Characterization of two distinct primary T cell populations that secrete interleukin 2 upon recognition of class I or class II major histocompatibility antigens

Inhibition of antiskin allograft immunity by infusions with syngeneic photoinactivated effector lymphocytes

Induction of tolerance for skin allotransplantation requires selective suppression of the host response to foreign histocompatibility antigens. This report describes a new approach that employs pretreatment of effector cells with 8-methoxy-psoralen (8-MOP) and ultraviolet A light (UVA) to render the effector cells of graft rejection immunogenic for the syngeneic recipient. Reinfusion of photodamaged cells resulted in an immunosuppressive host response that permitted prolonged retention of histoincompatible skin grafts and specifically inhibited in vitro and in vivo responses that correlate with allograft rejection. Eight days after BALB/c mice received CBA/j skin grafts, their splenocytes served as a source of alloreactive effector cells. The splenocytes were treated with 100 ng/ml 8-MOP and 1 J/cm2 UVA before reinfusion into naive BALB/c recipients. Recipient mice were tested for tolerance to alloantigens in mixed leukocyte culture (MLC), cytotoxicity (CTL), delayed type hypersensitivity assays (DTH), and challenge with a fresh CBA/j graft. Splenocytes from BALB/c recipients of photoinactivated splenocytes containing the effector cells of CBA/j alloantigen rejection proliferated poorly in MLC and generated lower cytotoxic T cell responses to CBA/j alloantigens in comparison with sensitized and naive controls. Splenocytes from these hyporesponsive mice suppressed the MLC and CTL response to alloantigen from sensitized and naive BALB/c mice. In vivo the DTH response was specifically suppressed to the relevant alloantigen in comparison with controls. Moreover, BALB/c mice treated in this fashion retained a CBA/j skin graft for up to 42 d posttransplantation without visual evidence of rejection. These results indicate that the in vivo and in vitro response to alloantigen can be attenuated by pretreating the host with photoinactivated splenocytes containing the effector cells of alloantigen rejection.

Ability of pure resting CD8+ human T cells to respond to alloantigen

The ability of highly purified resting human CD8 cells to respond to alloantigens in vitro was examined. Necessary conditions for induction of interleukin 2 receptors (IL-2R), IL-2 production, proliferative responses, and various effector functions were determined. Allogeneic non-T cells induced IL-2R expression in a high proportion of resting CD4 and CD8 cells, but only CD4 cells produced detectable amounts of IL-2. CD8 cells also became IL-2 responsive upon stimulation with purified resting allogeneic CD4 or CD8 cells, indicating that HLA class I+, II- cells alone may initiate activation of resting CD8 cells. The activated CD8 cells needed the presence of simultaneously activated CD4 cells or exogenous IL-2 to be able to synthesize DNA. Effector functions like cytotoxicity, mixed lymphocyte culture (MLC) suppression, or gamma interferon (IFN-gamma) production were also only detectable when the CD8 cells were activated in the presence of IL-2.

Responsiveness of T cells to mutant major histocompatibility complex class I antigen. II. Role of stimulator-type accessory cells with reference to interleukin 1 production

Mechanisms of the activation of T cells responding to major histocompatibility complex (MHC) class I antigen were investigated with special reference to interleukin 1 (IL-1) production from stimulator-type accessory cells. For this purpose, we used mainly fractionated Lyt-2+T cells of C57BL/6 (B6) mice as responder cells and irradiated spleen cells or those deprived of adherent cells of B6.C-H-2bm1 (bm1) mice as stimulator cells. Lyt-2+ T cells of B6 mice proliferated in the presence of irradiated whole spleen cells of bm1 mice but did not to Sephadex G-10 column-passed bm1 spleen cells. The unresponsiveness in the latter case was overcome by the supplement of recombinant IL-1 and/or IL-2 in the culture medium. These interleukins were shown to promote the proliferative response of B6 Lyt-2+ T cells in the presence of stimulator-type T or B cells. Both interleukins also facilitated the generation of cytotoxic T cells from B6 Lyt-2+ cells to H-2Kbm1 antigen in the mixed lymphocyte culture deficient in stimulator-type accessory cells. IL-1 was shown to enhance the expression of IL-2 receptor on the responding Lyt-2+ T cells as assessed by flow cytometry. IL-1 binding to responding T cells were also assayed by means of iodinated IL-1 and was shown to increase significantly on responding Lyt-2+ cells. Overall results indicate that accessory cells might play dual roles in the activation of Lyt-2+ T cells responding to allogeneic MHC class I antigen: direct presentation of the antigen to responder T cells and production of IL-1. Both signals are essentially required for Lyt-2+ T cells responding to allogeneic MHC class I antigen to initiate proliferation and also to differentiate into cytotoxic T cells.

