Idiotype-like determinants on human T lymphocytes alloactivated in mixed lymphocyte culture

T cells alloactivated in 5-d MLC with an HLA-DR-different stimulator acquire the capacity of stimulating the autologous mixed lymphocyte response (AMLR). We have demonstrated that activation of AMLR by allosensitized T cells is determined by the expression of the idiotype receptor for the stimulating HLA-DR alloantigen. This has been shown in experiments in which purified, OKT-3-positive T cell suspensions were first primed for 9 d with AMLR-activated T lymphoblasts, then tested in secondary AMLR with autologous lymphoblasts sensitized to various HLA- DR alloantigens. Accelerated memory responses were induced only by autologous lymphoblasts that had been sensitized against the same HLA- DR specificity as the primary AMLR stimulators. This response was not inhibited by a mouse monoclonal antibody recognizing Ia-like determinants, and was not triggered by human allogeneic resting peripheral blood lymphocytes. Thus, recognition of alloactivated T lymphoblasts in secondary AMLR seems to be specific for the idiotype- like determinants expressed by the autologous stimulators.     

Decreased autologous mixed lymphocyte reaction in Sj?gren's syndrome.

The autologous mixed lymphocyte reaction (AMLR) measures the response of peripheral blood T cells to antigens present on the surface of non-T cells. The AMLR was studied in 25 patients with Sjögren's syndrome (SS). The AMLR was decreased in 15 of 25 (60%) of patients with SS (5,272 +/- 6,738 cpm vs. 14,396 +/- 10,092 cpm for the normal controls, P < 0.001). The AMLR was decreased in 8 of 15 patients with only glandular disease who were not on any systemic medications. Patients with SS and associated disease had lower responses than patients with SS alone. Two patients with pseudolymphoma had absent response. The decreased AMLR correlated with a decreased response to concanavalin A, suggesting a possible abnormality of a T cell subpopulation. There was no correlation between the decreased AMLR and age, focus score, serum immunoglobulin concentration, the titer of antilymphocyte antibody, or phytohemagglutinin response. In allogeneic MLR, SS non-T cells and macrophages stimulated normal allogeneic T cells less well than normal non-T cells and macrophages, suggesting a possible abnormality in the cells that stimulate in the cells that stimulate in the allogeneic MLR.     

Analysis of the defects responsible for the impaired regulation of Epstein-Barr virus-induced B cell proliferation by rheumatoid arthritis lymphocytes. I. Diminished gamma interferon production in response to autologous stimulation

T cells of patients with rheumatoid arthritis (RA) do not control the rate of B lymphoblast transformation induced by Epstein-Barr virus (EBV) as efficiently as T cells from healthy individuals; thus, lymphoblast cell lines are established more readily in RA lymphocytes in vitro after EBV infection. In the present experiments, we have asked whether this T cell regulation can be reproduced by lymphocytes. We found that normal T cells, activated in allogeneic or autologous mixed leukocyte reactions (MLR), produce lymphokines that inhibit in vitro EBV-induced B cell proliferation. Allogeneic MLR supernatants inhibited EBV-induced DNA synthesis 62 +/- 4% (mean +/- SE) at 10 d post- infection, whereas autologous MLR supernatants suppressed it 50 +/- 3%. RA T cell supernatants produced in an allogeneic MLR suppressed as well as normal T cell supernatants (64 +/- 5% inhibition). In contrast, supernatants from RA autologous MLR had little inhibitory activity. EBV- induced DNA synthesis at 10 d was reduced only 8 +/- 3%, compared with the 50 +/- 3% suppressive activity of normal autologous MLR supernatants. The magnitude of the proliferative responses in the autologous MLR regenerating the lymphokines was similar in the normal and RA populations. After depletion of adherent cells from the RA auto- MLR stimulators, supernatant inhibitory activities increased to normal levels (from 11 +/- 6 [SE] to 52 +/- 6% [SE]). The inhibitory factor involved in the regulation of in vitro EBV infection is a protein with a molecular weight of approximately 50,000. Its activity is eliminated by hearing at 56 degrees C and by exposure to acid at pH 2. The inhibitory activity is blocked by mixing the MLR supernatants with a polyvalent antisera or monoclonal antibodies specific for human gamma interferon. Gamma interferon produced by activating T cells in allo- or auto-MLR can reproduce T cell-mediated regulation of EBV-induced B cell proliferation, and the failure of RA auto-MLR to generate that lymphokine parallels the defective T cell regulation of EBV-induced B cell proliferation characteristic of RA lymphoid cells.     

