive endothelial dysfunction plays a crucial role in the pathophysiology
of both autoimmune and renal diseases. Recent studies have demonstrated the involvement of
EV in the control of renal homeostasis by acting as intercellular signaling molecules, mediators
of inflammation and tissue regeneration. Moreover, circulating EV and urinary EV secreted by
renal cells have been investigated as potential early biomarkers of renal injury. In the present
review, we discuss the recent findings on the involvement of EV in autoimmunity and in renal
intercellular communication. We focused on EV-mediated interaction between the immune system
and the kidney in autoimmune diseases displaying common renal damage, such as antiphospholipid
syndrome, systemic lupus erythematosus, thrombotic microangiopathy, and vasculitis. Although
further studies are needed to extend our knowledge on EV in renal pathology, a deeper investigation
of the impact of EV in kidney autoimmune diseases may also provide insight into renal biological
processes. Furthermore, EV may represent promising biomarkers of renal diseases with potential
future applications as diagnostic and therapeutic tools.
Keywords: renal disease; autoimmune diseases; HUS; TTP; APS; antiphospholipid syndrome; vasculitis;
systemic lupus erythematosus; lupus nephritis; pathogenesis; microparticles; extracellular
vesicles; microvesicles; exosomes
Extracellular vesicles (EV) are extracellular structures bounded by a phospholipid
bilayer and released by different cell types in biological fluids (blood, urine, synovial
fluids) through various mechanisms. First described as “platelet dust” by Peter Wolf
in 1967, in recent years EV have gained interest as a commonly recognized important
player in cell-to-cell communication, both in physiological and pathological conditions.
This depends on their ability to transfer their cargo, consisting of proteins, lipids, or
nucleic acids. Interestingly, EV have a role in different biological processes including cell
proliferation and differentiation, inflammation, immune signaling, angiogenesis, and stress
responses . In this review, we will summarize the most recent data on EV biological
features and their pathogenic role in immune-associated renal disease, and their potential
use as disease biomarkers.
Int. J. Mol. Sci. 2021, 22, 4194. https://doi.org/10.3390/ijms22084194 https://www.mdpi.com/journal/ijms
Int. J. Mol. Sci. 2021, 22, 4194 2 of 20
1.1. EV Nomenclature
The most recently updated guidelines of the International Society for Extracellular
Vesicles (ISEV) recommend using the term “extracellular vesicles” as “the generic term for
particles naturally released from the cell that are delimited by a lipid bilayer and cannot
replicate” . EV were historically classified into three main subtypes according to their
size, biogenesis and biological features: exosomes (the smallest EV generated from the
invagination of the endosomal membrane) , microvesicles (or EV which are directly
released from the plasma membrane)  and apoptotic bodies (the largest EV released by
apoptotic cells) . However, since a consensus has not yet emerged on specific markers
defining each subtype, the ISEV guidelines recommend defining EV according to :
physical characteristics such as size (small EV and medium/large EV, with ranges
defined, for instance, respectively, <100 nm or <200 nm (small), or >200 nm (large
and/or medium)) or density (low, middle, high);
biochemical composition (CD63+/CD81+ EV, Annexin A5-stained EV, etc.);
descriptions of conditions or cell of origin (podocyte EV, hypoxic EV, large oncosomes,
apoptotic bodies) .
1.2. EV Isolation and Detection
EV can be detected in almost all human fluids (blood samples, cerebrospinal fluid,
synovial fluid, urine, bile, saliva, bronchoalveolar fluid) using different techniques depending
on the EV population. In the pre-analytical phase, body sample collection, handling,
and storage may impact EV concentration, composition, and function. Thus, to follow a
preanalytical protocol tailored to the specific body fluid, the cell of origin of EV is crucial .
After collection and isolation, EV can be analyzed through various methods. The most
commonly exploited and recommended are the following:
flow cytometry which detects EV passing through a laser beam. Modern flow cytometers
may have many lasers and fluorescence detectors, which allow to label them with
multiple conjugated antibodies using the same sample. Although widely used, the
analysis using flow cytometry has limitations in detecting the smallest EV whose number
and surface expression may be underestimated . To circumvent this limitation,
an alternative bead-based technique has been developed using specifically activated
beads that capture EV with a cocktail of different exosome marker epitopes allowing
subsequent simultaneous detection of multiple antigens ;
nanoparticle tracking analysis (NTA) which visualizes EV in the liquid phase by
light scattering using a light microscope. A video is taken and the NTA software
tracks the Brownian motion of individual vesicles and calculates their size and total
concentration. NTA with fluorescent mode detects labeled vesicles and provides
quantitative and qualitative analysis. NTA can detect vesicles smaller than those
distinguished by conventional flow cytometry .
1.3. EV and Cell-to-Cell Communication
EV are shed into the extracellular environment under physiological and pathological
conditions, and their release is increased by cellular stress conditions as inflammation,
hypoxia, oxidative stress or infections . Once released into the circulation, EV have a
half-life ranging from a few minutes to a few hours, during which they can be taken up
from cells by different mechanisms such as endocytosis or fusion with the membrane of the
recipient cell . Circulating EV mainly originate from platelets, erythrocytes, leukocytes,
and endothelial cells; while urinary EV mainly derive from podocytes, tubular cells, and
epithelial cells . EV may transfer to the target cell receptors, allowing cell signaling
in cells that are originally devoid of receptors or by enhancing their number. Moreover,
EV may release or transfer proteins as cytokines and growth factors translating in the
modulation of target cells and their extracellular environment. Furthermore, EV may
transfer messenger RNAs (mRNAs) and microRNAs (miRNAs) to target cells, modulating
their function or changing their phenotype .
Int. J. Mol. Sci. 2021, 22, 4194 3 of 20
- EV in Physiological and Pathological Settings
Based on their crucial role in cell-to-cell communication, EV have been involved in
several processes such as coagulation and thrombosis, endothelial dysfunction, angiogenesis
and immune modulation. Since all of these processes impact renal diseases, a brief
discussion will be reported (Figure 1).
Int. J. Mol. Sci. 2021, 22, x FOR PEER REVIEW 3 of 21
may transfer messenger RNAs (mRNAs) and microRNAs (miRNAs) to target cells,
modulating their function or changing their phenotype .