Inhibition of antiskin allograft immunity induced by infusions with photoinactivated effector T lymphocytes (PET cells)

Induction of tolerance for skin allotransplantation requires selective suppression of the host response to foreign histocompatibility antigens. This report describes a new approach which employs pre-treatment with 8-methoxypsoralen (8-MOP) and ultraviolet A light (UVA) to render the effector cells of graft rejection immunogenic for the syngeneic recipient. Eight days after BALB/c mice received CBA/j skin grafts, their splenocytes were treated with 100 ng/ml 8-MOP and 1 J/cm2 UVA prior to reinfusion into naive BALB/c recipients. Recipient mice were tested for tolerance to alloantigens in mixed leukocyte culture (MLC), cytotoxicity (CTL), delayed-type hypersensitivity assays (DTH), and challenge with a fresh CBA/j graft. Splenocytes from BALB/c recipients of photoinactivated splenocytes containing the effector cells of CBA/j alloantigen rejection proliferated poorly in MLC and generated lower cytotoxic T-cell responses to CBA/j alloantigens in comparison with sensitized and naive controls and suppressed the MLC and CTL response to alloantigen from sensitized and naive BALB/c mice. In vivo, the DTH response was specifically suppressed to the relevant alloantigen in comparison with controls. BALB/c mice treated in this fashion retained a CBA/j skin graft for up to 42 days post-transplantation without visual evidence of rejection. These results showed that reinfusion of photoinactivated effector cells resulted in an immunosuppressive host response which specifically inhibited in vitro and in vivo responses that correlate with allograft rejection and permitted prolonged retention of histoincompatible skin grafts.

Helper strategy in tumor immunology: expansion of helper lymphocytes and utilization of helper lymphokines for experimental and clinical immunotherapy

Two main kinds of immune strategy are possible against neoplasia. The first potentiates a selected effector arm. In vitro culture with exogenous interleukin-2 (IL-2) increases the activity of natural killer cells and leads to the expansion of T cytotoxic lymphocytes. Systemic reinfusion of both of these cells with high doses of IL-2 mediates the regression of a variety of murine and human tumors. In an alternative strategy, a few regulatory lymphocytes turn on immune reactivity by triggering a cascade of interconnected effector functions. The efficacy of this strategy rests on the repertoire of effector mechanisms moved to action. An effective immunoregulatory maneuver is the addition of helper determinants on the surface of tumor cells. Its power can be further increased by the pre-induction of helper T lymphocytes specific to the helper determinants. This approach can be achieved in mice by coupling muramyl dipeptides to tumor cells, along with eliciting T lymphocytes specifically reactive to Bacillus Calmette-Guerin. Noncytotoxic T helper lymphocytes produce factors which recruit nonspecific (macrophages) as well as specific (cytolytic T lymphocytes) anti-tumor attacking cells. In this way protection can be afforded against primary tumors and metastases, as well as leukemia cells. As the activity of helper lymphocytes rests mostly on lymphokine release, the use of molecularly defined lymphokines mimicking T-helper functions has also been attempted. In a few experimental models, the association of low doses of IL-2 with non-reactive lymphocytes from tumor-bearing mice promotes an effective anti-tumor reaction in the host. Moreover, the combination of distinct lymphokines can also build a molecularly defined helper system able to activate in sequence non-specific and specific anti-tumor reactions in vivo. Trials intended to evaluate the clinical impact of these helper approaches in the management of human tumors are being started or are already under way.

