Developmental changes in humoral suppressor activity released from concanavalin A-stimulated human lymphocytes on B cell differentiation

Cell-free culture supernatants (Con A-activated supernatants) were obtained by incubating peripheral blood lymphocytes (PBL) from cord blood, healthy children of various ages, and healthy adults with mitogenic doses of concanavalin A (Con A) for 48 hr. It is well known that human T lymphocytes are activated by Con A to manifest suppressor function in vitro. One mechanism whereby these suppressor cells act has been shown to be by the secretion of a soluble suppressor factor. The present study has investigated the Con A-inducible suppressor cell function in cord blood, children of various ages, and adults by comparing the ability of each Con A-activated supernatant to inhibit the generation of immunoglobulin-producing cells (Ig-PC) in pokeweed mitogen- (PWM) stimulated cultures of adult PBL. Con A-activated supernatants from adults could markedly suppress the generation of Ig-PC by allogeneic as well as autologous PBL in response to PWM. Such suppression appeared to be equally effective on the generation of IG-PC of 3 major classes, IgG, IgM, and IgA. On the contrary, Con A-activated supernatants from cord blood and newborn infants showed only a negligible suppression on PWM-induced adult B cell differentiation. But the suppressor activity found in Con A-activated supernatants gradually increased with advancing age, and reached approximately to the adult level at 4 yr of age or later. The results suggest that human T lymphocytes may be relatively deficient in their Con A-induced suppressor cell function in the early period of life.     

Activation of human B lymphocytes. V. Kinetics and mechanisms of suppression of plaque-forming cell responses by concanavalin A-generated suppressor cells.

The kinetics and mechanisms of suppression of the PWM-induced PFC response of human PB lymphocytes by Con A-activated suppressor cells were investigated. It was necessary that Con A suppressor cells be present early in the process of activation of human B cells toward antibody syntheses, but maximal suppression of the PFC response occurred later in the culture period. In addition, Con A-activated cells, although suppressing the PFC response to PWM greater that 90% of control, did not significantly suppress the blastogenic response to PWM after 3 or 5 days in culture. On the contrary, after 3 days in culture, background tritiated thymidine incorporation as well as tritiated thymidine incorporation to PWM stimulation was increased when Con A suppressor cells are added to fresh autologous peripheral blood lymphocytes. This increased blastogenic response after three days most likely represented an autologous mixed lymphocyte reaction (MLR) or Con A suppressor cells against fresh autologous non-T cells. The induction of autoreactive cells may be one of several modes of suppression of PFC responses by Con A activated suppressor cells.     

Deficiencies in suppressor T cell activity seen in patients with active systemic lupus erythematosus are due to the dilution of normally functioning suppressor T cells by nonsuppressor T cells

Concanavalin A (Con A)-activated T lymphocytes from patients with active, but not inactive, systemic lupus erythematosus (SLE) failed to express normal suppressor activity, regardless of the phenotype of CD4+ or CD8+. Con A-activated CD4+ or CD8+ T lymphocytes from the SLE patients and from normal controls were further separated into two populations, using the autologous erythrocyte rosette technique. One population very rich in cells capable of forming rosettes with autologous erythrocytes from the active patients showed the same degree of suppressor activity, as did that from normal controls; the CD4+ or CD8+ population poor in autorosetting cells derived from Con A-activated T lymphocytes from both the controls and patients did not express suppressor activity. Moreover, when autorosetting T cells from the active patients and nonrosetting cells from the same patients were mixed at a normal ratio (4:6), normal suppressor activity could be restored. It was notable that the frequency of autorosette-forming cells was markedly reduced in the Con A-activated T lymphocytes from the active, but not inactive, SLE patients, regardless of the phenotype of CD4+ or CD8+. These findings indicate the presence of a normally functioning suppressor T cell population in patients with active SLE. It seems that the lack of suppressor T cell function in patients with active SLE is due to the dilution of a few normal suppressor T cells by large numbers of nonsuppressor T lymphocytes.     

