Suppression of cytotoxic lymphocyte responses in vitro by soluble products of alloantigen-activated spleen cells

Suppression of in vitro cytotoxic lymphocyte (CL) responses was mediated by soluble factor(s) produced when in vivo alloantigen-activated suppressor cells were re-exposed to alloantigen in vitro. Elaboration of suppressor factor (SF) was T cell dependent and was optimal 7 days after alloantigen injection. Suppressor factor failed to inhibit CL generation when alloantigen-primed cells rather than normal spleen cells were used as responders. Moreover, SF added at day 3 of incubation rather than at culture initiation was also ineffective, suggesting that suppression probably occurs during antigen induction or early differentiation. Additionally, suppression was abrogated by the presence of 2-mercaptoethanol. Studies combining SF and CL responder cells from a variety of H-2 disparate mouse sdrains revealed that suppression of CL responses: 1) was not alloantigen specific; 2) did not require H-2 homology between responder and suppressor strains; and 3) could not be demonstrated with CBA/J mice. Although CBA/J CL responses were not suppressed by any SF preparation, allo-sensitized CBA/J spleen cells did elaborate SF that inhibited BALB/c CL responses.

Regulatory mechanisms in cell-mediated immune responses. VI. Interaction of H-2 and non-H-2 genes in elaboration of mixed leukocyte reaction suppressor factor

Previous studies have shown that alloantigen-activated spleen T cells produce a soluble factor which suppresses mixed lymphocyte reaction proliferative responses, and that the interaction between suppressor and responder cells is controlled by genes of the H-2 complex. However a defect in the expression of suppressor activity was identified in the mouse strain C57BL/6J. Factor prepared from alloactivated B6 spleen cells failed to suppress MLR responses of syngeneic or H-2 compatible responder cells. Unimpaired suppressor factor production by other H-2 (b) strains and failure of suppressor factor production by a B6 congenic strain, B6.C-H-2(d) isolated the defective gene to the non-H-2 portion of the genome. In addition, the defect appeared to be related specifically to inability to produce an active factor, while the capacity to respond to suppressor molecules was unimpaired. The genetic character of the non-H-2 gene action was identified in F1 hybrid studies. Initially F(1) hybrids of the nondefective histoincompatible strains were studied. Suppressor factor from F1 cells suppressed the responses of both parental strains, and parental factors each suppressed the response of F(1) cells. Adsorption of F(1) factor with Con A-activated thymocytes of either parental strain removed suppressor activity specific for that strain, leaving activity against the other parental strain intact. The data support cedominant expression and production of distinct, parental H-2 haplotype-specific suppressor molecules by F(1) suppressor cells. An F(1) hybrid of the defective B6 strain with nondefective BALB/c produced suppressor factor which was also capable of suppressing both parental strains. Production of a suppressive B6-reactive factor by F(1) cells was verified by adsorption studies. Thus it appears that non-H-2 genes of the BALB/c parent acted in a genetically dominant fashion to provide the function required for expression of B6 suppressor molecules. We conclude that multiple genes control the expression of alloactivated suppressor cell activity, with at least one gene mapped to the I-C subregion of the murine major histocompatibility complex and one or more genes mapped to the non-H-2 gene complement.

Regulatory mechanisms in cell-mediated immune responses. V. H-2 homology requirements for the production of a minor locus-induced suppressor factor

A mixed leukocyte reaction suppressor factor is produced by spleen cells sensitized in vivo and restimulated in vitro across non-H-2 antigenic barriers. Cells capable of producing this factor appear in the spleens of minor locus-immunized animals later than in animals sensitized to major histocompatibility complex-encoded antigens. However, both H-2 and non H-2-induced factors suppress proliferative responses to any alloantigen. Splenocytes from animals immunized with H-2-identical, minor locus-disparate cells produce suppressor factor in vitro only when restimulated with cells sharing both H-2 and non-H-2 antigens with the in vivo stimulators.

