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Objective Antibody-mediated rejection (ABMR) is an important cause of kidney allograft injury. In the last two decades, detection of complement split product C4d along transplant capillaries, a footprint of antibody-mediated classical complement activation, has evolved as a useful diagnostic marker of ABMR. While it was recognized that ABMR may occur also in the absence of C4d, numerous studies have shown that C4d deposition may indicate a more severe rejection phenotype associated with poor graft survival. Such studies suggest a possible diagnostic benefit of ex vivo monitoring the complement-activating capability of circulating alloantibodies. Design and methods We reviewed the literature between 1993 and 2015, focusing on in vivo (biopsy work-up) and in vitro detection (modified bead array technology) of HLA antibody-triggered classical complement activation in kidney transplantation. Results Precise HLA antibody detection methods, in particular Luminex-based single antigen bead (SAB) assays, have provided a valuable basis for the design of techniques for in vitro detection of HLA antibody-triggered complement activation reflected by C1q, C4 or C3 split product deposition to the bead surface. Establishing such assays it was recognized that deposition of complement products to SAB, which critically depends on antibody binding strength, may be a cardinal trigger of the prozone effect, a troublesome in vitro artifact caused by a steric interference with IgG detection reagents. False-low IgG results, especially on SAB with extensive antibody binding, have to be considered when interpreting studies analyzing the diagnostic value of complement in relation to standard IgG detection. Levels of complement-fixing donor-specific antibodies (DSA) were shown to correlate with the results of standard crossmatch tests, suggesting potential application for crossmatch prediction. Moreover, while the utility of pre-transplant complement detection, at least in crossmatch-negative transplant recipients, is controversially discussed, a series of studies have shown that the appearance of post-transplant complement-fixing DSA may be associated with C4d deposition in transplant capillaries and a particular risk of graft failure. Conclusions The independent value of modified single antigen bead assays, as compared to a careful analysis of standard IgG detection, which may be affected considerably by complement dependent artifacts, needs to be clarified. Whether they have the potential to improve the predictive accuracy of our current diagnostic repertoire warrants further study. [ABSTRACT FROM AUTHOR]

Abstract: An independent pool of 16 incompatible live donor–recipient pairs registered at the Vienna transplant unit was applied to test whether virtual crossmatch allocation used in the Australian kidney paired donation (KPD) program reliably predicts negative crossmatches. High resolution HLA data were entered into the computer-matching algorithm and allocation was performed excluding any DSA>2000MFI. CDC and flow crossmatch data of recipients against any of the donors were available for 112 crossmatch combinations. The computer program identified 19 possible pairings in 2-way or 3-way chains in multiple combinations. The top ranked combination included one 3-way and two 2-way ABO-compatible chains. Where crossmatches were available all recipients were CDC crossmatch negative with the computer-matched donor. Excluding allocation of KPD donors in the presence of DSA>2000MFI had a negative predictive of 99.9% for CDC and 96.4% for flow crossmatch. In the 12 pairings with ⩾1 DSA against crossmatched donors there was a negative CDC and flow crossmatch. These results show excellent correlation between matching using virtual crossmatch and actual crossmatch results. Using the 2000MFI cut-off the number of potentially unacceptable CDC and flow crossmatch positive pairings identified by virtual crossmatching is low, but some potential crossmatch negative pairings are missed. [Copyright &y& Elsevier]

Abstract: Antibody-mediated immunity is generally accepted to be a major cause of kidney allograft injury and loss. Post-transplantation monitoring for circulating alloantibodies was proposed to represent a useful noninvasive diagnostic approach to assess individual immunologic risks and to guide the implementation of specific therapeutic measures. This was supported by the recent establishment of highly sensitive and specific solid phase immunoassays for detailed characterisation of reactivity patterns. Nevertheless, imperfect associations of serologic results with biopsy-based criteria of antibody-mediated rejection, as well as the disputed long-term significance of circulating alloantibody detected in recipients with normal graft function, necessitate a careful interpretation of monitoring results. [Copyright &y& Elsevier]