Deficient autologous mixed lymphocyte reaction in Kaposi's sarcoma associated with deficiency of Leu-3+ responder T cells.

Autologous mixed lymphocyte reaction (AMLR) and T cell subsets defined with monoclonal antibodies were analyzed in the peripheral blood of homosexual males with Kaposi's sarcoma (KS). All seven patients demonstrated decreased AMLR (P less than 0.001) when compared with age- and sex-matched simultaneously studied controls. These patients also showed decreased proportions of Leu-3+ (helper/inducer phenotype) and an increase in the proportion of Leu-2+ (suppressor/cytotoxic phenotype) T cells. Leu-3+ T cells were purified from two patients by depleting Leu-2+ T cells in complement-dependent cytotoxicity. Leu-3+ T cells from both patients demonstrated poor proliferative response in the AMLR. In allogeneic MLR, patients' T cells were poor responders and their non-T cells were poor stimulators against healthy controls. This study demonstrates deficiency of both AMLR and allogeneic MLR in patients with KS. The decreased AMLR is associated with qualitative and functional deficiency of Leu-3+ responder T cells. Whether the functional deficiency of Leu-3+ responder T cells in the AMLR is a general phenomena or a feature of a subset of patients with KS remains to be determined.     

Production of a cytokine with interleukin 3-like properties and cytokine-dependent proliferation in human autologous mixed lymphocyte reaction

The autologous mixed lymphocyte reaction (AMLR) was assayed in a medium containing fresh autologous serum, by using nylon-adherent stimulator cells and nonadherent responder T cells, which were prepared from human peripheral blood mononuclear cells in the absence of fetal calf serum (FCS) to avoid any sensitization to xenogeneic protein antigens. DNA replication without a background proliferative response was induced by stimulator cells in the responder cells. The addition of monoclonal anti-HLA-DR antibody to the culture or treatment of the responder cells with complement plus anti-T4 but not anti-T8 monoclonal antibody suppressed the AMLR, suggesting that this specific AMLR involves an interaction between HLA-DR antigens and helper/inducer T cells. Regardless of this specific DNA replication, the AMLR generated no production of interleukin 2 (IL-2) and interferon gamma (IFN-gamma), both of which could be found in the allogeneic (allo) MLR. In addition, DNA replication in the AMLR was not inhibited by the addition of specific antisera for IL-2 and IFN-gamma, both of which significantly inhibited the DNA replication in allo-MLR. The AMLR was accompanied by production of a soluble factor, which could stimulate the proliferation of murine interleukin 3 (IL-3)-dependent cell line 32Dcl but not the proliferation of IL-2-dependent cell lines. This factor was also found to be responsible for proliferation of responder nonadherent cells in the AMLR. It strongly stimulated bone marrow cells, as did the murine IL-3. The factor had an Mr range, as determined by gel filtration, of 15,000-28,000, but it did not bind to fast protein liquid chromatography (FPLC)-MonoQ column. Thus, the factor is distinguishable from IL-2 in physicochemical or biological properties, but similar to murine IL-3. These results suggest that the human AMLR may be primarily a phenomenon in which non-T cells mediated by the HLA-DR antigens on the cell stimulate helper/inducer T cells to produce a lymphokine with IL-3-like properties, but no IL-2, which in turn stimulates the factor-dependent cells to proliferate.     

Autologous mixed lymphocyte reaction in man. X. T-T autologous mixed lymphocyte reaction in young and aging humans

T cells upon activation with mitogens or autologous non T cells express surface HLA-DR antigens and are capable of stimulating autologous T cells in the autologous mixed lymphocyte reaction (T-T AMLR). We have examined T-TA AMLR, using T-non T AMLR activated-(TA) T cells as stimulators in young (21-32 yr) and aging humans (62-84 yr). In aging subjects a significantly (p less than 0 . 01) higher proliferative response was observed in T-TA AMLR as compared to simultaneously studied young subjects. In allogeneic MLR, no significant difference was observed between young and aging subjects. The increased T-TA AMLR could be a mechanism responsible for deficient T-non T AMLR reported in aging humans.     

Deficiency of the autologous mixed lymphocyte reaction in patients with primary biliary cirrhosis.

