Role of L3T4+ and Lyt-2+ T cell subsets in protective immune responses of mice against infection with a low or high virulent strain of Toxoplasma gondii

In order to elucidate the role of T cell subsets in protective immunity against infection with high virulent and low virulent strains of Toxoplasma gondii, monoclonal antibodies specific for T cell subsets were injected into mice before immunization or challenge infection. Treatment of mice with monoclonal antibody to either L3T4+ or Lyt-2+ T cells before they were immunized with Toxoplasma cell homogenate prepared from high virulent RH strain tachyzoites markedly reduced survival after mice were challenged with low virulent bradyzoites of the Beverley strain. Thus, induction of protective immunity against bradyzoites of the Beverley strain requires the presence of both L3T4+ and Lyt-2+ T cells. In contrast, mice injected with living bradyzoites of the low virulent Beverley strain after immunization with Toxoplasma cell homogenate acquired protective immunity against high virulent tachyzoites of the RH strain. Lyt-2+ T cells alone appear to be final effector cells for protection against the challenge with high virulent RH strain tachyzoites, since treatment of the bradyzoite-immune mice with anti-Lyt-2 antibody, but not anti-L3T4 antibody, before challenge significantly increased mortality.     

The role of L3T4+ and Lyt-2+ T cells in the IgE response and immunity to Nippostrongylus brasiliensis

The role of L3T4+ and Lyt-2+ T cells in protective immunity to Nippostrongylus brasiliensis (Nb) was studied in BALB/c mice that were depleted of either the L3T4+ or Lyt-2+ T cell population by injection with rat mAb specific for the appropriate determinant. Host responses to Nb infection including spontaneous elimination of adult worms, development of intestinal mucosal mast cell hyperplasia and the generation of a polyclonal IgE response were all completely blocked by 0.5 mg anti-L3T4 antibody administered simultaneously with Nb inoculation. However, administration of 0.5 mg of anti-Lyt-2 antibody at the same time and 7 days after inoculation with Nb had no effect on any of these responses. Injection of anti-L3T4 antibody as late as 9 days after Nb inoculation interfered with spontaneous cure of Nb infection and anti-L3T4 antibody injection 11 days after Nb inoculation inhibited serum IgE levels measured on day 13 by 50%. In addition, administration of anti-L3T4 antibody at the time of the peak serum IgE response, 13 days after Nb inoculation, accelerated the decline in serum IgE levels. Injection of previously Nb-infected mice with anti-L3T4 antibody at the time of a second Nb inoculation prevented the development of a secondary IgE response but did not affect immunity to Nb infection based on finding no adult worms in the intestines of these mice. These data indicate that 1) L3T4+ T cells are required for spontaneous cure of Nb infection, development of intestinal mucosal mast cell hyperplasia, and the generation and persistence of an IgE response during primary infection with Nb and 2) L3T4+ T cells are required for a considerable time after inoculation for optimal development of these responses. However, L3T4+ T cells are not required for all protective responses in immune mice. In contrast, our data indicate that considerable depletion of the Lyt-2+ T cell population has no significant effect on either worm expulsion or the generation of serum IgE responses.     

Antibodies to the L3T4 and Lyt-2 molecules interfere with antigen receptor-driven activation of cloned murine T cells