- EV in Physiological and Pathological Settings
Based on their crucial role in cell-to-cell communication, EV have been involved in
several processes such as coagulation and thrombosis, endothelial dysfunction,
angiogenesis and immune modulation. Since all of these processes impact renal diseases,
a brief discussion will be reported (Figure 1).
Figure 1. EV in physiological and pathological processes. (A) EV and coagulation: EV enriched in phosphatidylserine (PS)
and tissue factor (TF) can promote the activation of the coagulation cascade as well as platelet aggregation. (B) EV and
endothelial activation: EV can modulate vasodilatation and vasoconstriction by activating endothelial cells, releasing
cytokines, reducing nitric oxide (NO) production and increasing reactive oxygen species (ROS) production. (C) EV and
angiogenesis: EV can modulate angiogenesis by increasing ROS production, downregulating the VEGF pathway,
modulating the migration and proliferation of endothelial cells and matrix degradation. This figure has been created using
Servier Medical Art templates, which are licensed under a Creative Commons Attribution 3.0 Unported License;
2.1. EV and Coagulation
Several autoimmune and renal diseases are associated with increased thrombotic risk
and thrombotic events. EV are involved in the coagulation cascade as carriers of
phosphatidylserine (PS) and tissue factor (TF) and are able to promote the activation of
the coagulation cascade. PS can act as a binding site for the coagulation factors II, Va and
Xa, enhancing the association between factor Xa and Va and the subsequent conversion
of prothrombin to thrombin . TF expressed on the EV surface can activate the extrinsic
coagulation pathway by binding factor VIIa . Interestingly, platelet-derived EV have
Figure 1. EV in physiological and pathological processes. (A) EV and coagulation: EV enriched in
phosphatidylserine (PS) and tissue factor (TF) can promote the activation of the coagulation cascade
as well as platelet aggregation. (B) EV and endothelial activation: EV can modulate vasodilatation
and vasoconstriction by activating endothelial cells, releasing cytokines, reducing nitric oxide (NO)
production and increasing reactive oxygen species (ROS) production. (C) EV and angiogenesis:
EV can modulate angiogenesis by increasing ROS production, downregulating the VEGF pathway,
modulating the migration and proliferation of endothelial cells and matrix degradation. This figure
has been created using Servier Medical Art templates, which are licensed under a Creative Commons
Attribution 3.0 Unported License; https://smart.servier.com (accessed on 28 March 2021).
2.1. EV and Coagulation
Several autoimmune and renal diseases are associated with increased thrombotic
risk and thrombotic events. EV are involved in the coagulation cascade as carriers of
phosphatidylserine (PS) and tissue factor (TF) and are able to promote the activation of
the coagulation cascade. PS can act as a binding site for the coagulation factors II, Va and
Xa, enhancing the association between factor Xa and Va and the subsequent conversion
of prothrombin to thrombin . TF expressed on the EV surface can activate the extrinsic
coagulation pathway by binding factor VIIa . Interestingly, platelet-derived EV have
higher pro-coagulant activity compared with activated platelets, possibly due to their
enrichment in phosphatidylserine, glycoprotein IIb/IIIa, factor Xa, and P-selectin .
Moreover, EV-mediated thrombotic events can be also promoted by their expression of the
multimers of vonWillebrand factor and stabilization of platelet aggregation (Figure 1A) .
2.2. EV and Endothelial Dysfunction
Endothelial dysfunction is frequently associated with the pathogenesis of autoimmune
diseases: EV contribute to endothelial regulation in physiological and pathological
conditions. EV can reduce endothelial and macrophage nitric oxide production, controlling
vasodilation. EV can also carry thromboxane A2 acting as vasoconstrictor and platelet
Int. J. Mol. Sci. 2021, 22, 4194 4 of 20
aggregation factor . In addition, EV may increase the production of reactive oxygen
species (ROS). Finally, as occurs in systemic vasculitis, activated neutrophils release EV expressing
the myeloperoxidase (MPO) which by activating the myeloperoxidase-hydrogen
peroxide-chloride system, leads to endothelial damage (Figure 1B) .
2.3. EV and Angiogenesis
Angiogenesis, defined as the growth of new blood vessels from pre-existing ones, is
frequently involved in the pathogenesis of autoimmune diseases. EV may be involved
in several angiogenesis-associated events  as matrix degradation, endothelial progenitor
recruitment, and differentiation, migration and proliferation of endothelial cells.
Endothelial- and macrophage-derived EV contain pro-angiogenic enzymes (MMP-2, MMP-
9, MT1-MMP) which promote extracellular matrix remodeling and favor endothelial cell
invasion . On the contrary, lymphocyte-derived EV can inhibit angiogenesis by generating
ROS and down-regulating the VEGF pathway (Figure 1C) .
2.4. EV and Immune System Modulation
EV may affect the immune response by activating innate and adaptive immunity
and by participating in the formation of the immune complexes (IC), by acting as autoantigens.
Immune cells release immunocompetent EV, which can modulate the immune
response by regulating antigen presentation, NK/T cell activation, T cell polarization and
immunosuppression (Figure 2) .
In the immune system, natural killer (NK) cells have a role in innate immunity, whereas
B and T cells are an essential part of adaptive immunity.
Antigen presentation B cells can recognize foreign antigens, while T cells require
antigen-presenting cells (APCs) for antigen recognition. Major histocompatibility
complex class I (MHC I) and class II (MHC-II) present antigens to CD8+ and CD4+
T cells, thereby activating the immune response. APCs- and B cells-derived EV
express the MHC-I, MHC-II and the T-cell costimulatory molecules, thus may take
part in the antigen presentation process and in the CD8+ and CD4+ T cell activation
(Figure 2A) .
Source of self-antigens and IC formation EV participate in the formation of IC. Indeed,
EV can express both self-antigens and MHC complexes and may activate autoreactive
T-cells in autoimmune disease. As an example, the synovial fluid of patients with
rheumatoid arthritis contains IC composed of platelet-derived EV and autoantibodies
against citrullinated peptides . Similarly, in systemic lupus erythematosus (SLE),
EV carry nuclear molecules, which represent a potential source of autoantigens and
participate in IC formation. Furthermore, EV-associated ICs may affect the recognition
and clearance of EV by phagocytes, leading to the accumulation of cell debris and
triggering the autoimmune response (Figure 2B,C) .