The role of the 2H4 molecule in the generation of suppressor function in Con A-activated T cells

The molecular basis for the suppression generated in a concanavalin A (Con A)-activated T cell culture remains unknown. In this study, we have attempted to determine whether the 2H4 and 4B4 molecules on Con A-activated T cells play some role in the generation of suppression by such cells. We have shown that Con A-activated suppressor cells belong to the 2H4+ subset of T cells but not the 4B4+ (2H4-) subset. Con A-activated T cells exerted their optimal suppressor function on day 2 in culture, a time at which the expression of 2H4 on such cells was maximal and 4B4 was minimal. Furthermore, the stimulation of T cells with the higher concentration of Con A generated the stronger suppressor function. At the same time, both 2H4 expression and density were increased and 4B4 expression and density were decreased on such Con A-activated T cells. More importantly, the treatment of Con A-activated T cells with anti-2H4 antibody but not with anti-4B4, anti-TQ1, or anti-T4 antibodies can block the suppressor function of such cells. Taken together, the above results strongly suggest that the 2H4 molecule itself may be involved in the generation of suppressor function in Con A-activated T cells. The 2H4 antigen on such cells was shown to be comprised of 220,000 and 200,000 m.w. glycoproteins. Thus this study indicates that the 220,000 and 200,000 m.w. structure of the 2H4 molecule may itself play a crucial role in the generation of suppressor signals of Con A-activated cells.     

Functional properties of a lymphocyte subpopulation responding to low suboptimal doses of concanavalin A

Incubation of human peripheral blood lymphocytes with concanavalin A (Con A), in a low suboptimal dose (0.5 microgram/ml), results in formation of the cells that inhibit proliferation of autologous cells in cultures activated with optimal but not with suboptimal dose of the mitogen. Nevertheless, 50 micrograms/ml Con A-activated cells efficiently suppress proliferation everywhere. Cell preincubation during 18 h before Con A activation leads to a reduction of lymphocyte responses to the mitogen in cultures reactivated with 5 micrograms/ml Con A in a mixture with autologous lymphocytes, containing no mitogen. Activation of T-T helper cells providing suppressor T cells differentiation seems to take place in the presence of a low suboptimal dose of Con A. Besides, 0.5 microgram/ml Con A prevents the preincubation-induced elimination of some lymphocytes responding to an optimal dose of Con A and autologous lymphocytes.     

Human suppressor T cells induced by concanavalin A: suppressor T cells belong to distinctive T cell subclasses.

Human peripheral blood lymphocytes were stimulated by concanavalin A (Con A) and then evaluated by their suppressive activity for thymus-derived (T) cell- and bone marrow-derived (B) cell-proliferative responses to mitogen and allogeneic cells. Con A-activated T cells markedly suppressed these responses, but Con A-activated B cells failed to demonstrate suppressor activity. Discontinuous bovine serum albumin (BSA) density gradient separation of T cells which had been activated by Con A demonstrated that a fraction containing blast cells as well as fractions containing unproliferated cells manifest the same degree of suppressor capabilities. However, when density gradient separation of T cells followed by subsequent incubation with Con A was performed, fractions of proliferating cells of low density exhibited no suppression; a fraction containing high density T cells produced marked suppression, but this fraction incorporated only little thymidine in response to Con A. Thus, these studies indicate that Con A-induced suppressor T cells belong to a distinctive subpopulation which has already been programmed to express this function before exposure to Con A and that cell proliferation may not be a prerequisite for the development of such suppressor T cells.     

5C6-F4, a novel 100,000-dalton rat lymphocyte activation antigen defined by monoclonal antibody

Con A-activated rat thymocytes were used to immunize mice, and immune spleen cells were fused with NS/1 myeloma cells. One clone, designated 5C6-F4, reacted strongly with Con A-activated rat thymocytes and some LPS-activated rat spleen cells but not with normal thymocytes, spleen cells, or bone marrow cells of rat origin. The 5C6-F4 did not react with Con A-activated thymocytes of mouse origin. Immunoprecipitation of 5C6-F4 antigen from surface-iodinated Con A-activated rat thymocytes or LPS-activated rat spleen cells revealed its m.w. to be approximately 100,000. The kinetic studies of the expression of 5C6-F4 antigen revealed that 5C6-F4 antigen was detectable at 6 hr after Con A stimulation of rat spleen cells, whereas IL 2 receptor (IL 2R) was detectable at 12 hr. The appearance of 5C6-F4 antigen and IL 2R precede the onset of DNA synthesis of Con A-activated spleen cells. Thus, 5C6-F4 antigen is classified as early activation antigen. The 5C6-F4 inhibits the lymphocyte proliferation induced by mitogen and the IL 2-driven rat T cell proliferation. Sequential immunoprecipitation study as well as binding inhibition study indicated that the 5C6-F4 antigen is distinct from IL 2R molecule. The 5C6-F4 antigen appears to be a novel rat lymphocyte activation antigen that exhibits immunoregulatory function and also may serve as a useful marker of T cell activation.     

