Modulation of the IgE immune response to BSA by fragments of the antigen. I. Suppression by free fragments and by fragments conjugated to homologous gamma-globulin

Nonimmunogenic peptic fragments of bovine serum albumin (BSA), Fraction Ia, suppressed immune response to BSA in mice. Splenic T lymphocytes from mice treated with these fragments suppressed the anti-DNP response in irradiated mice reconstituted with DNP-BSA-primed cells, indicating carrier-specific suppression. The conjugate of Fraction Ia with mouse γ-globulin (MGG) was found to be an effective suppressive substance but it did not induce suppressor T cells. B cells from mice given Ia-MGG were unresponsive to BSA when transferred to irradiated recipients along with either normal or BSA-primed T cells. Thus, unresponsiveness to BSA was mediated by either T or B lymphocytes, depending whether the inducing substance was a free fragment of the antigen or fragments conjugated to homologous γ-globulin.     

Regulation of granulomatous inflammation in murine schistosomiasis. III. Recruitment of antigen-specific I-J+ T suppressor cells of the granulomatous response by I-J+ soluble suppressor factor

Down-modulation of the schistosome egg-induced granulomatous response involves various interacting subsets of T suppressor (TS) lymphocytes. In the present study the inductive phase of the process of modulation was analyzed. A soluble, I-J+ granuloma TS cell recruiting factor (Gr-TSRF) derived from spleen cells of chronically infected mice is described. This factor eluted from immunoabsorbent columns coupled with anti-I-Jk alloantisera induced the recruitment and expansion of antigen-specific I-J+ TS cells from a TS precursor cell population in the spleens of acutely infected mice. The recruited TS cells suppressed the granulomatous response of normal recipients in a 2-day adoptive transfer model. The antigenic specificity of the recruited TS cells was demonstrated by their inability to suppress KLH-induced artificial granulomatous response. This mechanism of recruitment described in the current study and illustrated by adoptive transfer experiments is likely to be active in vivo in initiating the process of spontaneous modulation. The I-J+ Gr-TSRF and the I-J+ TS cell described in this paper, together with the previously described H-2 restricted I-C+ factor and the subsets of TS cells (THs, TSe, TSpr), indicate the existence of an intricate, regulatory pathway(s) that operates during the modulation of the granulomatous response.     

Adoptive suppression of granuloma formation by T lymphocytes and by lymphoid cells sensitive to cyclophosphamide.

Egg-induced granulomas formed in mice with chronic Schistosoma mansoni infection are smaller than those which develop during early (8-week) infection. Adoptive transfer of spleen cells from chronically infected mice (15–25 week), which displayed modulated granulomas, to 6-week-infected recipients effectively suppressed active granuloma formation in the recipients by 8 weeks after infection. Pretreatment of these suppressive spleen cells with anti-Thy 1.2 serum and complement eliminated their suppressive capacity. Administration of cyclophosphamide (CY) (20 mg/kg, 3 times/week for 3 weeks) to 12- to 15-week-infected mice reversed modulation of granuloma formation resulting in larger granulomas at 15 weeks. This abrogation of suppression was reflected in the spleens of the CY-treated mice, as seen by the inability of their spleen cells to adoptively transfer suppression to 6-week-infected mice. This regimen of CY treatment did not significantly alter anti-schistosome egg antigen hemagglutinating antibody titers. It is reasoned that the modulation of granuloma formation observed during chronic schistosomiasis mansoni is in part dependent upon a T lymphocyte and a CY-sensitive spleen cell.     

