Mechanisms Of Antibody-mediated Rejection Research Articles

Update on Treatment and Prevention of Chronic Antibody Mediated Rejection in Renal Transplant Recipients

Chronic antibody mediated rejection (AMR) is a major cause of allograft failure1,2. Chronic AMR clinically presents with proteinuria and gradual decline in renal function. The underlying mechanisms of AMR include both antibody mediated complement-dependent cytotoxicity, complement-independent cellular cytotoxicity and other mechanisms. The purpose of this review is to appraise recent literature on diagnosis, treatment and prevention of chronic AMR.

Methods to Detect MHC-Specific IgE in Mice and Men.

Humoral immunity is a major barrier limiting long-term outcome after organ transplantation. Especially, the production of antibodies directed against donor HLA/MHC antigens (i.e. donor-specific antibodies (DSA)) leading to antibody-mediated rejection (ABMR) is considered to be a major factor negatively affecting allograft survival. DSAs of the IgG isotype are routinely measured in transplant patients. However, not all patients diagnosed with IgG-DSA develop ABMR events. Therefore, research in better understanding the mechanisms of ABMR is of great importance. We recently demonstrated the production of MHC-specific IgE upon allograft rejection in mice and in transplant patients. IgE is classically connected with allergy and is known to be important for the humoral defense against helminths and worms. However, its role in autoimmune diseases and cancer has been reported recently as well. The concentration of IgE in blood is extremely low compared to other antibody isotypes. Therefore, detection of MHC-specific IgE from serum requires methods of high sensitivity. Since MHC-specific IgG—typically present at much higher serum levels—develops as well, high specificity is also required of IgE detection methods. In the murine model we developed an enzyme linked immunosorbent assay (ELISA) using MHC monomers for measurement of MHC-specific IgE, allowing us to distinguish between specificities of antibodies against different class I and class II antigens. For measurement of functional activity of MHC-specific IgE in vitro, a release assay using a rat basophil cell line (RBL-2H3) was established. For functional analysis of MHC-specific IgE in vivo, a cutaneous hypersensitivity reaction assay was adapted for this purpose using MHC monomers. Humanized RBL-2H3 cells transfected with cDNA coding for the human-high affinity IgE receptor were used for functionality measurement of donor-specific IgE in sensitized transplant patients. For detection of HLA-specific IgE, a bead assay was adapted, using beads expressing single HLA antigens. The aim of this publication is to demonstrate currently established methods for the detection and characterization of MHC-specific IgE in the murine and human setting.

An overview of T follicular cells in transplantation: spotlight on their clinical significance

ABSTRACTIntroduction: For late stage organ failure patients, transplantation is the best option to increase life expectancy with a superior quality of life. Unfortunately, after transplantation many patients are at risk of cellular and antibody-mediated rejection (ABMR). The latter is initiated by donor specific antibodies (DSA) which depend on the actions of B cells, T follicular helper (Tfh) cells and T follicular regulatory (Tfr) cells that are present in the germinal center of lymphoid organs.Areas covered: In this overview paper, we discuss the biology and function of Tfh and Tfr cells in lymphoid tissues, transplanted organs and their circulating counterparts. We report on their relevance to alloimmunity and on the effects of immunosuppressive drugs on these immunocompetent cell populations.Expert opinion: Growing knowledge about the actions of Tfh and Tfr allows for a better understanding of the immunological mechanisms of ABMR after organ transplantation. This understanding feeds the hypothesis that immunosuppressive drugs targeting the actions of Tfh cells have huge therapeutic potential. This new concept in the treatment of the humoral rejection response will improve graft and patient survival after organ transplantation.

Does the antibody mediated rejection grading scale have prognostic prediction? Yes, but the picture is still blurry.

Antibody-mediated rejection (ABMR) is a condition difficult to diagnose and treat, which may significantly impair the outcome of heart transplant recipients. In clinical practice, diagnosis is based on immunopathology grading of endomyocardial biopsies (EMB). Despite its value, the current diagnostic system has several pitfalls that have been addressed in recent literature. Pathology grading of ABMR (pAMR) has a relevant prognostic factor. However, it does not capture several nuances, such as chronic vs. acute ABMR, mixed rejection or microvascular inflammation. Molecular biology-based assays are shedding new light on the mechanisms of ABMR, which could improve the precision of ABMR diagnosis. These new findings have the potential to rearrange EMB grading system and to guide more precisely decision-making, but studies validating the therapeutic management based on molecular-pathology coupling are still missing.

Mechanisms of Antibody Mediated Rejection in the Absence of Donor Specific Antibodies