Membranes from both Th1 and Th2 T cell clones stimulate B cell proliferation and prepare B cells for lymphokine-induced differentiation to secrete Ig.

Plasma membranes from the mitogen-activated mouse Th2 cell clone D10.G4.1 have recently been shown to provide the cell contact-dependent signals necessary for the induction of small B cell proliferation. Together with the Th2-derived lymphokines IL-4 and IL-5, these membranes stimulate production of Ig isotypes identical to those produced when B cells were stimulated by intact Th2 cells. In contrast, Th1 clones are poor inducers of Ig production in vitro. This could be solely due to differences in the lymphokines released by Th1 and Th2 cells or to differences in the cell-cell contact signals delivered by activated Th1 and Th2 cells. We report that membranes from three different activated Th1 clones induced strong Ag-independent proliferation of small dense B cells. The level of B cell proliferation was enhanced approximately fourfold by the addition of lymphokine-containing supernatant from Con A-activated Th2 cells and was unaffected by any of the lymphokine-containing supernatants from Con A-activated Th1 clones. As with D10.G4.1 membranes, Th1 membranes alone induced B cell proliferation but not secretion of Ig. However, addition of supernatant from Con A-activated D10.G41 cells, but not any supernatants from Con A-activated Th1 cells, induced Ig secretion of all isotypes. These effects were shown to not simply result from increased B cell numbers after stimulation with Th2 lymphokines. Thus, Th1 cell clones seem to poorly induce antibody responses entirely because of their lymphokine repertoire and not because of differences or deficiencies in the ability of these cells to deliver cell contact-dependent signals to B cells.     

Mechanisms of corticosteroid action on lymphocyte subpopulations. IV. Effects of in vitro hydrocortisone on naturally occuring and mitogen-induced suppressor cells in man.

The effects of in vitro hydrocortisone (OHC) on human peripheral blood (PB) suppressor cell function were investigated. Two types of suppressor cells were studied: (i) the naturally occurring PB suppressor cell seen in 10% of normal people whose lymphocytes do not respond to in vitro PWM stimulation with direct anti-SRBC PFC responses, and (ii) Con A-generated suppressor cells. The addition of OHC to PWM-stimulated cultures from nonresponders reconstituted the PFC response in two of three individuals. The addition of OHC to allogenic cocultures of nonresponder and responder lymphocytes completely inhibited the ability of the naturally occurring suppressor cell of the nonresponder cultures to inhibit the PFC responses of normal responders. Preincubating the nonresponder cultures in 10^?5M OHC for 30 min followed by washing did not inhibit suppressor function, whereas readdition of OHC to cocultures did inhibit nonresponder suppressor cell function. The addition of up to 10^?4M OHC to previously generated Con A-activated suppressor cell-fresh cell cocultures in vitro did not prevent or inhibit mitogen-activated suppressor cell function. However, preincubation of PB cells for 6 hr prior to the addition of Con A prevented the generation of suppressor cells and in two of eight experiments generated a population of cells which were in and of themselves mitogenic for autologous fresh PB. Thus, the function of naturally occurring suppressor cells as well as the induction but not the function of Con A-activated suppressor cells is sensitive to pharmacologic levels of OHC. The effect of OHC on naturally occurring suppressor cell function or on the generation of suppressor cells by Con A did not involve cell lysis, but rather was a reversible phenomenon requiring the continued presence of OHC in culture.     

Abnormal activation and loss of suppressor T cells in the spontaneously hypertensive rat.