Regulation of cytotoxic lymphocyte responses in vitro by alloantigen-activated spleen cells

Spleen cells obtained from BALB/c mice 4 days after allosensitization to C57BL/6 spleen cells via footpad injection suppressed the in vitro generation of BALB/c cytotoxic lymphocytes (CL) against C57BL/6 spleen cells in mixed leukocyte cultures (MLC). Suppressor activity was demonstrated by spleen cells at 4 and 7 days but not at 2, 10, or 14 days after allosensitization and was abolished by treatment with anti-Thy-1,2 serum and complement. A weak and transient cytotoxic response directed against the sensitizing alloantigen was associated with suppressor spleen cell populations, but was dissociated from suppressor function by two experimental approaches. First, increasing stimulatory cell concentration in MLC did not competitively diminish the suppressor activity; rather, the magnitude of suppression increased as the stimulatory cell concentration was increased. Second. BALB/c suppressor cells generated in vivo by either H-2b or H-2k alloantigens suppressed CL responses generated simultaneously against both alloantigens in vitro. CL responses generated against one or the other H-2 haplotype in vitro were suppressed only by suppressor cells activated by that haplotype. Therefore, splenic suppressor cells activated by alloantigen in vivo required antigen-specific restimulation in vitro; thereafter, responder cells syngeneic with the suppressor cell were rendered hyporesponsive to alloantigens by an antigen-nonspecific mechanism.

Fractionation of lymphocyte subpopulations which regulate mixed lymphocyte reactions

Four days after injection of allogeneic lymphocytes BALB/c splenic T cells suppress proliferation of syngeneic cells in mixed lymphocyte reactions (MLR). Conversely, lymph node cells from the same mice amplify MLR responses. To further characterize these functional subpopulations, alloantigen-primed lymphocyte suspensions from both organs were fractionated by velocity sedimentation at unit-gravity. After fractionation MLR suppressor cells from spleens localized exclusively in rapidlly sedimenting fractions of large cells. MLR suppressor activity of cells from these fractions, as well as that of unfractionated spleen cell suspensions, was abolished by treatment with anti-Thy-1.2 serum and complement. Spleen cell fractions of similar sedimentation velocity also secreted a soluble MLR suppressor into culture supernatants. Although inhibitory of MLR, spleen cells of rapid sedimentation velocity did not suppress responses to T cell mitogens. In marked contrast with the effects of spleen cells, large 4-day-alloantigen-primed lymph node cells had no suppressive activity in MLR. MLR amplifier cells of uncertain derivation were found in fractions of medium sedimentation velocity from both spleens and lymph nodes. Fractionation of alloantigen-primed lymph node cell suspensions did reveal, however, a subpopulation of small cells with MLR suppressor acitivty which was unaffected by treatment with anti-Thy-1 serum and complement. The data thus indicate that large alloantigen-activated lymphocytes are not intrinsically suppressive nor are cells which suppress MLR necessarily large. We consequently conclude that regulation of MLR responses by alloantigen-primed lymphocytes involves a complex interaction between distinct functional subpopulations of cells which are separable both by physical and biologic properties.

Regulatory mechanisms in cell-mediated immune responses. IV. Expression of a receptor for mixed lymphocyte reaction suppressor factor on activated T lymphocytes

Suppression of the mixed lymphocyte reaction (MLR) by a soluble factor produced by alloantigen-activated spleen cells requires genetic homology between the factor-producing cells and responder cells in MLR. The ability of lymphocytes used as MLR responder cells to adsorb MLR suppressor factor was tested to investigate the expression of a receptor structure for suppressor molecules. Normal spleen or thymus cells had no effect on suppressor activity. Concanavalin A (Con A)-activated thymocytes, however, effectively removed suppressor activity, suggesting that the receptor is expressed only after activation and is not present or not functional on resting cells. Significantly neither phytohemagglutinin- nor lipopolysaccharide-activated lymphoid cells absorbed the factor. Furthermore, only Con A-activated thymocytes demonstrating genetic homology with the cell producing suppressor factor for H-2 regions to the right of I-E were effective absorbants. Alloantigen-stimulated spleen cells syngeneic to the suppressor cell also removed suppressor activity. These data support an hypothesis that subsequent to stimulation in MLR, T lymphocytes express a receptor, either through synthesis or alteration of an existing molecular structure, which then provides the appropriate site for interaction with suppressor molecules.