Adoptive transfer of immunity to Listeria monocytogenes. The influence of in vitro stimulation on lymphocyte subset requirements

BALB/c mice develop specific and relatively long lasting immunity after exposure to sublethal numbers of viable Listeria monocytogenes. This immunity can be passively transferred to naive recipients with maximal protection conferred by spleen cells obtained from donors 6 days after immunization. Immunity that can be directly transferred to syngeneic recipients is surprisingly short lived. Cell recipients lose immunity as early as 72 hr after transfer, and recipients express no detectable immunity after 1 wk. This short lived immunity requires both L3T4+ and Lyt-2+ T cell populations for full expression. Both the level of immunity transferred and the duration of the protective response expressed in recipients are dramatically increased if the spleen cell population is cultured in vitro with concanavalin A before cell transfer. Recipients of concanavalin A-activated cells express antigen-specific levels of immunity increased 100- to 1000-fold compared with syngeneic recipients of directly transferred immune spleen cells. In addition, this elevated level of adoptively transferred immunity remains constant for at least 8 wk. Transfer of this culture-enhanced immunity requires only an Lyt-2+ T cell population and is not influenced by cells of the L3T4+T cell subpopulation. Both direct as well as culture-enhanced transfer of immunity require major histocompatibility complex-compatible recipients. These findings suggest that two phenotypically distinct T cell subpopulations function in the development of the immune response to L. monocytogenes and that only one cell subpopulation is required for expression of immunity to this intracellular parasite.     

Two defects in old New Zealand Black mice are involved in the loss of low-dose paralysis to type III pneumococcal polysaccharide

Treatment of normal mice with a subimmunogenic dose of type III pneumococcal polysaccharide (SSS-III) results in the development of an antigen-specific state of unresponsiveness termed low-dose paralysis. This unresponsiveness is mediated by T suppressor cells and can be transferred by Lyt-2+ T cells, but not by L3T4+ T cells, obtained 18 hr after priming. As autoimmune New Zealand Black (NZB) mice age, there is a progressive decrease in low-dose paralysis to SSS-III. The defect in older NZB mice resulting in decreased suppressive activity was investigated by transferring primed Lyt-2+ T cells from young into old mice, and vice versa. Enlarged Lyt-2+ T cells from old NZB mice could not suppress the SSS-III response of young recipients. However, Lyt-2+ T cells of normal cell size were efficient in inhibiting the antibody response upon transfer. Primed Lyt-2+ T cells from young NZB mice did not affect the response of old recipients, but effectively suppressed the response of young mice. These results suggest that there are two defects involved in the decline of low-dose paralysis to SSS-III in aging NZB mice: Enlarged Lyt-2+ T cells may lose their ability to function as mediators of suppression; and B cells may become resistant to T cell-mediated suppression.     

Acquired resistance and granuloma formation in experimental visceral leishmaniasis. Differential T cell and lymphokine roles in initial versus established immunity.

In naive BALB/c mice, acquisition of resistance to Leishmania donovani and formation of antileishmanial tissue granulomas are linked expressions that require both L3T4+ and Lyt 2+ cells as well as both IL-2 and IFN-gamma. To determine the mechanisms of established resistance to L. donovani, rechallenged immune BALB/c mice were treated with T cell- and lymphokine-depleting mAb or cyclosporin A. In the liver, resistance to rechallenge was inhibited by treatment with anti-Lyt 2 but not anti-L3T4 mAb. Resistance was also impaired by anti-IL-2 treatment but not by anti-IFN-gamma mAb. The hepatic granulomatous response to rechallenge, however, was not impaired by either anti-Lyt 2 or anti-IL-2 mAb nor by anti-L3T4 or anti-IFN-gamma treatment. In contrast, cyclosporin A suppressed granuloma formation but not antileishmanial activity. These results indicate a particularly important antileishmanial host defense role for Lyt 2+ cells and IL-2 in sensitized animals, and when compared to prior observations in L. donovani-infected naive mice, suggest that 1) discrete T cell- and lymphokine-dependent mechanisms are involved in initial acquisition of resistance vs established immunity, 2) more than one mechanism can mediate the development of tissue granulomas, and 3) granuloma formation by itself may not be required nor necessarily sufficient to confer antimicrobial activity.     