Suppressor T cell function in the spontaneously hypertensive rat (SHR) and normotensive Wistar Kyoto (WKY) rats was analyzed using syngeneic mixed lymphocyte reaction (SMLR) and concanavalin A (Con A) activation. A depressed SMLR was found in adult SHR but not in adult WKY. IL-2 synthesized by SHR was 40-fold lower than that of WKY, and the suppressor T cells generated in the SMLR were incapable of suppressing IgG synthesis. Precursors of cells that can be activated by Con A to become functional suppressor cells are reduced in adult SHR. Supernatant fluids derived from Con A-activated spleen cells from adult SHR failed to significantly inhibit IgG synthesis by cultures of syngeneic spleen cells compared to supernatant fluids from young SHR or WKY Con A-activated spleen cells. However, spleen cells from both adult SHR and WKY proliferated strongly and released equivalent amounts of IL-2 in response to Con A. Addition of exogenous IL-2 to the SMLR cultures in vitro restored the ability of SHR T cells to respond in the SMLR, with generation of cells capable of suppressing IgG synthesis. Administration of SHR with IL-2 in vivo also restored the suppressor T cell function in the SMLR. These results suggest a defective suppressor T cell activation and loss of suppressor T cell activity as the SHR age.     

Cellular requirements for production and release of the lymphocyte costimulator

The lymphocyte costimulator (CoS) is a lymphokine required for the activation of T cell responses to H-2 alloantigens or mitogen, CoS activity is found in the supernatant medium of Concanavalin A (Con A) stimulated spleen cells, In this paper we investigate the cellular requirements for CoS production by Con A-activated mouse spleen cells. Maximal lymphokine production in response to Con A depends on a co-operative interaction between T cells and a nylon wool-adherent cell present in the spleen of nude mice. T cells appear to be the major producers of CoS activity, doing so only in response to an initial inductive stimulus supplied by nude spleen cells. The inductive stimulus is found as a soluble factor in the supernatant of Con A-activated spleen cells, and can also be provided by stimulatory (S+), but not by non-stimulatory (S-), tumour cells H-2 identical with the responding T cells. The activation of lymphokine-producing T cells is thus a two-signal process, requiring both mitogen and an additional inductive signal. Once activated, homogeneous populations of T cells will release lymphokine in response to mitogen alone.     

Synergistic effect of concanavalin A and Bu-WSA on DNA synthesis in human peripheral blood lymphocytes

Butanol-extracted water soluble adjuvant (Bu-WSA) obtained from Bacterionema matruchotii was not mitogenic for human peripheral blood mononuclear cells (PBM) but was capable of enhancing (3H) thymidine uptake of T cells stimulated by concanavalin A (Con A) in the presence of B cells or macrophages (M phi) in vitro. The mechanisms of the synergy of Con A and Bu-WSA were studied by using separated cell populations from PBM. Both subfractioned OKT4+ and OKT8+ cells were responsive to co-stimulation by Con A and Bu-WSA in the presence of an accessory cell population. Allogeneic B cells and M phi as well as autologous cells had helper function as accessory cells. Heavy irradiation with gamma-rays did not affect the function of the accessory cells, but previous treatment of B cells with anti-Ig serum plus complement (C) or treatment of M phi with anti-M phi serum plus C deprived them of their function. The treatment of accessory cells with anti-HLA-DR serum, regardless of the presence or absence of C, resulted in loss of their helper function. Cultures in Marbrook-type vessels showed that a mixed cell population of T cells and accessory cells in the lower chamber produced some active factor(s) after co-stimulation with Con A and Bu-WSA, and by passing through the membrane filter separating the chambers, the factor(s) enhanced the proliferation of the Con A-activated T cell population in the upper chamber. The factor(s) was presumed to be interleukin 2 (IL 2), because it supported the growth of IL 2-dependent CTLL cells. These results indicate that the synergy of Con A and Bu-WSA on the proliferative response of human PBM is due to the elevation of growth factor production from T cells stimulated by those mitogens.     

Soluble suppressor activity of concanavalin A-activated spleen cells on B-lymphocyte colony formation in vitro.