Dual-label immunocytochemistry of the active multiple sclerosis lesion: major histocompatibility complex and activation antigens

Fresh-frozen autopsy material containing active inflammatory lesions from 9 different patients with multiple sclerosis (MS) was analyzed by immunocytochemistry using a panel of monoclonal antibodies, and a dual-label immunocytochemical method was developed which permitted the simultaneous detection of two different surface markers on a single cell. We now report the following. (1) The predominant T-cell phenotype within MS lesions is CD2,3,8. This phenotype marks the suppressor-cytotoxic subset. (2) These cells do not express the natural killer cell marker NKH-1, which is present on a subset of CD8-positive cells in peripheral blood. (3) The infiltrating cell expresses class I (HLA A, B, C), but not class II (DR and DQ), major histocompatibility complex (MHC) molecules. (4) Other T-cell surface molecules, including the activation antigens interleukin-2 receptor, Ta1, and T11-3, as well as the marker 2H4, are largely not expressed. (5) Endothelial cells express both class I and class II MHC molecules and the 4B4 molecule in both MS and control tissue. (6) Astrocytes within the vicinity of MS lesions are predominantly class II MHC-negative. These results demonstrate that the T-cell infiltrate present in MS tissue on autopsy has a restricted phenotypic profile, but they also raise the possibility that, within this population, few activated effector cells are present.

Evidence for involvement of dual-function T cells in rejection of MHC class I disparate skin grafts. Assessment of MHC class I alloantigens as in vivo helper determinants

The present study further characterizes the cellular mechanisms involved in the in vivo rejection of MHC class I-disparate skin allografts. Previously, we demonstrated that class I-specific rejection responses could result from collaborations between distinct populations of lymphokine-secreting T helper (Th) and lymphokine-responsive T effector (Teff) cells. In the present study, we have assessed the possibility that class I-specific rejection responses could also result from a second cellular mechanism involving a single population of dual-function Th/Teff cells that would not have any further requirement for cell-cell collaboration. Our experimental strategy was to determine the ability of MHC class I-allospecific T cells, in response to class I allodeterminants expressed on skin grafts, to provide help in vivo for activation of helper-dependent Teff cells. We found that class I anti-Kbm1-allospecific T cells would reject bm1 skin allografts, but would not generate help for the activation of helper-dependent effector cells that were specific for third-party skin allografts (e.g., grafts expressing Kbm6, Qa1a, or H-Y allodeterminants). This failure of anti-Kbm1 T cells to provide help in response to bm1 skin allografts was not due to an inability of lymphokine-secreting anti-Kbm1 Th cells to recognize and respond in vivo to Kbm1 allodeterminants expressed on skin, since lymphokine-secreting anti-Kbm1 Th cells were specifically primed in animals engrafted with bm1 skin allografts. Nor was any evidence found that this failure was due to active suppression of anti-Kbm1 helper activity. Rather, we found that anti-Kbm1 T cells consumed nearly all of the helper factors they secreted. Taken together, these results are most consistent with the in vivo activity of dual-function Th/Teff cells that consume the lymphokines they secrete. Thus, this study demonstrates that MHC class I-disparate skin allografts can be rejected by two mechanisms, depending on the ability of the allospecific Teff cell to secrete helper lymphokines. MHC class I-disparate grafts can be rejected by (a) class I-allospecific Teff cells that are unable to produce lymphokine but are responsive to exogenous T cell help; and (b) class I-allospecific dual-function Th/Teff cells that are able to both produce and consume soluble lymphokine.