In this study we show that patients with primary biliary cirrhosis (PCB) have a marked deficiency in the ability to generate an autologous mixed lymphocyte reaction (AMLR) but have a normal ability to generate an allogeneic mixed lymphocyte reaction (MLR). This deficiency is not due to differences in the time-course of the proliferative response or to an altered response to variable numbers of stimulator cells. The deficiency was consistently found irrespective of the methods used to isolate autologous stimulator cells. Both responder cells and stimulator cells obtained from patients with PBC were similar to normal cells in their ability to generate an MLR in allogeneic normal human serum. In addition, serum from patients with PBC inhibited the ability of normal lymphocytes to generate both the AMLR and MLR to a similar degree, suggesting that the defect of the AMLR in PBC is not due to a serum factor. It has been shown that the responder cell population in the AMLR contains a subpopulation of cells that mediate suppression. Therefore, it is possible that the deficiency of the AMLR may be related to previously described abnormalities of suppressor function in patients with PBC.     

Immune response to alien histocompatibility antigens on Epstein-Barr virus transformed cells

Expression of alien histocompatibility antigens on Epstein-Barr virus transformed, cultured lymphoblastoid cell lines (LCL), which were established from normal peripheral blood lymphocytes (PBL), was studied by means of mixed lymphocyte reaction (MLR), cell mediated lysis (CML) and primed lymphocyte typing (PLT). Stimulation of PBL by autologous LCL resulted in some MLR responses and generation of cytotoxic effector cells against autologous LCL. Restimulation of PBL by 16 individual allogeneic PBL failed to prime an individual lymphocytes against autologous LCL in PLT tests. However, stimulation of PBL by a pooled normal PBL resulted in generation of cytotoxic cells against autologous LCL. Culturing of stimulated PBL in the presence of T cell growth factor (TCGF) for 30 days was shown to maintain cytotoxic effector cells in the cell population.     

Autologous rosette-forming T cells as the responding cells in human autologous mixed-lymphocyte reaction.

Autologous rosette-forming cells (Tar cells) have surface and functional characteristics of post-thymic precursors and among these characteristics there are some that have been identified in the responsive cell of the autologous mixed-lymphocyte reaction (AMLR). We therefore did AMLR with circulating mononuclear cells from normal subjects using as responding cells either total T cells, T cells depleted of Tar cells, or purified Tar cells. The response of Tar cells in AMLR was significantly greater than that of total T cells and these responded significantly more than Tar-depleted T cells. Conversely, Tar cells responded less than total T cells or T cells depleted of Tar cells in allogeneic mixed-lymphocyte reactions. Increasing numbers of Tar cells gave significantly greater AMLR responses both alone and when added to diminishing proportions of Tar-depleted T cells to keep the number of T cells constant in the system. Tar cells are the responding cells in AMLR but not in allogeneic mixed-lymphocyte reactions.     

T cells reactive to a single immunodominant self-restricted allopeptide induce skin graft rejection in mice.

Alloreactive T lymphocytes can respond to foreign MHC complexed with foreign peptides through the direct pathway of allorecognition and can additionally recognize allopeptides expressed in the context of recipient (self) MHC through the indirect pathway. To better elucidate how indirect pathway-responsive CD4(+) T cells mediate allograft rejection, we isolated and characterized a TH1 T cell line from BALB/c recipients of B10.A skin that responds to a defined immunodominant, self-restricted allopeptide, I-Abetak58-71. When transferred into BALB/c severe combined immunodeficiency recipients of B10.A skin allografts, this cell line specifically induced a form of skin graft rejection characterized by the presence of TH1 cytokines, macrophage infiltration, and extensive fibrosis. Recall immune responses and immunofluorescence of the rejecting skin revealed only the presence of the peptide-specific T cells within the recipient animals, with no evidence of a direct pathway alloresponse. These studies demonstrate that T cells reactive to a single self-restricted allopeptide can mediate a form of allogeneic skin graft rejection that exhibits characteristics of a chronic, fibrosing process.     