Supernates from concanavalin A (Con A)-activated mouse spleen cell cultures suppress the formation of B-lymphocyte colonies (BLC) in soft agar culture by 30 to 95%. Con A-induced BLC suppressive culture supernates can be heated at 80 °C for 1 hr without losing activity. The BLC suppressive activity is eliminated totally by trypsin treatment and partly by treatment with β-galactosidase. Activity is unaffected by treatment with DNAse, RNAse, and α-glucosidase. By ultrafiltration the BLC suppressive factor(s) was shown to have a molecular weight greater than 300,000. These data suggest that BLC suppression is mediated by a protein-carbohydrate complex. BLC suppression was obtained when normal spleen cells were preincubated in Con A-activated supernates for only 1 hr at 37 °C. BLC suppressor activity was absent in the supernatant fluid of Con A exposed anti-θ-treated spleen cells, nonadherent spleen cells, extensively washed spleen cells, and spleen cells from nude (athymic) mice suggesting that cells responsible for Con A-induced BLC suppression are adherent, fragile cells of the T lineage. Con A-activated spleen cell supernates do not suppress colony formation in soft agar by normal mouse granulocyte-macrophage precursors, by plasmacytoma cells, T-lymphoma cells, or by carcinoma cells. However, colony formation by Abelson's murine leukemia virus transformed B-lymphoma cells was suppressed by 95% suggesting a relationship between this immature B-lymphoma line and B-lymphocyte colony-forming cells. Con A-activated spleen cell supernates do not suppress lymphocyte activation in liquid culture by phytohemagglutinin, Con A, or lipopolysaccharide. Heat-treated supernates—which inhibited BLC development by 90–95%—did not suppress the plaque formation by spleen cells immunized in vivo or in vitro by sheep red blood cells.     

Identification and characterization of a B cell growth inhibitory factor (BIF) on BCGF-dependent B cell proliferation

The culture supernatants of Con A-activated human peripheral blood mononuclear cells (PBM) contained at least two regulatory factors upon B cell proliferation. One was B cell growth factor (BCGF), which activated antigen-stimulated B cells to proliferation and clonal expansion, and the other was its inhibitory factor, arbitrarily named B cell growth inhibitory factor (BIF). This BIF inhibited the effect of BCGF on anti-mu-stimulated B cells or the monoclonal mature B cell line (CLL-T.H.) obtained from the peripheral blood lymphocytes of B cell-type chronic lymphocytic leukemia patients, which were activated only with BCGF and without adding other proliferating stimuli (e.g., anti-mu). BIF activity was detected in the 24 hr culture supernatants of Con A-activated human PBM in FCS containing medium and also in serum-free RPMI 1640 medium. This substance with BIF activity could not be derived from FCS. Con A-induced BIF (m.w. of 80,000 and an isoelectric point of pH 5.4) was analyzed by Sephadex G-200 gel filtration and chromatofocusing. BIF was stable at pH 2.0 and at 56 degrees C for 30 min. Partially purified BIF had no effect on cell viability and almost no interferon activity (less than 1 IU/ml). BIF with high titer had a slight but significant inhibition on TCGF-dependent T cell growth and on PHA or Con A responses, but the extent of these inhibitions was far less than that of BCGF-dependent B cell growth. Absorption of BIF with Con A blasts made its inhibition on T cell growth even less. On the other hand, BIF activity could not be absorbed with Con A blasts but was almost absorbed with large numbers of CLL-T.H. cells. BIF had almost no inhibitory effect on the proliferation of a mouse fibroblast cell line (NIH 3T3), a mouse myeloma cell line (NS-1), human lymphoid cell lines (MOLT-4, HSB-2, and Daudi), or a human myeloid cell line (K-562). BIF-producing cells were estimated to be T cells and were identified as T8+ T cells. On the other hand, Con A-induced BCGF was demonstrated to be produced predominantly by T4+ T cells. These results show that human B cell proliferation is regulated by interaction between T4+ and T8+ cells via soluble factors, namely BCGF and BIF, respectively.     

Evidence that Con A induces cytotoxicity in the same subclass of T cells as does alloimmunization.

We have studied the induction of cytoxic activity in murine T cells by the T cell mitogen Con A. Here we report the results of experiments that indicate that this cytotoxicity develops in the same class of T cells potentially activatable to cytotoxicity by immunization with allogeneic cells. Cytotoxic activity does not result from activation of cells of the T-helper class by PHA, and extensive reduction of the proportion of cells of the T-helper class by in vivo treatment with ATS does not comparably reduce the cytotoxicity developed in response to Con A. The Con A-activated cytotoxic cell sediments as a large cell. Furthermore, spleen cell populations previously immunized to alloantigens in vivo develop greatly increased cytotoxicity specific for the alloantigen of the immunizing haplotype after culture with Con A in vitro.     

