Modulation of carrier-induced epitopic suppression by Bordetella pertussis components and muramyl peptide

Synthetic antigens employed in experimental synthetic vaccines are generally small haptenic peptides. Therefore, effective immunization with these antigens usually requires the use of an immunogenic carrier. Tetanus toxoid has been proposed for use as a carrier in future synthetic vaccines due to its high immunogenicity and acceptance for human use. Previous studies employing standard hapten/carrier systems such as DNP/KLH have demonstrated, however, that an epitope-specific suppression occurs when mice previously primed with carrier are subsequently immunized with an haptenic epitope conjugated to the same carrier. These same studies have shown that Bordetella pertussis vaccine administered at the time of carrier priming abrogates epitopic suppression. In the present investigation, epitopic suppression was studied in a synthetic vaccine model employing tetanus toxoid as a carrier. Results from these studies indicated that mice primed with tetanus toxoid 1 month before immunization with a peptide-tetanus toxoid conjugate exhibited enhanced secondary anti-tetanus toxin responses but decreased anti-peptide responses. Furthermore, injection of pertussis vaccine or purified B. pertussis toxin or endotoxin at the time of carrier priming could block the establishment of epitopic suppression. Administration of B. pertussis components enhanced antibody responses to both the carrier and the synthetic peptides as compared with responses of control animals. In addition, administration of an adjuvant-active nonpyrogenic derivative of muramyl dipeptide. Murabutide, with carrier priming reduced epitopic suppression of anti-peptide responses. B. pertussis toxin or endotoxin administered to mice previously suppressed by carrier priming with the first injection of carrier-peptide conjugate overcame epitopic suppression with resultant titers of anti-peptide antibody equal to or greater than nonsuppressed controls. These results suggest that the use of adjuvants with future synthetic vaccines may contribute the additional advantage of overcoming epitopic suppression, thus permitting the use of common, well-tolerated carrier systems such as tetanus toxoid in synthetic vaccine preparations.     

Carrier-induced epitopic suppression is initiated through clonal dominance

Injection of mice with an immunogenic dose of carrier followed by immunization with hapten-carrier conjugate selectively suppresses anti-hapten antibody response. Previous studies have proposed that this epitopic suppression is related to the induction of carrier-specific Ts cells which in turn could inhibit selectively anti-hapten response. In the present study, we propose that the epitopic suppression is in fact due to clonal dominance. Immunization with a carrier such as tetanus toxoid induces a clonal expansion of carrier-specific B cells, thus decreasing the probability of hapten-specific B cells to react with the Ag. Increasing the density of the TNP-hapten on the conjugate has totally prevented the induction of the epitopic suppression. Moreover, using low hapten-carrier concentrations to challenge carrier-primed mice has enhanced the induction of the suppression. Finally, priming hapten-specific B cells before carrier/hapten-carrier immunization has also abrogated the suppression. The results of these experiments support the view that epitopic suppression is induced through the expansion of the clones specific for the carrier epitopes and resulted from intra-molecular antigenic competition between hapten and carrier epitopes. Based on these findings a regulatory role is proposed for B cells, where through their capacity to process and present antigen, they would exercise a strong influence on the selection of immune responses.     

The in vivo elimination of CD4+ T cells prevents the induction but not the expression of carrier-induced epitopic suppression.

Injection of mice with an immunogenic dose of carrier (keyhole limpet hemocyanin (KLH)) followed by immunization with hapten-carrier conjugate (TNP-KLH) selectively suppresses anti-hapten antibody response. In this study, the cellular basis of this epitopic suppression and also of the suppression induced by a high dose of carrier were analyzed by in vivo depletion of CD4+ or CD8+ T cell subsets by using mAb. The mAb treatments were performed either at the time of carrier priming or at the time of hapten-carrier immunization. The elimination of CD8+ T cells has not modified the anti-carrier antibody response, whether this treatment was performed at the time of KLH-priming or during TNP-KLH immunization. Moreover, the in vivo treatment with the anti-CD8 mAb did not modify the carrier-induced epitopic suppression induced either by a low immunogenic dose of KLH or by a high dose of this Ag. The elimination of CD4+ T cells at the time of KLH immunization has prevented the induction of a memory response to KLH, clearly establishing that CD4+ T cells are essential in memory B cell development to T-dependent Ag. Moreover, this treatment has totally abrogated the epitopic suppression induced either by low or high dosages of KLH. In contrast, the in vivo elimination of CD4+ T cells after carrier immunization did not abolish the secondary anti-carrier antibody response and did not prevent the expression of epitopic suppression. These data indicate that primed CD4+ T cells are required neither for memory B cell expression nor for the expression of suppression. Finally, once induced, the suppression can be evidenced after in vivo depletion of both primed CD4+ and CD8+ T cells. These data support the view that epitopic suppression is induced through the expansion of carrier-specific B cells and resulted from intramolecular antigenic competition between hapten and carrier epitopes.     

