Allograft response in vitro

Identical genetic control of MLC reactivity to different MHC incompatibilities, independent of production of and response to IL-2

The inbred strain STS/A exhibits a higher proliferative response in the mixed lymphocyte culture (MLC) to stimulator cells of all 11 tested inbred mouse strains with 10 different major histocompatibility complex (MHC) haplotypes, as well as to stimulation with IL-2 than does the strain BALB/cHeA. However, alloantigen-stimulated BALB/c cells produce more IL-2 than STS/A cells. To study the genetic basis of these differences, we used 20 recombinant congenic strains (RCS) of the CcS/Dem series. Each of these CcS/Dem RC strains contains a different subset of about 12.5% of genes from the STS/A strain and the remaining approximately 87.5% of BALB/c origin genes. As a result the multiple non-linked genes responsible for phenotypic differences between BALB/c and STS/A became separated into different CcS/Dem strains. The strain distribution pattern (SD) of high or low MLC response of individual CcS/Dem strains to stimulator cells of four different strains was almost identical, indicating that differences in responsiveness, rather than the alloantigenic difference itself, determine the magnitude of the response, and that the responsiveness to different alloantigens is largely controlled by the same genes. The SDP of IL-2 stimulation was different from that of MLC responsiveness. The differences in the proliferative responses observed among individual CcS/Dem strains were not due to differences in numbers of CD3+, CD4+ or CD8+ cells or to the observed differences in IL-2 production, and hence they likely reflect genetically determined intrinsic properties of T cells. These results show that a set of non-linked genes controls proliferative responses in MLC irrespective of the MHC haplotype of the stimulator cells, and that stimulation with IL-2 and production of IL-2 are controlled by different subsets of genes. Since the genomes of all RCS are extensively characterized by microsatellite markers, they can be used to map the genes controlling proliferative responsiveness to stimulation with alloantigens and IL-2.

Immunomodulatory effects of three macrolides, midecamycin acetate, josamycin, and clarithromycin, on human T-lymphocyte function in vitro

The effect of three macrolide antibiotics, midecamycin acetate, josamycin, and clarithromycin, on human T-cell function was investigated in vitro. Midecamycin acetate and josamycin suppressed the proliferative response of peripheral blood mononuclear cells stimulated by polyclonal T-cell mitogens at concentrations between 1.6 and 8 micrograms/ml. At higher concentrations (40 to 200 micrograms/ml), all these drugs showed a marked inhibitory effect. At concentrations of 1.6 to 40 micrograms/ml, these drugs suppressed interleukin-2 (IL-2) production induced by mitogen-stimulated T cells, but not the expression of IL-2 receptor (CD25), in a dose-dependent manner. Therefore, the suppressive action on T-lymphocyte proliferation seems to be based on the ability of these drugs to inhibit IL-2 production by T cells. The drug also inhibited mixed lymphocyte reaction at the same concentrations. Combined treatment with these macrolides and the known immunosuppressants such as FK506 and cyclosporin A resulted in an increased inhibition of T-cell proliferation. The immunomodulatory properties of the antibiotics may have clinical relevance for modulation of the immune response in transplant patients and in patients with inflammatory diseases.

Immunosuppressive activity of bromocriptine on human T lymphocyte function in vitro

Bromocriptine (BRC), a dopamine type 2 agonist, prevents secretion of pituitary prolactin (PRL). BRC has been shown to impair lymphocyte responsiveness toward antigenic stimulation by decreasing serum PRL levels. Hypoprolactinaemia induced by BRC produces a similar immunosuppressive effect, as observed in hypophysectomized rats, which is restored by the administration of PRL. Therefore, the immunosuppression induced by BRC has been interpreted as the result of hypoprolactinaemia. However, the direct mechanism of BRC in immune response has never been evoked. We recently reported that BRC has an immunosuppressive activity on human B lymphocyte function in vitro. In the present study we demonstrate that BRC suppresses T cell proliferation by means of blocking IL-2 production by T cells as well as mixed lymphocyte reaction (MLR) in a dose-dependent manner. We could not detect the immunoreactive PRL activity in the conditioned medium from polyclonal T cell mitogen-stimulated T cell cultures. Then, the immunosuppressive activity of BRC on human T cell function appeared to be independent of its hypoprolactinaemic effect. Treatment with low-dose cyclosporin A (CsA) or FK506 in combination with BRC has proved more effective than either drug alone in suppression of T cell proliferation and CD25 antigen expression. Thus, the therapeutic application of BRC in combination with immunosuppressants may enhance the immunosuppressive effect, while at the same time decreasing the toxicity.

Immunosuppressive activity of fosfomycin on human T-lymphocyte function in vitro

Recent investigations have shown that some antibiotics also work as immunomodulators. We have recently reported that fosfomycin (FOM) has an immunomodulatory effect on human B-cell activation. FOM is a unique antibiotic which is chemically unrelated to any other known antibacterial agent. In the present study, we examined the effect of FOM on human T-cell function. FOM inhibited the proliferation of human lymphocytes induced by polyclonal T-cell mitogens in a dose-dependent manner. FOM also strongly suppressed mixed lymphocyte reaction and interleukin-2 (IL-2) production by T cells. Moreover, FOM inhibited the expressions of IL-2 receptor (CD25) and transferrin receptor (CD71) on the activated T-cell surfaces. These data suggest that FOM may block the T-cell division during the transition from G1 to S phase of the cell cycle. Combined treatment with FOM and low-dose cyclosporin A or FK506 caused additive or synergistic suppression of T-cell proliferation, but not on IL-2 receptor expression. It seems that the mode of action of FOM on T-cell function involves a specific suppression of IL-2 production.