When L3T4+ cloned murine helper T lymphocytes (HTL) are stimulated with antigen or immobilized anti-T cell receptor (TCR) monoclonal antibodies (mAb) at concentrations which are optimal for proliferation, anti-L3T4 mAb inhibits activation as measured by proliferation and lymphokine production. Under similar conditions, IL 2-independent proliferation of Lyt-2+ cloned murine cytolytic T lymphocytes (CTL) stimulated by anti-TCR mAb is inhibited by anti-Lyt-2 antibodies. Proliferation of cloned HTL and CTL cells stimulated by IL 2 is not affected by the anti-L3T4 and anti-Lyt-2 mAb. The inhibition of TCR-induced activation of the T cell clones is not due to interference with the binding of the anti-TCR mAb. Stimulation of the TCR has been proposed to induce lymphokine secretion and proliferation by T cells through a pathway involving the activation of protein kinase C and the stimulation of an increase in the concentration of intracellular free calcium. However, proliferation of T cells stimulated by PMA (which activates protein kinase C) plus the calcium ionophore A23187 (which increases the concentration of intracellular free calcium) is not affected by mAb reactive with the Lyt-2 or L3T4 structures. If TCR stimulation does indeed activate T cells by activating protein kinase and increasing intracellular free calcium, then our data suggest that anti-L3T4 and anti-Lyt-2 mAb inhibit TCR-driven proliferation at some step before the activation of protein kinase C and the stimulation of a rise in intracellular free calcium concentration. Our results suggest that anti-L3T4 and anti-Lyt-2 mAb interfere with early biochemical processes induced by stimulation of the TCR. In HTL, which proliferate via an autocrine pathway, anti-L3T4 mAb appears to inhibit proliferation by interfering with signaling events involved in lymphokine production. Inhibition of IL 2-independent proliferation of Lyt-2+ cells by anti-Lyt-2 mAb appears to occur by a different mechanism. The precise molecular basis for the interference of each cell type has not yet been characterized.     

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.     

A role for Lyt-2+ T cells in resistance to cutaneous leishmaniasis in immunized mice

The role of Lyt-2+ T cells in immunologic resistance to cutaneous leishmaniasis was analyzed by comparing infection patterns in resistant C57BL/6 mice and susceptible BALB/c mice induced to heal their infections after sub-lethal irradiation or i.v. immunization, with similar mice treated in vivo with anti-Lyt-2 antibodies. Administration of anti-Lyt-2 mAb resulted in a dramatic reduction in the number of lymphoid cells expressing the Lyt-2+ phenotype. Such treatment led to enhanced disease in both resistant C57BL/6 and irradiated BALB/c mice, as assessed by lesion size, but did not affect the capacity of these mice to ultimately resolve their infections. In contrast, anti-Lyt-2 treatment totally blocked the induction of resistance in i.v. immunized mice. These results suggest, that Lyt-2+ T cells may play a role in immunity to a Leishmania major infection and that their relative importance to resistance may depend on how resistance is induced.     

T cell subsets and IFN-gamma production in resistance to systemic candidosis in immunized mice

In addition to previous evidence for the roles of T cell-dependent immunity and delayed-type hypersensitivity in acquired resistance to systemic candidosis in mice, in the present study we have investigated the relative contributions of L3T4+ and Lyt-2+ lymphocytes in the protective immunity induced by vaccination with low virulence Candida albicans cells. We have also addressed the issue of the mode of Candida Ag recognition by specific T cells leading to cytokine release. Spleen cells from immunized mice produced high levels of IFN-gamma in vitro in response to Candida Ag, and this activity was abolished only by the combined treatment of the responder population with anti-L3T4 and anti-Lyt-2.2 mAb plus C. Positively selected L3T4+ and Lyt-2+ cells also produced IFN-gamma in vitro, provided accessory cells (plastic-adherent and Thy-1- Ia- splenocytes, respectively) were added to the lymphocyte-yeast cell cocultures. The production of IFN-gamma by purified L3T4+ and Lyt-2+ cells was inhibited by addition of the respective anti-class II and anti-class I H-2 antibody to the cultures. In vivo, administration of anti-L3T4, anti-Lyt-2.2 mAb or a combination of both significantly impaired the resistance of immunized mice to challenge with virulent C. albicans, as manifested by increased recovery of the yeast from the mouse kidneys. A similar effect was observed upon neutralization of endogenous IFN-gamma by treatment with rat mAb. These results suggest that both L3T4+ and Lyt-2+ T cells play a role in acquired immunity to systemic C. albicans infection, and that their activity may involve IFN-gamma-mediated stimulation of candidacidal mechanisms.     