Immunoregulatory T cell circuits in man. Alloantigen-primed inducer T cells activate alloantigen-specific suppressor T cells in the absence of the initial antigenic stimulus

Although alloantigen-specific suppressor T cells are generated in MLR, the cellular signals that lead to activation of suppressor T cells as opposed to cytotoxic T cells are unknown. The current study was undertaken to characterize interactions among T cell subsets involved in the generation of suppressor T cells in MLR. Human peripheral blood Leu-2+ (suppressor/cytotoxic) and Leu-3+ (helper/inducer) T cell subsets were activated with allogeneic non-T cells and then examined for their inductive effects on fresh autologous T cells. Fresh Leu-2+ cells proliferated in response to alloantigen-primed Leu-3+ cells and subsequently suppressed the response of fresh autologous Leu-3+ cells to the original, but not third party, allogeneic stimulator non-T cells. Moreover, only Leu-2+ cells that lacked the 9.3 marker, an antigen present on the majority of T cells including precursors of cytotoxic T cells, differentiated into suppressor cells. The alloantigen-specific suppressive effect of Leu-2+,9.3-cells was not mediated by cytolysis of allogeneic stimulator cells, nor could it be explained by alteration of MLR kinetics. Suppression was observed only when activated Leu-2+ cells were added to fresh MLRs within 24 h of initiation of cultures, suggesting that these cells block an early phase of the activation of Leu-3+ cells in MLR. These results indicate that alloantigen-primed inducer T cells can activate alloantigen- specific suppressor T cells in the absence of allogeneic stimulator cells.     

Autologous rosette-forming T cells regulate responses of T cells. Phenotypic and functional analysis of suppressor cells generated from autologous rosette-forming T cells after autologous mixed lymphocyte reactions.

An average of 5--9% of human peripheral blood of T lymphocytes from rosettes with autologous erythrocytes (ARFT). This population responded only slightly against autologous and allogeneic non-T cells. In contrast, T cells that did not form rosettes with autologous erythrocytes (NRFT) proliferated to a greater degree in auto- and allogeneic mixed lymphocyte reactions (MLR) and also in reactions to trinitrophenyl (TNP) modified autologous non-T cells (TNP-auto-MLR) as compared with ARFT or unfractionated T cells. The ARFT populations could suppress the increased allogeneic (allo)MLR and TNP-auto-MLR of NRFT when the ARFT were added to the NRFT at the beginning of the cultures. Fluorescence-activated cell-sorter (FACS) analysis of these freshly obtained T cell fractions using monoclonal antibodies to subpopulations of T cells did not demonstrate any selective gain or less of T cell subsets in the ARFT and NRFT as compared with unfractionated T cells. But when each T cell fraction was cultured separately for a week in the presence of autologous non-T cells (auto-MLR) and the cells were again analyzed by fluorescence-activated cell sorter, there was an increase in OKT8-positive cells (suppressor/cytotoxic subset) only in the ARFT fraction. The above findings strongly suggest that suppressor T cells are generated from the ARFT fraction during an auto-MLR, these may then regulate the responses on NRFT.     

Inhibition of T cell responses by activated human CD8+ T cells is mediated by interferon-gamma and is defective in chronic progressive multiple sclerosis.

The autologous mixed lymphocyte reaction (AMLR) involves the activation of T cells by autologous antigen presenting cells. Cells are generated during the course of the AMLR that have suppressive properties in vitro. In the present study we investigated the induction of CD8+ T cells in the AMLR with suppressive properties and the mechanism by which these cells downregulate in vitro proliferative responses. Purified CD8+ but not CD4+ T cells activated in the AMLR in conditioned medium inhibited proliferation of autologous T cells by anti-CD3 or PPD. Nonactivated CD8+ T cells did not suppress. The CD8+ T cells activated in the AMLR in the presence of conditioned medium (CD8+ Tact) were CD11b negative and were noncytotoxic. The inhibitory effect of CD8+ Tact cells was completely abrogated by anti-IFN-gamma antibody, but not by anti-IL-4, anti-IL-10, or anti-TGF-beta antibody. The induction of CD8+ Tact cells in the AMLR was blocked by anti-IL-2 or by anti-GM-CSF antibody and the combination of these two recombinant cytokines could support the induction of suppressive CD8+ Tact cells. CD8+ Tact cells were defective in patients with chronic progressive multiple sclerosis (MS) as compared to patients with relapsing-remitting MS or normal controls. Our studies provide a basis for understanding the mechanism of suppression by human CD8+ T cells in terms of specific cytokines, and demonstrate the potential importance of these cells in a human autoimmune disease as their function is defective in patients with progressive MS.     

Impairment of the autologous mixed lymphocyte reaction in atopic dermatitis.