Role of adjuvants in innate immune response Leukocyte-derived EV activate the
endothelium by upregulating adhesion molecules and releasing cytokines. This
leads to leukocyte recruitment via platelet-derived EV, which promotes monocyte
adhesion to the endothelium . Dendritic cell-derived EV increase the NK cytotoxic
activity and stimulate the release of proinflammatory cytokines by epithelial cells
(Figure 2D) .
Role in complement activation When the complement system undergoes activation, the
membrane attack complex may be set down on blood cells and complement-coated EV
may be released. C3-positive EV reflect the activation of the alternative pathway of the
complement, while C1q-positive EV reflect the activation of the classic pathway .
Moreover, EV may express complement regulators on their surface (complement
receptor type 1, membrane cofactor protein, decay-accelerating factor also denoted as
CD59), thereby inhibiting the membrane attack complex (Figure 2E) .
Int. J. Mol. Sci. 2021, 22, 4194 5 of 20
Int. J. Mol. Sci. 2021, 22, x FOR PEER REVIEW 5 of 21
Figure 2. EV and immune system modulation: (A) Self-antigen presentation: antigen-presenting cells
(APC) can vehicle self-antigens and release extracellular vesicles (EV) which present autoantigens
to autoreactive T cells. (B) Self-antigen transfer: EV carrying self-antigens transfer them to APC
which present them to T cells, triggering an autoimmune response. (C) Immune complex formation
(IC): EV can participate in IC formation by carrying self-antigens that are bound by circulating
autoantibodies. (D) Activation of innate immunity: EV can stimulate cytokine release and the upregulation
of adhesion molecules on endothelial cells, which favor circulating immune cell recruitment.
(E) Interaction with the complement system: the complement cascade can be activated on circulating
leukocytes which can then release EV exposing complement molecules (e.g., C3, C1q). EV can also
convey complement inhibitors and modulate the complement system. This Figure has been created
using Servier Medical Art templates, which are licensed under a Creative Commons Attribution 3.0
Unported License; https://smart.servier.com (accessed on 28 March 2021).
Int. J. Mol. Sci. 2021, 22, 4194 6 of 20
- EV and Renal Intercellular Communication
Recent studies have shown the relevance of EV in renal intercellular communication.
Although their role has not been yet fully understood, their potential application as diagnostic,
prognostic, or therapeutic biomarkers for various kidney diseases is currently being
In physiological conditions, the glomerular filtration apparatus prevents circulating
EV from reaching the lumen of renal nephrons, thus circulating EV may stimulate kidney
cells facing the vascular compartment and the immune cells . However, EV are released
from renal cells into the renal tubule and can be detected in urine. The release of renal
EV may vary during renal disease, thus urinary EV have been proposed as potential
biomarkers of kidney injury. Urinary EV are largely composed of EV released from renal
cells as confirmed by proteomic analysis. Urinary EV carry specific proteins, mRNAs
and miRNAs, which reflect their cellular origin. Indeed, EV from glomerular podocytes
contain podocin and podocalyxin , EVs from proximal tubular cells express cubilin,
megalin, aminopeptidase  and aquaporin-1; EVs from the Henle’s loop contain type 2
Na-K-2Cl cotransporter, CD9 and Tamm–Horsfall protein ; EVs from collecting ducts
carry AQP-2 and mucin-1 . The majority of urinary EV are released from the first part of
the renal nephron, with a limited contribution from the lower urinary collecting system .
Interestingly, EV may have a role in cell-to-cell communication between the proximal and
distal renal tubules. EV released from glomerular podocytes, via the urine flux, reach and
can be taken up by the epithelial cells of the distal tubule and the collecting duct . A
recent study has investigated a potential hormonal mechanism that regulates EV uptake. It
has been demonstrated that in vitro stimulation with desmopressin selectively stimulates
the EV uptake in tubular cells, while a vasopressin antagonist reduced in vivo the uptake
of EV injected within the renal tissue . Moreover, EV may take part in the regulation of
renal inflammation. Indeed, it was reported that EV from proximal tubular cells cultured
in the presence of a dopamine receptor antagonist are able to reduce ROS production in
distal tubular cells . Interestingly, EV can modulate renal tissue repair and fibrosis
after renal damage [33–35]. In vitro studies have demonstrated that hypoxic conditions
increase the release of tubular cell-derived EV, which induced fibroblast activation and
proliferation by the transfer of TGF mRNA . EV may also control the ion transport, as
EV from proximal tubule cells can decrease ENaC activity in the distal tubule and collective
ducts . Moreover, EV can also mediate the transfer of aquaporin 2 from cells of the
upper collective duct to those of the lower collective duct, increasing water transport in
the recipient cells . Urinary EV may also exert protection against bacterial infection
of the urinary tract. As a matter of fact, urinary EV carry antimicrobial peptides and can
inhibit the growth of the most common urinary pathogen Escherichia coli by inducing their
lysis . Mesenchymal-to-epithelial transition is a crucial process in kidney development
and regeneration. It has been reported that this process is mediated by tubular epithelial
cell-derived EV which carry a specific subset of miRNAs, driving the differentiation of
mesenchymal stem cells into epithelial cells . Interestingly, mesenchymal stem cells
and endothelial progenitor cells release EV that induce nephron regeneration and repair by
promoting tubular proliferation and by inhibiting apoptosis [41,42].
- EV in Renal Disease
4.1. Antiphospholipid Syndrome
Antiphospholipid syndrome (APS) is a systemic autoimmune disease characterized
by recurrent arterial or venous thrombosis and/or obstetric complications in the presence
of antiphospholipid antibodies (aPL). APS is the most common cause of acquired
thrombophilia and is associated with decreased survival. A severe form of APS, termed
catastrophic antiphospholipid syndrome, occurs in <1% of patients with aPL and is associated
with high mortality . Despite the clinical relevance of this syndrome, its
pathogenesis is not yet fully understood and recent studies have focused on EV as potential
Int. J. Mol. Sci. 2021, 22, 4194 7 of 20
Various studies have reported an increased level of EV in APS patients. Štok et al. 
have compared APS patients, patients with idiopathic thrombosis and healthy controls and
found that circulating EV were increased in patients with a history of thrombotic events
(APS patients and patients with idiopathic thrombosis) compared to healthy subjects,
suggesting a chronic cell activation even in the absence of an acute thrombotic event.