Cationization of protein antigens. II. Alteration of regulatory properties

Immunoregulatory effects of cationized bovine serum albumin (cBSA) and native bovine serum albumin (nBSA) have been investigated. Intravenous administration of nBSA to BDF1 mice substantially suppressed the antibody response to subsequent immunization with either nBSA or cBSA, whereas pretreatment with cBSA by the same route significantly enhanced the responses to both antigens. The functional properties of BSA-specific T and B cells from mice immunized with cBSA or nBSA were examined in reconstitution experiments in which splenic T populations together with B cells were transferred into irradiated syngeneic recipients. Transfer of splenic T cells from mice primed with nBSA caused profound suppression of the response to subsequent immunization with nBSA or cBSA, whereas transfer of either B or T cells from cBSA treated mice produced an enhanced response to both antigens. C57BL/6 mice, which are considered to be low responders to BSA, produced a significant antibody response to BSA when immunized with cBSA. In contrast, immunization with nBSA did not produce measureable amounts of antibody in mice of this strain. Our data clearly demonstrate that cationized BSA exhibits unique immunogenic properties due to alterations in the self-regulation of the immune response.     

Activation in vivo of a major antisuppressor T-cell pathway immediately after immunization. I. Its regulation by I-A gene products

It has previously been demonstrated that within 6 hr after immunogenic stimulation the serum of mice contains a unique form of immunogenic antigen which represents complexes of Ig and antigen. The complexes are known to be strongly cytophilic for Ly2+ Ia+ FcR+ T cells and markedly enhance the IgG response. Anti-I-A treatment of mice suppresses the IgG antibody response and results in the generation of antigen specific T suppressor cells (Ts). Furthermore, anti-I-A treatment blocks the induction of the complexes and abolishes the enhancing effect the complexes exert on the IgG antibody response. The 6-hr cytophilic complexes were shown to block the function of Ts and allow a normal IgG response to take place; therefore, they act as mediators of a novel T-cell pathway called antisuppression. The blocking of the induction of the antisuppressor complexes by anti-I-A antibody was at least in part due to an effect on T cells. In conclusion, products of genes of the I-A subregion of the MHC control the activation early after immunization of a T-cell pathway which is called antisuppression since its major function is interference with the expression of suppression. Its early induction (within 6 hr) suggests that antisuppression may play a pivotal role in determining between immunity and unresponsiveness.     

Regulatory mechanism of reagin production in mice at the T cell level. I. Suggestive evidence for the generation of class specific PPD-reactive helper T cell population in Mycobacterium-primed cells.

Helper T cell activities specific for purified protein derivative (PPD) generated by immunization with Mycobacterium tuberculosis (Tbc) or PPD were investigated concerning adoptive IgE and IgG antibody responses. It is interesting that preferential triggering activity of IgG antibody response was observed when PPD-reactive cells from mice immunized with Tbc were used as a helper cell source. The selective triggering of IgG B cells by Tbc-primed cells was consistently observed using DNP-primed B cell populations from mice immunized with DNP-carrier conjugate in either ICFA or alum. T cell dependency of helper activity was demonstrated by the fact that treatment of Tbc-primed cells with anti-Thy 1 antiserum plus complement abolished their helper activity. We also demonstrated that purified T cell populations selectively triggerred IgG B cells. Selective triggering of IgG B lymphocytes by Tbc-primed T cells may not be due to the influence of suppressor T cells supposedly present in Tbc-primed cells since this selectivity was not affected by X-irradiation of Tbc-primed T cell populations which may inactivate suppressor T cells. Furthermore, passive transfer of Tbc-primed cells into normal recipient mice, the condition which may detect the suppressor T cell effect much more sensitively in IgE production, or preimmunization with Tbc 2 weeks before, did not suppress primary anti-DNP IgE antibody response to DNP-PPD. Thus, the observations presented here are favorable to the concept of the presence of IgG class-specific helper T lymphocytes. Furthermore, PPD-reactive T cells from mice immunized with PPD itself exerted their helper function for triggering B cells of both IgE and IgG classes. This may also indicate that some of the components associated with Tbc other than PPD might negatively affect the development of PPD-reactive helper T cells specific to the IgE class. The generation of such IgG-specific T cell activity in the presence of Tbc will be discussed in the light of the T cell population involved in the regulation of antibody responses of different immunoglobulin classes.     