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.     

Biosynthesis and surface expression of T8 by peripheral blood T4+ cells in vitro

Biosynthetic labeling with 35S-methionine and 35S-cysteine of isolated T4+ cells from Con A-activated T cells demonstrated that the T8 antigen was synthesized by activated T4+ cells. Two-color fluorescence analysis of the activated T cell population from which the T4+ fraction was obtained showed that both T4+T8- and T4+T8+ cells were present. The T8 antigen that was immunoprecipitated by monoclonal anti-T8 from activated T4+ cells migrated with an electrophoretic mobility corresponding to an m.w. of approximately 33,000, a previously reported m.w. value for T8 antigen. Con A activation of highly purified peripheral T4+T8- and T8+T4- subsets indicated that both T4+T8- and T8+T4- cells can give rise to T4+T8+ cells. However, substantial T4, T8 coexpression by T4+T8- cells required a signal from T8+T4- cells which could be supplied by incubating T4+T8- cells with irradiated T8+ cells or the supernatant from Con A-activated T8+T4- cells. The generation of T4+T8+ cells from a subset of T4+T8- T cells may be an important mechanism in immune activation and/or the further differentiation of peripheral T4+ cells.     

Origin of autoreactive T helper cells. I. Characterization of Thy-1+, Lyt-, L3T4- precursors in the spleen of normal mice

A new population of dull Thy-1+, Ly-1-, Lyt-2-, L3T4- PNA- cells, resistant to a double cytotoxic treatment by monoclonal antibodies to these T cell markers plus complement, has been isolated from the spleen of normal adult BALB/c and DBA/2 mice (Tkr cells). These cells exhibit no spontaneous autoreactivity or alloreactivity but can be activated with concanavalin A (Con A). Once activated, they differentiate into bright Thy-1+, Ly-1+, Lyt-2-, L3T4+ PNA- T lymphocytes. Con A-activated Tkr cells also strongly proliferate in the presence of allogeneic or syngeneic dendritic cells in secondary cultures. Moreover, contrary to other Con A-stimulated T cell populations, they induce B lymphocytes to proliferate and to differentiate into Ig-secreting cells at a very high level. Con A-activated Tkr cells are therefore very potent polyclonal B cell activators. Restimulated of Tkr cells by syngeneic dendritic cells can be inhibited by anti-L3T4 or anti-class II monoclonal antibodies. The results suggest that Tkr cells are the precursors of class II-specific autoreactive T helper cells. Tkr cells are absent in the spleen of B6 animals. This indicates that their expression might be genetically controlled. It also suggests that Tkr cells may not be the unique splenic precursors of autoreactive T cells. Con A activation of Tkr cells in Click's medium is 2-mercaptoethanol dependent and highly sensitive to pCO2, like the response of thymocytes. Tkr cells are also absent in the spleen of nude mice. We conclude that Tkr cells represent splenic precursors of autoreactive T helper cells equivalent to Thy-1+, Ly-2-, L3T4- PNA- cortical thymocytes.     

Genetic control of lymphocyte suppression. I. Lack of suppression in aged NZB mice is due to a B cell defect.

Con A-activated cells from old NZB mice were found capable of inhibiting the polyclonal response of cells from young NZB and BALB/c animals. Furthermore, Con A-preactivated spleen cells from young NZB and BALB/c mice did not significantly affect the response of spleen cells from old NZB mice. These results suggest that the defective suppressive activity in old NZB mice may be traced to a defect at the B cell level.     

Independent analysis of T helper and T killer cell function in young and old NZB mice.

With age, NZB mice lose their ability to develop a cytotoxic response after alloimmunization in vitro. This decline is shown to coincide with a diminution of T-helper cell activity as assessed by proliferation in mixed lymphocyte culture or in response to PHA. When cytotoxic T cell precursors are activated with the polyclonal activator Con A, there is no reduction in the number of cytotoxic effector T cells that develop. No autoreactive cytotoxic cells are seen in Con A-activated cultures. These findings are related to previous work on cell-mediated immunity in NZB and B/W mice.