Interleukin 4 (BSF-1) induces growth in resting murine CD8 T cells triggered via cross-linking of T3 cell surface structures

To analyze the role of interleukin 4 (IL4, BSF-1) during primary activation of resting (high-density) murine CD8 T cells, a model system was used which bypasses antigen-presenting cells by the use of anti-T3 monoclonal antibodies immobilized on Sepharose beads. In high, but not in low cell density cultures, IL4 alone induced cell growth. In low cell density cultures, further to T3 cross-linking a soluble macrophage product was required as co-stimulator to induce sensitivity to IL4. This co-stimulator activity was unrelated to recombinant (r)IL1, rIL6 and rTNF-alpha (tumor necrosis factor alpha). In primary CD8 T cell responses rIL4-driven growth was about half of that induced by rIL2, and not inhibitable by anti-IL2 receptor antibodies. Higher concentrations of IL4 down-regulated cell proliferation. In the course of IL4-driven growth, the proliferating cells acquired sensitivity to the growth-promoting effect of IL2. Activated CD4 or CD8 T cells were found to be equally sensitive to the IL4 and IL2-driven growth pathway. Taken together, these results define a physiologic role of IL4 as growth factor during primary activation of resting CD8 T cells and thus extend the spectrum of target cells for IL4.

Evidence for active immunological regulation in prevention of testicular autoimmune disease independent of the blood-testis barrier

It has long been considered that autoimmune disease of the testis is prevented by sequestration of testis-specific autoantigens on germ cells behind the blood-testis (BT) barrier. However, we now have evidence that not all such antigens are sequestered. Some appear to reside on germ cells in the basal compartment of the seminiferous tubule where they are accessible to antibodies and to circulating activated T cells. Mice immunized with syngeneic testis homogenate are found to have immunoglobulin G (IgG) bound to cells in the basal compartment before onset of orchitis. This IgG is absorbed from circulation by the testis and, therefore, found only in the serum of mice orchiectomized before immunization. When the IgG is eluted from the testis, it is found to react preferentially with testicular cells enriched in preleptotene spermatocytes. T cells from mice immunized with testis can be transferred to naive syngeneic mice where they infiltrate the testis to cause orchitis. This implies that the BT barrier does not need to be breached directly for specific T cells to have access to testicular autoantigens on antigen presenting cells. Thus, active systemic and/or local immunoregulatory mechanisms must operate to prevent testicular autoimmune disease. These mechanisms may operate at the level of suppressor T cells, nonspecific suppression in the local environment of the testis, antigen presentation in the testis, or lymphocyte trafficking in the testis. These mechanisms probably operate only on the afferent limb of the immune response since they are overridden and orchitis occurs once testis-specific activated T cells are generated.

Reactivity of Ly-2+ T cells against 2,4,6-trinitrophenyl (TNP)-modified syngeneic stimulator cells: specificity, frequency of interleukin 2-producing Ly-2+ helper T cells and clonal segregation from Ly-2+ cytotoxic T lymphocytes

The in vitro reactivity of purified murine Ly-2+ and L3T4+ T cells towards 2,4,6-trinitrophenyl (TNP)-modified syngeneic stimulator cells was analyzed. Both T cell subpopulations autonomously proliferated and produced interleukin 2. In either the Ly-2+ or L3T4+ T cell subset the frequencies of TNP-specific interleukin 2 (IL 2)-producing T lymphocyte precursors (IL 2 TL-p) were equally high (f = 1/400-1/1000). Clonally developing IL 2 TL of either T cell subset showed an exquisite antigen (TNP) specificity as shown by the split culture approach. TNP-specific Ly-2+ IL-2 TL used class I MHC (H-2Kk) gene products as major histocompatibility complex (MHC) restriction elements, while L3T4+ IL 2 TL proved to be class II MHC (H-2I-AkI-Ek) restricted. Clonal segregation analyses revealed that the majority of clonally developing TNP-reactive Ly-2+ TL segregated into either IL 2 TL-p or cytotoxic T lymphocyte presursors, i.e. both functions appear to be mutually exclusive. Less than 10% of the responding Ly-2+ T cells seemed to be bifunctional. These findings provide compelling evidence for the L3T4+ T cell-independent, autonomous reactivity of Ly-2+ T cells in MHC-restricted antigen-specific responses and suggest T-T cell interactions within the functional heterogenous Ly-2+ T cell population.