CD40 ligation in vivo can induce T cell independent antitumor effects even against immunogenic tumors

Antitumor effects of CD40 ligation appear to involve distinct antitumor effector cells in different experimental models. In this study, we tested whether T cells were required for antitumor effects of agonistic anti-CD40 mAb (alphaCD40) against immunogenic versus poorly immunogenic tumors. Treatment of mice bearing poorly immunogenic B16 melanoma and its more immunogenic variant, B16-hsp72.1, with alphaCD40 resulted in a similar level of tumor growth suppression. Depletion of T cells did not reduce the antitumor effects in these 2 tumor models. To generate antitumor T cell responses, C57BL/6 mice were immunized with irradiated B16-hsp72.1. Treatment of these vaccinated mice challenged with a high dose of B16-hsp72.1 tumor cells with alphaCD40 induced tumor growth suppression, which was reduced by T-cell depletion, demonstrating that T cells were involved in the antitumor effect of alphaCD40. However, immunized mice depleted of T cells and treated with alphaCD40 were still able to suppress tumor growth as compared to tumor growth in immunized, T cell-depleted mice not treated with alphaCD40, suggesting that T cells were not required for the antitumor effect of alphaCD40. To confirm a lack of correlation between tumor immunogenicity and T-cell requirement in antitumor effects of CD40 ligation, we found that alphaCD40 induced tumor growth suppression in nude and SCID/beige mice bearing highly immunogenic tumors such as Meth A sarcoma, suggesting that macrophages may play a role. Indeed, both poorly immunogenic and highly immunogenic tumors were sensitive to in vitro growth inhibition by macrophages from alphaCD40-treated mice. Taken together, our results indicate that antitumor effects induced by alphaCD40, even against immunogenic tumors, can be observed in the absence of T cells and may involve macrophages.     

In vitro T cell-mediated killing of Pseudomonas aeruginosa. IV. Nonresponsiveness in polysaccharide-immunized BALB/c mice is attributable to vinblastine-sensitive suppressor T cells

We reported previously that BALB/c mice immunized with a polysaccharide (PS) antigen isolated from immunotype 1 Pseudomonas aeruginosa and vinblastine sulfate develop T cell-mediated protective immunity, despite their failure to produce specific antibody. In vitro, Lyt-1-,2+, I-J+ T cells from vinblastine- and PS-immunized mice kill P. aeruginosa by secretion of a bactericidal lymphokine. BALB/c mice immunized with PS alone generate neither protective antibodies nor a protective T cell response. The current studies indicate that T cells from mice immunized with PS alone significantly suppress the bactericidal activity of T cells from mice immunized with vinblastine and PS. The suppressor T cells are of the same Lyt-1-,2+, I-J+ phenotype as the bactericidal T cells. Suppression is mediated by a soluble product of these suppressor T cells which both inhibits T cell proliferation and interferes with the production or release of the bactericidal lymphokine. Cyclophosphamide, used in other systems to remove suppressor T cells, fails to enhance bacterial killing and does not inhibit suppressor cell activity. These studies indicate that immunization with PS elicits responses in two functionally distinct subgroups of Lyt-1-,2+, I-J+ T cells, and that these cells are distinguishable by their sensitivity to vinblastine sulfate.     