Background Donor-specific antibodies of the IgG isotype are measured routinely for diagnostic purposes in renal transplant recipients and are associated with antibody-mediated rejection and long-term graft loss. Objective This study aimed to investigate whether MHC-specific antibodies of the IgE isotype are induced during allograft rejection. Methods Anti-MHC/HLA IgE levels were measured in sera of mice grafted with skin or heart transplants from various donor strains and in sera of kidney transplant patients with high levels of HLA IgG. Mediator release was triggered in vitro by stimulating basophils that were coated with murine or human IgE-positive serum, respectively, with specific recombinant MHC/HLA antigens. Kidney tissue samples obtained from organ donors were analyzed by using flow cytometry for cells expressing the high-affinity receptor for IgE (FcεRI). Results Donor MHC class I– and MHC class II–specific IgE was found on acute rejection of skin and heart grafts in several murine strain combinations, as well as during chronic antibody-mediated heart graft rejection. Anti-HLA IgE, including donor HLA class I and II specificities, was identified in a group of sensitized transplant recipients. Murine and human anti-MHC/HLA IgE triggered mediator release in coated basophils on stimulation with specific MHC/HLA antigens. HLA-specific IgE was not linked to atopy, and allergen-specific IgE present in allergic patients did not cross-react with HLA antigens. FcεRI+ cells were found in the human renal cortex and medulla and provide targets for HLA-specific IgE. Conclusion These results demonstrate that MHC/HLA-specific IgE develops during an alloresponse and is functional in mediating effector mechanisms. Graphical abstract [ABSTRACT FROM AUTHOR]

By the Banff classification, the score of peritubular capillaritis, its extent, and its cellular composition should normally be reported in renal allograft pathology. While the score represents an important diagnostic and prognostic variable, the clinical value of capillaritis extent or composition has yet to be resolved. In a retrospective study of 749 renal transplant recipients subjected to 1322 indication biopsies, we found that prevalence scores of 1, 2, or 3 in the biopsy specimens were 10.7, 11.6, and 2.6%, respectively. Focal and diffuse peritubular capillaritis (inflammation over 50% of cortical peritubular capillaries) was diagnosed in 10.5 or 14.4% of cases, respectively. Mononuclear, granulocytic, and mixed peritubular capillaritis was present in 13.1, 3.3, and 8.5%, respectively. While peritubular capillaritis without further subclassification was not related to higher allograft loss rates, a score of 3 (hazard ratio 2.57 (CI: 1.25-5.28)) and diffuse peritubular capillaritis (1.67 (1.1-2.54)) were significant impartial risk factors for allograft loss. Diffuse peritubular capillaritis was independently associated with features of chronic antibody-mediated rejection and greater eGFR decline after 3 years. In contrast, detailed report of leukocytic composition in peritubular capillaritis did not confer additional prognostic information. Thus, in contrast to typing the infiltrating inflammatory cells, the score and extent of peritubular capillaritis in kidney allograft pathology is essential to assess transplant prognosis. [ABSTRACT FROM AUTHOR]

Abstract: Virtual crossmatching based on single-antigen bead (SAB) assays for the detection of donor-specific antibodies (DSA) has limited accuracy of predicting complement-dependent cytotoxicity crossmatch (CDCXM) results. In this study, 672 crossmatch combinations (32 allosensitized patients tested against cells from 21 high resolution-typed individuals) were analyzed to assess the potential of modified SAB tests in predicting T- or B-cell-CDCXM outcomes. Test modifications included measurement of C4d-fixation to detect complement-activating DSA ([C4d]DSA), or addition of dithiotreitol to abrogate the prozone effect ([IgG/DTT]DSA). Receiver operating characteristic (ROC) analysis revealed superior predictive accuracy of [C4d]DSA detection. Computing the mean fluorescence intensity (MFI) sum value of HLA class I [C4d]DSA in relation to T-cell-CDCXM revealed an area under the ROC curve (AUC) of 0.81. Other parameters, including DSA MFI maximum or number, were less predictive. Computing MFI sum values, AUC levels were lower for [IgG/DTT] (0.77) or [IgG]DSA detection (0.72), and did not considerably increase upon combining classifiers ([C4d] plus [IgG/DTT]: 0.82). ROC analysis revealed that [C4d]DSA detection (HLA class II) was also better at predicting B-cell-CDCXM results, even though, at very low MFI thresholds, the assay was found to provide comparably lower levels of specificity. Overall, B-cell-CDXM prediction was less precise, but could be enhanced by adjusting CDCXM thresholds to higher levels. Our data suggest particular efficiency of solid-phase complement detection as a tool for virtual crossmatching. [Copyright &y& Elsevier]