Regulatory mechanisms in cell-mediated immune responses. III. I-region control of suppressor cell interaction with responder cells in mixed lymphocyte reactions

Active suppression of mixed lymphocyte reaction (MLR) response is mediated by a soluble factor released by alloantigen-activated murine suppressor cells. Genetic restrictions controlling suppressor factor interaction with MLR responder cells were elucidated in this study. Non-H-2 genetic background was irrelevant to effective interaction. Using congenic strains and strains with intra-H-2 recombinants the genetic locus controlling suppressor T-cell-responder cell interaction was mapped in the I-C or S regions of the H-2 complex. Similarly, recombinant strains were used to exclude the presence of another suppressor cell-responder cell interaction locus in K,I-A, and I-B regions. It thus appears that the I-C subregion of the H-2 complex controls suppressive cell interactions in this T-cell-mediated immune response.

Regulatory mechanisms in cell-mediated immune responses. II. A genetically restricted suppressor of mixed lymphocyte reactions released by alloantigen-activated spleen cells

The mechanism of alloantigen-activated spleen cell suppression of mixed lymphocyte reaction (MLR) is explored in this report. Activated murine suppressor spleen cells elaborated a soluble noncytotoxic factor which suppressed MLR responses by 55-95%. Generation of suppressor factor required both in vivo alloantigen sensitization and specific in vitro restimulation. Suppressor factor was not produced by activated spleen cells which had been treated with anti-Thy-1.2 serum and complement. Antigenic specificity toward alloantigens of the stimulator cells was not demonstrable. In contrast, suppressor factor effectively inhibited MLR response only of responder cells of those strains that shared the D-end and the I-C subregion of the H-2 complex with the cells producing suppressor factor. Therefore, active suppression appears to require an MHC-directed homology relationship between regulating and responder cells in MLR.

Biological expressions of lymphocyte activation. IV. Concanavalin A-activated suppressor cells in mouse mixed lymphocyte reactions

Thymus-derived lymphocytes (T cells) from mouse spleen, activated in vitro or in vivo with concanavalin A (Con A), suppress proliferative responses of syngenic lymphocytes in mixed lymphocyte reactions (MLR). Replication in vitro was not required for expression of suppressor activity by Con A-activated cells and was blocked in MLR by treating suppressor cells with mitomycin C or irradiation. Kinetics of MLR responses and viability of cultures were not altered by addition of activated suppressor cells. The data are consistent with a direct inhibitory effect of suppressor T cells on antigen-induced DNA replication. These observations extend a model previously described for regulation of antibody synthesis by Con A-activated T cells to control of cell-mediated immune responses. This model should be particularly useful in further definition of regulatory T cell subpopulations, and in investigation of interactions and relationships between such populations.

Regulatory mechanisms in cell-mediated immune responses. I. Regulation of mixed lymphocyte reactions by alloantigen-activated thymus-derived lymphocytes

Regulatory effects of alloantigen-activated thymus-derived lymphocytes in mixed lymphocyte reactions have been demonstrated. Mice were injected into foot pads with allogeneic spleen cells; 4 days following sensitization spleen or regional lymph node cells from these animals were treated with mitomycin C and incorporated into MLR as regulator populations syngeneic to the responder cell type. Activated spleen cells suppressed MLR responses 60-90% whereas activated lymph node cells from the same animals enhanced MLR responses. Suppression by activated spleen cells was not due to cytotoxic effects nor to altered kinetics of the proliferative response. Studies of splenic suppressor cell generation in vivo revealed peak activity four days after alloantigen stimulation with no activity demonstrable at 7 days or at later times. Suppressor cell activity was abrogated by treatment with anti-thetaC3H serum and complement, and was not alloantigen specific.