This study demonstrated the presence of platelet, endothelial cell, lymphocyte, antigenpresenting
cell-derived EV in patients with a history of thrombosis as well as in healthy
controls. These EV express molecules involved in platelet/endothelial function, immune
regulation extracellular matrix regulation and cell-to-cell adhesion. The analysis of EV
surface proteins demonstrated an increased expression of CD8, CD44, CD133/1 and CD62P
in the aPL patients. The increased expression of CD133/1 and CD62P on the EV surface in
APS patients could reflect the increased endothelial and platelet activation, respectively, and
their possible contribution to the thrombotic events . Endothelial- and platelet-derived
EV were increased in aPL patients, suggesting a chronic activation of endothelial cells and
platelets. Interestingly, a correlation between the level of endothelial-derived EV and the
level of anti-2GPI has been demonstrated which closely correlates with thrombosis .
Breen et al.  have shown an increased level of endothelial- and platelet-derived EV
in aPL patients compared with healthy subjects, while no difference between obstetric APS
or asymptomatic aPL patients was detected. Moreover, plasma from patients with APS
and from patients with SLE aPL+ or SLE aPL- increased the release of EV from cultured
endothelial cells compared to the plasma of healthy subjects. Of note, only plasma from
APS patients caused the release of EV with significant procoagulant activity . aPL
induces tissue factor (TF) synthesis in endothelial cells in vitro, and it has been reported
that TF+ EV are elevated in aPL+ patients . In particular, TF expression on endothelialderived
EV is increased in APS patients compared to healthy subjects . Moreover,
Willemze et al.  have demonstrated that EV from APS patients display a higher TF
activity compared to asymptomatic aPL+ patients.
More recently, Mobarrez et al.  have compared anti-2GPI-positive SLE patients,
aPL-negative SLE patients and healthy controls. They found that SLE patients are depleted
of 2GPI-positive EV when compared to healthy subjects, and their level is particularly
low in anti-2GPI-positive patients. They also found that 2GPI preferentially binds to the
phosphatidylserine (PS)-positive EV, thus suggesting that anti-2GPI antibodies may bind
to the 2GPI-PS complexes on EV resulting in the loss of EV 2GPI expression. 2GPI
promotes the clearance of PS+ EV, thus the increased number of PS-negative EV may act as
a possible source of autoantigens and thus trigger the autoimmune response .
Regarding obstetric APS, pregnant women with APS had increased PS+ EV, endoglin+
EV and endothelium-derived EV compared to healthy controls in the first and second
trimester of pregnancy. Conversely, in the third trimester, higher levels of TF+ EV and
platelet-derived EV can be detected. According to the authors, this finding could reflect the
activation of both endothelial cells and platelets during pregnancy. In particular, high-risk
APS patients (triple aPL positivity plus vascular thrombosis and/or severe pregnancy
complications/placental insufficiency) have higher endoglin+ EV, TF+ EV and platelet
derived-EV in all three trimesters, sustaining a major vascular activation. Interestingly,
endoglin is expressed by vascular endothelium and by syncytiotrophoblasts and altered
levels of soluble endoglin are linked to vascular disorders as pre-eclampsia .
In conclusion, patients with aPL have an elevated level of circulating EV, which may
reflect a state of systemic vascular activation. EV have been shown to act as procoagulant
and proinflammatory mediators, thus their level may correlate with the thrombotic risk.
However, at present, a clear relationship between elevated EV levels and thrombotic events
is still missing (Table 1).
Int. J. Mol. Sci. 2021, 22, 4194 8 of 20
Table 1. Extracellular vesicles in antiphospholipid syndrome (APS).
Study EV Biomarkers Cellular Origin of EV Study Findings Reference
Štok, U.; et al.
CD8, CD44, CD133/1,
EV increased in patients with thrombotic events
EV reflect endothelial and platelet chronic
Chaturvedi, S.; et al.,
Breen, K.A.; et al.
CD41, CD61, CD51,
EV increased in aPL+ patients
EV reflect endothelial and platelet chronic
Chaturvedi, S.; et al.,
Willemze, R.; et al. Tissue factor (TF) Endothelial cells TF + EV increased in APS
TF activity increased in EV from aPL+ patients [44,48]
Mobarrez, F.; et al. 2GPI+ EV 2GPI+ reduced in SLE aPL+
Anti-2GPI may bind to 2GPI expressed by EV 
Campello, E.; et al.
Tissue factor (TF)
PS+ EV, endoglin+ EV and endothelium-derived
EV increased in 1st and 2nd trimester of
TF+ EV and platelet-derived EV increased in 3rd
trimester of pregnancy
Correlation with thrombosis and systemic platelet
and endothelial activation in obstetric APS
4.2. Systemic Lupus Erythematosus
Systemic lupus erythematosus (SLE) is a systemic autoimmune disease characterized
by the production of autoantibodies against nuclear antigens and the deposition of immune
complex (IC) leading to systemic inflammation and tissue damage. Lupus nephritis (LN)
is one of the most severe organ manifestations and a primary cause of morbidity and
Studies on circulating EV in SLE patients revealed divergent results regarding their
circulating level and characterization. EV were found increased in SLE [51,52], or decreased
compared to healthy controls . Those different results reflect the lack of standardized
methods for EV evaluation and characterization.
In SLE, circulating EV expose chromatin on their surface and may represent a source
of nuclear antigens which can bound both the IgG and the complement, resulting in the
formation of IC, which correlate with the disease activity and the vascular damage [52,54].
Circulating EV can bind both IgG and IgM to form immune complexes (EV-ICs) and
EV-IgG+ were positively correlated with the disease activity. Platelet-derived EV (PEV),
mainly PEV-IgG+, stimulated monocytes in vitro changing their phenotype and promoting
their inflammatory response . Several studies have supported the role of the deoxyribonuclease
DNASE1L3 as a genetic determinant of susceptibility [55,56]. Sisirak et al. 
have found that DNASE1L3 can digest chromatin in apoptotic cell-derived EV and, in the
absence of DNASE1L3, EV-associated DNA may gather in an extracellular environment
and promote autoantibody production by autoreactive B cells. DNASE1L3 is produced by
dendritic cells and macrophages, and its circulating level was inversely correlated with
anti-dsDNA level .