Stimulation with dendritic cells decreases or obviates the CD4+ helper cell requirement in cytotoxic T lymphocyte responses

We investigated the need for CD4+ helper T (Th) cells in the induction of murine cytotoxic T lymphocyte (Tc) responses across minor or major histocompatibility (MHC) antigenic differences with either normal spleen cells (NSC) or purified dendritic cells (DC) as antigen-presenting cells (APC). Generation of a secondary in vitro class II MHC-specific Tc response was totally CD4+ Th cell-dependent with both types of APC. Likewise, male antigen (H-Y)-primed class II mutant bm12 T cells, which do not respond to H-Y presented on NSC, do respond to H-Y presented on DC in a completely CD4+ Th cell-dependent fashion. All other Tc responses, including primary anti-class I MHC, primary anti-class I + II MHC plus anti-minor H, and secondary C57BL/6 (B6) anti-H-Y, although not completely CD4+ Th cell dependent, were greatly augmented in the presence of CD4+ Th cells, but only with NSC as APC. In contrast, with DC as APC these responses were entirely or largely CD4+ Th cell independent. Similarly, H-Y primed class I MHC mutant bm14 T cells, which do not respond to H-Y presented on NSC, do respond to H-Y presented on DC in a completely CD4+ Th cell-independent fashion. The combined results indicate that DC can directly present class I MHC alloantigen or class I MHC plus nominal antigen (e.g. minor H) to CD8+ cells and generate a Tc response by these cells without the requirement for CD4+ Th cells.

Limiting dilution analysis of interleukin-2-producing mature T cells. Interleukin 2 secretion is an exclusive property of L3T4+ lymphocytes

Evaluation of lymphokine production by individual activated T cells is necessary to characterize their growth requirements. We have studied interleukin 2 (IL-2) secretion by mature T lymphocytes using a high resolution assay system with the following characteristics: (a) a threshold of IL-2 detection 25 times lower than classic IL-2 titration; (b) the ability to discriminate between IL-2 and IL-4 activities; (c) absence of 'in situ' IL-2 absorption; (d) IL-2 production revealed at the single cell level. By this method an average of 10% of spleen cells, and 75% of L3T4+ cells were detected as producers in a concanavalin A (Con A)-dependent T cell activation system. Our results also suggest the complete restriction of IL-2 secretion to cells with this phenotype. Therefore, factors other than IL-2 must play a major role in Lyt 2+ mitogen-driven, helper-independent T cell proliferation.

L3T4+ T-cell-independent reactivity of Lyt2+ T cells in vivo

The aim of this study was to analyze in vivo the L3T4+ T-cell-subset-independent reactivity of Lyt2+ T cells toward transplantation alloantigens. To this end, we depleted normal mice of L3T4+ T cells by injection of monoclonal antibodies to the L3T4 antigen. This procedure not only led phenotypically to a disappearance of L3T4+ T cells, but also effectively abolished reactivity toward class II MHC antigens in vitro and in vivo. However, L3T4+ T-cell-depleted mice still reacted to class I MHC alloantigens in vivo: after immunization with class I MHC alloantigens Il-2 receptor-bearing T cells appeared in the draining lymph nodes, and developed antigen-specific cytolytic activity. Moreover, upon in vivo priming the frequencies of class I MHC-specific precursors of Il-2-producing and cytolytic Lyt2+ T lymphocytes increased up to 20-fold. L3T4+ T-cell-depleted mice rejected class I MHC-bearing skin grafts promptly. We conclude that not only in vitro but also in vivo Lyt2+ T cells remain reactive toward class I MHC antigens in the absence of L3T4+ T helper cells.

