Impact of C1q fixing donor‐specific antibodies on renal transplant outcome

Not all anti‐HLA donor‐specific antibodies (HLA‐DSAs) are detrimental to renal allograft. In this context, the C1q complement activating ability of antibodies appears to be an important parameter to distinguish clinically inert versus detrimental DSAs. We evaluated sera of 206 consecutive primary live donor renal transplant recipients before transplant and at post‐operative day 7, 30, 90, 180 and at the time of graft dysfunction for quantifying HLA‐DSAs using single antigen bead assay on a Luminex platform. Patients positive for these antibodies with an MFI >500 were further screened for C1q fixing nature of DSA. Fourteen of the 18 antibody‐positive patients had C1q fixing DSA with MFI value >5000. Only 4 antibody‐positive patients did not have C1q fixing DSA. The MFI values of DSA detected by C1q assay were generally higher at least by 25% than those detected by the conventional IgG‐SAB assay. Twelve of the 14 patients (85.71%) with C1q+ DSA developed antibody‐mediated rejection during the mean follow‐up period of 21.43 ± 8.03 months as compared to none of the four C1q‐negative DSA (85.71% vs 0%; P = .001). These results suggest deleterious effect of C1q+ DSA vis‐à‐vis C1q‐negative DSA on renal allograft.