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Regulation of in vitro cytotoxic t lymphocyte generation 3. interactions of regulatory t cell subsets in suppressor and target populations

JMCI (Journal of Molecular and Cellular Immunology) 1(4): 237-250
Regulation of in vitro cytotoxic t lymphocyte generation 3. interactions of regulatory t cell subsets in suppressor and target populations
During allogeneic mixed leukocyte cultures (MLC), cytotoxic T lymphocytes (CTL) and at least 2 kinds of suppressor T lymphocyte (Ts) functions are induced. One Ts, termed nonspecific (TsN), can suppress the in vitro generation of CTL when it is transferred to any allogeneic MLC. The other Ts has specificity for MLC in which stimulator cells are homologous at the major histocompatibility complex (MHC) with stimulator cells used to induce the Ts (TsS). Previously, it was shown that addition of a 10-4 M concentration of the histamine1 antagonist pyrilamine to the MLC strongly influences the kind of T cell function generated. The generation of CTL and TsN are inhibited while the induction of TsS is not. CTL precursors are activated (CTL-PA) in such cultures, as witnessed by their differentiating into CTL effectors upon removal of pyrilamine and transfer to a salubrious environment (e.g., any fresh MLC). This 2nd step in the differentiation of CTL can be prevented by exposure of pyrilamine-treated MLC derived cells to .gtoreq. 500 rad .gamma.-irradiation. Therefore, by using these combined in vitro manipulations, under the proper experimental conditions, it is possible to study TsS in the absence of both TsN and CTL. Antibodies to the cell surface alloantigens Lyt 1, Lyt 2 and TL/Qa-1 were used to study whether [mouse] TsN and TsS also can be separated by virtue of their having different cell surface phenotypes. The existence of interactions between subsets of T cells in the suppression of CTL generation and whether these interactions (circuits) are akin to those previously demonstrated to be important in the regulation of B cell responses to antigen were also studied. Since CTL generation likely is important in the host defense against viruses and other pathogens, neoplasms and transplants of foreign tissues, a firm understanding of regulatory interactions modifying this response is important. Negative selection with alloantigen-specific antibodies and complement (C') was used in this study. Immune Lyt 1+2+ (Ly 123) T lymphocytes are strongly involved in MLC-induced nonspecific suppression, but are not required for the expression of specific suppression. Rather, both immune Lyt 1+2- (Ly 1) and Lyt 1-2+ (Ly 2) T lymphocytes appear to be involved in optimal TsS function. TsN and TsS activities could not be separated using a serum that contains antibodies to Qa-1 and TL alloantigens; i.e., both Ts activities were removed by treating alloantigen-activated Ts with this serum and C'. Immune TsS often are not sufficient for the expression of suppression. In most experiments, suppression failed to occur if nonimmune Ly 123 cells had been removed from the target responding population. Suppression of only T helper cell precursors and/or CTL precursors of the Ly 123 phenotype cannot account for the results presented because in certain experiments, CTL generation by unfractionated responder cells was suppressed by TsS to a level that must include inhibition of virtually all CTL precursors in the population. These data are compatible with the existence of regulatory T cell interactions in CTL generation, which are similar to both feedback suppression and suppressor amplification circuits, that are active in the regulation of B lymphocyte responses.

Accession: 006288706

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