Platelet activation plays a key role in the pathogenesis of SLE. They promote T and
B cell activation, NETosis, type I IFN production, and dendritic cell activation resulting
in systemic organ damage. Platelet-derived EV are the most prevalent circulating EV in
healthy subjects, while conflicting results have been reported regarding platelet-derived
EV in SLE. Burbano et al.  have found an increased number of circulating EV (mainly
platelet-derived EV) in patients with SLE compared to healthy controls. However, plateletderived
EV level was unrelated to disease activity measured with SLEDAI score. Lopez
et al.  have observed an increased level of platelet-, monocyte- and T lymphocytederived
EV. Interestingly, the authors found that EV level is influenced by the disease
activity and is related to the activation status of blood parental cells. They also reported
that glucocorticoid therapy may influence EV production and T cell activation, as EV
from patients treated with glucocorticoids induced the upregulation of CD25 and the
Int. J. Mol. Sci. 2021, 22, 4194 9 of 20
accumulation of IL-10 in T cells . Moreover, circulating platelet-derived EV correlated
with endothelial-independent vasodilatation in SLE .
Patients with SLE have increased cardiovascular risk due to platelet activation and
systemic endothelial activation. EV may be involved in this process, as EV and EV-ICs
from SLE patients can activate endothelial cells by increasing the expression of adhesion
molecules (CD54, CD102), the production of chemokine (CCL2, CCL5, IL-6) and the
adherence of monocytes. EV may also mediate endothelial injury by increasing endothelial
permeability through the alteration of cytoskeletal proteins leading to adhesion and
migration of monocyte to the inflamed organs .
Polymorphonuclear leukocytes (PMNs) are greatly involved in SLE pathogenesis, as
PMNs showed generalized hyperactivity, with enhanced apoptosis and increased production
of neutrophil extracellular traps (NETs) . Moreover, increased oxidative stress
has been observed in SLE, which may contribute to immune dysregulation . Winberg
et al.  have found that EV from SLE patients induced ROS production in the patient’s
own PMNs re-suspended in autologous serum, particularly in patients with low circulating
C3 level, which reflects disease activity. The ROS production partly depends on EV properties,
serum components (including autoantibodies) and PMN hyper-responsiveness .
In vitro studies have shown the proinflammatory effect of EV on blood-derived plasmacytoid
dendritic cells and myeloid dendritic cells by increasing the expression of costimulatory
molecules (CD40, CD80, CD83, CD86) and the release of proinflammatory cytokines
(IL-6, TNF, IFN). Moreover, EV enhanced the formation of neutrophil extracellular traps
(NETs) which may represent a source of nuclear autoantigens thus contributing to the
pathogenesis of SLE and renal inflammation . EV from patients with active LN contain
a higher level of acetylated chromatin compared to patients with remissive LN, without
LN, or healthy controls. Rother et al.  have found that the degree of EV acetylated
chromatin determines their strength to stimulate neutrophils to form NETs.
According to proteomic and flow cytometry analysis, circulating EV in SLE patients
have an increased content of IgG and galectin-3 binding protein (G3BP), a glycoprotein
that may contribute to the pathogenesis of SLE. G3BP is induced by type I IFN and exhibits
a high binding capacity toward components of the glomerular basement membrane
(GBM) , including collagen IV, fibronectin and galectin-3. Interestingly, patients suffering
from lupus nephritis show a glomerular G3BP/IgG co-localization pattern specifically
in the GBM, suggesting the presence of G3BP in the IC delivered either by EV from the
circulation or locally formed . In SLE patients, in vitro stimulation of peripheral blood
mononuclear cells (PBMCs) with TLR-9 agonist increases the release of EV expressing both
G3BP and dsDNA. This was particularly relevant in patients with active LN, compared to
healthy donors .
Urinary EV may reflect structural damage and renal dysfunction, and they have been
investigated as potential LN diagnostic and prognostic biomarkers. Urinary podocytederived
EV reflecting the glomerular podocyte damage are increased in LN and SLE
patients compared to healthy controls. Interestingly, urinary EV level is correlated to the
SLE disease activity index (SLEDAI) score, anti-dsDNA antibodies titer, proteinuria and
histopathological lesions . A recent study demonstrated that urinary EV expressing
the high-mobility group box 1 molecule (HMGB1) are higher in SLE patients with active
LN than in those without renal involvement, and correlate with proteinuria. HMGB1 is
involved in the pathogenesis of several autoimmune diseases and it may be an important
mediator in LN. Indeed, its expression is increased in glomerular endothelium and
mesangium, and its blood and urinary level is increased in LN .
Several studies have identified EV-derived miRNA as markers of renal damage which
can also discriminate active LN ; miR-21, miR-150, and miR-29c were correlated to
renal fibrosis and could predict the progression to the end-stage renal disease [72,73]. A
unique circulating miRNA expression profile was detected in class IV LN  and urinary
EV-derived miRNA have been proposed as peculiar biomarkers of class IV LN .
Int. J. Mol. Sci. 2021, 22, 4194 10 of 20
Recently, Garcia-Vives et al. investigated the miRNA expression profile of urinary EV
in proliferative LN as a new potential prognostic biomarker. Patients with clinical responses
to therapy are characterized by an increased level of miR-31, miR-107, and miR-135b-5p
in urine and in renal tissue (mostly localized in epithelial tubular cells), compared to nonresponder
patients. In vitro stimulation of tubular epithelial cells with proinflammatory
cytokines increases the release of these miRNA, which can be taken up by endothelial cells
and mesangial cells in responder patients .
Recent studies have evaluated the role of mitochondria in autoimmune diseases.
Activated cells can release EV containing mitochondria or free mitochondria which may
stimulate immunity. Mobarretz et al.  have demonstrated the presence of circulating
particles (approximately 3 m), and among them, a population of large EV carrying
mitochondrial molecules (mitoEV) were found that both increased and associated with
the disease activity in SLE patients. Furthermore, patients suffering from active LN have
higher levels of mitoEV and IgG-coated mitoEV, suggesting that they may contribute to
the formation of IC and thus be involved in renal damage .
In conclusion, EV may play a crucial role in the pathogenesis of SLE, and particularly
in LN-associated renal injury. For these reasons, EV have been proposed as potential
biomarkers of disease in SLE patients as well as early biomarkers of renal damage in LN
Table 2. Extracellular vesicles in systemic lupus erythematosus.
Study EV Concentration Cellular Origin of EV EV Pathological Significance Reference
Burbano, C.; et al.