BCG-induced macrophage suppression in mice: Suppression of specific and nonspecific antibody-medicated and cellular immunologic responses

The intravenous injection of killed BCG in an oil-in-saline emulsion (BCG-E) results in the development of intense chronic granulomatous inflammation in the lungs and spleen of C57B1/6 (B6) but not CBA mice. B6 mice injected intravenously with BCG-E exhibited marked suppression of antibody responsiveness and delayed hypersensitivity to sheep erythrocytes, as well as proliferation in response to PPD. In contrast, CBA mice similarly treated with BCG-E were not suppressed in any of these reactivities. The spleen is an important organ in this phenomenon since suppression was reversed by splenectomy and could be transferred to normal recipients with spleen cells from BCG-treated mice. Spleen cells responsible for suppression were adherent to plastic petri plates, removed with carbonyl iron, and were not eliminated with either anti-Thy-1 or anti-immunoglobulin serum + C. This study indicates that macrophages from BCG-inflamed spleen are capable of potent suppression of both antibody- and cellular-mediated immunologic reactivity.     

Regulatory mechanism of delayed-type hypersensitivity in mice. I. Properties of memory cpells and suppressor cells for delayed-type hypersensitivity against ovalbumin.

Delayed-type hypersensitivity (DTH) response in mice induced by sc injection of alum-absorbed ovalbumin (OA) was accelerated and enhanced by priming sc with a low dose of urea-denatured ovalbumin (UD-OA), 2 or more days earlier, whereas it was suppressed by priming sc with a high dose of UD-OA, 0 or more days earlier. The ability in primed mice to accelerate or suppress the DTH response could be transferred antigen specifically into cyclophosphamide (CY)-pretreated recipients or normal recipients by spleen cells from primed mice, but not by the T-cell-depleted spleen cells. Furthermore, the ability of spleen cells to transfer the acceleration or the suppression appeared transiently around 7 or 4 days after priming, although the acceleration or the suppression in donor mice persisted for a much longer time. Pretreatment with CY abolished the suppression of DTH response in high dose-primed mice and resulted in the acceleration of DTH response. These results suggest that the activity of DTH-related memory T cells which accelerate and enhance the response can be inhibited by suppressor T cells for the DTH response.     

Role of L3T4+ and LyT-2+ cells in experimental visceral leishmaniasis

In contrast to euthymic (nu/+) BALB/c mice, athymic nude (nu/nu) BALB/c mice fail to control the visceral intracellular replication of Leishmania donovani, do not generate the macrophage-activating lymphokine IFN-gamma, and show little or no granulomatous tissue response. To characterize the T cell requirement for successful defense against L. donovani, nude mice were first reconstituted with unfractionated nu/+ immune spleen cells, which readily conferred the capacity to control and eliminate visceral (hepatic) L. donovani. In reconstituted mice, acquired resistance was paralleled by the ability of spleen cells to generate high levels of leishmanial Ag-stimulated IFN-gamma and the development of well formed liver granulomas. In contrast, nude mice reconstituted with either L3T4+- or Lyt-2+-enriched immune spleen cells alone failed to control visceral parasite replication and did not develop effective granulomas despite the finding that transfer of L3T4+ cells largely and Lyt-2+ cells partially restored the capacity to secrete IFN-gamma. To determine whether both T cell subsets were also required in a normal host, nu/+ BALB/c mice were treated with cell-depleting anti-L3T4 and anti-Lyt-2 mAb. Depletion of either T cell subset inhibited the acquisition of resistance to L. donovani and impaired the tissue granulomatous response. Thus, successful T cell-dependent host defense towards intracellular L. donovani and the tissue expression (granulomas) of this mechanism appear to require both L3T4+ and Lyt-2+ cells. A primary role for the L3T4+ cell may be IFN-gamma production; the role of the Lyt-2+ cell and the precise interaction of the two T cell subsets remain to be identified.     

