Endothelial cell chimerism occurs more often and earlier in female than in male recipients of kidney transplants.

Background: Endothelial chimerism occurs in renal transplants, but factors involved in its development and its impact on outcome, are unknown. Most studies on chimerism are restricted to gender-mismatched combinations of female donor organs into male recipients. By using blood group antigen mismatches to detect chimeric cells, we circumvented this restriction. We determined which factors predispose for the development of endothelial chimerism, and how it influences graft survival.
Methods: We studied 85 renal transplant biopsies of 24 patients with either blood group A or B, who received a blood group O kidney. Biopsies were scored according to BANFF '97. Blood group antigens were stained by immunohistochemistry. Semiquantitative scoring was performed by four independent observers.
Results: Endothelial chimerism was found in 27/85 biopsies from 16/24 patients. All female recipients, but only half of the male recipients, had endothelial chimerism in their grafts (P < 0.025). In female recipients, endothelial chimerism occurred significantly earlier than in male recipients (P < 0.02). The presence of endothelial chimerism was not associated with: rejection, outcome, original renal disease, previous transplantations, age, warm/cold ischemia time, pretransplantation blood urea levels, or erythropoietin therapy.
Conclusion: We are the first to report that endothelial chimerism occurs significantly more often in female than in male recipients of renal transplants. Endothelial chimerism had no influence on graft outcome. We hypothesize that hormonal factors may influence the development of endothelial chimerism, in parallel with differences in endothelial function between males and females in cardiovascular disease.