Cells mediating graft rejection in the mouse. I. Lyt-1 cells mediate skin graft rejection

The Ly phenotype of cells mediating skin graft rejection was determined using monoclonal anti-Lyt-1.1 and Lyt-2.1 antibodies in CBA mice that received CBA lymphoid cells from mice sensitized to C57BL/6; i.e., alloantigenic differences arising from the H-2 and non-H-2 loci. It was clear that graft rejection was due wholly to the presence of Lyt-1 cells in the inoculum and that Lyt-123 or Lyt-23 cells had no effect. Furthermore, no synergism was noted between Lyt-1 and Lyt-2 cells. In this model, both the cytotoxic T cell and cytotoxic lymphocyte precursors were shown to be Lyt-123 and these could be depleted from sensitized Lyt-1 populations that mediated graft rejection. Thus cytotoxic T cells are not responsible for skin graft rejection, but rather, this is mediated by an Lyt-1 cell. Whether this T cell is distinct from other Lyt-1 cells (T helper, T cells mediating delayed hypersensitivity) is not clear at present, but other evidence, and traditional concepts, link graft rejection and delayed type hypersensitivity as being different manifestations of the same mechanism.

Synergistic and suppressive interactions among mouse T lymphocytes in the response to phytohemagglutinin

A synergistic effect in the proliferative response to phytohemagglutinin (PHA) can be observed in cultures containing a mixture of mouse CBA/Ca lymph node cells (LNC) and syngeneic CBA/T6T6 thymocytes (ThC) when compared to cultures containing only one cell type. This effect was analyzed, at various days of culture and in LNC-ThC mixtures of different ratios, by comparing the origin of the cells in mitosis (detected by caryotypic analysis), the stimulation of DNA synthesis, the number of blasts, and the percentage of blasts labeled after pulses of [3H]thymidine (detected by autoradiography). The following conclusions were reached: (a) ThC are induced to proliferate by the presence of LNC, while they are almost unresponsive to PHA when cultured alone; and (b) the strongest "synergistic" effect is exerted on LNC, whose proliferation is markedly enhanced. Evidence is presented that this last effect is not specific to the presence of ThC, but results from a dilution of LNC which retards the time when the culture reaches a critical concentration of blasts, above which proliferation progressively stops. Thus, conditions of culture allowing the response to PHA of a low concentration of LNC leads to the most prolonged T-cell proliferation. These observations may be relevant to the types of T-cell interactions, "synergistic" or "suppressive," occurring during in vitro or in vivo immune responses.

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.

Generation of cytotoxic T lymphocytes in vitro. I. Response of normal and immune mouse spleen cells in mixed leukocyte cultures

Mouse cytotoxic T lymphocytes (CTL) were generated in mixed leukocyte cultures (MLC) using spleen cells as responding cells and irradiated allogeneic spleen cells as stimulating cells. Cytotoxicity was assessed by a quantitative (51)Cr assay system and the relative frequency of CTL in individual cell populations was estimated from dose-response curves. Inclusion of 2-mercaptoethanol in the MLC medium resulted in a 20-40-fold increase in the relative number of CTL generated at the peak of the response. Under these culture conditions, cell-mediated cytotoxic activity was detectable in MLC populations as early as 48 h after the onset of the cultures. When spleen cells from mice immunized with allogeneic tumor cells 2-4 mo previously were cultured with irradiated spleen cells of the same alloantigenic specificity (MLC-Imm), it was found that the cell-mediated cytotoxic response was detectable earlier and reached higher levels than that observed in a primary MLC. At the peak of the response, MLC-Imm populations were observed to lyse up to 50% of the target cells within 3 h at a lymphocyte: target cell ratio of 0.3:1. Immunological and physical characterization of the effector cells generated in MLC-Imm indicated that they were medium to large-sized T lymphocytes. Altogether, these studies suggested the existence of an anamnestic cell-mediated cytotoxic response in MLC-Imm.

Cell-mediated immune responses in vitro. I. Suppression of the generation of cytotoxic lymphocytes by concanavalin A and concanavalin A-activated spleen cells

The effects of soluble concanavalin A (Con A) or Con A-activated spleen cells on the generation of cytotoxic lymphocytes (CL) in mixed leukocyte cultures (MLC) were examined. Mitogenic concentrations of soluble Con A or small numbers of Con A-activated spleen cells substantially inhibited CL responses. The suppression was partial rather than absolute and was critically dependent upon the concentration and time of addition of soluble Con A or Con A-activated spleen cells to the MLC. Suppressive effects of Con-A activated spleen cells were mediated by T cells since suppressor cell activity was abrogated by treatment of spleen cells with anti-theta serum and complement before or after Con A activation. X irradiation of spleen cells before Con A treatment also abrogated generation of suppressor cell activity. After activation by Con A, however, the function of suppressor cells was radioresistant. Although the precise mechanism(s) of suppression is, as yet, unknown, the precursors of CL must be exposed to Con A-activated cells during the early phases of the immune response for suppression to occur. Kinetic studies revealed that suppression of CL responses was not due to a failure to initiate an immune response, but represented a response which developed initially, but subsequently aborted. The relevance of these observations to the concepts of T-cell-T-cell interaction and regulatory control of immune responses by T cells is discussed.

Proliferation of B and T cells in mixed lymphocyte cultures

Electrophoretically fractionated CBA/Ca spleen T cells alone respond to allogeneic cells in one-way MLC and to PHA. They do not respond to E. coli LPS. B cells alone do not respond to allogeneic cells nor to PHA, but do respond to LPS. When karyotypically distinguishable syngeneic mixtures of T and B lymphocytes are stimulated with allogeneic cells, at the most 5% of mitoses on 5-9th culture day are of B cell origin. This indicates that B cells are not substantially recruited to proliferate in the MLC.