Functional analysis of T lymphocyte subsets in antiviral host defense

The role of different T cell subsets in antiviral host defense was investigated by treating thymectomized C57BL/6 and CBA/J mice with monoclonal rat anti-Lyt-2 or anti-L3/T4 IgG 2b antibodies 14 and 10 days before infection. This treatment depleted the respective T cell subsets to undetectable levels in peripheral blood when assayed by immunofluorescence. In mice treated with anti-Lyt-2, induction of cytotoxic T cells was reduced to less than 1 to 2% after intravenous infection with Armstrong strain of lymphocytic choriomeningitis virus (LCMV). In addition, no primary swelling of the footpad could be detected following local inoculation of the virus. In animals treated with anti-L3/T4, antiviral cytotoxic T lymphocyte responses were reduced by a factor of 10. These L3/T4+ cell-depleted mice showed delayed footpad swelling after local injection of LCMV Armstrong. After intracerebral infection with LCMV, anti-Lyt-2-treated mice were resistant and those injected with anti-L3/T4 were totally susceptible to LCMV Armstrong-triggered immunopathologic disease. Virus could be detected in the blood of antibody-treated mice 7 days after inoculation; however, no virus could be measured in the blood of surviving anti-Lyt-2-treated animals 15 days after intracerebral infection. Serum titers of interferon-alpha,beta induced by viral infection remained unaffected by depletion of T cell subsets. Anti-L3/T4 antibody-treated C57BL/6 mice failed to generate IgG antibodies against the New Jersey strain of vesicular stomatitis virus, whereas Lyt-2+ cell-depleted mice had normal antivesicular stomatitis virus (New Jersey strain) IgG antibody titers.     

Impact of genetically regulated T cell proliferation on acquired resistance to Listeria monocytogenes

Two lines of mice genetically selected for high and low in vitro responses to PHA were used to evaluate the impact of T cell polyclonal expansion on acquired resistance to Listeria monocytogenes. The selective breeding induced two major consequences in low responder mice: (1) a reduction of the number of L3T4+ cells and (2) a restriction of T cell expansion upon PHA stimulation, predominantly affecting the Lyt-2+ subset, and associated with an abridgment of IL-2 production. In vivo PHA stimulation induced anti-Listeria protection in high responder mice, but was much less effective in low responder mice. Flow cytometer analysis revealed that T cell proliferation was also reduced in low responder mice during the course of Listeria infection, implying both L3T4+ and Lyt-2+ subsets. This defect did not apparently influence the kinetics of bacterial elimination in host tissues, which was similar in both lines during primary Listeria infection. In contrast, the expression of delayed-type hypersensitivity to Listeria antigens and the level of immunologic memory were significantly reduced in low responder mice. In vivo selective T cell depletion by anti-L3T4 or anti-Lyt-2 mAb allowed us to demonstrate the predominant role of Lyt-2+ cells in protection and that of L3T4+ cells in the expression of delayed-type hypersensitivity.     

Enterically induced regulation of systemic immune responses. II. Suppression of proliferating T cells by an Lyt-1+, 2- T effector cell

Peripheral lymph node cells from C3H mice that were fed and injected with bovine serum albumin (REG cells) demonstrate an impaired proliferative response to antigenic stimulation in vitro compared to cells from mice only injected with BSA. To determine whether suppressor cells contributed to this enterically induced impairment of systemic T cell responses, REG cells were pretreated with various monoclonal antibodies and complement (C), and were then co-cultured with antigen-reactive indicator T cells (IND) from parenterally immunized mice. Proliferation of IND cells [( 3H]thymidine uptake) was suppressed only if REG cells were treated with anti-Lyt-2 and C before co-culture. The ability of anti-Lyt-1 plus anti-Lyt-2 and C treatment to abrogate suppression suggested that the suppressor effect was due to an Lyt-1+, 2- REG cell. Suppression was independent of Lyt-2+ IND cells, and was observed at different antigen concentrations, cultivation times, and cell densities. The cells responsible for suppressor activity were radiosensitive, nylon wool nonadherent, and antigen specific. These data suggest that an Lyt-1+, 2- T cell could be an important component in mediating enterically induced regulation of systemic T cell responses.     