Increased in SLE
compared to healthy
Formation of immune complexes,
source of nuclear antigens,
correlation with disease activity
López, P.; et al.
Increased in SLE
compared to healthy
EV level correlated with:
Atehortúa, L.; et al. Endothelial cell activation,
endothelial injury, 
Winberg, L.-K.; et al.,
Dieker, J.J.; et al.,
Rother, N.; et al.
In vitro stimulation of
polymorphonuclear leukocytes with EV
from SLE patients increased ROS
EV promote neutrophil activation and
Nielsen, C.T.; et al.,
Rasmussen, N.S.; et al.
IgG/galectin-3 binding protein (G3BP)+
EV are involved in the pathogenesis of
Lu, J.; et al.,
Vanegas-García, A.; et al.
EV increased in SLE Urinary EV
Urinary podocyte-derived EV level
correlated with systemic disease activity
and renal injury
Urinary EV high-mobility group box 1
molecule (HMGB1)+ were found to be
higher in lupus nephritis
Felip, M.L.; et al.,
Solé, C.; et al.,
Navarro-Quiroz, E.; et al.,
Li, Y.; et al.,
Garcia-Vives, E.; et al.
EV derived miRNA
miR-21, miR-150, and miR-29c, miR-31,
miR-107, and miR-135b-5p correlated
with renal injury in lupus nephritis
Mobarrez, F.; et al.
mitoEV were associated with disease
activity, immune complex formation and
Int. J. Mol. Sci. 2021, 22, 4194 11 of 20
4.3. Thrombotic Microangiopathies
Thrombotic microangiopathies include different diseases characterized by microangiopathic
hemolytic anemia and thrombocytopenia also potentially involving the kidney.
Thrombotic microangiopathies include Shiga toxin-producing Escherichia coli (STEC-HUS)
and thrombotic thrombocytopenic purpura (TTP).
Haemolytic uremic syndrome (HUS) is characterized by nonimmune microangiopathic
haemolytic anemia, thrombocytopenia and acute kidney injury. Typical HUS is
subordinate to Shiga toxin-producing Escherichia coli (STEC-HUS) infection, which first
colonizes the intestine and produces the toxin which enters the bloodstream and causes
In STEC-HUS, EV mainly derive from platelets, monocytes, neutrophils and red blood
cells. Ståhl et al. have found EV expressing TF and phosphatidylserine potentially involved
in the formation of microthrombi. Moreover, in the acute phase of the disease, circulating
EV derived from platelets, monocytes, and neutrophils show deposition of C3 and C9
on their surface. Interestingly, EV also express phosphatidylserine, which activates the
coagulation factor V and X, thus enhancing and promoting thrombosis . Those findings
may reflect the systemic complement activation and the role of EV in the inflammatory and
thrombogenic events in HUS .
In vitro experiments showed that whole blood incubated with Shiga-toxin and/or
STEC-lipopolysaccharide increased the release of TF-positive EV, C3- and C9-positive EV
derived from platelets, monocytes and red blood cells [10,22]. It has been speculated that
activated complement factors carried by EV can be transferred to recipient cells, driving
cell damage .
Since STEC are non-invasive bacteria, a small amount of Shiga toxin is present in the
circulation; however, EV may transfer the toxin to the kidneys via peritubular capillaries.
EV containing Shiga toxin were found within the kidney into renal cells, and in vivo
experiments showed that EV enriched in Shiga toxin can reach renal cells through the
glomerular and tubular basement membranes. In vitro studies also demonstrated that EV
undergo endocytosis in glomerular endothelial cells, leading to cell damage .
Shiga toxin interaction with circulating cells is mediated by two different receptors:
the globotriaosylceramide (Gb3) toxin receptor and TLR4. Shiga toxin can be taken up
by cells after binding to Gb3 or by cellular uptake of EV carrying the toxin derived from
different host cells. EV expressing Shiga toxin are taken up by both Gb3-positive and
Gb3-negative recipient cells. However, only Gb3-positive host cells are susceptible to
toxin-induced cellular damage, reduced cellular metabolism and protein synthesis .
Of note, renal endothelial cells express both Gb3 and TLR4. In vitro experiments using
soluble Shiga toxin have shown that TLR4 acts as a Gb3 coreceptor, thus facilitating renal
cell injury .
TTP is a rare microangiopathic hemolytic anemia in which mutations of vWF protease
(ADAMTS13) or autoantibodies against ADAMTS13 lead to the deposition of von
Willebrand factor (vWF) multimers within capillaries. Systemic endothelial cell injury and
platelet aggregation activate systemic microthrombosis mainly involving the brain and
A comparison of circulating EV in TTP patients and healthy subjects has shown
that platelet-derived EV are the most represented EV subtype in both groups. Moreover,
in TTP patients the platelet-derived EV level is significantly higher, as are EV express
markers of platelet activation such as CD62p. Interestingly, platelet-derived EV have a
procoagulant activity greater than platelets due to phospholipid expression on their surface
which triggers the coagulation cascade .
Other studies have found higher levels of platelet-derived and endothelial-derived
EV in TTP. Endothelial-derived EV have shown procoagulant and proadhesive roles as
they express CD62E (E-selectin), VWF, intercellular adhesion molecule 1 (ICAM-1), platelet
endothelial cell adhesion molecules (PECAM-1; CD31) and endoglin (CD105) . Tati
et al.  have shown that circulating endothelial-derived EV are coated with C3 and
Int. J. Mol. Sci. 2021, 22, 4194 12 of 20
C9 and complement activated on platelets and glomerular endothelium. Complement
activation may represent an ancillary phenomenon to platelet activation and endothelial
injury, and thus may drive the microangiopathic process .
Unfortunately, only a few studies have investigated the role of EV in TTP, and future
research is needed to better understand the pathogenesis of TTP (Table 3).
Table 3. Extracellular vesicles in thrombotic microangiopathies.
Disease Study Cellular Origin of EV EV Biomarkers EV Pathological Significance Reference
STEC-HUS Ståhl, A.-L.; et al.,
Arvidsson, I.; et al.
(PS), C3, C9
Promotion of thrombosis
EV reflect complement
Varrone, E.; et al.,
Ståhl, A.-L.; et al.,
Johansson, K.; et al.
