Early humoral-mediated graft injuries in ABO-incompatible kidney transplantation in human beings.

INTRODUCTION: Acute humoral rejection is the most important risk factor for early graft loss in ABO-incompatible (ABO-i) renal transplantation (RTx) and is present from the early period after RTx. However, the characteristics of early humoral-mediated graft injury are pathologically uncertain. OBJECTIVE: To analyze tissue from 10 protocol graft biopsies performed in 10 patients within 30 days post-RTx to clarify the pathologic features of early humoral-mediated graft injuries in ABO-i RTx. METHODS: Pathologic findings were examined using light and electron microscopy and immunofluorescence studies for C4d. Protocol biopsies were performed within 30 days after RTx in the absence of an episode of dysfunction (creatinine concentration 1.21-1.81 mg/dL). RESULTS: The immunofluorescence study demonstrated C4d deposition in peritubular and glomerular capillaries. Acute glomerulitis with infiltration of mononuclear cells and neutrophils was observed in 3 patients. Furthermore, glomerulitis was accompanied by endothelial cell injuries, widening of subendothelial spaces with a double-contoured glomerular basement membrane, and mesangiolysis. CONCLUSION: In ABO-i RTx, early humoral-mediated graft injuries were observed in approximately 30% of patients despite normal graft function. They were characterized by C4d deposition and glomerular capillary injury. These findings suggest that renal glomeruli are the first site of graft injury by anti-A or anti-B blood type antibody with complement activation in ABO-i RTx.