Suppressor T cells induced by soluble immune complexes can adoptively transfer inhibition of cytophilic antibody receptors on macrophages.

Immune complexes (soluble antigens of L1210 and antibody to L1210) when given to allogeneic C3H mice generated suppressor cells that inhibited receptors for cytophilic antibody on macrophages. Thymocytes or nylon-nonadherent splenic T cells (4 × 10⁷) from immune-complex-treated mice transferred this suppressive activity when injected into normal syngeneic mice. Maximal suppression of macrophages occurred 4 to 6 days after transfer. In contrast, even 5 × 10⁷ nylon-adherent, non-T spleen cells from immune-complex-treated (“suppressed”) mice failed to induce macrophage suppression in the syngeneic recipients. When T-cell-depleted “B” mice were used as recipients, neither thymocytes nor splenic T cells from suppressed mice were able to transfer suppressive activity. However, the admixture of 2 × 10⁷ normal syngeneic thymocytes with 4 × 10⁷ thymocytes from suppressed mice restored the latter's ability to elicit suppression of macrophages in T-cell-deprived recipients. Peritoneal monocytes from recipients of suppressor thymocytes (to L1210) could not attach cytophilic antibody to L1210 but could attach cytophilic antibody to EL-4 and sheep erythrocytes. Thus, suppressor T cells induced by immune complexes can transfer immunologically specific macrophage suppression (inhibition of cytophilic antibody receptors) to syngeneic recipients. The suppressor cells required the cooperation of normal T cells, suggesting either recruitment of suppressor cells from, or a helper effect by, the normal T cells, in order to produce their effect.     

Suppression of natural killer cytolytic activity in mice undergoing pulmonary granulomatous inflammation

CBA/J mice undergoing pulmonary granulomatous inflammation exhibited depressed NK cytolytic activity. Granulomas induced by i.v. embolization of Schistosoma mansoni eggs (hypersensitivity type) or Sephadex beads (foreign body type) both caused reduced NK activity, although hypersensitivity granulomas induced a significantly higher level of NK suppression. Kinetic analysis of hypersensitivity lesions at 4, 8, 16, and 32 days post-embolization indicated that NK activity was significantly suppressed by day 8, maximally suppressed by day 16 (at the peak of the inflammatory response) then returned to near control values by day 32 (as the granulomas resolved). Suppression of NK activity ranged from three- to 15-fold in different experiments. NK cells obtained from both spleen and peripheral blood demonstrated reduced NK activity with kinetic patterns similar to the granuloma NK cells. Suppression was not due to reduced splenic NK cells as the frequency of YAC-1 binding cells, as well as asialo GM1+ or laminin+ cells remained constant over the entire study period. Suppression of NK activity did not appear to be due to serum components or suppressor cells present in the spleen preparations. However, the suppression of NK activity could be reversed by overnight incubation of spleen cells at 25 or 37 degrees C or daily treatment of the mice with indomethacin. Suppression also appeared relatively specific for NK cells as the generation and expression of cytotoxic T lymphocyte activity was not affected.     

Perturbation of the autoimmune network. II. Immunization with isologous idiotype induces auto-anti-idiotypic antibodies and suppresses the autoantibody response elicited by antigen: a serologic and cellular analysis

We report on the humoral and cellular events following autologous immunization against an idiotype (Id62) borne on a murine monoclonal autoantibody to thyroglobulin, and their impact on the autoantibody response to thyroglobulin. BALB/c mice with a state of active auto-anti-idiotypic immunity and challenged with thyroglobulin in complete Freund's adjuvant 2 wk after the last immunization with idiotype were found to have a suppressed autoantibody response. This suppression could be adoptively transferred to syngeneic x-irradiated recipients by using whole spleen cells from idiotype-primed mice. Transfer of separate T and B lymphocyte populations proved instrumental in disecting humoral from cellular events and in establishing that whereas B cells were required for transferring an intact anti-idiotype antibody response, T cells from idiotype-primed mice were necessary to transfer suppression. These findings contribute to our understanding of the interrelationship between antigen, idiotype, and anti-idiotype in the immune response to self-antigens, and the role of certain idiotypes in regulating autoimmune responses.     