Abstract: In pregnant women, circulating alloantibodies, triggered by exposure to paternal HLA antigens, are frequently detectable. The finding of lower alloantibody levels in women who experience spontaneous abortion (miscarriage) has led to the speculation that antipaternal antibodies could favor maintenance of pregnancy, whereas their lack poses a risk of miscarriage. Postulating a role of alloantibodies in the pathogenesis of unexplained abortion, we examined whether different categories of recurrent miscarriage (RM) can be distinguished according to prevalence or distinct qualitative properties of anti–human leukocyte antigen (HLA) antibody patterns. Sera obtained from 167 women with RM were assessed for complement- and non–complement-fixing anti-HLA alloreactivity using Luminex-based bead array technology. Women with RM had less often detectable anti-HLA class I and/or II reactivity (19%) compared with a control group of 96 multiparous women without a history of miscarriage (49%). However, analysis of different categories of RM (unknown [n = 112] versus known cause [n = 55]; primary [n = 125] versus secondary RM [n = 42]) did not reveal any differences regarding antibody prevalence, number of targeted HLA single antigens, antigen specificity, binding density, or complement-fixing ability of detected alloantibodies. Our results do not support a link between anti-HLA antibody formation and RM, and argue against a diagnostic value of alloantibody detection in the diagnostic work-up of women with RM. [ABSTRACT FROM AUTHOR]

Abstract: On waiting lists, transplant candidates are routinely screened for potentially harmful complement-fixing alloantibodies using complement-dependent cytotoxicity (CDC) panel-reactive antibody (PRA) testing. We have recently developed a novel cell-independent assay for assessment of complement-activating panel reactivity ([C4d]FlowPRA), which is based on selective flow-cytometric detection of alloantibody-triggered C4 complement split product deposition to human leukocyte antigen (HLA)-coated FlowPRA beads. Serum specimens selected from 120 transplant candidates were evaluated by [C4d]FlowPRA (HLA class I vs II) in comparison with FlowPRA IgG alloantibody screening (HLA class I vs II), a method detecting both complement- and noncomplement-activating alloantibodies, and with CDC-PRA on separated T (T-CDC) or B cells (B-CDC, evaluation on platelet-absorbed sera). For each assay, ≥10% PRA reactivity was considered positive. Comparing complement-dependent PRA assays with standard FlowPRA, the specificity calculated for [C4d]FlowPRA (HLA class I: 92%; class II: 100%) was found to be superior to that of CDC testing (T-CDC-PRA: 79%; B-CDC-PRA: 86%). Because noncomplement-activating alloreactivities were not detected for both techniques, low sensitivities were calculated ([C4d]FlowPRA HLA class I: 61%; class II: 31%; T-CDC-PRA: 70%; B-CDC-PRA: 55%). Compared with CDC-PRA, [C4d]FlowPRA gave a high specificity (HLA class I compared with T-CDC: 89%, HLA class II compared with B-CDC: 95%) but, at least in part because of false-positive CDC results, a modest sensitivity (66% and 38%, respectively). For both HLA classes, we found a highly significant association between absolute [C4d]FlowPRA and CDC-PRA levels (p < 0.0001). Our results suggest that detection of C4 split product deposition to FlowPRA beads may represent an attractive HLA-specific and time-effective alternative to CDC-PRA screening. [Copyright &y& Elsevier]

Highlights from the article: P203 Late antibody-mediated rejection (ABMR) after kidney transplantation - Role of the eGFR slope within the first year after biopsy as a surrogate endpoint predicting graft failure There is currently no effective, evidence-proven treatment for late ABMR. Median eGFR at the time of biopsy was 42 mL/min/1.73 m SP 2 sp (IQR: 39-45) and the median eGFR slope (first 12 months after ABMR diagnosis) was -4.4 mL/min/1.73 m SP 2 sp .