A positive B cell crossmatch due to IgG anti‐HLA‐DQ antibody present at the time of transplantation in a successful renal allograft

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Abstract
The role of a positive B cell crossmatch in renal transplantation is uncertain, partly because of the difficulty in determining the true specificity of the various antibodies that may cause a positive crossmatch. We have used monoclonal antibodies against HLA class I, HLA‐DR and HLA‐DQ antigens to inhibit cytotoxicity of sera from renal patients, in order to define the specificity of a positive B cell crossmatch. We have used reduction with dithiothreitol (DTT) to identify the immunoglobulin class. These methods were used to identify the specificity and immunoglobulin class of the antibody causing a positive B cell crossmatch in a highly sensitised patient. The results show that the antibody was IgG anti HLA‐DQ and the graft was functioning 1 year after transplantation. Immunoperoxidase techniques demonstrated a normal expression of HLA‐DQ antigen in biopsies of the transplanted kidney. The successful outcome of the transplant raises questions about the role of anti‐HLA class II antibodies in renal transplantation.