EV carrying Shiga
Delivery system of Shiga toxin
to the kidney
involvement in renal cell injury
TTP Tahmasbi, L.; et al.,
Jimenez, J.J.; et al.
adhesion molecule 1
Pro-coagulant and pro-adhesive
TTP Tati, R.; et al. Endothelial cells C3, C9 EV reflect complement
4.4. ANCA-Associated Vasculitis
Systemic vasculitis consists of different syndromes characterized by blood vessel
inflammation and multiple organ involvement. Small vessel vasculitis is often associated
with anti-neutrophil cytoplasmic antibodies (ANCA), predominantly IgG autoantibodies
directed against neutrophil cytoplasmatic constituents such as proteinase 3 (PR3, named
cANCA) and myeloperoxidase (MPO, named pANCA). ANCA-associated vasculitis (AAV)
comprises microscopic polyangiitis (MPA), granulomatosis with polyangiitis (Wegener’s)
(GPA), and eosinophilic granulomatosis with polyangiitis (Churg-Strauss) (EGPA). AAV
can affect small vessels in different organs resulting in pauci-immune glomerulonephritis,
vasculitis involving the respiratory tract, and is associated with an increased risk of systemic
thrombosis . Despite new treatment options that have recently improved AAV
prognosis, early diagnostic and prognostic biomarkers are still an unmet need.
Patients with AAV have an increased risk of thromboembolic events due to the hypercoagulable
state . ANCA can induce neutrophil activation, neutrophil degranulation
and release of neutrophil extracellular traps (NETs), which are involved in the development
of vasculitis lesions . Moreover, complement activation via the alternative pathway
is crucial for the development of the disease . In vitro experiments have found that
both pANCA IgG and cANCA IgG can stimulate C5a-primed neutrophils to produce TFexpressing
EV and TF-expressing NETs which, in turn, promote thrombin generation and
the activation of the coagulation cascade . Notably, Mendoza et al.  have measured
the TF activity of EV and found higher TF activity in patients with AAV and associated
venous thromboembolism, compared to patients without thrombotic events .
Recent studies have demonstrated a potential role of platelet- and neutrophil-derived
EV in the pathogenesis of vasculitis. Polyclonal ANCAs isolated from patients and chimeric
PR3–ANCA induces the release of EV from primed neutrophils in vitro. Moreover, these EV
are enriched in PR3 and MPO, exhibit thrombin-generating capacity, can bind the endothelium
and induce its activation, induce ROS production and the release of proinflammatory
cytokines (IL-6, IL-8) .
An increased level of circulating platelet-, neutrophil- and endothelial-derived EV in
patients with vasculitis has also been found . In particular, a high level of neutrophil-EV
Int. J. Mol. Sci. 2021, 22, 4194 13 of 20
during the acute phase of the disease which decreased after steroid treatment has been
reported, reflecting the key role of neutrophil activation. Of note, endothelial-EV level
correlated with the Birmingham Activity Vasculitis Score (BVAS) and acute phase reactants,
suggesting their potential application as disease biomarkers .
The kinin system contributes to the inflammatory response and the development of
vasculitis. The kinins regulate local blood pressure, promote inflammation, and capillary
leakage. The kinins achieve their effect through B2 and B1 receptors. The B2 receptor is
constitutively expressed and involved in inflammation and hyperalgesia, while the B1
is upregulated during chronic inflammation (such as vasculitis), and controls neutrophil
migration. Kahn et al.  have found increased circulating leukocyte-derived EV bearing
the B1-kinin receptor during vasculitis. In particular, neutrophil-derived EV bearing the B1
receptor were found docking to glomerular endothelial cells in kidney biopsies of patients
with AAV. In vitro experiments showed that neutrophil-derived EV transfer functional B1-
receptors to wild-type human embryonic kidney cells, which suggests a similar mechanism
in vivo and could potentially promote kinin-associated inflammation. The observation
that the main inhibitor of the kinin system, named the C1-inhibitor, is also involved in the
inhibition of the release of EV enriched in B1-receptor has suggested a novel therapeutic
target in vasculitis .
Prikryl et al.  recently performed proteomic profiling of urinary EV isolated from
patients with AAV and renal involvement and in healthy controls. The study showed
different levels of proteins potentially involved in AAV pathogenesis. As an example, they
found a significantly decreased level of Golgi mannosidases, such as MAN1A1, both in
urinary EV and in the whole urine in active AAV. Interestingly, MAN1A1 is involved in
protein glycosylation, which is considered to be involved in autoimmune disease and T cell
activation, supporting its role in the pathogenesis of AAV. Moreover, they showed different
levels of proteins related to neutrophil activation and degranulation, platelet regulation
and podocyte-associated proteins, to name a few .
Several studies have also shown that EV may contain enzymes linked to lipid metabo
lism. Indeed, a comparison between EV in active GPA and healthy controls showed an
increased content of leukotriene (LT)B4 and 5-oxo-eicosatetraenoic acid (5-oxo-ETE) in
EV from GPA patients. Moreover, neutrophils primed with GM-CSF, and stimulated
with EV recovered from GPA patients, generate ROS and release dsDNA. Interestingly,
in vitro-primed neutrophils were stimulated by LTB4 and 5-oxo-ETE, thus EV carrying
lipid enzymes may contribute to AAV pathogenesis . In a recent study, Surmiak
et al.  stimulated human umbilical endothelial cells (HUVEC) with EV from anti-
PR3-activated neutrophils and analyzed their miRNA and mRNA content. They found a
miRNA/mRNA profile consistent with the release of proinflammatory cytokines, which
may be involved in endothelial injury in vasculitis. The most increased cytokines were
IL-8, IL-33, Dickkopf-related protein 1 (DKK-1), soluble interleukin (IL)-1 like receptor-1
(ST2) and angiopoietin-2. Interestingly this cytokine profile is similar to the circulating
cytokine profile in GPA patients .
Recent studies have investigated the role of EV in mediating endothelial injury in MPA.
EV can be taken up by glomerular endothelial cells in vitro and can increase the release of
soluble cellular adhesion molecules (sICAM-1 and sVCAM-1) leading to the injury of the
glomerular endothelial barrier. A sequencing analysis of EV miRNA cargo in MPA patients
revealed a different miRNA profile in MPA patients. In particular, a correlation between
miR-185-3p, miR-125a-3p and clinical parameters, such as BVAS and 24-h urine proteins,
was reported. Thus, the EV-miRNA content has been proposed as a biomarker of renal
involvement in MPA .
