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

Amplification of the polyclonal activation of human T cells. I. Null-cell products promote the polyclonal proliferation of T cells

Synergy can be observed in the proliferative response to mitogens of cultures containing human T and Null cells when compared with those containing only highly purified cells of those two types. This synergy was analysed (i) by evaluation of the proliferative response at each step of the purification process leading to separation of T and Null cells; (ii) by back-mixing T and Nul cells at different rations; and (iii) by evaluation of the proliferative response of free suspension cultures of T cells overlaying a semi-solid layer containing Null cells, or of free suspension cultures of Null cells over a semi-solid culture layer of T cells. The following conclusions were reached: (i) purified Null cells are unresponsive to mitogen when cultured alone or in the presence of diffusible T-cell products; (ii) the T cells are less responsive when cultured alone than in the presence of Null cells or diffusible Null cell products. Thus the synergistic effect observed between T and Null cells is not due to the promotion of Null-cell proliferation by T -cell products but can be accounted for by diffusible Null-cell products enhancing the process of T lymphocyte activation by mitogens.

Post-thymic T lymphocyte maturation during ontogenesis

Peripheral T lymphocytes from newborn (4-6-d-old) mice, isolated from the spleen or lymph nodes, show phenotypic features of immature cortical thymocytes, such as high frequencies of proliferating cells and of peanut lectin-binding cells. These are features of peripheral T cells of recent thymic origin, as shown by in situ labeling of thymocytes and subsequent observation of the migrants to the spleen, which were mainly peanut lectin-binding cells. The function of newborn peripheral T cells was compared, on a per T cell basis, with that of thymocytes and of fully mature peripheral T cells of the adult, using preparations of newborn lymph node cells containing approximately 80% of T lymphocytes. They were strikingly (about 10-fold) less competent than adult T cells in their phytohemagglutinin responsiveness, their capacities to induce a graft vs. host reaction, to proliferate in the mixed lymphocyte reaction, and to help B lymphocytes in a humoral response in vivo and in vitro. In contrast, newborn T lymphocytes were comparable to those of adults in their capacity to generate cytotoxic T lymphocytes. No suppressive effect of newborn T lymphocytes could be demonstrated in several of these assays. These results argue for an asynchronous maturation of two T cell subsets during ontogeny and demonstrate that at least some T lymphocytes leave the thymus as immature T cells resembling cortical thymocytes and further mature at the periphery. Investigation of mice submitted to thymectomy of 5 d of age showed that these incompetent post-thymic T lymphocytes are capable of considerable expansion and maturation in the peripheral lymphoid organs in the absence of a thymic influence.

Proliferative response of bone marrow cells to concanavalin A does not require Ia antigen-positive cells

The in vitro proliferative response of murine bone marrow cells to concanavalin A (Con A) and the effect of anti-Ia serum on the response were studied. The incorporation of [3H]thymidine into cells prepared from the bone marrow of C3H/He, ATL, ATH, and C57BL/6 mice increased in the presence of certain doses of Con A. The bone marrow cells of athymic nude mice were also capable of responding to Con A, but cells prepared from the spleens of such mice were not. The addition of anti-Ia serum to the cultures of bone marrow cells did not affect the responses of these cells to Con A, though their proliferative response to bacterial lipopolysaccharide was greatly reduced in the presence of the serum. Moreover, pretreatment of the bone marrow cells with anti-Ia serum or anti-Thy. 1.2 serum and rabbit complement did not abolish the ability of these cells to respond to Con A. These results indicate that there are some Ia negative and Thy. 1.2 negative cell populations in the marrow capable of responding to Con A. Furthermore, the effect of anti-Ia serum on the Con A-induced proliferative response of the spleen cells which had been obtained from gamma-irradiated and syngeneic bone marrow cell-reconstituted mice was examined. The ability of these cells to respond to Con A increased gradually week by week after the reconstitution. The suppressive effect of anti-Ia serum on the response of these cells gradually became much more pronounced after the reconstitution.

The role of the maturation stage of thymocytes on the phytohemagglutinin and concanavalin A responses in thymocyte and lymph node lymphocyte cocultures in guinea pig. Effects of pretreatment of thymocytes with thymosin or levamisole

Guinea pig thymocytes (TH) and lymph node lymphocytes (LNL) synergized optimally in both phytohemagglutinin (PHA) and concanavalin (Con A) responses in mixtures containing 0.3 x 10(6) TH and 0.2 x 10(6) LNL. Using discontinuous albumin gradient centrifugation thymocytes were separated into two subpopulations (F4 and F6) at different stages of maturation. Immature, PHA and Con A unresponsive F6 thymocytes synergized significantly only in the PHA response. More mature, PHA and Con A responsive F4 thymocytes cooperated well in the Con A response, but only a small synergy was observed in the PHA response. Pretreatment of the unfractionated thymocytes with the low concentration (0.05 microgram/ml) of thymosin decreased significantly their capacity to interact with LNL in both PHA and Con A responses. Preincubation of F4 thymocytes with the high concentration (200 microgram/ml) of thymosin increased the synergy in PHA response. All other combinations with thymosin or levamisole and thymocytes were ineffective on the mitogenic responses in the TH and LNL cocultures. Altogether, the results how that the thymocyte populations that induce synergy in PHA, or in (PHA and) Con A responses represent the two subpopulations of thymocytes with different maturation stages. The differential effects of the two concentrations of thymosin on the thymocytes support further the concept that the thymocytes synergizing in responses to both mitogens are more mature than those synergizing only PHA response. Thus, the ability of thymocytes to interact with LNL is dependent on the maturation stage of thymocytes, and can be utilized to study the differentiation of thymocytes.