Autoimmune thyroiditis induced in mice depleted of particular T cell subsets. I. Requirement of Lyt-1 dull L3T4 bright normal T cells for the induction of thyroiditis

T cell-depleted C3H/He or (C57BL/6xC3H/He)F1 (B6C3F1) mice were prepared by adult thymectomy and injection of antithymocyte serum, followed 3 wk later by lethal x-irradiation and bone marrow reconstitution. When these T cell-depleted mice were not injected or injected i.v. with normal spleen and lymph node cells treated with either anti-Thy-1, -L3T4 or -Lyt-2 antibody plus C or C alone, none of the groups of mice developed thyroiditis. In contrast, the adoptive transfer of normal cells treated with anti-Lyt-1 plus C resulted in high incidence of the production of antithyroglobulin antibody and the induction of typical thyroiditis lesion. The thyroid was the sole organ involved, because neither typical inflammatory lesion in other organs nor autoantibody such as anti-DNA antibody was detected in mice that exhibited thyroiditis. Analyses of surface phenotypes of cells required for inducing thyroiditis by the adoptive transfer revealed that an appreciable percentage of Lyt-1 dull T cells remained after the treatment of normal lymphoid cells with anti-Lyt-1 plus C. Almost all of these Lyt-1 dull T cells expressed magnitudes of L3T4 or Lyt-2 Ag comparable to those detected on Lyt-1 bright T cells. More important, the induction of thyroiditis was almost completely prevented by either in vitro or in vivo elimination of Lyt-1 dull L3T4+(bright) but not of Lyt-1 dull Lyt-2+(bright) T cells. These results indicate that Lyt-1 dull L3T4+ T cells existing in normal healthy individuals have potential to induce typical thyroiditis which is associated with the production of antithyroglobulin autoantibody, and that the activation and/or function of this T cell subset is regulated by the Lyt-1 bright T cell population coexisting in normal lymphoid cell population.     

Cloned Listeria monocytogenes specific non-MHC-restricted Lyt-2+ T cells with cytolytic and protective activity

Mice were infected with Listeria monocytogenes and Lyt-2+ T cell clones capable of lysing Ag-primed bone marrow macrophages were established. In accordance with earlier findings obtained at the population level, some T cell clones were identified which lysed bone marrow macrophages of different MHC type provided the relevant Ag was present. This unusual target cell recognition was further analyzed using a T3+, L3T4-, Lyt-2+, F23+, KJ16+ T cell clone, designated L-28. Target cell lysis by this clone was Ag specific, apparently non-MHC restricted. In contrast, YAC cells and P815 cells were not lysed by clone L-28. However, lysis of irrelevant targets could be induced by anti-T3, F23, or KJ16 mAb. Furthermore, Ag-specific lysis was blocked by anti-Lyt-2 mAb and by F(ab)2 fragments of F23 mAb. In addition to its cytolytic activity, clone L-28 produced IFN-gamma after co-stimulation with accessory cells, Ag, and rIL-2 and conferred significant protection on recipient mice when given together with rIL-2. These data suggest that non-MHC-restricted Lyt-2+ killer cells generated during listeriosis are cytolytic T lymphocytes that interact with their target Ag via the T cell receptor/T3 complex and the Lyt-2 molecule and, furthermore, that these cells play a role in anti-listerial resistance. The possible relevance of IFN-gamma secretion and target cell lysis for antibacterial protection is discussed.     