A study of the mechanism of Con A-induced immunosuppression in vivo

The plaque-forming cell (PFC) response to sheep erythrocytes (SRBC) is suppressed in a dose-related manner when concanavalin A (Con A) is administered intravenously to mice prior to or after immunization with antigen. The magnitude of suppression as well as the duration of the Con A effect greatly depends on the concentration of antigen used for immunization. Although profound suppression of the anti-SRBC PFC response is observed in intact mice pretreated with Con A for 4-24 hr, spleen cells from these mice do not exhibit suppressive activity when transferred into normal recipients or when cotransferred with normal spleen cells into irradiated recipients. Moreover, the cells from Con A-treated mice respond as normal spleen cells to SRBC when transferred alone into irradiated hosts. Suppression of the anti-SRBC PFC is only observed when adoptive hosts of cells from Con A-treated mice are also injected with Con A within 48 hr (but not 72 hr) of cell transfer and immunization. This time course of responsiveness to the suppressive effects of Con A is similar to that observed in normal mice and in irradiated recipients of normal spleen cells. The immune response to SRBC is also suppressed in adoptive hosts of normal spleen cells that are pretreated with Con A 4-24 hr prior to irradiation and cell transfer. Although functionally inactive when transferred into adoptive hosts, spleen cells from mice pretreated with Con A for 4-24 hr can suppress a primary antibody response to SRBC in vitro. The suppressive activity, which cannot be detected in the spleens of mice when the interval between pretreatment and assay is longer than 24 hr, is present in a subpopulation that bears the Thy 1.2 and Lyt 2 phenotype. Taken together the results obtained in in vivo and in vitro functional assays suggest that a suppressor cell population is activated following in vivo treatment with Con A, but that the cells rapidly lose their state of activation when removed from a Con A environment. This phenomenon is in all probability responsible for the failure to demonstrate suppressive activity in the spleens of Con A-treated mice using in vivo functional assays.     

Suppression of antigen-specific interleukin 2 production in the MRL/MpJ-lpr/lpr mouse

Several murine strains with spontaneously occurring systemic lupus erythematosus-like disease demonstrate defects in immunoregulation. The MRL/MpJ-lpr/lpr (MRL-1) strain develops a severe age-progressive defect in interleukin 2 (IL 2) production in response to mitogen or antigen. In this study, we demonstrate in vitro the presence of suppressor cells in the lymph nodes of naive mice of the MRL background. Suppression by MRL-1 lymph node cells was partially reversed by treatment with anti-Lyt-1.2 monoclonal antibody and complement and was moderately radiosensitive. Suppression by lymph node cells from the congenic MRL/MpJ-+/+ (MRL-+) mouse was somewhat more resistant to treatment with anti-Lyt-1.2 and complement, or radiation. Lymph node cells from the H-2-syngeneic mouse strain, C3H/HeJ, failed to suppress. Thus, lymph nodes from mice of the MRL background contain cells capable of suppressing in vitro IL 2 responses. We next performed cell transfers to determine whether suppressor cells contribute in vivo to the IL 2 defect. Lymph node cells, but not spleen cells, from MRL-1 mice by 5 to 6 mo of age suppressed antigen-specific IL 2, CTL, and DTH responses when transferred into young MRL-+ recipients. Transfer of identical numbers of lymph node cells from age-matched MRL-+ mice failed to suppress IL 2 production. Transfer of suppression was sensitive to treatment with monoclonal anti-Lyt-2.1 and complement, and to 250 rad of radiation. Thus, this study suggests a role for active suppression of IL 2 production in the establishment of the IL 2 defect in the MRL-1 mouse. Further, suppression may involve phenotypically distinct T lymphocyte subpopulations.     

