Abstract: Ｏｂｊｅｃｔｉｖｅ：To analyze the clinicopathological and prognostic characteristics of C3 glomerulonephritis (C3GN) in renal allograft.
Ｍｅｔｈｏｄｏｌｏｇｙ：A retrospective analysis was conducted of clinical and pathological data from patients diagnosed with transplant kidney C3GN through renal biopsy at the National Clinical Research Center for Kidney Diseases between January 2008 and December 2023.
Ｒｅｓｕｌｔｓ：A total of 8 patients with transplant kidney C3GN were included. The median time from kidney transplant to biopsy was 32(7, 135)months. At biopsy, the mean age was 39 ± 7 years, and mean urine protein quantification was 3.89 ± 2.10 g/24h. Microscopic hematuria was observed in 5 cases, and the average serum creatinine was 162.66±70.72 μmol/L. Serum complement 3 was measured in 5 patients, all showing hypocomplementemia. One patient had a family history of C3GN. One patient underwent genetic testing, which revealed a heterozygous mutation in complement factor I. The light microscopic presentation of the transplanted kidney biopsies shows mesangial proliferative, membranoproliferative, or endocapillary proliferative lesions. Immunofluorescence showed predominantly C3 deposition with or without minimal immunoglobulin deposition. Electron microscopy revealed dense deposits in the mesangial area and subendothelial space of the glomerular capillary loops. The median time from biopsy to follow-up was 66 (3, 118)months, and three patients developed graft renal failure.
Ｃｏｎｃｌｕｓｉｏｎ：Transplant kidney C3GN clinically presents with persistent hypocomplementemic C3 and nephritic syndrome. Transplant kidney biopsy is a crucial tool to confirm the diagnosis, and the prognosis is generally poor.

Key words: kidney transplantation, transplantation pathology, C3 glomerulonephritis