Surface markers of T cells causing lethal graft-vs-host disease to class I vs class II H-2 differences

Information was sought on the phenotype of lymphoid cells causing lethal graft-vs-host disease (GVHD) in irradiated mice expressing whole or partial H-2 differences. In all strain combinations tested, pretreating donor lymph node (LN) cells with anti-Thy-1 monoclonal antibodies (MAb) plus complement (C) abolished mortality. With GVHD directed to class I H-2 differences, pretreating LN cells with anti-Lyt-2 MAb prevented mortality, whereas MAb specific for Ly-1 or L3T4 cell surface determinants caused severe mortality. These data imply that lethal GVHD directed to class I H-2 differences is mediated by L3T4-, Lyt-2+ cells; this subset of T cells was shown previously to control GVHD directed to multiple minor histocompatibility antigens, i.e., antigens seen in the context of self-class I molecules. With whole H-2 differences, GVHD appeared to be controlled largely but not exclusively by L3T4+, Lyt-2-T cells. This T cell subset was also the predominant cause of GVHD directed to class II differences. With class II incompatibilities, depleting donor cells of L3T4+ T cells, either by pretreatment with anti-L3T4 MAb + C or by fluorescence activated cell sorter selection, greatly reduced but did not completely abolish GVHD. These data might imply that L3T4-, Lyt-2+ cells have some capacity to elicit anti-class II GVHD. A more likely possibility, however, is that the residual GVHD to class II differences observed with Lyt-2+-enriched cells reflected minor contamination with L3T4+ cells.     

Antigen-specific Lyt-2+ cytolytic T lymphocytes from mice infected with the intracellular bacterium Listeria monocytogenes

In vitro expanded T cell lines were used to determine whether antigen-specific cytolytic T lymphocytes are generated after infection with the intracellular bacterium, Listeria monocytogenes. Spleen cells from infected mice were cultured in the presence of syngeneic accessory cells, listerial antigen, and interleukin 2 containing supernatants. Cell lines were greater than 98% Thy-1+, L3T4-, Lyt-2+. Bone-marrow macrophages were used as target cells in two in vitro cytolytic assay systems. The Lyt-2+ T cells killed bone marrow macrophages only when infected with L. monocytogenes as assessed in a 4-hr 51Cr release assay and in an 18-hr neutral red uptake assay. Cytolysis was blocked by anti-LFA-1 and anti-Lyt-2 monoclonal antibodies. These cytolytic T cells produced interferon-gamma after co-stimulation with antigen, accessory cells, and recombinant interleukin 2. Bone marrow macrophages infected with Mycobacterium bovis were not killed by T cells from L. monocytogenes-infected mice but by T cell lines from M. bovis-infected mice, indicating that cytolysis was antigen specific. L. monocytogenes-infected target cells of different haplotype were lysed by the Lyt-2+ T cells. By using a low cell density split culture system, antigen-specific, H-2-restricted cytolytic T cells could be identified. These findings demonstrate that during infection with intracellular bacteria, Lyt-2+ T cells with cytolytic activity are generated that may be involved in antibacterial protection.     

Functional analysis of T cell subsets from mice bearing the lpr gene

The autosomal recessive lpr (lymphoproliferation) gene is responsible for a thymus-dependent massive lymphoproliferation associated with the development of lupus-like autoimmune disease. Phenotypic analysis of adult lpr/lpr lymph nodes has demonstrated accumulation of a dull Lyt-1+, Thy-1+ population that expresses neither Lyt-2 nor L3T4 antigens. With the use of a depletion method based on complement-mediated lysis with an anti-Lyt-2 monoclonal antibody (31 M) and a new anti-L3T4 monoclonal antibody (RL 172.4), we have purified the Lyt-2- L3T4- subset from lymph nodes or spleens of C57BL/6-lpr/lpr mice and determined whether they are immunologically functional in vitro. Production of neither interleukin 2 nor interferon-gamma was detected by the double-negative subset after stimulation with concanavalin A and/or phorbol myristate acetate. The frequencies of allospecific cytotoxic T lymphocyte (CTL) precursors and lectin-induced antigen-nonspecific CTL precursors were diminished to almost undetectable levels, whereas the Lyt-2+ population from lpr/lpr mice had CTL-precursor frequencies comparable with that of +/+ mice. These results show that the major cell subset of adult lpr/lpr lymph nodes or spleens is composed of lymphocytes with markedly limited potential for lymphokine production or antigenic stimulation.     

