Vimentin autoantibodies induce platelet activation and formation of platelet-leukocyte conjugates via platelet-activating factor

The Pathophysiology of The Antiphospholipid Syndrome: A Perspective From The Blood Coagulation System

The antiphospholipid syndrome (APS), a systemic autoimmune disease characterized by a hypercoagulability associated to vascular thrombosis and/or obstetric morbidity, is caused by the presence of antiphospholipid antibodies such as lupus anticoagulant, anti-β-2-glycoprotein 1, and/or anticardiolipin antibodies. In the obstetrical APS, antiphospholipid antibodies induce the production of proinflammatory cytokines and tissue factor by placental tissues and recruited neutrophils. Moreover, antiphospholipid antibodies activate the complement system which, in turn, induces a positive feedback leading to recruitment of neutrophils as well as activation of the placenta. Activation of these cells triggers myometrial contractions and cervical ripening provoking the induction of labor. In thrombotic and obstetrical APS, antiphospholipid antibodies activate endothelial cells, platelets, and neutrophils and they may alter the multimeric pattern and concentration of von Willebrand factor, increase the concentration of thrombospondin 1, reduce the inactivation of factor XI by antithrombin, increase the activation of factor XII, and reduce the activity of tissue plasminogen activator with the subsequent production of plasmin. All these effects result in less permeable clots, denser, thinner, and with more branched fibrin fibers which are more difficult to lysate. As a consequence, thrombosis, the defining clinical criterion of APS, complicates the clinical course of the patient.

Autoimmunity roots of the thrombotic events after COVID-19 vaccination

Although vaccination represents the most promising way to stop or contain the coronavirus disease 2019 (COVID-19) pandemic and safety and effectiveness of available vaccines were proven, a small number of individuals who received anti-SARS-CoV-2 vaccines developed a prothrombotic syndrome. Vaccine-induced immune thrombotic thrombocytopenia (VITT) can be triggered by the adenoviral vector-based vaccine, whereas lipid nanoparticle-mRNA-based vaccines can induce rare cases of deep vein thrombosis (DVT). Although the main pathogenic mechanisms behind this rare phenomenon have not yet been identified, both host and vaccine factors might be involved, with pathology at least in part being related to the vaccine-triggered autoimmune reaction. In this review, we are considering some aspects related to pathogenesis, major risk factors, as well as peculiarities of diagnosis and treatment of this rare condition.

Discovery of non-HLA antibodies associated with cardiac allograft rejection and development and validation of a non-HLA antigen multiplex panel: From bench to bedside

We analyzed humoral immune responses to nonhuman leukocyte antigen (HLA) after cardiac transplantation to identify antibodies associated with allograft rejection. Protein microarray identified 366 non-HLA antibodies (>1.5 fold, P < .5) from a discovery cohort of HLA antibody-negative, endothelial cell crossmatch-positive sera obtained from 12 cardiac allograft recipients at the time of biopsy-proven rejection. From these, 19 plasma membrane proteins and 10 autoantigens identified from gene ontology analysis were combined with 48 proteins identified through literature search to generate a multiplex bead array. Longitudinal sera from a multicenter cohort of adult cardiac allograft recipients (samples: n = 477 no rejection; n = 69 rejection) identified 18 non-HLA antibodies associated with rejection (P < .1) including 4 newly identified non-HLA antigenic targets (DEXI, EMCN, LPHN1, and SSB). CART analysis showed 5/18 non-HLA antibodies distinguished rejection vs nonrejection. Antibodies to 4/18 non-HLA antigens synergize with HLA donor-specific antibodies and significantly increase the odds of rejection (P < .1). The non-HLA panel was validated using an independent adult cardiac transplant cohort (n = 21 no rejection; n = 42 rejection, >1R) with an area under the curve of 0.87 (P < .05) with 92.86% sensitivity and 66.67% specificity. We conclude that multiplex bead array assessment of non-HLA antibodies identifies cardiac transplant recipients at risk of rejection.

Multiple Arterial Thrombosis in Seronegative Antiphospholipid Syndrome: Need for New Diagnostic Criteria?

Background

Antiphospholipid syndrome (APS) is defined as thromboembolic complications and/or pregnancy morbidity in the presence of persistent increased titres of antiphospholipid antibodies. Nevertheless, some patients with clinical signs suggestive of APS are negative for diagnostic antibodies and may be classified as having seronegative-APS (SN-APS). Among the ‘non-diagnostic’ antibodies, a few studies have suggested that the IgG anti-vimentin/cardiolipin antibodies (AVA/CL) may be associated with risk of thrombosis.

Aims

The aim of this case report is to encourage the assessment of non-conventional antibodies in APS.

Patient and methods: We report the case of a 69-year-old male patient with rapid onset of apparently unexplained multiple exclusively arterial thrombotic events in both coronary and peripheral vascular beds.

Results

The patient did not meet the diagnostic criteria for APS but was positive for AVA/CL, which result persisted on further testing at 3 and 6 months.

Discussion

Ongoing research has revealed the existence of non-criteria antibodies which may be relevant for the diagnosis of SN-APS and should be included in the classification criteria for the disease.

LEARNING POINTS

Anti-vimentin antibodies in transplant and disease

Non-HLA antibodies are recognized as a potential source of antibody mediated rejection following transplantation. The epitopes which lead to production of these antibodies are a result of tissue disruption, specifically endothelium, secondary to inflammation and injury. Vimentin is a cytoskeletal protein involved in many aspects of cellular organization, signaling, and proliferation. Recently, antivimentin antibodies have been shown to be important not only for rheumatological autoimmune diseases, but also cardiac and renal transplant dysfunction. In cardiac transplant recipients, antivimentin antibodies are associated with coronary artery vasculopathy and chronic graft loss. In renal transplantation, antivimentin antibodies are detected prior to transplantation and are also correlated with chronic graft dysfunction. In renal transplant recipients, antivimentin antibodies seen prior to transplantation are thought to be secondary to chronic endothelial injury during hemodialysis and therefore more prevalent prior to renal transplant than cardiac transplantation. In this review, we will examine the generation and pathogenesis of antivimentin antibodies. Given that these antibodies appear to be associated with both post-cardiac and -renal transplant dysfunction, developing standard detection paradigms may be important for risk stratification prior to transplantation. Finally, understanding the pathogenesis of antivimentin antibodies may lead to the development potential therapies in order to improve long-term survival.

