Human skin xenograft rejection in CD45 exon-6 knockout mice: The implication of involvement of a direct pathway

The results of previous studies indicate that only D4(+) T cells generated via the indirect pathway play an essential role in causing discordant skin xenograft rejection. The present study was conducted in an attempt to clari fy further the roles of effector T cells generated via direct pathways on d iscordant xenograft rejection using CD45 exon-6 knockout (CD45-/-; C57BL/6 (B6): H-2(b)) mice. It has been strongly suggested that CD45 exon-6 knockou t mice have profound impairment in T-cell functions via an indirect pathway . When human skin was grafted onto untreated normal C57BL/6 (B6; H-2(b)) mi ce, rejection occurred within 12 days: however, in the CD45 exon-6 knockout mice, the grafts lasted for slightly longer as in fully allogeneic C3H (H- 2(k)) skin rejection, with a mean survival time +/- SD of 19.4 +/- 1.5 days and median survival times of 19 days, The difference in survival periods b etween the human and C3H skin grafts in the CD45 knockout mice was not stat istically significant. Both CD4(+) and CD8(+) T cells seemed activated in t he spleens of these CD45 exon-6 knockout mice 10 days after the human skin grafting. These results suggest that effector T cells generated via a direc t pathway can cause discordant skin xenograft rejection, and that CD45 exon -g knockout mice can generate effector T cells via a direct pathway to reje ct discordant skin xenografts, similarly to fully allogeneic skin allograft s.