In vivo T cell depletion regulates resistance and morbidity in murine schistosomiasis

These studies assessed the roles of subpopulations of T lymphocytes in inducing and modulating resistance to schistosomiasis and thereby influencing subsequent morbidity. C57BL/6 mice were depleted in vivo of Lyt-1+, Lyt-2+, and L3T4+ cells by the daily administration of monoclonal antibodies. The development of protective immunity, induced by exposure to irradiated Schistosoma mansoni cercariae as expressed in depleted animals, was compared to that demonstrated in undepleted, normal, and congenitally athymic C57BL/6 mice. The development of morbidity was determined by spleen weight, portal pressure and reticuloendothelial system activity. The results indicated that depletion of specific subpopulations of T lymphocytes minimally affected the primary development of parasites; however, depletion strongly influenced the development of resistance to the parasite and subsequent morbidity due to infection. Depletion of T lymphocytes by anti-Lyt-1+ or anti-L3T4+ antibody decreased the development of resistance, antibody and delayed-type hypersensitivity directed against schistosome antigens. Morbidity due to disease was increased. Depletion of Lyt-2+ cells produced opposite changes with augmented resistance and reduced morbidity. Congenitally athymic mice developed minimal resistance and morbidity. Moreover, resistance was inversely related to the morbidity shown by a given animal. These studies indicate that the development of protective immunity to S. mansoni cercariae is regulated by discrete subpopulations of T lymphocytes. The feasibility of decreasing morbidity by increasing specific immunologically mediated resistance is suggested.     

Class II antigen-specific murine cytolytic T lymphocytes (CTL). I. Analysis of bulk populations and establishment of Lyt-2+L3T4- and Lyt-2-L3T4+ bulk CTL lines

Murine allogeneic cytolytic T lymphocytes (CTLs), including long-term bulk CTL lines, were induced in I-region-incompatible combinations of strains in vitro in order to study the phenotypes of class II major histocompatibility complex (MHC) antigen-specific CTLs, as well as the possible functional involvement of accessory cell interaction molecules such as Lyt-2 and L3T4. This report shows that class II-specific allogeneic CTL populations consist of two types of T cells. Lyt-2+L3T4- (2+4-) and Lyt-2-L3T4+ (2-4+), in variable proportions depending on the strain combination, that in vitro bulk CTL lines with each of these phenotypes can be established, that the killing function of 2-4+ CTL is sensitive to the blocking effect of anti-L3T4 antibodies, suggesting functional involvement of this molecule in the CTL-target interaction, that anti-Lyt-2 antibodies fail to block killing by 2+4- cells, suggesting that such CTLs do not utilize this molecule in their killing function, and that while I-A-specific CTLs of both phenotypes are detectable, 2-4+ cells could not be detected among I-E-specific CTL populations.     

Mechanism of recovery from acute virus infection: treatment of lymphocytic choriomeningitis virus-infected mice with monoclonal antibodies reveals that Lyt-2+ T lymphocytes mediate clearance of virus and regulate the antiviral antibody response.

After intravenous infection of mice, lymphocytic choriomeningitis virus multiplied in spleens and livers, attaining highest concentrations on days 4 to 6. The subsequent clearance was as rapid, and 8 to 10 days after inoculation, infectivity was usually below detectability. During the effector phase of virus elimination, both cytotoxic T-cell (CTL) activity and the number of cells producing antiviral antibodies were high. Monoclonal antibodies directed against T lymphocytes and T-lymphocyte subsets were inoculated once intravenously 5, 6, or 7 days after infection of the animals, and the effects on antiviral immune responses, as well as on elimination of virus from the organs, were determined. Treatment with anti-Thy-1 and anti-Lyt-2 antibodies blocked elimination of the virus and profoundly diminished the activity of spleen CTLs but reduced the antibody response partially (anti-Thy-1) or increased it (anti-Lyt-2). In contrast, treatment with the anti-L3T4 antibody had essentially no effect on either virus elimination or CTL response but abolished antibody production. We conclude that Lyt-2+ (cytotoxic-suppressive) T lymphocytes are needed for elimination of the virus and also regulate the humoral response but that antiviral antibodies are not essential for control of the infection.     