Autoimmunity to Vimentin Is Associated with Outcomes of Patients with Idiopathic Pulmonary Fibrosis

Autoimmunity has been implicated in the pathogenesis of idiopathic pulmonary fibrosis (IPF); however, the repertoire of autoantigens involved in this disease and the clinical relevance of these autoimmune responses are still being explored. Our initial discovery assays demonstrated that circulating and intrapulmonary vimentin levels are increased in IPF patients. Subsequent studies showed native vimentin induced HLA-DR-dependent in vitro proliferation of CD4 T cells from IPF patients and enhanced the production of IL-4, IL-17, and TGF-β1 by these lymphocytes in contrast to normal control specimens. Vimentin supplementation of IPF PBMC cultures also resulted in HLA-DR-dependent production of IgG with anti-vimentin specificities. Circulating anti-vimentin IgG autoantibody levels were much greater in IPF subjects from the University of Alabama at Birmingham (n = 102) and the University of Pittsburgh (U. Pitt., n = 70) than in normal controls. Anti-vimentin autoantibody levels in IPF patients were HLA biased and inversely correlated with physiological measurements of lung function (i.e., forced expiratory volumes and diffusing capacities). Despite considerable intergroup differences in transplant-free survival between these two independent IPF cohorts, serious adverse outcomes were most frequent among the patients within each population that had the highest anti-vimentin autoantibody levels (University of Alabama at Birmingham: hazard ratio 2.5, 95% confidence interval 1.2-5.3, p = 0.012; University of Pittsburgh: hazard ratio 2.7, 95% confidence interval 1.3-5.5, p = 0.006). These data show that anti-vimentin autoreactivity is prevalent in IPF patients and is strongly associated with disease manifestations. These findings have implications with regard to the pathogenesis of this enigmatic disease and raise the possibility that therapies specifically directed at these autoimmune processes could have therapeutic efficacy.

Anti-vimentin Antibodies Present at the Time of Transplantation May Predict Early Development of Interstitial Fibrosis/Tubular Atrophy

BACKGROUND

Anti-vimentin (a cytoskeletal protein) autoantibodies in renal transplant recipients have been correlated with interstitial fibrosis/tubular atrophy (IFTA). In this study, we examine the association between pretransplantation anti-vimentin antibodies and the subsequent development of IFTA.

METHODS

Sera obtained before renal transplantation from 97 transplant recipients were analyzed for the presence of anti-vimentin antibodies via Luminex assays to determine the concentration of anti-vimentin antibodies. Results were correlated with findings of IFTA on biopsy as well as graft function and patient and graft survival.

RESULTS

In our patient population, 56 of 97 patients were diagnosed by biopsy with IFTA 2.9 (±2.1) years after renal transplantation. Patients with IFTA on biopsy had higher mean concentration of anti-vimentin antibodies when compared to patients without IFTA (32.2 μg/mL [3.97-269.12 μg/mL] vs 14.57 μg/mL [4.71-87.81 μg/mL]). The risk of developing IFTA with a concentration of anti-vimentin antibody >15 μg/mL before transplantation was 1.96 (95% CI = 1.38-2.79, P = .011). Patients with elevated anti-vimentin antibody concentrations (>15 μg/mL) at the time of transplantation also had a higher risk of developing IFTA (81.4% vs 41.2%; P < .05). In addition, graft function was worse at 1, 3, and 5 years posttransplantation in patients with elevated concentrations of pretransplantation anti-vimentin antibody. Although there were more graft losses in the IFTA groups (49.12% vs 25.64%, P = .021) and the IFTA patients loss their grafts earlier (4.3 years vs 3.6 years), there was no statistical difference in graft loss rates.

CONCLUSIONS

Pretransplantation anti-vimentin antibody concentrations >15 μg/mL may be a risk factor for IFTA.

Immune Responses to Tissue-Restricted Nonmajor Histocompatibility Complex Antigens in Allograft Rejection

Chronic diseases that result in end-stage organ damage cause inflammation, which can reveal sequestered self-antigens (SAgs) in that organ and trigger autoimmunity. The thymus gland deletes self-reactive T-cells against ubiquitously expressed SAgs, while regulatory mechanisms in the periphery control immune responses to tissue-restricted SAgs. It is now established that T-cells reactive to SAgs present in certain organs (e.g., lungs, pancreas, and intestine) are incompletely eliminated, and the dysregulation of peripheral immuneregulation can generate immune responses to SAgs. Therefore, chronic diseases can activate self-reactive lymphocytes, inducing tissue-restricted autoimmunity. During organ transplantation, donor lymphocytes are tested against recipient serum (i.e., cross-matching) to detect antibodies (Abs) against donor human leukocyte antigens, which has been shown to reduce Ab-mediated hyperacute rejection. However, primary allograft dysfunction and rejection still occur frequently. Because donor lymphocytes do not express tissue-restricted SAgs, preexisting Abs against SAgs are undetectable during conventional cross-matching. Preexisting and de novo immune responses to tissue-restricted SAgs (i.e., autoimmunity) play a major role in rejection. In this review, we discuss the evidence that supports autoimmunity as a contributor to rejection. Testing for preexisting and de novo immune responses to tissue-restricted SAgs and treatment based on immune responses after organ transplantation may improve short- and long-term outcomes after transplantation.