Induction of granuloma modulation in murine schistosomiasis mansoni by enteric exposure to schistosome eggs

Enteric administration of antigen can induce systemic tolerance. In murine schistosomiasis mansoni, blood flukes produce eggs which enter the intestine. An immunologic phenomenon associated with this disease is a spontaneous diminution in the intensity of the granulomatous response in the liver, lungs, and colonic mucosa with chronic infection, which is termed modulation. It was determined whether modulation of liver granulomas could be induced by enteric immunization with schistosome eggs. Mice infected for 4 wk were immunized by injection of 25,000 eggs into cecal pouches. This induced modulation of liver granulomas by the eighth week of infection. Neither cecal injection of normal saline nor i.p. or subcutaneous injection of eggs could induce the modulatory process. Modulation could be adoptively transferred from enterically immunized donors by injection of spleen cells into infected recipients or into uninfected recipients with synchronous liver granulomas induced by the hepatic embolization of schistosome eggs. Spleen cells treated with anti-Thy-1.2 or anti-Lyt-1.1 and complement could no longer adoptively transfer modulation. These data show that enteric immunization with schistosome eggs can induce modulation of the liver granuloma by a cellular mechanism similar to that described for the natural infection.     

Aryl hydrocarbon receptor activation impairs the priming but not the recall of influenza virus-specific CD8+ T cells in the lung

The response of CD8+ T cells to influenza virus is very sensitive to modulation by aryl hydrocarbon receptor (AhR) agonists; however, the mechanism underlying AhR-mediated alterations in CD8+ T cell function remains unclear. Moreover, very little is known regarding how AhR activation affects anamnestic CD8+ T cell responses. In this study, we analyzed how AhR activation by the pollutant 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) alters the in vivo distribution and frequency of CD8+ T cells specific for three different influenza A virus epitopes during and after the resolution of a primary infection. We then determined the effects of TCDD on the expansion of virus-specific memory CD8+ T cells during recall challenge. Adoptive transfer of AhR-null CD8+ T cells into congenic AhR(+/+) recipients, and the generation of CD45.2AhR(-/-)-->CD45.1AhR(+/+) chimeric mice demonstrate that AhR-regulated events within hemopoietic cells, but not directly within CD8+ T cells, underlie suppressed expansion of virus-specific CD8+ T cells during primary infection. Using a dual-adoptive transfer approach, we directly compared the responsiveness of virus-specific memory CD8+ T cells created in the presence or absence of TCDD, which revealed that despite profound suppression of the primary response to influenza virus, the recall response of virus-specific CD8+ T cells that form in the presence of TCDD is only mildly impaired. Thus, the delayed kinetics of the recall response in TCDD-treated mice reflects the fact that there are fewer memory cells at the time of reinfection rather than an inherent defect in the responsive capacity of virus-specific memory CD8+ cells.     

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.     

In vivo molecular analysis of lymphokines involved in the murine immune response during Schistosoma mansoni infection. II. Quantification of IL-4 mRNA, IFN-gamma mRNA, and IL-2 mRNA levels in the granulomatous livers, mesenteric lymph nodes, and spleens during the course of modulation.

