Expression of complement regulatory proteins in the developing human kidney

Complement homologous restriction factor CD59 and complement receptor CD35 are typically involved in the regulation of the host defense system. Recent observations in the human fetal kidney suggest a further role for complement cell surface regulators CD35 and CD59 in kidney development and maturation. We investigated this possible role by localizing CD35 and CD59 protein and mRNA in the developing and adult kidney. Adult tissue and fetal tissue ontogeny were analyzed using immunohistochemistry and in situ hybridization. CD35 protein and mRNA were localized to the podocyte of the glomerulus in the human fetal and adult kidney. Expression was initiated after vascularization of the early developing glomerulus. CD59 protein and mRNA were observed as early as 8 weeks' gestation and were localized primarily to the ureteric duct epithelium in the fetal kidney and predominantly to the collecting duct in the adult. Interestingly, CD59 expression was translocated from the basolateral surface in the fetal kidney to the apical surface in the adult kidney. The specific spatial and temporal expression of CD35 and CD59 suggests a possible role for these complement regulatory proteins in renal cell differentiation.