Advances in Pretransplant Donor-Specific Antibody Testing in Solid Organ Transplantation: From Bench to Bedside

Immunological risk stratification has a central role in determining both the feasibility of solid organ transplantation and the type (and amount) of induction and maintenance immunosuppressive therapy. Currently there is poor consensus on how to exactly estimate the global immunological risk, and most transplant centers adopt complicated internal guidelines for risk stratification. Here we systematically review published evidences that should drive appropriateness in risk stratification, focusing on donor-specific antibodies against HLA and other antigens.

Cardiac Transplantation in the New Era

The prevalence of heart failure continues to rise due to the aging population and longer survival of people with conditions that lead to heart failure, eg, hypertension, diabetes, and coronary artery disease. Although medical therapy has had an important impact on survival of patients and improving quality of life, heart transplantation remains the definitive therapy for patients that eventually deteriorate. Since the first successful heart transplantation in 1967, significant improvements have been made regarding donor and recipient selection, surgical techniques, and postoperative care. However, the number of potential organ donors has not changed and the growing number of patients in need for transplantation has resulted an increase in waiting list time, and the need for mechanical support. To overcome this issue, the United Network for Organ Sharing implemented an allocation system to prioritize the sickest patients on the list to receive organs. Despite the careful selection of patients, pretransplant immunological screening, and multidrug immunosuppressive regimens, acute and chronic rejections occur and potentially limit graft and patient survival. Treatment for rejection largely depends on the type of rejection, the presence of hemodynamic compromise, and time after transplantation. The limiting factor for long-term graft survival is allograft vasculopathy, an immune-mediated process causing diffuse narrowing of the coronary arteries. Percutaneous coronary intervention and coronary artery bypass surgery are often not an option for this vasculopathy due to the lack of focal lesions, and retransplantation is the only option in appropriate patients.

Altered Traffic of Cardiolipin during Apoptosis: Exposure on the Cell Surface as a Trigger for "Antiphospholipid Antibodies"

Apoptosis has been reported to induce changes in the remodelling of membrane lipids; after death receptor engagement, specific changes of lipid composition occur not only at the plasma membrane, but also in intracellular membranes. This paper focuses on one important aspect of apoptotic changes in cellular lipids, namely, the redistribution of the mitochondria-specific phospholipid, cardiolipin (CL). CL predominantly resides in the inner mitochondrial membrane, even if the rapid remodelling of its acyl chains and the subsequent degradation occur in other membrane organelles. After death receptor stimulation, CL appears to concentrate into mitochondrial “raft-like” microdomains at contact sites between inner and outer mitochondrial membranes, leading to local oligomerization of proapoptotic proteins, including Bid. Clustering of Bid in CL-enriched contacts sites is interconnected with pathways of CL remodelling that intersect membrane traffic routes dependent upon actin. In addition, CL association with cytoskeleton protein vimentin was observed. Such novel association also indicated that CL molecules may be expressed at the cell surface following apoptotic stimuli. This observation adds a novel implication of biomedical relevance. The association of CL with vimentin at the cell surface may represent a “new” target antigen in the context of the apoptotic origin of anti-vimentin/CL autoantibodies in Antiphospholipid Syndrome.

Acute Antibody-Mediated Rejection in Presence of MICA-DSA and Successful Renal Re-Transplant with Negative-MICA Virtual Crossmatch

The presence of donor-specific alloantibodies (DSAs) against the MICA antigen results in high risk for antibody-mediated rejection (AMR) of a transplanted kidney, especially in patients receiving a re-transplant. We describe the incidence of acute C4d+ AMR in a patient who had received a first kidney transplant with a zero HLA antigen mismatch. Retrospective analysis of post-transplant T and B cell crossmatches were negative, but a high level of MICA alloantibody was detected in sera collected both before and after transplant. The DSA against the first allograft mismatched MICA*018 was in the recipient. Flow cytometry and cytotoxicity tests with five samples of freshly isolated human umbilical vein endothelial cells demonstrated the alloantibody nature of patient’s MICA-DSA. Prior to the second transplant, a MICA virtual crossmatch and T and B cell crossmatches were used to identify a suitable donor. The patient received a second kidney transplant, and allograft was functioning well at one-year follow-up. Our study indicates that MICA virtual crossmatch is important in selection of a kidney donor if the recipient has been sensitized with MICA antigens.

Expression of Vimentin Intermediate Filament for Vascular Development in Olive Flounder (Paralichthys olivaceus)

Cardiovascular system is the primary organ to develop and reach a functional state, which underscores the essential role of the vasculature in the developing embryo. The vasculature is a highly specialized organ that functions in a number of key physiological works including the carrying of oxygen and nutrients to tissues. It is closely involved in the formation of heart, and hence it is essential for survival during the hatching period. The expression of genes involved during vascular development in the olive flounder (Paralichthys olivaceus) in the days after hatching is not fully understood. Therefore, we examined the expression patterns of genes activated during the development of flounder. Microscopic observations showed that formation of blood vessels is related to the expression of the vimentin gene. Also, the temporal expression patterns of this vimentin-like gene in the developmental stages and in the normal tissues of olive flounder. The purpose of this study was to examine the expression patterns of vimentin in normal tissues of the olive flounder and during the development of the vascular system in newly hatched olive flounders and HIF-1 plays a vital role in the formation of blood vessels during development. Vimentin expression was strong at the beginning of the development of blood vessels, and was present throughout all developmental stages. Our findings have important implications with respect to the roles of vimentin and HIF-1 in the development and evolution of the first blood vessels in olive flounder. Further studies are required to elucidate the vimentin-mediated hypoxic response signal transduction and to decipher the functional role of vimentin in developmental stages.