Purpose Antibody mediated rejection (AMR) is an increasingly studied cause of graft failure and cardiac allograft vasculopathy. The 1990 ISHLT Working Formulation first defined AMR as positive immunofluorescence staining of active complement in the graft endothelium and/or histologic evidence of vasculitis or severe edema in the absence of cellular infiltrates. Subsequent criteria included LV dysfunction plus donor specific antibodies (DSA); however the most recent criteria require pathological findings alone. This created a subset of patients with AMR without known mechanism. We hypothesized that non-HLA antibodies, i.e. other autoantibodies or natural antibodies (Nabs, poly-reactive antibodies against apoptotic cells), not identified by standard Luminex analysis, could be responsible for DSA-negative AMR. Methods We evaluated the pre-transplant sera of 74 heart transplant (HT) recipients between 2011-14 at our institution. Patients were categorized as having pathologic findings of AMR (pAMR1 or higher) in the presence of DSA, AMR in the absence of DSA or no AMR (controls). Serum obtained at the time of endomyocardial biopsy was analyzed for the presence of Nabs by MDA assay and apoptotic cell assay, as previously described by our lab. Furthermore, Immucor analyzed these serum samples for the presence of antibodies against a panel of 44 autoantigens. Results There was no difference in Nabs production, measured by MDA assay or reactivity to apoptotic cells, among the DSA-negative AMR, DSA-positive AMR and no AMR groups. The DSA-positive AMR group had more reactivity to autoantigens tested in the Immucor panel than the other groups. Each autoantigen had a significantly higher percentage of patients with reactivity in the DSA-positive AMR group compared to the DSA-negative AMR or no AMR groups. This difference was driven by statistically significant increases in reactivity against 16 of the 44 autoantigens tested. There was no difference between the DSA-negative AMR group and the no AMR group. Conclusion These data indicate that the autoantibodies tested for in this panel, as well as Nabs, are not associated with DSA-negative AMR. This suggests that autoantibodies may not be responsible for the effects manifested in patients experiencing this complication. Further research will be needed to investigate the mechanisms involved in DSA-negative AMR.

Endothelial Cells in Antibody-Mediated Rejection of Kidney Transplantation: Pathogenesis Mechanisms and Therapeutic Implications.

Antibody-mediated rejection (AMR) has been identified as a main obstacle for stable immune tolerance and long survival of kidney allografts. In spite of new insights into the underlying mechanisms of AMR, accurate diagnosis and efficient treatment are still challenges in clinical practice. Endothelium is the first barrier between recipients' immune systems and grafts in vascularized organ transplants. Considering that endothelial cells express a number of antigens that can be attacked by various allo- and autoantibodies, endothelial cells act as main targets for the recipients' humoral immune responses. Importantly, emerging evidence has shown that endothelial cells in transplants could also initiate protective mechanisms in response to immune injuries. A better understanding of the role of endothelial cells during the pathogenesis of AMR might provide novel therapeutic targets. In the present review, we summarize the antigens expressed by endothelial cells and also discuss the activation and accommodation of endothelial cells as well as their clinical implications. Collectively, the progress discussed in this review indicates endothelial cells as promising targets to improve current diagnosis and therapeutic regimens for AMR.

Notch signaling mediates crosstalk between endothelial cells and macrophages via Dll4 and IL6 in cardiac microvascular inflammation

Although short-term outcomes have improved with modern era immunosuppression, little progress has been made in long-term graft survival in cardiac transplantation. Antibody-mediated rejection (AMR) is one of the leading causes of graft failure and contributes significantly to poor long-term outcomes. Endothelial cell (EC) injury, intravascular macrophage infiltrate and microvascular inflammation are the histological features of AMR. Nevertheless, mechanisms of AMR remain unclear and treatment is still limited. Here, we investigated the mechanisms underlying vascular and inflammatory cell network involved in AMR at endothelial and macrophage levels, using endomyocardial transplant biopsies and EC/monocyte cocultures. First, we found that AMR associates with changes in Notch signaling at endothelium/monocyte interface including loss of endothelial Notch4 and the acquisition of the Notch ligand Dll4 in both cell types. We showed that endothelial Dll4 induces macrophage polarization into a pro-inflammatory fate (CD40highCD64highCD200Rlow HLA-DRlowCD11blow) eliciting the production of IL-6. Dll4 and IL-6 are both Notch-dependent and are required for macrophage polarization through selective down and upregulation of M2- and M1-type markers, respectively. Overall, these findings highlight the impact of the graft’s endothelium on macrophage recruitment and differentiation upon AMR via Notch signaling. We identified Dll4 and IL-6 as coregulators of vascular inflammation in cardiac transplantation and as potential targets for immunotherapy.

Endothelial transcripts uncover a previously unknown phenotype: C4d-negative antibody-mediated rejection

In the last decade, there has been a growing recognition of alloantibody responses in organ transplantation, but phenotypes related to antibody-mediated rejection (ABMR) remain incompletely defined. This article reviews recent molecular studies in kidney allograft tissues that decipher molecular burden and mechanisms of ABMR, leading to discovery of a new phenotype: 'C4d-negative ABMR'. High endothelial gene expression in kidney transplant biopsies with anti-human leukocyte antigen alloantibody indicates active antibody-mediated damage and poor graft survival, defining a previously unknown group of C4d-negative ABMR. C4d-negative ABMR is characterized by high intragraft endothelial gene expression, alloantibodies, histology of chronic ABMR (less frequently acute ABMR), and poor outcomes. Thus, endothelial molecular phenotype in biopsies with circulating antibody detects degree of active graft injury, and many of these transcripts reflect endothelial activation. C4d-negative ABMR is twice as common as C4d-positive ABMR. Recognition of this new phenotype reveals ABMR (C4d positive or negative) as the most common cause of late kidney transplant loss. C4d staining, although very useful, is insensitive for detecting ABMR. Measuring endothelial gene expression in biopsies from kidneys with alloantibody is a sensitive and specific method to diagnose ABMR and predict graft outcomes.

The humoral response to an allograft.

Antibodies are known to damage grafted tissues by a variety of means, so it is important to know how the humoral response is initiated. In this paper we summarise the cellular events in B cell activation, the mechanisms of antibody-mediated rejection and the evidence that antibody apparently does not contribute to early corneal graft rejection. The role of antibodies in chronic graft loss is discussed.