Identification of the antibodies involved in B-cell crossmatch positivity in renal transplantation.

Background: The significance of a positive B-cell crossmatch (BCM) in kidney transplantation has always been controversial in the evaluation of its implications on graft survival and specificity of the antibodies involved.
Methods: We have investigated the sera of 62 recipients of a kidney allograft transplanted across a positive BCM (T negative) for the presence of autoantibodies and anti-human leukocyte antigen (HLA) class I and II antibodies, using a combination of lymphocytotoxicity, enzyme-linked immunosorbent assay (ELISA), and flow cytometry tests. The controls were the 930 patients transplanted over the same period of time with a negative T and BCM.
Results: Autoantibodies were detected in 16%, and donor specific anti-HLA class II antibodies, mainly DQ, in 23% of the patients. None had antibodies against donor HLA class I. The target of the antibodies was not identified in 61%. Graft survival was comparable in the controls and in the +BCM patients, with nondonor-specific HLA reactivity. Patients with donor-specific anti-HLA class II antibodies had lower early graft survival and a higher incidence of vascular rejection. However, long-term allograft survival was similar to that of the other groups.
Conclusion: These data suggest that in 77% of the patients, BCM positivity was not related with anti-HLA antibodies, and, in this case, graft survival was similar to that of the -BCM controls. In a minority of patients, anti-HLA class II antibodies were responsible for the +BCM, and their presence was associated with lower early, but not long-term, graft survival. Consequently, a +BCM should not systematically contraindicate kidney transplantation.