Vascular endothelium as a target of immune response in renal transplant rejection

This review of clinical and experimental studies aims at analyzing the interplay between graft endothelium and host immune system in renal transplantation, and how it affects the survival of the graft. Graft endothelium is indeed the first barrier between self and non-self that is encountered by host lymphocytes upon reperfusion of vascularized solid transplants. Endothelial cells (EC) express all the major sets of antigens (Ag) that elicit host immune response, and therefore represent a preferential target in organ rejection. Some of the Ag expressed by EC are target of the antibody-mediated response, such as the AB0 blood group system, the human leukocyte antigens (HLA), and MHC class I related chain A antigens (MICA) systems, and the endothelial cell-restricted Ag; for each of these systems, the mechanisms of interaction and damage of both preformed and de novo donor-specific antibodies are reviewed along with their impact on renal graft survival. Moreover, the rejection process can force injured EC to expose cryptic self-Ag, toward which an autoimmune response mounts, overlapping to the allo-immune response in the damaging of the graft. Not only are EC a passive target of the host immune response but also an active player in lymphocyte activation; therefore, their interaction with allogenic T-cells is analyzed on the basis of experimental in vitro and in vivo studies, according to the patterns of expression of the HLA class I and II and the co-stimulatory molecules specific for cytotoxic and helper T-cells. Finally, as the response that follows transplantation has proven to be not necessarily destructive, the factors that foster graft endothelium functioning in spite of rejection, and how they could be therapeutically harnessed to promote long-term graft acceptance, are described: accommodation that is resistance of EC to donor-specific antibodies, and endothelial cell ability to induce Foxp3+ regulatory T-cells, that are crucial mediators of tolerance.

Role of anti-vimentin antibodies in renal transplantation

BACKGROUND

The role of non-HLA antibodies in rejection is not clear. We investigate whether antibodies to vimentin are made after renal transplantation and if production is associated with interstitial fibrosis and tubular atrophy (IFTA).

METHODS

In this retrospective study, sera from 70 recipients of renal allografts (40 controls, 30 IFTA) were studied. The biopsy diagnosis of interstitial fibrosis and tubular atrophy (IFTA) was based on random, cause-indicating biopsies. Sera were collected pretransplant and at 3 monthly intervals up to 5 years posttransplant or diagnosis of IFTA and assayed by ELISA for IgM and IgG anti-vimentin antibodies (AVA) and HLA antibodies.

RESULTS

Mean titers of IgM AVA were higher at every year after transplantation compared with pretransplant for both IFTA and controls groups (P<0.001). There was no difference in the mean level of IgM AVA achieved by IFTA and control groups. The mean pretransplant levels of IgG AVA in the IFTA and control group were 18.2±11.7 and 11.0±8.1, respectively (P=0.001). There was a significant increase between the pretransplant mean levels of IgG AVA and the levels at years 1 to 4 in the IFTA group (years 1-3, P<0.0001, year 4 P=0.003) but not in the controls. There was no significant difference between the numbers of IFTA or control patients achieving a positive value (mean+2SD of pretransplant antibody titers) of IgM AVA (50% versus 37.5%, respectively) or IgG AVA (26.6% versus 12.5%, respectively). There was no association between production of HLA and AVA antibodies.

CONCLUSION

Posttransplant production of IgM AVA is not associated with IFTA. The production of IgG AVA by a minority of IFTA patients suggests that in some individuals, IgG AVA may be involved in the pathology of IFTA.

Interplay between immune responses to HLA and non-HLA self-antigens in allograft rejection

Recent studies strongly suggest an increasing role for immune responses against self-antigens (Ags) which are not encoded by the major histocompatibility complex in the immunopathogenesis of allograft rejection. Although, improved surgical techniques coupled with improved methods to detect and avoid sensitization against donor human leukocyte antigen (HLA) have improved the immediate and short term function of transplanted organs. However, acute and chronic rejection still remains a vexing problem for the long term function of the transplanted organ. Immediately following organ transplantation, several factors both immune and non immune mechanisms lead to the development of local inflammatory milieu which sets the stage for allograft rejection. Traditionally, development of antibodies (Abs) against mismatched donor HLA have been implicated in the development of Ab mediated rejection. However, recent studies from our laboratory and others have demonstrated that development of humoral and cellular immune responses against non-HLA self-Ags may contribute in the pathogenesis of allograft rejection. There are reports demonstrating that immune responses to self-Ags especially Abs to the self-Ags as well as cellular immune responses especially through IL17 has significant pro-fibrotic properties leading to chronic allograft failure. This review summarizes recent studies demonstrating the role for immune responses to self-Ags in allograft immunity leading to rejection as well as present recent evidence suggesting there is interplay between allo- and autoimmunity leading to allograft dysfunction.

Platelets: versatile modifiers of innate and adaptive immune responses to transplants

PURPOSE OF REVIEW

Over the last decade there has been mounting experimental data demonstrating that platelets contribute to acute vascular inflammation and atherosclerosis. This review focuses on recent findings that link platelets to inflammatory responses of relevance to transplants.

RECENT FINDINGS

Although it has been known that platelets modify vascular inflammation by secretion of soluble mediators and release of microparticles, new aspects of these mechanisms are being defined. For example, platelet-derived CCL5 not only functions in homomers, but also forms more potent heteromers with platelet factor 4 (PF4; CXCL4). This heteromer formation can be inhibited with small molecules. New findings also demonstrate heterologous interactions of platelet microparticles with leukocytes that may increase their range of impact. By attaching to neutrophils, platelet microparticles appear to migrate out of blood vessels and into other compartments where they stimulate secretion of cytokines. Contact of platelets with extracellular matrix also can result in cleavage of hyaluronan into fragments that serve as an endogenous danger signal.

SUMMARY

Recent findings have expanded the range of interactions by which platelets can modify innate and adaptive immune responses to transplants.