Change in the humoral response of athymic nude mice with ageing

The evolution of the serum Ig levels of Balb/c-nu/nu mice was investigated between 1 month and 12 months of age. An increase as a function of age was observed in all classes and subclasses, which was, expressed in percentage of a nu/+ serum, from 130% to 230% for IgM, from 3% to 24% for IgG1, from 12% to 164% for IgG2a, from 28% to 62% for IgG2b, and from 10% to 50% for IgA. This increase correlates with an increase of plasma cells of each class in the bone marrow, whereas the number of plasma cells in the plasma cells in the spleen, the lymph node, and the intestinal mucosa did not change markedly with age. The humoral response after an injection of heterologous erythrocytes was compared in young and aged nu/nu mice; aged mice had a higher haemagglutination titre mainly due to direct (IgM) antibodies. The response of the spleen, as judged by plaque-forming cells (PFC), was similar in young and aged mice, but the bone marrow response, not detectable in young mice, was about as high in aged nude mice as in nu/+ mice. Although the content of Thy 1 cells in the spleen and lymph nodes was markedly higher in aged than in young nude mice, no T-cell function could be detected at any age, either in the response to phytohaemagglutinin or concanavalin A or in a graft-versus-host assay. Increase in the Ig production with age is interpreted as the result of progressive priming and hyperimmunization by environmental antigens, leading to a T-independent immune response (even against antigens considered to be T-dependent) predominantly located in the bone marrow.

Failure of allogeneic thymocytes to survive in nude mice

Athymic nude mice or thymectomized mice, irradiated and reconstituted with T-depleted bone marrow cells ("B mice"), were injected with allogeneic or syngeneic thymocytes bearing caryotypically distinct chromosomes. The fate of the thymocytes was investigated after various periods of time using two methods: (a) frequency of the cells bearing the Thy-1 antigen as detected by immunofluorescence with a heteroantiserum among the recipient spleen cells, (b) presence of chromosomally detectable donor cells in phytohemagglutinin-stimulated spleen cell cultures. These two methods indicate that allogeneic thymocytes disappear after about 7 days, semiallogeneic thymocytes after about 20 days, while syngeneic thymocytes, even when injected in 50 times lower number (10(6) cells), are detectable for months, thanks to the sensitivity of the caryotypic method. Allogeneic thymocytes induce the production of high titers of alloantibodies, which were shown to react specifically against their own H-2, a phenomenon interpreted as a "suicidal" allogeneic collaboration. These experiments demonstrate that the failure of allogeneic thymocytes, in contrast to syngeneic thymocytes, to achieve long-term restoration of the immune responsiveness of T-depleted mice is due to a rejection of the foreign thymocytes, and not to a failure of T and B cells to collaborate across the histocompatibility barrier.

The in vitro effects of Bordetella pertussis lymphocytosis-promoting factor on murine lymphocytes. III. B-cell dependence for T-cell proliferation

The nature of the helper lymphocytes in lymphocytosis-promoting factor (LPF)-induced proliferation was explored. Removal of macrophages from adherent splenocytes by either carbonyl-iron incubation or passage through Sephadex G-10 columns did not affect their synergistic function. Nor did cytolysis with Thy-1.2 antiserum and complement. The helper cells were found to be surface immunoglobulin-positive (sIg+) because they are retained by anti-Ig columns, susceptible to lysis by rabbit anti-mouse immunoglobulin and complement, and occurred in the sIg+ fractions of splenocytes after separation on the fluorescence-activated cell sorter. Further delineation of the surface markers on helper cells showed that complement receptors are not the determining marker for synergistic function. The requirement for B-helper cells in the stimulation of T lymphocytes by LPF is unique for a mouse of T-cell mitogen.

Characterization of rat spleen-cell populations. I. Cell interactions in the regulation of in vitro response to concanavalin A

Spleen cells from BN rats were separated in a discontinuous density gradient. Cells from different fractions were shown to be functionally diverse, light cells enhancing DNA synthesis and cell division of the dense cell fractions, while dense cells suppressed DNA synthesis and cell division of light cells. Both these effects were also present in the absence of cell stimulation, were proportional to the number of modulating cells added to the cultures, and totally independent of the magnitude of response of controls. In Con A-stimulated cultures, mitogen dose also influenced the intensity of help and suppression. Both these effects are blocked by cell treatment with cycloheximide and can be mediated by cell supernatants. A T cell seems to be responsible for both helper and suppressor effects.