Mediation of in vivo tumor-neutralizing activity by Lyt-2+ as well as L3T4+ T cell subsets

The present study reexamines the cell surface nature of T cells mediating in vivo protective tumor immunity with the use of anti-L3T4 and -Lyt-2 antibodies. C3H/HeN mice hyperimmune against syngeneic MH134 hepatoma or MCH-l-Al fibrosarcoma were prepared by intradermal (id) inoculation of viable tumor cells followed by surgical resection of the tumor and by repeated challenges with viable tumor cells. Spleen cells from these mice were fractionated into L3T4+ or Lyt-2+ T cell subset by treatment with anti-Lyt-2 or -L3T4 antibody plus complement (C). Winn assays performed by utilizing such fractionated T cells have revealed that both L3T4+ and Lyt-2+ T cell subsets from hyperimmune mice produced complete tumor protection. Flow microfluorometry study illustrated that the treatment with anti-L3T4 or -Lyt-2 antibody plus C resulted in the complete isolation of L3T4- Lyt-2+ (Lyt-2+) or L3T4+ Lyt-2- (L3T4+) T cell subset, respectively. This contrasted with the failure of treatment with anti-Lyt-1 antibody plus C to isolate all T cells expressing Lyt-2 marker. It was further demonstrated that each subset of T cells exerted its anti-tumor effect in a tumor-specific way and without a requirement for the other alternative subpopulation of unprimed T cells. These results indicate that Lyt-2+ T cell subset can be successfully isolated by treatment with anti-L3T4 but not with anti-Lyt-1 antibody plus C, and that each single subset of Lyt-2+ and L3T4+ T cells can function as in vivo effector T cells.

CD4+ helper T cells are required for resistance to a highly metastatic murine tumor

A role of CD4+ T helper cells in induction of tumor transplant rejection leading to complete regression of a highly metastatic DBA/2 mouse lymphoma was analyzed. Using an anti-CD4 monoclonal antibody (GK1.5) which eliminates T helper cells in vivo and in vitro, we found that CD4+ cells are required for tumor resistance in syngeneic DBA/2 mice or allogeneic but major histocompatibility complex-identical B10.D2 mice. In contrast, in allogeneic C57BL/6 mice tumor rejection was independent of CD4+ cells. An analogous requirement for immune CD4+ cells for in vitro induction of CD8+ tumor-specific cytotoxic T cells was found in these respective strains. The requirement for immune CD4+ cells in vitro could be replaced by recombinant interleukin 2. These results demonstrate a role of CD4+ regulatory T cells and T-T cell cooperation in the induction of anti-tumor immunity and tumor rejection, and point to possible therapeutic interventions in the afferent phase of anti-tumor immune responses.

Recognition requirements for the activation, differentiation and function of T-helper cells specific for class I MHC alloantigens

The present review has focused on the specificity of the T-helper cell populations initiating MHC class I alloreactions. In contrast to conventional immune responses against soluble antigens, responses against membrane-bound class I alloantigens are initiated by two distinct antigen-specific T-helper cell populations that can be distinguished by their Lyt phenotype, MHC restriction specificity, antigen specificity, and requirement for thymically determined self-recognition. Alloresponses were shown to be a composite consisting of two distinct components: one mediated by L3T4+ Th cells and very similar to conventional self + X responses; and one mediated by Lyt2+ Th cells and unique to alloresponses against MHC class I antigens. As would befit an unusual Th cell population, the recognition/response spectrum of Lyt2+ Th cells was highly unusual and was found to be the basis for much of the uniqueness we attribute to immune alloreactions, including rapid rejection of tissue allografts in vivo.