T cell subsets regulating antibody responses to L-glutamic acid60-L-alanine30-L-tyrosine10 (GAT) in virgin and immunized nonresponder mice

T cell subsets from virgin and immunized mice, which are Ir gene controlled nonresponders to GAT, which regulate antibody responses to GAT have been characterized. Virgin nonresponder B10.Q B cells develop GAT-specific antibody responses to GAT, B10.Q GAT-M phi, and GAT-MBSA when cultured with virgin or GAT-primed Lyt-1+, I-J-, Qa1- B10.Q helper T cells. Virgin T cells are radiosensitive, whereas immune T cells are radioresistant (750 R); qualitatively identical helper activity is obtained with T cells from mice immunized with soluble GAT, B10.Q GAT-M phi, and GAT-MBSA. Responses to GAT and GAT-M phi are not observed when virgin or GAT-primed Lyt-1+, I-J+, Qal+ T cells are added to culture of virgin or GAT-primed Lyt-1+, I-J-, Qa1- helper T cells and virgin B cells; the GAT-specific response to GAT-MBSA is intact. The Lyt-1+, I-J+, Qa1+ T cells from mice primed with GAT, GAT-M phi, and GAT-MBSA were qualitatively identical in mediating this suppression. Virgin Lyt-2+ T cells have no suppressive activity alone or with virgin Lyt-1+, I-J+, Qa1+ T cells, whereas responses to GAT, GAT-M phi, and GAT-MBSA are suppressed in cultures of GAT-primed helper T cells containing GAT-primed Lyt-2+ T cells (with or without GAT-primed Lyt-1+, I-J+, Qa1+ T cells). Suppression of responses to GAT-MBSA in cultures of GAT-M phi-primed helper T cells requires both GAT-M phi-primed Lyt-1+, I-J+, Qa1+ T cells and Lyt-2+ T cells; the Lyt-1+, I-J+, Qa1+ T cells appear to function as inducer cells in this case. In cultures containing GAT-MBSA-primed helper T cells, either GAT-MBSA-primed Lyt-1+, I-J+, Qa1+ or Lyt-2+ T cells suppress responses to GAT and GAT-M phi; under no circumstances are responses to GAT-MBSA suppressed by GAT-MBSA-primed regulatory T cells. This regulation of antibody responses to GAT by suppressor T cells is discussed in the context of the involvement of suppressor T cells in responses to antigens under Ir control, and of the evidence that nonresponsiveness to GAT is not due to a defect in the T cell repertoire, but rather is due to an imbalance in the activation of suppressor vs helper T cells.     

Determinant specific suppression of antigen-induced T cell proliferation in the guinea pig. II. Determinant specific suppression of in vitro T cell responsiveness parallels a selective suppression of anti-hapten but not anti-carrier antibody responses

Using an antigen of defined physical structure with precisely mapped immunogenic sites, we asked whether those molecular sites previously shown to be critical for immune response gene-mediated initiation of T cell proliferation and T help correspond to the same molecular regions capable of inducing antigen-specific suppression of T cell proliferation and antibody production. Inbred strain 2, 13, and 2 x 13 F1 hybrid guinea pigs were immunized with various species variants or fragments of insulin adjuvant before subsequent immunization with antigen in complete Freund's adjuvant. Analysis of the patterns of depressed T cell responsiveness showed a striking correspondence to the Ir gene-dependent mechanism that controls the recognition of discrete regions within the insulin molecule observed in T cell help in antibody production. In addition, suppression of carrier-specific T cells parallels suppression of anti-hapten antibody responses when hapten is presented on the suppressed carrier without a concomitant suppression of the anti-carrier antibody response.     

Reaginic antibody formation in the mouse. X. Possible role of suppressor T cells in transient IgE antibody responses.

The kinetics of IgE antibody response to alum-absorbed dinitrophenyl derivatives of ovalbumin (DNP-OA) was dependent on the dose of immunogen. A persistent IgE antibody response was obtained when high responder BDF1 mice were immunized with a minimum (0.05 microgram) dose. An increase of the immunogen to 10 microgram depressed IgE antibody responses but enhanced IgG antibody responses of both hapten and carrier specificities. Determination of T helper cell activity and B memory cells after immunization with different doses of antigen indicated that minimum immunogen was favorable for developing helper activity, whereas 1 to 10 microgram immunogen were more favorable than a 0.05-microgram dose for developing both IgE and IgG B memory cells. Nevertheless, neither helper T cells nor B memory cells in the spleen explains a transient IgE antibody response to a high (10 microgram) dose of DNP-OA. Evidence was obtained that immunization with 10 microgram OA induced generation of antigen-specific suppressor T cells, which were not detectable after immunization with 0.05 microgram OA. Transfer of suppressor T cells to DNP-OA-primed mice depressed both anti-hapten and anti-carrier IgE antibody responses. The results suggested strongly that suppressor T cells are involved in a transient IgE antibody response to a high-dose immunogen.     