Circulating EV expressing MPO are elevated in AAV patients compared with healthy
subjects. Interestingly, MPO+ EV expressing inflammatory biomarkers such as PTX3 and
HMGB1 are associated with disease activity. Of interest, PTX3 is released by neutrophils
during the inflammatory process, while HMGB1 may be associated with renal injury in
AAV . HMGB1 enhanced neutrophil activation and migration towards glomerular
Int. J. Mol. Sci. 2021, 22, 4194 14 of 20
endothelial cells in the presence of ANCA, leading to glomerular cell injury and the release
of TF-positive EV and endothelin-1, which is involved in the fibrogenesis .
The comparison of circulating EV expressing MPO in AAV patients and healthy
controls reveals an increased expression of the complement components C3a and C5a on
EV from AAV patients. Moreover, among AAV patients, C3a and C5a expression is higher
in patients with active renal involvement compared to non-renal disease. Interestingly,
the level of C3a and C5a expression on EV correlated with disease activity evaluated by
Platelet-derived EV were also found to be increased in AAV patients, particularly
in MPO-positive patients with active disease in whom EV also expressed higher levels
of chemokines, adhesion molecules, growth and apoptotic factors. Moreover, EV level
correlated with the disease activity and the renal involvement, with serum creatinine and
glomerular histologic lesions .
Taken together, these results may provide insight into the role of EV in the pathogenesis
of renal injury in AAV (Table 4).
Table 4. Extracellular vesicles in ANCA-associated vasculitis.
Study EV Biomarkers EV Cellular Origin Study Findings Reference
Daniel, L.; et al. proteinase 3 (PR3),
EV released from primed
neutrophils in vitro
EV can induce endothelial activation,
ROS production, cytokines release 
Brogan, P.A.; et al.
EV level increased in vasculitis
Decrease of neutrophil-derived EV
Endothelial-derived EV correlated
with disease activity
Kahn, R.; et al. B1 kinin receptor Leukocytes
EV level increased in vasculitis
Neutrophil-derived B1+ EV found
on glomerular endothelial cells and
Prikryl, P.; et al. Urinary EV
Proteomic EV profiling showed
different regulation of proteins
potentially involved in vasculitis
Surmiak, M.; et al.
EV enriched in LTB4 and 5-oxo-ETE
in granulomatosis with polyangiitis 
Wang, Y.; et al.
Sequencing analysis of EV miRNA
cargo in microscopic polyangiitis
identified a correlation between
miR-185-3p, miR-125a-3p and both
the clinical activity score and
Manojlovic, M.; et al.
PTX3, high mobility group
box 1 (HMGB1)
PTX3+ and HMGB1+ EV correlated
with disease activity
HMGB1 potentially associated with
Antovic, A.; et al. myeloperoxidase (MPO),
MPO C3a+ and C5a+ EV increased
in vasculitis, particularly in patients
with renal involvement
C3a and C5a expressed on EV
correlated with disease activity
Miao, D.; et al.
molecules, growth and
Increased EV in vasculitis
EV correlate with disease activity
and renal injury
Int. J. Mol. Sci. 2021, 22, 4194 15 of 20
Recent studies have demonstrated the relevance of EV in physiological and pathological
processes . Due to their role in immune system modulation, EV are considered
crucial actors in the pathogenesis of autoimmune diseases .
Although current treatment options have improved their prognosis, autoimmune
conditions remain rare diseases with high mortality and morbidity, particularly when
the kidney is involved. Currently, kidney biopsy is the most important diagnostic and
prognostic tool; however, recent investigations have focused on the identification and
development of non-invasive biomarkers for early diagnosis and for the assessment of the
Recently, the impact of EV in autoimmune disease with renal involvement has been
investigated . EV numbers and features seem to correlate with pathological processes.
In addition, EV have been reported to enhance the autoimmune process and promote
renal injury. In APS, the EV circulating level has been shown to reflect endothelial and
platelet chronic activation and may correlate with thrombotic events [6,44,49]. Moreover,
EV can actively contribute to SLE pathogenesis as an autoantigen source, part of the
immune complexes, endothelial and leukocytes activation promoters [52,63]. Of interest,
the galectin-3 binding protein (G3BP)+ EV and urinary high-mobility group box 1 molecule
(HMGB1)+ EV seem to be involved in lupus nephritis pathogenesis [67,68,70]. Likewise,
EV contribute to renal injury in STEC-HUS [79–81]. In ANCA-associated vasculitis, EV are
involved in endothelial activation and correlate with disease activity [91,94]. Of interest,
HMGB1+ EV and B1-receptor + EV can be directly involved in renal cell injury and
have been proposed as a novel therapeutic target [93,98]. Moreover, miRNA carried
by circulating EV can be investigated as novel diagnostic biomarkers for both lupus
nephritis [72,74,76] and ANCA-associated vasculitis .
Encouraging discoveries on EV as diagnostic tools have been provided; however, being
a recent research field, contradictory results reflecting the lack of standardized evaluation
methods make their application in the clinical practice still challenging. Future studies
should focus on defining standardized methods of EV collection and cargo evaluation. Of
note, interesting observations have been reported in the research field, which need further
investigation to be transferred in clinical settings.
However, the rareness of these diseases made it difficult to investigate the potential
clinical impact of EV as diagnostic and prognostic tools in large clinical studies. For this
reason, multicenter studies are needed to collect relevant data.
Despite these limitations, future studies on the role of EV in renal pathology should
be pursued to better identify new targets in autoimmune diseases. Overall, the future
challenge is to develop tools exploiting EV as diagnostic biomarkers, therapeutic targets or
drug vectors for novel treatment options in autoimmune renal diseases.
Author Contributions: M.M. contributed to data curation and writing the original draft; G.C. contributed
to editing; M.F.B. contributed to writing, visualization, founding and editing. All authors
have read and agreed to the published version of the manuscript.
Funding: This work has been supported by grants obtained by MFB from Ministero dell’Istruzione,
Università e Ricerca (MIUR) ex 60%.
Institutional Review Board Statement: Not applicable.
Informed Consent Statement: Not applicable.
Data Availability Statement: Not applicable.
Conflicts of Interest: G.C. is a component of the Scientific Advisory Board of UNICYTE. The other
authors have no conflict of interest.
Int. J. Mol. Sci. 2021, 22, 4194 16 of 20
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