In vitro maturation of immature thymocytes into immunocompetent T cells in the absence of direct thymic influence

Peanut lectin (PNL) binds to a majority of mouse thymocytes (Thc) in suspension. By using cell affinity chromatography on a column of anti-PNL antibody, Thc populations at least 96 percent pure in PNL + or - cells, as judged by immunofluorescence, were obtained. PNL(+) cells are rich in Thy 1 and poor in H(2) antigens, cortisone sensitive, unresponsive to phytohemagglutinin (PHA), and immunologically incompetent, as judged by mixed lymphocyte reaction, popliteal lymph node graft-versus-host assay, and by testing helper activity in a primary in vitro antibody response to sheep erythrocytes; the converse is true of PNL(-) cells. Thus, PNL(+) and (-) cells appear to correspond to cortical and medullary Thc, respectively, as previously suggested. In culture, PNL(+) Thc show poor viability and a weak proliferative response to concanavalin A (Con A), except when supernate (SUP) of 24 h Con A stimulated lymph node lymphocyte cultures, or irradiated lymph node cells, are added, in which cases a strong proliferative response to the mitogen is observed. A variety of control experiments showed that the proliferating cells did not result from preferential stimulation of a few contaminating PNL(-) Thc present in the PNL(+) Thc cultures. The blasts resulting from PNL(+) Thc proliferation display mitogen-induced cytotoxicity, and give rise to a population of medium-sized lymphocytes, mostly PNL(-), poor in Thy 1 and rich in H(2) antigens, PHA responsive, and immunologically competent in the above-mentioned assays. Fresh PNL(+) Thc responded in mixed lymphocyte reaction in the presence of SUP (lectin depleted) and since incubation in SUP alone did not confer reactivity on PNL(+) Thc, it appears therefore that (a) immature Thc possess alloantigen and mitogen-specific surface receptors but lack the capacity to respond by proliferation to receptor triggering without the help of extracellular factor(s) released by mature lymphoid cells stimulated by mitogens (b) cell division is associated with the acquisition of immunological responsiveness, characteristic of mature T lymphocytes. The implications of these findings for the ontogenesis of thymus-derived lymphocytes, and for the possible traffic of Thc within and from the thymus, are discussed.

Ia-bearing cells promote the concanavalin A mitogenic response of Ia-negative T cells

Nylon wool column-purified T cell populations depleted of Ia-bearing cells do not respond to the T cell mitogen concanavalin A (Con A). The response of this population can be restored by admixture of untreated nylon wool-nonadherent T cells. These promotor cells express Thy-1, are not sensitive to mitomycin C treatment and cannot be replaced with adherent spleen cells. Experiments using the T6 chromosome marker demonstrate that Ia-depleted populations respond to ConA only in the presence of the Ia-positive population.

Helper T cells are required for the polyclonal stimulation of cytotoxic T cells by concanavalin A

Concanavalin A stimulation of T-cell cytotoxicity has been shown to be absolutely dependent on helper T-cell collaboration. Thymocytes stimulated with ConA do not differentiate to yield cytotoxic effector cells. However, thymocytes cocultured with irradiated spleen cells as helpers and ConA yield high levels of cytotoxicity. The helper cell bears theta antigens on its surface, is not an adherent cell, and does not require any adherent cell functions in our culture conditions. The ConA-dependent helper cells appear to be polyclonal in specificity. Thus, polyclonal stimulation of cytotoxicity by ConA requires T helper-T precursor collaboration in analogy to antigen-specific T helper-T precursor interactions. Unlike the antigen-specific interacitons, the ConA-driven cytotoxicity does not appear to require linked associative recognition for induction of cytotoxicity.

T-cell regulation of immunoglobulin synthesis and proliferation in pokeweed (Pa-1)-stimulated human lymphocyte cultures

In pokeweed (Pa-1)-stimulated human lymphocyte cultures, T cells are essential for the survival, proliferation, plasma-cell development, and high-rate Ig secretion of B cells. Their effects are T-cell-specific in the sense that B-cell stimulation does not take place in the absence of T cells even when fibroblasts or monocytes are provided. The experimental system is the most effective model for activation of human B lymphocytes so far described. Plasmablast development requires approximately 7 days in culture. In T + B-cell cultures established at 1 X 10(6)/ml (1 X 10(4)/mm2) initial cell density, plasma cells can secrete, on the average, as much as 40-70 pg IgM or IgG per cell per day. When the initial T-cell density is increased well above 1.0 X 10(6)/ml, a T-cell-mediated depression of Ig synthesis becomes predominant. Thus, in the pokeweed model T-cell effects represent a balance of helper and suppressor influences. The study also shows that B cells are heterogeneous. A non-adherent IgG-committed (smIg-?) TONSIL B-cell population seems to be less susceptible to T suppressor effects than normal tonsil B cells. This subset proliferates particularly well and synthesizes large quantities of IgG in the presence of large initial proportions of T cells.