Mechanisms of suppressed cell-mediated immunity and impaired antigen-induced interleukin 2 production in granuloma-bearing mice

Pulmonary granulomas were induced in BALB/c mice immunized with methylated bovine serum albumin in complete Freund's adjuvant by the intratracheal injection of plain agarose beads or beads conjugated to specific antigen. Large hypersensitivity granulomas developed around antigen-coupled beads in immunized animals. Smaller but still prominent granulomatous reactions developed around plain beads in immunized mice. In nonimmunized animals, both plain and antigen conjugated beads produced very small granulomas. Granuloma formation in sensitized animals was associated with suppressed delayed-type hypersensitivity reactions induced by the footpad injection of specific and nonspecific antigens. Lymph node cells from sensitized granuloma-bearing mice with cutaneous anergy showed suppressed specific and nonspecific antigen-induced proliferative responses in vitro. These cells also showed suppressed interleukin 2 production in response to specific antigen. Although no soluble suppressive factor was detected in granuloma extracts, suppressor cells were found in lymph nodes of granuloma-bearing mice, which could inhibit antigen-induced production of interleukin 2 by lymph node cells from immunized mice. Antigen-specific immunoglobulin G antibody production was not suppressed in immunized granuloma-bearing mice. Previous studies from our laboratory have demonstrated migration inhibition factor and interleukin 1 activities in aqueous extracts prepared from granuloma-bearing lungs of immunized mice. These results and the findings reported here indicate that granuloma formation and the associated anergy observed in this system are primarily expressions of cell-mediated immunity; selective suppression of in vivo and in vitro expressions of cell-mediated immunity in granuloma-bearing mice may be due to impaired antigen-induced interleukin 2 production; and such impairment is caused by suppressor cells.     

Suppressor cells in mice infected with Trypanosoma brucei.

Within 2 to 3 days of infection with Trypanosoma brucei strain S42, the ability of spleen cells from infected CBA mice to mount a primary in vitro antibody response to sheep red blood cells (SRBC) is profoundly reduced, and suppressor cells are generated as detected by cell mixture experiments. Suppressor cell activity lies in the T and adherent cell compartments of spleens from infected mice, but not in the B cell compartment, although antibody responses to a thymus-independent antigen, DNP-Ficoll, are significantly reduced. Suppression of antibody responses of normal spleen cells depends on viable cells from infected mice. The trypanosome, itself, plays no direct role in suppression, and we have ruled out the possibility of antigenic competition as a mechanism of suppression. Our data is consistent with the model of suppressor T cells induced by concanavalin A mitogenesis. We hypothesize that trypanosome antigens may directly stimulate T cells with the concomitant release of factors with affinity for macrophage surfaces thus becoming suppressive for T and B cell responses.     

Modulation of immune responses by suppressor T cells.

The activity of suppressor T cells has been demonstrated in almost every phase of the immune response. These regulatory cells modulate both humoral and cell-mediated immunity utilizing antigen-specific and nonspecific mechanisms. For comparative purposes two murine models are described, the nonspecific suppressor T cell stimulated by the mitogen concanavalin A and the antigen-specific suppressor T cell stimulated by injection of the synthetic terpolymer acid 60-L-alanine30-L-tyrosine10 (GAT) in nonresponder mice. These two T cells are similar to expression of Ly alloantigens, ability to inhibit antibody responses, and the mediation of suppression, at least in part, by soluble products. However, differences in radio-resistance and antigenic specificity of the suppressor T cells, as well as differences in molecular characteristics of the soluble factors and their targets suggest that these T cells regulate the immune response by different mechanisms. The relationship of these two suppressor T cells to other nonspecific and antigen-specific suppressor T cells is discussed.     