Role of anti-vimentin antibodies in allograft rejection

Production of anti-vimentin antibodies (AVA) after solid organ transplantation are common. Although classically thought to be expressed mainly within the cytosol, recent evidence demonstrates that extracellular or cell surface expression of vimentin is not unusual. This review examines the evidence to assess whether AVA contribute to allograft pathology. Clinical studies suggest that AVA are associated with cardiac allograft vasculopathy in heart transplant recipients. Studies in non-human primates confirm that production of AVA after renal and heart transplantation are not inhibited by Cyclosporine. Experimental studies have demonstrated that mice pre-immunised with vimentin undergo accelerated acute rejection and vascular intimal occlusion of cardiac allografts. Adoptive transfer of hyperimmune sera containing AVA into B-cell-knock-out mice caused accelerated rejection of allografted hearts, this is clear evidence that antibodies to vimentin accelerate rejection. AVA act in concert with the alloimmune response and AVA do not damage syngeneic or native heart allografts. Confocal microscopy of allografted organs in vimentin immunised mice shows extensive expression of vimentin on endothelial cells, apoptotic leukocytes and platelet/leukocyte conjugates, co-localising with C4d. One explanation for the ability of AVA to accelerate rejection would be fixation of complement within the graft and subsequent pro-inflammatory effects; there may also be interactions with platelets within the vasculature.

Consensus guidelines on the testing and clinical management issues associated with HLA and non-HLA antibodies in transplantation

BACKGROUND

The introduction of solid-phase immunoassay (SPI) technology for the detection and characterization of human leukocyte antigen (HLA) antibodies in transplantation while providing greater sensitivity than was obtainable by complement-dependent lymphocytotoxicity (CDC) assays has resulted in a new paradigm with respect to the interpretation of donor-specific antibodies (DSA). Although the SPI assay performed on the Luminex instrument (hereafter referred to as the Luminex assay), in particular, has permitted the detection of antibodies not detectable by CDC, the clinical significance of these antibodies is incompletely understood. Nevertheless, the detection of these antibodies has led to changes in the clinical management of sensitized patients. In addition, SPI testing raises technical issues that require resolution and careful consideration when interpreting antibody results.

METHODS

With this background, The Transplantation Society convened a group of laboratory and clinical experts in the field of transplantation to prepare a consensus report and make recommendations on the use of this new technology based on both published evidence and expert opinion. Three working groups were formed to address (a) the technical issues with respect to the use of this technology, (b) the interpretation of pretransplantation antibody testing in the context of various clinical settings and organ transplant types (kidney, heart, lung, liver, pancreas, intestinal, and islet cells), and (c) the application of antibody testing in the posttransplantation setting. The three groups were established in November 2011 and convened for a "Consensus Conference on Antibodies in Transplantation" in Rome, Italy, in May 2012. The deliberations of the three groups meeting independently and then together are the bases for this report.

RESULTS

A comprehensive list of recommendations was prepared by each group. A summary of the key recommendations follows. Technical Group: (a) SPI must be used for the detection of pretransplantation HLA antibodies in solid organ transplant recipients and, in particular, the use of the single-antigen bead assay to detect antibodies to HLA loci, such as Cw, DQA, DPA, and DPB, which are not readily detected by other methods. (b) The use of SPI for antibody detection should be supplemented with cell-based assays to examine the correlations between the two types of assays and to establish the likelihood of a positive crossmatch (XM). (c) There must be an awareness of the technical factors that can influence the results and their clinical interpretation when using the Luminex bead technology, such as variation in antigen density and the presence of denatured antigen on the beads. Pretransplantation Group: (a) Risk categories should be established based on the antibody and the XM results obtained. (b) DSA detected by CDC and a positive XM should be avoided due to their strong association with antibody-mediated rejection and graft loss. (c) A renal transplantation can be performed in the absence of a prospective XM if single-antigen bead screening for antibodies to all class I and II HLA loci is negative. This decision, however, needs to be taken in agreement with local clinical programs and the relevant regulatory bodies. (d) The presence of DSA HLA antibodies should be avoided in heart and lung transplantation and considered a risk factor for liver, intestinal, and islet cell transplantation. Posttransplantation Group: (a) High-risk patients (i.e., desensitized or DSA positive/XM negative) should be monitored by measurement of DSA and protocol biopsies in the first 3 months after transplantation. (b) Intermediate-risk patients (history of DSA but currently negative) should be monitored for DSA within the first month. If DSA is present, a biopsy should be performed. (c) Low-risk patients (nonsensitized first transplantation) should be screened for DSA at least once 3 to 12 months after transplantation. If DSA is detected, a biopsy should be performed. In all three categories, the recommendations for subsequent treatment are based on the biopsy results.

CONCLUSIONS

A comprehensive list of recommendations is provided covering the technical and pretransplantation and posttransplantation monitoring of HLA antibodies in solid organ transplantation. The recommendations are intended to provide state-of-the-art guidance in the use and clinical application of recently developed methods for HLA antibody detection when used in conjunction with traditional methods.

Nonstereotyped lymphoma B cell receptors recognize vimentin as a shared autoantigen

Ag activation of the BCR may play a role in the pathogenesis of human follicular lymphoma (FL) and other B cell malignancies. However, the nature of the Ag(s) recognized by tumor BCRs has not been well studied. In this study, we used unbiased approaches to demonstrate that 42 (19.35%) of 217 tested FL Igs recognized vimentin as a shared autoantigen. The epitope was localized to the N-terminal region of vimentin for all vimentin-reactive tumor Igs. We confirmed specific binding to vimentin by using recombinant vimentin and by performing competitive inhibition studies. Furthermore, using indirect immunofluorescence staining, we showed that the vimentin-reactive tumor Igs colocalized with an anti-vimentin mAb in HEp-2 cells. The reactivity to N-terminal vimentin of IgG FL Igs was significantly higher than that of IgM FL Igs (30.4 versus 10%; p = 0.0022). However, vimentin-reactive FL Igs did not share CDR3 motifs and were not homologous. Vimentin was expressed in the T cell-rich regions of FL, suggesting that vimentin is available for binding with tumor BCRs within the tumor microenvironment. Vimentin was also frequently recognized by mantle cell lymphoma and multiple myeloma Igs. Our results demonstrate that vimentin is a shared autoantigen recognized by nonstereotyped FL BCRs and by the Igs of mantle cell lymphoma and multiple myeloma and suggest that vimentin may play a role in the pathogenesis of multiple B cell malignancies. These findings may lead to a better understanding of the biology and natural history of FL and other B cell malignancies.

