Molecular analysis of C3 allotypes related to transplant outcome in human renal allografts.
The third component of complement (C3) exists in two main allotypic forms, C3S and C3F, which can be distinguished at the molecular level using a variation of the polymerase chain reaction. An increased frequency of the C3F allele has been noted in a number of autoimmune and inflammatory conditions affecting the kidney, including systemic vasculitis, IgA nephropathy, and type II mesangiocapillary nephritis. Recently, in an unrelated study, we found (with small numbers) an increased incidence of graft loss associated with the presence of the C3F allele. To further assess this, we analyzed the S/F polymorphism in 183 donor-recipient pairs of patients undergoing renal transplantation. Forty-one of 183 grafts were lost, but graft loss was not associated with the C3F allele over 14-month follow-up. However, the presence of the C3F allele predicted an increased risk of graft dysfunction (defined as serum creatinine > 150 mumol/L): 61/105 versus 36/78, with a relative risk of 1.4 (P < 0.05). The C3F allele predisposed toward graft dysfunction when present in either donor or recipient. The presence of two C3F alleles gave a relative risk for graft dysfunction of 1.8, suggesting a dose-dependent effect, although numbers were small. The presence of the C3F allele was not significantly correlated with the number of rejection episodes, serum creatinine, or duration of primary nonfunction. These findings suggest that C3F may be a susceptibility allele for allograft injury. Possible mechanisms for this association are discussed.