Lymphocyte activation and serine-esterase induction following recombinant interleukin-2 infusion for lymphomas and acute leukaemias

Summary C57BL mice inoculated with radiation leukemia virus (RadLV) develop preleukemic cells long before the onset of leukemia. These cells are potentially immunogenic but fail to elicit an immune response in the host because of the appearance of virus-specific suppressor T cells. We have studied the effect of polysaccharide K (PSK) on the generation of RadLV-specific cell-mediated immune responses in vitro. Long-term exposure to PSK in culture potentiated the ability of immunized T cells to respond to a RadLV-induced lymphoma. It also abrogated the suppressive activity of suppressor T cells and simultaneously boosted the ability of reactive T cells to respond. The dual immunostimulating activity of PSK resulted in the generation of T cytotoxic lymphocytes that could lyse lymphoma cells in vitro. The results suggest that PSK could be used as a prophylactic immune response modifier in preleukemia.     

Prophylactic immunization against experimental leishmaniasis. V. Mechanism of the anti-protective blocking effect induced by subcutaneous immunization against Leishmania major infection

The responsiveness of BALB/c mice to protective i.v. immunization with 150,000-rad irradiated or heat-killed Leishmania major promastigotes can be totally suppressed by prior subcutaneous (s.c.) injection of the same "vaccine." Induction of this effect is leishmania specific for although prevention of protection against L. major infection can be obtained with either homologous or Leishmania donovani promastigotes, it does not follow s.c. administration of an immunogenic Trypanosoma cruzi epimastigote preparation. Multiple s.c. injections of irradiated L. major promastigotes do not inhibit the subsequent antibody response of any major isotype to i.v. immunization, but rather induce some priming. The same s.c. injections induced delayed-type hypersensitivity (DTH) reactivity that could be transferred locally or systemically, although it was weaker than in mice with cured infections. Parallel cell-mediated immunity (CMI) responses were also reflected in vitro in specific lymphocyte transformation assays. Despite this evidence of a DTH/helper type of T cell response, transfer of 5 X 10(7) viable T cell-enriched spleen cells from 4 X s.c. immunized donors to normal recipients completely abrogated the protective response to i.v. immunization. Conversely, T cell-depleted (anti-Thy-1.2 + C treated) cells were without effect. The inhibitory T cells were defined by monoclonal antibody pretreatment as possessing an Lyt-1+2-,L3T4+ phenotype. T cells from s.c. immunized donors were also shown, by mixed transfer experiments, to counteract completely the protective effect of T cells from i.v. immunized donors in 550-rad irradiated recipients. They were as potent as suppressor T cells from donors with progressive disease both in this capacity and in abrogating the prophylactic effect of sublethal irradiation itself. The similarities and differences between suppressor and immune effector T cells induced by s.c. or i.v. immunization and those arising in response to leishmanial infection itself are discussed.     

The regulation of resistance to Schistosoma mansoni by auto-anti-idiotypic immunity. III. An analysis of effects on epitopic recognition, idiotypic expression, and anti-idiotypic reactivity at the clonal level.

Auto-anti-idiotypic mechanisms can regulate the protective immune response against Schistosoma mansoni. Anti-idiotypic responses were stimulated by immunization of mice either with nonspecifically induced lymphoblasts, produced with Con A, or with Ag-induced lymphoblasts bearing specific idiotypic receptors. The effect of the induced anti-idiotypic response upon clonotypic cellular reactivity was assessed in vitro through the suppression of antigen-mediated blast transformation by cloned T cells and in vivo by suppression of resistance to S. mansoni and delayed-type hypersensitivity responses against specific Ag. Differential regulation of humoral immune responses was studied at the levels of specific epitopic recognition, the expression of specific Id, and the production of anti-idiotypic responses directed against mAb bearing specific Id. Anti-idiotypic sensitization resulted in variable (10 to 90%) suppression of the immune response to discrete antigenic epitopes, the expression of specific idiotypic phenotypes, and anti-idiotypic, antiparatopic responses against T cell clonotypes and antibody idiotypic phenotypes. In vitro admixture and in vivo challenge studies resulted in consonant differential suppression. Thus idiotypic regulation can mold the fine specificities of the protective immune response to S. mansoni at the clonal level and may provide an approach to optimize the expression and assessment of resistance.     