Detection of antibodies to self-antigens (K-alpha 1 tubulin, collagen I, II, IV, and V, myosin, and vimentin) by enzyme-linked immunosorbent assay (ELISA)

The enzyme-linked immunosorbent assay (ELISA) is a widely used technique for detecting antibodies (Abs) and is employed in clinical laboratories to identify Abs against various self-antigens-autoAb development and quantitation. This method relies on specific antigen-Ab interactions where one of the components is immobilized on a solid surface. Using this method, the concentrations of antigens or Ab present in the serum can be quantified with high specificity and accuracy. Here, we describe the detection of autoAbs to various self-antigens with different tissue restriction patterns which includes collagens, k-α1 tubulin, vimentin, and myosin. We also discuss their relevance in monitoring for rejection following solid organ transplantation.

Role of antibodies to self-antigens in chronic allograft rejection: potential mechanism and therapeutic implications

Significant progress has been made in preventing acute allograft rejection following solid organ transplantation resulting in improved allograft survival. However, long term function still remains disappointing primarily due to chronic allograft rejection. Alloimmune responses primarily defined by the development of antibodies (Abs) to donor mismatched major histocompatibility antigens during the post-transplantation period have been strongly correlated to the development of chronic rejection. In addition, recent studies have demonstrated an important role for autoimmunity including the development of Abs to organ specific self-antigens in the pathogenesis of chronic allograft rejection. Based on this, a new paradigm has evolved indicating a possible cross-talk between the alloimmune responses and autoimmunity leading to chronic rejection. In this review, we will discuss the emerging concept for the role of cellular and humoral immune responses to self-antigens in the immunopathogenesis of chronic allograft rejection which has the potential to develop new strategies for the prevention and/or treatment of chronic rejection.

An important role for autoimmunity in the immunopathogenesis of chronic allograft rejection

Organ transplantation is the treatment of choice for patients with end-stage organ dysfunction. In spite of advances in understanding of donor and recipient physiology, organ preservation, operative techniques and immunosuppression, long-term graft survival still remains a major problem primarily due to chronic rejection. Alloimmune responses to mismatched major histocompatibility antigens have been implicated as an important factor leading to rejection. However, there is increasing evidence pointing towards cross-talk between the alloimmune and autoimmune responses creating a local inflammatory milieu, which eventually leads to fibrosis and occlusion of the lumen in the transplanted organ i.e. chronic rejection. In this review, we will discuss recent studies and emerging concepts for the interdependence of alloimmune and autoimmune responses in the immunopathogenesis of chronic allograft rejection. The role of autoimmunity in the development of chronic rejection is an intriguing and exciting area of research in the field of solid-organ transplantation with a significant potential to develop novel therapeutic strategies towards preventing chronic allograft rejection.

Interaction of cowpea mosaic virus nanoparticles with surface vimentin and inflammatory cells in atherosclerotic lesions

AIMS

Detection of atherosclerosis has generally been limited to the late stages of development, after cardiovascular symptoms present or a clinical event occurs. One possibility for early detection is the use of functionalized nanoparticles. The aim of this study was the early imaging of atherosclerosis using nanoparticles with a natural affinity for inflammatory cells in the lesion.

MATERIALS & METHODS

We investigated uptake of cowpea mosaic virus by macrophages and foam cells in vitro and correlated this with vimentin expression. We also examined the ability of cowpea mosaic virus to interact with atherosclerotic lesions in a murine model of atherosclerosis.

RESULTS & CONCLUSION

We found that uptake of cowpea mosaic virus is increased in areas of atherosclerotic lesion. This correlated with increased surface vimentin in the lesion compared with nonlesion vasculature. In conclusion, cowpea mosaic virus and its vimentin-binding region holds potential for use as a targeting ligand for early atherosclerotic lesions, and as a probe for detecting upregulation of surface vimentin during inflammation.

A shift in the collagen V antigenic epitope leads to T helper phenotype switch and immune response to self-antigen leading to chronic lung allograft rejection

Immune responses to human leucocyte antigen (HLA) and self-antigen collagen V (Col-V) have been proposed in the pathogenesis of chronic rejection (bronchiolitis obliterans syndrome, BOS) following human lung transplantation (LTx). In this study, we defined the role for the shift in immunodominant epitopes of Col-V in inducing T helper phenotype switch leading to immunity to Col-V and BOS. Sera and lavage from BOS(+) LTx recipients with antibodies to Col-V were analysed. Two years prior to BOS, patients developed antibodies to both Col-V,α1(V) and α2(V) chains. However, at clinical diagnosis of BOS, antibodies became restricted to α1(V). Further, lung biopsy from BOS(+) patients bound to antibodies to α1(V), indicating that these epitopes are exposed. Fourteen Col-V peptides [pep1-14, pep1-4 specific to α1(V), pep5-8 to α1,2(V) and pep9-14 to α2(V)] which bind to HLA-DR4 and -DR7, demonstrated that prior to BOS, pep 6, 7, 9, 11 and 14 were immunodominant and induced interleukin (IL)-10. However, at BOS, the response switched to pep1, 4 and 5 and induced interferon (IFN)-γ and IL-17 responses, but not IL-10. The T helper (Th) phenotype switch is accompanied by decreased frequency of regulatory T cells (T(regs) ) in the lavage. LTx recipients with antibodies to α1(V) also demonstrated increased matrix metalloproteinase (MMP) activation with decreased MMP inhibitor, tissue inhibitor of metalloproteinase (TIMP), suggesting that MMP activation may play a role in the exposure of new Col-V antigenic epitopes. We conclude that a shift in immunodominance of self-antigenic determinants of Col-V results in induction of IFN-γ and IL-17 with loss of tolerance leading to autoimmunity to Col-V, which leads to chronic lung allograft rejection.

