THE INDUCTION OF SKIN XENOGRAFT TOLERANCE IN RAT-TO-MOUSE COMBINATIONCOULD BE AFFECTED BY DFR MEDIATING CELLS AND ANTIBODIES AGAINST RAT BONE-MARROW CELLS AS WELL AS NK CELLS IN THE CYCLO-PHOSPHAMIDE-INDUCED TOLERANCE SYSTEM

We investigated whether the prolongation of skin xenograft survival wa s obtained by a tolerance-inducing method using cyclophosphamide (CY), by which long-lasting skin allograft tolerance could be induce; The l ong-lasting skin allograft survival could be obtained in the recipient C3H/HeN (C3H) mice which were given 100 mu g Of anti-CD4 mAb on day - 3, 1 x 10(8) spleen cells (SC) plus 3 x 10(7) bone mal rop; cells (BMC ) derived from C57BL/6 (B6) mice on day -2, 200 mg/kg CY on day 0, and which were grafted with allogeneic B6 skin on day 14. When the C3H mi ce were treated with anti-CD4 mAb, 1 x 10(8) SC plus 5 x 10(7) BMC der ived from F344 rat and CY, the F344 skin grafts survived slightly long er (about 15 days) than those in untreated recipients (about 8.4 days) . Such a prolongation of skin xenograft survival was considered donor- specific because rejection of 3rd party skin grafts from BN rats occur red significantly earlier than that of F344 skin grafts. In the recipi ent C3H mice treated with anti-CD4 mAb, F344 SC plus BMC and CY, mixed chimerism in the periphery was detected for a few days after CY admin istration, although intrathymic chimerism was not detected throughout this study. In these recipient C3H mice, cytotoxic T lymphocytes (CTL) against F344 antigens were completely abrogated though the delayed fo otpad reaction (DFR) remained at a low but significant level. Moreover , though antibody (Ab) activity against F344 SC was completely abrogat ed, neither Ab activity against F344 BMC, which seemed to have a backg round common to natural Ab activity, nor NK activity were abrogated by this treatment. These results suggested that DFR mediating cells dire ctly mediated skin xenograft rejection in the recipient mice treated w ith anti-CD4 mAb, F344 cells, and CY. Such cells may interfere with es tablishment of mixed chimerism and long-lasting skin xenograft toleran ce, presumably in cooperation with CY-resistant Ab activity and NK cel ls.