Hyperacute renal allograft rejection from anti-HLA class 1 antibody to B cells - Antibody detection by two color FCXM was possible only after using pronase-digested donor lymphocytes

We present a report of a transplant recipient who lost her renal allograft from hyperacute rejection. This was secondary to a weak IgG anti-HLA class I antibody that was only reactive to donor B lymphocytes. This antibody was not detected in her pretransplant serum by the conventional complement-dependent cytotoxicity assays using donor blood lymphocytes. Pretransplant sera were analyzed retrospectively by two-color flow cytometric crossmatching (FCXM). It was difficult to determine if the recipient's serum contained an IgG antibody specific for HLA on donor B cells since IgG from control AB sera and pretransplant sera bound equally well to CD19 B cells. However, when donor lymphocytes were pretreated with pronase to digest the membrane receptor for Fc domain of IgG (Fc gamma R) on non-T-cells, control IgG in AB serum did not bind to B cells and, hence, it was easy to detect binding of IgG (in pretransplant sera) to HLA on B cells. This case underscores the importance of identifying weak anti-HLA class I antibodies reactive only to B cells. Moreover, it shows that the currently used two-color FCXM lacks the specificity to detect such antibodies.