Validation of flow cytometric detection of platelet microparticles and liposomes by atomic force microscopy

BACKGROUND

Platelet microparticles (PMPs) are a promising prognostic marker for thrombotic disorders because of their release during platelet activation. The use of flow cytometry for the enumeration of PMPs in plasma has generated controversy due to their size, which is below the stated detection limits of conventional flow cytometry instruments. The potential impact of this is an underestimation of PMP counts.

OBJECTIVES/METHODS

To address this possibility, we used a combination of fluorescence-activated cell sorting (FACS) and atomic force microscopy (AFM) to determine the size distribution of PMPs present in plasma from acute myocardial infarction (AMI) patients and normal volunteers, and PMPs generated by expired platelet concentrates and washed platelets treated with agonists such as thrombin and calcium ionophore (A23187).

RESULTS

According to AFM image analysis, there was no statistically significant difference in height or volume distributions in PMPs from thrombin-activated, calcium ionophore-activated, expired platelet concentrates and plasma from healthy volunteers and AMI patients. Based on volume, expired platelets released the greatest proportion of exosomes (< 1.0 × 10(-22) L(3) in volume) in relation to the entire PMP population (29.7%) and the smallest proportion of exosomes was observed in AMI patient plasma (1.8%). Moreover, AFM imaging revealed that PMPs from expired platelets exhibited smooth surfaces compared with other PMP types but this was not statistically significant.

CONCLUSIONS

We confirm that flow cytometry is capable of analyzing PMPs from plasma by using AFM to perform nanoscale measurements of individual PMP events isolated by FACS. This method also provided the first quantitative nanoscale images of PMP ultrastructure.

B cells in cardiac transplants: from clinical questions to experimental models

After many years of debate, there is now general agreement that B cells can participate in the immune response to cardiac transplants. Acute antibody-mediated rejection (AMR) is the best defined manifestation of B cell responses, but diagnostic and mechanistic questions still surround AMR. Many complement dependent mechanisms of antibody-mediated injury have been elucidated. C5 has become a therapeutic target that may not just truncate complement activation, but also may tip the balance away from inflammation by altering macrophage function. Additional complement independent effects have been identified. These may escape diagnosis and progress to chronic graft injury. The function of B cell infiltrates in cardiac transplants is even more enigmatic. Nodular endocardial infiltrates that contain B cells and plasma cells have been described in protocol biopsies of cardiac transplants for decades, but an understanding of their significance is still evolving based on more critical morphological and molecular evaluation of these infiltrates. A range of infiltrates containing B cells has also been described in the epicardial fat in transplants with advanced chronic rejection. B cells have been observed in endocardial and epicardial tertiary lymphoid nodules, but their impact on antigen presentation or antibody production remains to be determined. Experimental models in small and large animals suggest that B cells could be essential for the formation of lymphoid nodules through cytokine production. Similarly, the role of proinflammatory adipokines in the formation or function of epicardial lymphoid nodules has not been studied. These clinical observations provide critical questions to be addressed in experimental models.

A role for antibodies to human leukocyte antigens, collagen-V, and K-α1-Tubulin in antibody-mediated rejection and cardiac allograft vasculopathy

BACKGROUND

We determined the role of donor-specific antibodies (DSA) and antibodies (Abs) to self-antigens, collagen-V (Col-V), and K-α1-Tubulin (KAT) in pathogenesis of acute antibody-mediated rejection (AMR) and cardiac allograft vasculopathy (CAV) after human heart transplantation (HTx).

METHODS

One hundred thirty-seven HTx recipients, with 60 early period (≤ 12 months) and 77 late period (>12 months), were enrolled in this study. Circulating DSA was determined using LUMINEX. Abs against Col-I, II, IV, V, and KAT were measured using ELISA. Frequency of CD4+T helper cells (CD4+Th) secreting interferon (IFN)-γ, interleukin (IL)-5, -10, or -17 specific to self-antigens were determined using Enzyme Linked Immunosorbent Spot assay.

RESULTS

A significant association between AMR and DSA was demonstrated. Development of DSA in AMR patients correlated well with the development of auto-Abs to Col-V (AMR[+]: 383 ± 72 μg/mL, AMR[-]: 172 ± 49 μg/mL, P=0.033) and KAT (AMR[+]: 252 ± 49 μg/mL, AMR[-]: 61 ± 21 μg/mL, P=0.014). Patients who developed AMR demonstrated increased frequencies of CD4+Th secreting IFN-γ and IL-5 with reduction in IL-10 specific for Col-V/KAT. Patients diagnosed with CAV also developed DSA and auto-Abs to Col-V (CAV[+]: 835 ± 142 μg/mL, CAV[-]: 242 ± 68 μg/mL, P=0.025) and KAT (CAV[+]: 768 ± 206 μg/mL, CAV[-]: 196 ± 72 μg/mL, P=0.001) with increased frequencies of CD4+Th secreting IL-17 with reduction in IL-10 specific for Col-V/KAT. CONCLUSIONS.: Development of Abs to human leukocyte antigens and self-antigens are associated with increases in CD4+Th secreting IFN-γ and IL-5 in AMR and IL-17 in CAV, with reduction in CD4+Th secreting IL-10 in both AMR and CAV.

Cardiac allograft vasculopathy: do adipocytes bridge alloimmune and metabolic risk factors?

PURPOSE OF REVIEW

Cardiac allograft vasculopathy (CAV) is still a major cause of chronic graft failure. CAV develops in the coronary arteries as a diffuse, concentric expansion of the intima in conjunction with inflammation and fibrosis of the adventitia. We review recent publications that could link metabolic and immunologic risk factors for CAV.A concept is offered that periarterial adipocytes may provide proinflammatory cytokines that augment immune injury of the coronary arteries.

RECENT FINDINGS

Clinical and experimental evidence indicate that some alloantibodies and autoantibodies are associated with CAV. Limited data are available on the expression of target antigens on coronary arteries at different times after transplantation. Perivascular adipose tissue is an abundant source of IL-6, IL-8 and MCP-1. Adding to the inflammatory bias, perivascular adipocytes secrete less of the anti-inflammatory adiponectin in comparison to other types of fat. Adiponectin modulates expression of adhesion molecules on the vascular endothelium. It also decreases neointimal formation in arteries following mechanical endovascular injury.

