Decreased immunogenicity of fetal kidneys: the role of passenger leukocytes.

Early in gestation, fetal rat kidneys are less immunogenic than in later fetal stages, and also less immunogenic than early-gestation fetal hepatic tissue. The purpose of this study was to test this observation in an allogeneic model, and to explore the basis of the decreased immunogenicity of early-gestation fetal kidneys. Kidneys were harvested from Fischer (FSH) fetal rats on the 15th, 17th, 18th, and 19th gestational day (GD), and then grafted under the kidney capsule of incompatible Wistar/Furth (W/F) adult male rats. Fetal hepatic tissue was harvested from 15th-GD FSH fetal rats, and then grafted under the kidney capsule of W/F adult male rats. Each recipient received either one kidney or a 3-mm piece of liver. Graft biopsies were obtained 10, 20, 30, and 40 days posttransplantation, and evaluated histologically. The severity of rejection was divided into three grades according to the degree of mononuclear infiltration and percentage of original fetal structures preserved. All fetal hepatic grafts were completely rejected (grade III) by the tenth posttransplantation day. In contrast, the degree of rejection of the kidneys was age-dependent. Fifteenth-GD kidneys showed a minimal or moderate degree of rejection (grade I or II) at 10, 20, and 30 days; however, 18th- and 19-GD kidneys were rejected (grade III) by the tenth post-transplantation day. To explore the basis for the decreased immunogenicity of 15th-GD kidneys, 20 adult W/F rats were divided into two groups. Each animal in the first group received one FSH 15th-GD kidney implanted under the kidney capsule.(ABSTRACT TRUNCATED AT 250 WORDS)