THE IN VIVO IMMUNOSUPPRESSIVE ACTION OF SUPPRESSOR CELLS FROM ALLOANTIGEN-CYCLOSPORINE-TREATED MICE AND THE CAPACITY OF SPLEEN CELLS TO RELEASE INTERLEUKINS AND -INTERFERON1

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Abstract
Antigen-nonspecific suppressor T cells were identified in spleens of mice rendered unresponsive by sensitization of allogeneic antigen in combination with cyclosporine (CsA) treatment. Suppressor cells were obtained from C57BL/6 (B6, H-2b) mice trated with a single i.p. injection of 1.times.107 allogeneic P815 (H-2d) cells combined with a five-day course of CsA, a group that did not show any cytotoxic activity of spleen cells against P815 targets. These noncytolytic spleen cells displayed suppressor activity on the induction of cytotoxic T (Tc) cells of normal lymphocytes against not only P815 stimulator (80.9% suppression, P<0.01, responder:additional cell ratio = 2.5:1) but also third-party BW5147 (H-2k) stimulator (68.2% suppression, P<0.01). The unresponsive state appears to be due to suppressor T (Ts) cells that are nonadherent to plastic or nylon-wool, 1500 rads-sensitive, and Thy-1-positive. Capacities of spleen cells from CsA-P815-treated mice to release cytokines (interleukin 1 [IL-1], interleukin 2 [IL-2], inteleukin 3 [IL-3], and .gamma.-interferon [.gamma.-IFN]) were examined. Spleen cells from CsA-P815-treated B6 mice displayed 84.1%, 91.7% and 90.8% inhibition (0.35.+-.0.07 U/ml, 1.4.+-.0.29 U/ml, and 7.0.+-.0.9 U/ml) of IL-1, IL-2, and .gamma.-IFN production compared with normal mice (2.2.+-.0.54 U/ml, 16.9.+-.2.1 U/ml, and 76.0.+-.3.1 U/ml, P<0.01), respectively. However, IL-3 production was significantly less inhibition (46.1%, 2.35.+-.1.0U/ml in CsA-P815-treated mice and 4.36.+-.1.7 U/ml in normal mice) compared with other cytokines (IL-1, IL-2, .gamma.-IFN). Two systems were employed to assess the immunosuppressive efficacy of antigen-nonspecific Ts cells in vivo. First, adoptive transfer (i.p.) of spleen cells harvested from CsA-P815-treated mice ten days after treatment on 3 consecutive days (0, 1, 2) at a 3.times.107 cell dose into virgin B6 mice that were immunized with P815 cells (1.times.107, day 0) completely inhibited the development of Tc cells against P815 targets (5% specific cytolysis, effector:target ratio [E:T] = 200). The suppessor effect was immunologically non-specific; adoptive transfer of Ts cells from CsA-P815-treated mice also abrogated the development of Tc cells against third-party BW5147 cells. Second, introvenous injection of spleen cells (1.times.107) from CsA-P815-treated B6 mice on three consecutive days (days 0, 1, 2) abolished the capacity of the B6 mice to develop delayed-type hypersensitivity (DTH) responses, as induced by s.c. o, immunization, not only with DBA/2 but also with AKR spleen cells. The suppressor T cells appeared to mediate its suppressor effect by soluble factor. The culture supernates of suppressor cells added to the mixed lymphocyte reaction between normal responder B6 spleen cells and irradiated p815 or BW5147 cells significantly inhibited the Tc cell induction against each stimulator (48.5% d 34.4% suppression compared with culture without suppressor factor, E:T=10). Thus, these studies demonstrated that both impairment of cytokine generation and induction and/or sparing of suppressor T cells mediate the unresponsive state induced by CsA.