The T cell proliferative response to autologous non-T cells is termed the autologous mixed lymphocyte reaction (AMLR). Recent studies have suggested that the AMLR represents an inducer circuit for the activation of T8+ suppressor/cytotoxic effector cells. Since atopic dermatitis (AD) patients are deficient in T8+ cytolytic T cell function, we investigated the AMLR in AD. When sheep erythrocytes were used to separate T cells from non-T cells, the AMLR was found to be significantly decreased (P less than 0.001) in AD patients (n = 11; delta cpm = 1,550 +/- 393) when compared with normal control subjects (n = 13; delta cpm = 25,819 +/- 4,609). To exclude the possibility that these results were an artifact of the sheep erythrocyte separation, T cells were also separated on a fluorescence-activated cell sorter after treatment of peripheral blood lymphocytes with the OKT3 monoclonal antibody. AD T cells separated by the latter method were also found to have a significantly reduced AMLR response when compared with similarly treated normal T cells. Co-culture studies using cells from AD patients and their HLA identical siblings indicated that the defect resided at the responder T cell level rather than at the stimulator non-T cell level. Co-culture studies revealed no evidence for excessive suppressor cell activity resulting in the decreased AMLR. However, enumeration of T cells reactive with the monoclonal antibody T29, which recognizes a subset of T cells proliferating in the AMLR, demonstrated that AD patients (n = 8; % T29 = 2.5 +/- 0.7) had a significantly decreased (P less than 0.001) number of circulating T29+ T cells when compared with normal controls (n = 8; % T29 = 10.4 +/- 0.8). These studies suggest that a deficiency of T4+ T29+ cells contributes to the deficient AMLR in AD and possibly underlies the abnormalities of T8+ effector cells present in this disease.     

Dendritic cells genetically engineered to express IL-4 exhibit enhanced IL-12p70 production in response to CD40 ligation and accelerate organ allograft rejection

C57BL/10 (B10; H2(b)) bone marrow-derived myeloid dendritic cells (DC) propagated in GM-CSF + IL-4 were transduced with r adenoviral (Ad) vectors encoding either control neomycin-resistance gene (Ad-Neo) or murine IL-4 (Ad-IL-4) on day 5 of culture following CD11c immunomagnetic bead purification. Both Ad-Neo- and Ad-IL-4-transduced DC displayed upregulated surface MHC class II and costimulatory molecules (CD40, CD80, CD86). Ad-IL-4 DC secreted higher levels of bioactive IL-12p70 after CD40 ligation or LPS stimulation than either Ad-Neo or unmodified DC. Only Ad-IL-4 DC produced IL-12p70 in primary MLR, in which they induced augmented proliferative responses of na?ve allogeneic C3H/HeJ (C3H; H2(k)) T-cells. Compared with Ad-Neo DC, Ad-IL-4 DC were also more effective in priming na?ve allogeneic recipients to exhibit specifically enhanced anti-donor T-cell proliferative and CTL responses. T-cells primed in vivo 7 days previously with Ad-IL-4 DC displayed enhanced secretion of Th2 (IL-4, IL-10) but also higher Th1 cytokine (IFNgamma) production following ex vivo challenge with donor alloAg. Moreover, pretreatment of vascularized heart graft recipients with i.v. Ad-IL-4 DC, 1 week before transplant, significantly accelerated rejection and antagonized the therapeutic effect of anti-CD40L (CD154) mAb. These data contrast markedly with recently reported inhibitory effects of autologous Ad-IL-4 DC on autoimmune inflammatory disease.     

Autologous mixed lymphocyte reaction in man. VI. Deficiency of autologous mixed lymphocyte reaction in type I (insulin-dependent) diabetes mellitus

Autologous mixed lymphocyte reaction (AMLR) was examined in the peripheral blood from 20 patients with type I (insulin-dependent) diabetes mellitus. Six of 20 patients demonstrated deficient AMLR when compared to the range for simultaneously studied age and sex matched healthy controls. The kinetics of AMLR with regard to duration of the peak proliferative response was similar to controls, the peak response being on day 6. In allogeneic MLR. T cells from patients responded normally. However, non-T cells from patients were poor stimulators against responder T cells from healthy controls. This study demonstrates a deficiency of AMLR in a subset of patients with type I diabetes that further supports an abnormal immune regulation and might be an important mechanism in the pathogenesis and autoimmune manifestations of type I diabetes.     