Involvement of L3T4+, LYT2.2+ T cell subsets and non-T cells in the resistance of mice against Trypanosoma cruzi infection

Cellular populations involved in resistance against T. cruzi infection were characterized from mice chronically infected with the parasite. Mice transfused with spleen cells (SC), nylon-wool-non-adherent spleen cells (NWNA) or sera from mice chronically infected with T. cruzi, showed an enhanced resistance against challenge with the parasite. The protective activity of NWNA but not of SC was completely abrogated by treatment with anti-Thy1.2 monoclonal antibodies (mAb) and complement (C). Pretreatment of NWNA cells from chronically infected mice with either anti-L3T4 or anti-Lyt 2.2 mAb partially reduced the transfer of resistance. When both L3T4+ and Lyt2.2+ cells were depleted from NWNA populations, transfer of resistance was abolished. These results appear to indicate that L3T4+, Lyt2.2+ T cell subsets and non-T cells are involved in the immunity to T. cruzi.     

Role of L3T4 antigen in the activation of various functions of Lyt-1+2- T cells against vaccinia virus

The present study defines assay systems for vaccinia virus-reactive Lyt-1+2- T cells mediating various functions and investigates the positivity of L3T4 antigen on these Lyt-1+2- T cells as well as the role of L3T4 antigen in the activation of these T cells with respect to their functions. C3H/He mice were immunized against vaccinia virus by inoculating viable virus intraperitoneally (i.p.). Anti-vaccinia virus reactivity in lymphoid cells from these immunized mice was assessed by proliferative response, helper T cell activities involved in cytotoxic T lymphocyte (CTL) and B cell (antibody) responses, delayed type-hypersensitivity (DTH) response, and production of lymphokines such as interleukin 2 (IL2) and macrophage-activating factor (MAF). The results demonstrate that all of the above anti-vaccinia virus responses were mediated by Lyt-1+2- T cells and that these Lyt-1+2- T cells expressed L3T4 antigens on their cell surfaces. Moreover, such anti-vaccinia Lyt-1+2- T cell responses were inhibited in the presence of anti-L3T4 antigen antibody. These results indicate that there is a reciprocal relationship between Lyt-2 and L3T4 markers, and that L3T4 antigen is closely related to the activation of various functions of anti-vaccinia virus Lyt-1+2- T cells.     

Isolation of monoclonal antibodies to antigen Lyt-3.2

A hybridoma producing monoclonal antibodies (McAb) NATF9.9 (F9) was obtained from fusion of murine myeloma X63 and splenocytes of AKR mice immunized with a single intravenous injection of 5 X 10(7) thymocytes of CBA mice. F9 McAb were cytotoxic for 80% thymocytes, 10% splenocytes, 20% lymph node cells, 85% cortical and 32% medullary thymocytes of CBA, C57BL/6, BALB/c, DBA/2 and SJL but not for the cells of C58 and AKR mice. F9 McAb reacted only with T cells and did not react with B cells and EL4 thymoma cells (Thy-1.2+, Lyt-1+2-3-). The proportion of F9+ cells accounts for about 40% among T lymphocytes of the lymph nodes and spleen as tested by flow-type cytometry. Lymph node cells treated with F9 McAb plus complement completely lost their reactivity with rat anti-Lyt-2 McAb and only partly (by 30%) with anti-Lyt-1 McAb. The reactivity pattern of F9 McAb attests to their specificity for Lyt-3.2 antigen.