Parasite egg-induced granulomas are the primary pathogenic lesions in murine schistosomiasis mansoni. This cell-mediated granulomatous response is specific for soluble egg Ag and appears to be mediated predominantly by CD4+ Th2 cells. As infection progresses from the acute to the chronic phase, the cell-mediated anti-soluble egg Ag responses attenuate in a process termed modulation. In this study the hypothesis that modulation is effected by a chronic phase increase in Th2-inhibiting Th1 cell activity was investigated. Northern blot quantification of mRNA specific for the Th2 lymphokine, IL-4, and the Th1 lymphokines, IFN-gamma and IL-2, in the spleens, mesenteric lymph nodes, and granulomatous livers of mice infected for various lengths of time over the course of modulation was performed. Also, the capacity of mitogen- and Ag-stimulated spleen cells to produce message for these lymphokines was compared. Peak tissue levels of both IL-4 mRNA and IFN-gamma mRNA were seen in acutely infected mice, and levels of both messages declined as infection became chronic. Stimulated spleen cells from acutely infected mice also produced higher levels of IL-4 and IFN-gamma mRNA than cells from chronically infected mice. IL-2 mRNA was never detected in any tissue sample but was detected in the stimulated spleen cells, again with acute phase levels higher than chronic phase levels. Hence, this study shows no evidence for increased Th1 cell activity during chronic infection and suggests that modulation may be effected by a generalized suppression of lymphokine synthesis.     

Role of dextran-specific suppressor T cells in the regulation of the immune response by a reactive form of dextran

Reactive forms of antigens or haptens have been shown to induce a state of hyporesponsiveness mediated in part by suppressor T cells. Injection of Balb/c x C57B16 F1 (CB6F1) mice with a reactive form of dextran B1355S (periodate oxidized dextran, dex-P) specifically reduced responses to dextran immunization within 1 day after dex-P treatment. This unresponsiveness lasted at least 23 days and required a reactive form of dextran for its induction since native dextran and oxidized/reduced dextran failed to induce tolerance. Furthermore, hyporesponsiveness could be induced by iv injection of dextran-coupled cells, especially peripheral blood lymphocytes, a result which suggests that in vivo coupling to cellular antigens is involved in dex-P-induced hyporesponsiveness. Suppression of the anti-dextran response could be transferred to normal mice with T-cell-enriched spleen cell populations from dex-P-injected mice. Interestingly, the presence of B cells in the transferred cell preparations interfered with detection of suppression. Both Lyt 1+2- and Lyt 1-2+ cells were involved in the dex-P-induced suppression; indeed, mixtures of these types of T cells led to the most profound degree of suppression. The suppressive activity of spleen cells from dex-P-injected mice could be removed by passage over dextran-coated plates. Moreover, cells eluted from the plates specifically suppressed anti-dextran responses of normal mice, indicating that dex-P injection induces a population of antigen-binding suppressor cells. This system will allow the study of the suppressor-T-cell receptors in a well-defined idiotypic system.     

Dysfunction of irradiated thymus for the development of helper T cells

The development of cytotoxic T cells and helper T cells in an intact or irradiated thymus was investigated. C57BL/6 (H-2b, Thy-1.2) mice were whole body-irradiated, or were irradiated with shielding over either the thymus or right leg and tail, and were transferred with 1.5 X 10(7) bone marrow cells from B10.Thy-1.1 mice (H-2b, Thy-1.1). At various days after reconstitution, thymus cells from the recipient mice were harvested and a peanut agglutinin low-binding population was isolated. This population was further treated with anti-Thy-1.2 plus complement to remove host-derived cells and was assayed for the frequency of cytotoxic T cell precursors (CTLp) and for the activity of helper T cells (Th). In the thymus of thymus-shielded and irradiated mice, Th activity reached normal control level by day 25, whereas CTLp frequency remained at a very low level during these days. In the thymus of whole body-irradiated mice, generation of CTLp was highly accelerated while that of Th was retarded, the period required for reconstitution being 25 days and more than 42 days for CTLp and Th, respectively. Preferential development of CTLp was also seen in right leg- and tail-shielded (L-T-shielded) and irradiated recipients. Histological observation indicated that Ia+ nonlymphoid cells were well preserved in the thymus of thymus-shielded and irradiated recipients, whereas in L-T-shielded and irradiated recipients, such cells in the medulla were markedly reduced in number. These results suggest strongly that the generation of Th but not CTLp is dependent on radiosensitive thymic component(s), and that such components may represent Ia+ cells themselves in the medulla or some microenvironment related to Ia+ cells.