Induction of transplantation tolerance in rats by spleen allografts. I. Evidence that rats tolerant of spleen allografts contain two phenotypically distinct T suppressor cells.

We have examined suppressor cell activity in transplantation tolerant (TT) rats bearing vascularized spleen allografts in several different donor-recipient combinations. More than 60% of WAG (RT-1u) and 65% of AGUS (RT-1l) spleen allografts were permanently accepted when transplanted to AGUS and PVG (RT-1c) rats, respectively. All (WAG X AGUS)F1 to AGUS and (AGUS X PVG)F1 to PVG spleen allografts survived indefinitely. Unseparated LNC, TDL, and whole T cell or W3/25+, OX8- T cell populations obtained from AGUS rats bearing (WAG X AGUS)F1 spleens exhibited reduced mixed lymphocyte reaction (MLR) responses to the spleen donor, and to some extent to BN(RT1n) third-party stimulators, but responded normally to PVG.A(RT1a) stimulators. Coculture experiments demonstrated that lymph node cells (LNC) and thoracic duct lymphocytes (TDL) of TT rats contain RT1 specific suppressor cells. Furthermore, T cells isolated from all donor-recipient combinations contained two phenotypically distinct suppressor cell populations: a radiosensitive W3/25+, OX8- (Th/i) and a relatively radioresistant W3/25-, OX8+ (Ts/c). These Ts may be responsible for the maintenance of TT.