Linear C3 deposits on the tubular basement membrane in renal allograft biopsies.

Linear and granular tubular basement membrane (TBM) deposits of C3 occur in renal allograft biopsies, but their significance is unknown. We retrospectively analyzed the predictive importance of C3 deposits in 88 biopsied transplant patients with allograft dysfunction. All patients were followed for greater than or equal to 2 years from biopsy. Patients were divided into three groups: group I: no C3 deposits, 47 patients; group II: granular deposits of C3, 28 patients; and group III: linear TBM deposits, 13 patients. The incidence of acute and chronic rejection was not different. In group III, 12 grafts were lost by 5 years (92%), and the remaining patient has chronic rejection. Group III survival was significantly less than groups I and II (Kaplan-Meier curves), P = 0.02, but graft survival in groups I and II were similar. There was no association of anti-TBM antibody deposits with C3, and the mechanism of deposition is unknown. We conclude that the presence of linear C3 deposits along the TBM in the setting of allograft dysfunction is associated with decreased allograft survival.