Direct activation of CD8+ cytotoxic T lymphocytes by dendritic cells

Recent experiments (11-13) have shown that antigen-specific, CD8+, CD4- T lymphocytes can be induced to proliferate and become killer cells in the absence of a second population of "helper" CD8-, CD4+ cells. We have studied early events in the activation of CD4+ and CD8+ T cell subsets in the primary mixed leukocyte reaction. Dendritic cells are a major if not essential accessory cell for the activation of both subpopulations. Antigen-bearing macrophages fail to stimulate unprimed CD8+ cells, but act as targets for the sensitized cytolytic lymphocytes that are induced by dendritic cells. The initial proliferative response is comparable for CD4+ and CD8+ lymphocyte subsets. For both subpopulations, dendritic cells efficiently cluster the responding lymphocytes on the first day and induce the release of IL-2. The data indicate that CD4+ and CD8+ lymphocytes can be activated by a similar mechanism, and illustrate the special role of dendritic cells in the sensitization stage of cell-mediated immunity.

Phenotype, specificity, and function of T cell subsets and T cell interactions involved in skin allograft rejection

In the present study we used an adoptive transfer model with athymic nude mice to characterize the T cells involved in initiating and mediating skin allograft rejection. It was found that skin allograft rejection in nude mice required the transfer of immunocompetent T cells and that such reconstitution did not itself stimulate the appearance of T cells derived from the nude host. Reconstitution with isolated populations of Lyt-2+/L3T4- T cells resulted in the rapid rejection of MHC class I-disparate skin allografts, whereas reconstitution with isolated populations of L3T4+/Lyt-2- T cells resulted in the rapid rejection of MHC class II-disparate and minor H-disparate skin allografts. By correlating these rejection responses with the functional capabilities of antigen-specific T cells contained within the reconstituting Lyt-2+ and L3T4+ T cell populations, it was noted that skin allografts were only rejected by mice that, as shown by in vitro assessment, contained both lymphokine-secreting Th cells and lymphokine-responsive Tk cells specific for the alloantigens of the graft. The ability of two such functionally distinct T cell subsets to interact in vivo to reject skin allografts was directly demonstrated in H-Y-specific rejection responses by taking advantage of the fact that H-Y-specific Th cells are L3T4+ while H-Y specific Tk cells are Lyt-2+. Finally, the importance of in vivo interactions between functionally distinct Th/T-inducer cells and T killer (Tk)/T-effector cells in skin allograft rejection was demonstrated by the observation that normal B6 mice retain Qala and Kbm6 skin allografts because of a selective deficiency in antigen-specific Th cells, even though they contain T-effector cells that, when activated, are able to reject such allografts. Thus, the ability to reject skin allografts is neither unique to a specialized subset of T cells with a given Lyt phenotype, nor unique to a specialized subset of helper-independent effector T cells with so-called dual function capability. Rather, skin allograft rejection can be mediated by in vivo collaborations between T-inducer cells and T-effector cells, and the two interacting T cell subsets can express different Lyt phenotypes as well as different antigen specificities.

Coxsackievirus B3-induced myocarditis. Autoimmunity is L3T4+ T helper cell and IL-2 independent in BALB/c mice

Male BALB/c mice inoculated with 6 X 10(4) plaque-forming units (pfu) coxsackievirus, group B, type 3 (CVB3), develop myocarditis within 7 days. Two cytolytic T lymphocyte (CTL) populations arise in infected animals. One population belongs to the Lyt 2+ T (cytolytic/suppressor) lymphocyte subset and reacts specifically with uninfected heart cells (autoreactive CTLs, ACTLs), whereas the other belongs to the L3T4+ T (helper) lymphocyte subset and reacts with infected targets (virus-specific CTLs, VSCTLs). Although both immune T lymphocyte populations can induce cardiac inflammation in vivo, ACTLs predominantly cause tissue injury. VSCTL generation can be inhibited by either anti-Tac (antibody to the interleukin 2 [IL-2] receptor) or anti-Iad but not by anti-IAk, indicating that this response is probably both IL-2-dependent and Class II (major histocompatibility complex [MHC] antigen restricted. ACTL generation is independent of IL-2, because neither anti-Tac or cyclosporin A inhibit this response.