Cutaneous leishmaniasis in anti-IgM-treated mice: enhanced resistance due to functional depletion of a B cell-dependent T cell involved in the suppressor pathway

The contribution of B cells and antibodies to either the resistance or susceptibility to cutaneous leishmaniasis has been investigated in mouse strains rendered B cell-deficient by treatment with anti-mouse IgM antisera from birth (mu-suppressed). These studies confirm that immunity to cutaneous disease in a normally resistant mouse strain (C3H/HeJ) is independent of antibody, but that B cells and/or antibodies are required for the evolution of suppressed DTH and the consequent disease susceptibility of BALB/c mice. Anti-IgM-treated BALB/c mice, which lacked detectable anti-leishmanial antibodies during the course of infection, displayed a sustained DTH response to leishmanial antigen and were able to control their cutaneous lesions. The enhanced resistance of mu-suppressed mice could be completely abrogated by transfer of suppressor T cells from infected control animals into mu-suppressed mice before their infection. Thus the suppressor T cells, which are generated during leishmanial infection in BALB/c mice, can effect suppression in the absence of antibody. Evidence that B cells or antibodies are required for the generation of suppressor T cells was demonstrated by using BALB/c mice in which suppressor T cells fail to be generated during infection as a result of prior sublethal irradiation. Splenic T cells from normal mice could overcome the resistance conferred by sublethal irradiation, whereas splenic T cells from mu-suppressed mice could not. Thus the enhanced resistance of mu-suppressed BALB/c mice appears to be a consequence of their lack of functional expression of a B cell-dependent T cell critical to the suppressor pathway.     

Insulin-specific suppressor T cell factors

Murine antibody responses to heterologous insulins are controlled by MHC-linked immune response genes. Although nonresponder mice fail to make antibody when injected with nonimmunogenic variants of insulin, we have recently shown that nonimmunogenic variants stimulate radioresistant, Lyt- 1+2- helper T cells that support secondary antibody responses. However, the helper activity can not be detected unless dominant, radiosensitive Lyt-1-2+, I-J+ suppressor T cells are removed. In this paper we report that extracts of primed Lyt-2+ suppressor T cells contain insulin-specific suppressor factors (TsF) that are capable of replacing the activity of suppressor T cells in vitro. The activity of these factors is restricted by MHC-linked genes that map to the I-J region, and immunoadsorption studies indicated that they bind antigen and bear I-J-encoded determinants. Insulin-specific TsF consists of at least two chains, one-bearing I-J and the other the antigen-binding site. Furthermore, mixing of isolated chains from different strains of mice indicates that the antigenic specificity is determined by the antigen-binding chain and the MHC restriction by the H-2 haplotype of the source of the non-antigen-binding, I-J+ chain. Moreover, mixtures containing antigen-binding chain from allogeneic cell donors and I-J+ chain from responder cell donors have activity in cultures containing responder lymphocytes. This suggests that preferential activation of suppressor T cells, rather than differential sensitivity to suppression, results in the nonresponder phenotype to insulin.     

Macrophage-mediated suppression of immune responses in Toxoplasma-infected mice. II. Both H-2-linked and -nonlinked control of induction of suppressor macrophages

The suppressive effect of Toxoplasma infection on initiation of memory cells to dinitrophenylated keyhole limpet hemocyanin (DNP-KLH) was drastically different among inbred strains of mice. C57BL/6 (B6), C57BL/10 (B10), and SJL mice showed markedly suppressed secondary anti-DNP responses when infected. In contrast, the suppression did not occur in BALB/c mice. The infected DBA/2 and C3H/He mice produced moderately suppressed responses. In B6 mice, an injection with 1 X 10(2) organisms of T. gondii induced a suppressed elicitation of the memory cells to DNP-KLH. However, in BALB/c mice, the responses were not affected even by inoculation with 1 X 10(4) organisms. The difference in the suppressive effect of infection between B6 and BALB/c mice was also observed in the primary anti-DNP antibody responses to DNP-KLH. Both H-2-linked and -nonlinked genes appeared to be responsible for the regulation of the immunosuppression, since the suppressive effect of infection in B10.D2 mice, which have the B10 background and the same H-2 haplotype as BALB/c, was weaker than that of B10 mice, but stronger than in BALB/c mice. In vitro studies using a primary anti-sheep erythrocytes (SRBC) antibody response system demonstrated that the activation of plastic-adherent suppressor cells by Toxoplasma infection, in which suppressor macrophages have been proved to be the responsible cells for the suppressive activity, was controlled by both H-2-linked and -nonlinked genes.