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

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.