Regulatory mechanisms in cell-mediated immune response. V. Distinct Lyt subsets mediate antigen-specific and antigen-nonspecific suppression

Immunosuppressive activity of staphylococcal enterotoxin B. I. Characterization of staphylococcal enterotoxin-B-induced suppressor cells

Staphylococcal enterotoxin B (SEB) binds specifically to major histocompatibility complex class II molecules on the surface of accessory cells and stimulates virtually all T cells bearing certain, but not all, T cell-receptor V beta alleles. We have previously shown that this superantigen is a potent inducer of multiple regulatory T cell populations. In the present report we show that SEB induces a population of suppressor T cells which inhibits the generation of alloantigen-induced cytotoxic T cell activity. Using both negative- and positive-selection analysis, we found that this suppressor population is a CD4- CD8- CD5+ IL-2R+ T cell. This cell population inhibited both syngeneic and allogeneic cytotoxic T lymphocyte activity, but the cell population which inhibited allogeneic CTL activity was radiation sensitive. In addition, allogeneic SEB-primed cells appeared to develop cytolytic activity as a result of the additional stimulation in the mixed-lymphocyte reaction culture. The relationship of the SEB-primed CD4- CD8- CD5+ T cells to related regulatory T cell populations is discussed.

Alloinduced suppression and cytotoxicity: two functions of a single cell

Using different experimental approaches we here show that the suppression and cytotoxicity generated during a one-way mixed lymphocyte culture (MLC) are mediated by a single cell population, in this case the cytotoxic T lymphocyte (CTL). Results of limiting-dilution analysis of cells from a 4-day MLC demonstrate the coexpression of both functions and argue against the existence of a separate suppressor cell population that regulates the in vitro alloresponse. The suppressive quality of CTL is also exemplified in cells with a clonal origin, such as cloned cytotoxic T lymphocytes and the mouse X rat hybridoma PC60. Further experiments demonstrate that this suppression is not primarily mediated through lysis of the stimulator cells, and studies in the PC60 model suggest that lysis and suppression may have different induction requirements.

Suppression of cytolytic T-cell activity by staphylococcal enterotoxin B-induced suppressor cells: role of interleukin 2

We have previously shown that staphylococcal enterotoxin B (SEB) is a potent inducer of suppressor T cells which function to inhibit antibody production in vitro. In the present paper we extend these studies and show that the SEB-induced suppressor cells also inhibit the development of cytotoxic lymphocytes in mixed-lymphocyte reaction (MLR) cultures. Since further analysis also showed that the level of interleukin 2 (IL-2) in cultures of SEB-primed cells was significantly reduced, experiments were carried out to determine the role of IL-2 in the inhibition of cytotoxic cell activity. Attempts to neutralize the suppression by supplementing MLR cocultures with delectinated supernatants from concanavalin A (Con A)-stimulated rat splenocytes were not successful. In addition, MLR cocultures supplemented on Day 0 with 50 units of affinity-purified IL-2 were also suppressed. Further analysis showed that the IL-2 activity in the supplemented MLR cocultures containing suppressor cells were significantly reduced by Day 3. However, repeated supplementation of the MLR cocultures with exogenous IL-2 was successful in achieving (and maintaining) "normal" levels of IL-2. The cytotoxic cell activity in these MLR cocultures remained suppressed. These results suggest that the inhibition of cytotoxic cell activity by SEB-induced suppressor cells is independent of IL-2 levels in the MLR coculture.

Regulatory mechanisms in cytotoxic T lymphocyte development. II. Dissociation of in vitro cytotoxic T-lymphocyte and suppressor T-cell activities with L-ornithine

L-ornithine was found to differentially affect the induction of allospecific cytotoxic T lymphocytes (CTL) and suppressor T cells (Ts). At a concentration of 10 mM, ornithine inhibited the development of CTL in a mixed-leukocyte culture (MLC). This same population of cells suppressed the generation of CTL when irradiated and cocultured with fresh syngeneic lymphocytes and alloantigen. Suppression was mediated by Lyt-1-2+ cells and was antigen specific. Suppression was abrogated when IL-2 (10 U/ml) was added to the cocultures, but could not be reversed by increasing the antigen dose. Ornithine was not toxic to CTL precursors but rather arrested their development. Cells from MLC plus ornithine developed CTL activity within 2 days of transfer to secondary cultures in the absence of ornithine. Development of CTL effector cells (CTLe) was augmented by but did not require exogenous IL-2. Generation of CTLe from the MLC plus ornithine population was radiation sensitive and could be inhibited by reexposure to ornithine, even in the presence of IL-2. Thus, Lyt-1-2+ T cells allostimulated in vitro in MLC plus ornithine and lacking CTL activity convey radiation-resistant, antigen-specific suppression.

Suppressor T cells in BCG-treated mice interfere with an in vivo specific antitumoral immune response

The interference by BCG in the induction and expression of a specific antitumoral immune reaction was studied in B6 mice, using the in vivo Winn assay and also active immunization. T cells immunized against MCA-induced fibrosarcoma (MC B6-1) transferred together with the tumour cells protected the syngeneic host against tumour take. Pretreatment of normal B6 mice with moderate or high doses of BCG prevented the development of a protective immune response after immunization. Moreover, a single dose of 1 mg, or 2 doses of 0.01 mg BCG, completely eliminated an established antitumour immunity. Suppressor cells are involved in the BCG-induced inhibitory effect; they interfered (1) with the expression of the antitumour response, since their addition to immune T cells in the Winn test resulted in decreased protection and (2) with the induction of the antitumour response, since injection of spleen cells from BCG-treated mice (BCG SpC) into normal mice before immunization inhibited the development of immunity. Treatment of BCG SpC with anti Thy 1.2 and anti Lyt 1.2 antibodies plus complement before injection into normal mice significantly decreased the suppressive activity, showing that the suppressor cells induced by BCG are T cells expressing the Lyt 1+ phenotype. The partial increase in protection obtained after IL-2 administration to BCG-treated mice suggests that the suppressive action of BCG SpC on the IL-2 producing capacity of helper T cells is only one of a number of possible mechanisms of T-cell-mediated suppression.