Identification of interleukin 2-producing T helper cells within murine Lyt-2+ T lymphocytes: frequency, specificity and clonal segregation from Lyt-2+ precursors of cytotoxic T lymphocytes

The prime aim of this study was to assess whether the autonomous primary mixed lymphocyte culture response of Lyt-2+ T cells towards class I major histocompatibility complex (MHC) antigens reflects in terms of interleukin 2 (IL2) production and cytotoxicity the activation of multifunctional Lyt-2+ T cells, or the activation of functionally distinct T cell subsets. The results demonstrate that highly purified Lyt-2+ T cells proliferate in response to class I MHC antigens, as opposed to L3T4+ T cells which react towards class II MHC antigens. In both responder cell types proliferative responses are associated with IL2 secretion, while only Lyt-2+ T cells develop measurable cytotoxic effector cells. The precursor frequency of IL2-producing helper cells in MHC class I-reactive Lyt-2+ T cells equals that in MHC class II-reactive L3T4+ T cells (f = 1/500-1/1000). In clonal segregation analysis greater than 90% of Lyt-2+ colonies secreting IL2 do not develop cytotoxic activity, while greater than 90% of Lyt-2+ cytotoxic T cells fail to produce detectable IL2. A minority of less than 10% of Lyt-2+ T cells appears to be bifunctional. As such the results point out the existence of functionally committed T cells within class I MHC-reactive Lyt-2+ T cells able to produce either IL2 or to develop into cytotoxic effector cells.

Coxsackievirus B-3 myocarditis. T-cell autoimmunity to heart antigens is resistant to cyclosporin-A treatment

A cardiotropic variant of coxsackievirus group B, Type 3 (CVB3) induces myocarditis in inbred Balb/c mice. Myocardial injury is predominantly mediated by T lymphocytes recognizing normal myocyte antigens, making this an autoimmune disease. Nonetheless, the autoimmune response cannot be inhibited by cyclosporin A (CSA) treatment of the infected animals. Mortality in treated mice was increased 2-4 times, but neither virus-specific antibody or cytolytic T-lymphocyte responses were affected, and maximal virus concentrations in the hearts of CSA-treated and control animals were similar. Cardiac damage remains T-cell-mediated, because mice given both CSA and rabbit anti-thymocyte serum (ATS) failed to develop significant myocardial inflammation. CSA did suppress immunity in Balb/c mice to an allogeneic C57B1 lymphoma, EL4. Subcutaneous inoculation of mice with 2.5 X 10(6) ascites tumor cells resulted in 100% of the CSA-treated animals having tumors averaging 340 mg 10 days later, compared with less than 10% of control animals having tumors averaging only 30 mg. Humoral immunity to the tumor was absent in CSA-treated mice. Therefore, whether CSA induces immunosuppression depends upon the antigenic stimulus used.

Analysis of T-cell subsets in rejection of Kb mutant skin allografts differing at class I MHC

The T-cell subpopulations which initiate and mediate tissue allograft rejection remain controversial. In the present study we attempted to identify the phenotype and function of the T-cell subset(s) primarily responsible for the rejection of skin allografts differing at a single class I locus in the major histocompatibility complex (MHC). We found that the rejection rates by B6 mice (H-2b) of four different class I mutant (Kbm) skin allografts form a distinct hierarchy. This hierarchy correlates strikingly and uniquely with the relative precursor frequencies of Lyt2+ interleukin-2-secreting T-helper cells reactive against the various Kbm mutants. To investigate the role of Lyt2+ T cells in the rejection of class I-disparate skin allografts directly, H-2b nude mice were engrafted with Kbm skin allografts and then reconstituted with L3T4+ or Lyt2+ T-cell subpopulations from syngeneic H-2b mice. Lyt2+ T cells were observed to be both necessary and sufficient for the rejection of class I-disparate Kbm skin allografts, whereas L3T4+ T cells were neither necessary nor sufficient. These results identify the Lyt2+ interleukin-2-secreting T-cell subset as the critical cell type determining the rejection rate of class I-disparate Kbm skin allografts.