SUMMARY

Alterations in the balance between proinflammatory and anti-inflammatory cytokines secreted by perivascular fat have been implicated in atherosclerosis and restenosis. This imbalance may also augment the immune responses in the coronary arteries of transplanted hearts.

Alloimmunity and autoimmunity in chronic rejection

PURPOSE OF REVIEW

Recent studies demonstrate an increasing role for alloimmune responses in the disruption of self-tolerance leading to immune responses to self-antigens that play a role in the immunopathogenesis of chronic rejection following solid organ transplantation. This review summarizes recent studies and implications for the alloimmune-response-induced de-novo development of autoimmune responses following solid organ transplantations.

RECENT FINDINGS

Immediately following organ transplantation, several factors lead to enduring an inflammatory milieu. Studies from our laboratory and others have demonstrated that development of antihuman leukocyte antigen antibodies precedes the development of chronic rejection. Using an in-vivo murine model, we have demonstrated that administration of anti-major histocompatibility complex (MHC) class I directly into the native lungs leads to chronic rejection pathology. Further, the in-vitro ligation of epithelial cell surface MHC class I molecules by specific anti-MHC can lead to cell activation and production of fibrinogenic growth factors.

SUMMARY

On the basis of these findings, we hypothesized that alloimmune responses can lead to autoimmunity, thus playing an important role in chronic rejection. Characterization of both the temporal occurrence and functional significance of antibodies to self-antigens may provide insight into the pathogenesis of chronic rejection and these antibodies can serve as clinically useful biomarkers.

Non-MHC antigenic targets of the humoral immune response in transplantation

There is a growing body of data supporting a role for non-HLA antibodies in acute and chronic rejection of solid organ transplants. While many of these non-HLA antigens remain poorly defined, the principal antigenic targets are expressed on cells of the allograft including endothelium and epithelium. These non-HLA antigens are classified as either alloantigens, such as the major histocompatibility complex class I chain-related gene A (MICA) or MICB, or tissue-specific autoantigens such as vimentin, cardiac myosin (CM), collagen V (Col V), agrin, and angiotensin II receptor type I (AT1). Herein we provide an overview of the non-MHC antigenic targets that have been implicated in graft rejection and discuss the interplay between alloimmunity and autoreactivity in graft rejection.

Humoral autoimmunity and transplant vasculopathy: when allo is not enough

For several decades, allograft rejection was believed to be mediated almost exclusively by cellular immune responses, but it is now realized that humoral responses also play a major role. Although directed typically against donor human leukocyte antigen, it is becoming increasingly evident that the antibody response can also target autoantigens that are shared between donor and recipient and that this autoantibody may contribute to graft rejection. Many aspects of transplant-induced humoral autoimmunity remain poorly understood and key questions persist; not least what triggers the response and how autoantibody causes graft damage. Here, we collate results from recent clinical and experimental studies in transplantation and autoimmune diseases to propose answers to these questions.

Vimentin/cardiolipin complex as a new antigenic target of the antiphospholipid syndrome

Antiphospholipid syndrome (APS) is an autoimmune disease characterized by arterial and venous thrombosis, recurrent abortions, and antiphospholipid antibodies (aPL). However, it is possible to find patients with clinical signs of APS who persistently test negative for aPL (seronegative APS, or SN-APS). The aim of this study was to identify new antigenic target(s) of autoantibodies in APS patients, which may also be recognized in SN-APS. We tested sera from patients with SN-APS with a proteomic approach by analyzing endothelial cell-surface membrane proteins. Sera from SN-APS patients revealed 2 reactive spots corresponding to vimentin, a protein that is shown to bind cardiolipin in vitro. Antivimentin/cardiolipin antibodies were tested in 29 SN-APS patients, 40 APS patients, 30 patients with systemic lupus erythematosus, 30 with rheumatoid arthritis, 30 with venous or arterial thrombosis, and 32 healthy control patients. We observed that not only a large proportion of SN-APS patients but also almost all the APS patients displayed the presence of antivimentin/cardiolipin antibodies. To verify the possible pathogenic role of these autoantibodies, we demonstrated that affinity-purified antivimentin/cardiolipin antibodies induced interleukin receptor-associated kinase phosphorylation and nuclear factor-κB activation in endothelial cells. Our results prompt to identify vimentin as a "new" cofactor for aPL, which may represent a useful tool mainly in SN-APS patients.

Antihuman leukocyte antigen antibody-induced autoimmunity: role in chronic rejection

PURPOSE OF REVIEW

We provide evidence for the role of de-novo development of immune responses to self-antigens in the posttransplant period and its possible induction by alloimmunity in the pathogenesis of chronic rejection following lung, heart and kidney transplantation. The present review details recent findings for the two distinct yet interdependent immune processes in the immunopathogenesis of chronic rejection.

RECENT FINDINGS

The contribution of both humoral and cell-mediated alloimmune responses against mismatched donor histocompatibility antigens (HLA) in the pathogenesis of chronic rejection is well established. Recent studies have focused on development of immune responses to self-antigens during the posttransplant period and its correlation with chronic rejection. These self-antigens include myosin and vimentin in cardiac, K-alpha-1-tubulin and collagen-V in lung and angiotensin II type 1 receptor, collagen-IV and VI in kidney transplants. During the posttransplant period, the development of immune responses to self-antigens is facilitated by induction of a distinct subset of autoreactive T-helper cells referred to as Th17 cells.

SUMMARY

Following organ transplantation, tissue injury and remodeling inflicted by antibodies (Abs) to HLA antigens is conducive to develop autoimmunity. Abs to HLA and self-antigens are detectable in the serum of transplant recipients who develop chronic rejection. Anti-HLA Abs are often present transiently but precede the development of Abs to self-antigens.