A Suppressor T Cell of the Mixed Lymphocyte Reaction Specific for the HLA-D Region in Man

The mixed lymphocyte reaction (MLR) is the proliferative response of one individual's lymphocytes cultured in the presence of another individual's lymphocytes. In man, the MLR is elicited by cell surface antigens coded for by the HLA-D gene locus. This locus is among a cluster of genes which are located on the sixth chromosome and which include genes coding for the major histocompatibility antigens HLA-A, B, and C as well as HLA-D. If the stimulator cell possesses D locus antigens not present in the responder, the lymphocytes of the latter will undergo blast transformation resulting in DNA synthesis which can be measured. A vigorous response in the MLR to allogeneic cells is the rule among healthy individuals.We describe studies of a 23-yr-old man whose lymphocytes respond normally to mitogens and soluble antigens but fail to respond to allogeneic cells in the MLR. His medical history is unremarkable except that he received thymic irradiation as an infant. HLA typing revealed that he is homozygous for HLA-A2, B12, and Cw5 as well as for the D locus antigen Dw4. When his lymphocytes were added to the responder lymphocytes of other persons homozygous for the same HLA antigens, their responses to allogeneic cells but not mitogens were suppressed by 50-95%. Their responses to a soluble antigen, tetanus toxoid, were suppressed to a lesser degree. These inhibitory effects were mediated by a relatively radioresistant thymus-derived (T) lymphocyte.Further studies of the requirements for MLR suppression revealed that only persons heterozygous or homozygous for the Dw4 antigen were inhibited by the suppressor T cell. This effect was not altered by differences in the HLA-A, B, or C antigens between the suppressor and responder. It is concluded that genes in or near the HLA-D locus code not only for antigens (primarily on bone marrow-derived (B) cells), that elicit the MLR, but also for structures on T cells, or possibly macrophages, which are recognized by MLR suppressor T cells.     

Generation of antigen receptor-specific suppressor T cell clones in man

We have shown previously that CD8+ T cells proliferate upon exposure to autologous, antigen primed CD4+ T cells, and suppress the response of fresh T cells to the priming antigen but not irrelevant antigens. The stimulus and target of suppression in this system appears to be the antigen receptor on the surface of CD4+ cells, rather than the nominal antigen. In the current study, alloantigen primed CD4+ inducer cells and IL-2-containing medium were used to generate clones of suppressor cells from several individuals. The clones inhibited the response of fresh autologous T cells only to the original allogeneic stimulator cell and to stimulator cells that shared HLA-DR antigens with the priming cell. The clones were also genetically restricted, since they inhibited the response of HLA-A,B-compatible but not HLA-A,B-incompatible individuals. The availability of a method for reproducibly generating antigen receptor-specific suppressor T cell clones in vitro should make it possible to clarify the mechanism, whereby such cells are activated and exert their suppressive effect.     

Regulatory mechanisms in cell-mediated immune responses. Role of I-J and I-C determinants in the activation of H-2I and H-2K/D alloantigen-specific suppressor T cells

The role of individual H-2I subregion determinants in the activation of H-2I alloantigen-primed mixed leukocyte response suppressor T cells (MLR Ts), as well as their possible expression on stimulator cells required to trigger primed H-2K- or D-specific MLR Ts, was addressed in these studies. Both genetic and serologic studies demonstrated that MLR Ts potentially primed to alloantigens encoded by the entire H-2I region were triggered to MLR Ts factor production only by stimulator cells bearing the priming I-J and/or I-C, but not I-A or I-E alloantigens. The relevant I-J and I-C determinants were demonstrated on a single antigen-presenting cell population that is used in common by independent I-J-specific and I-C-specific MLR Ts. Unexpectedly, the stimulator cell population necessary to trigger MLR Ts primed to class I H-2K or D alloantigens expressed not only the priming class I determinant, but in addition, I-C alloantigens syngeneic with the MLR Ts haplotype. Stimulator populations bearing the appropriate H-2K or D alloantigen but serologically depleted of I-C+ cells or genetically constructed to display MLR Ts-disparate I-C determinants were ineffective stimulators of class I antigen-primed MLR Ts. Thus these data suggest that as allogeneic determinants, I-J- and I-C-encoded molecules are together the major triggering elements for MLR Ts primed to disparate H-2I region determinants. In addition, self-I-C molecule recognition appears to constitute an important feature of the triggering, and by implication, priming process of H-2 class I antigen-specific Ts cells.     

Suppressor T cell growth and differentiation. Identification of a cofactor required for suppressor T cell function and distinct from interleukin 2

This report describes a Ts costimulator assay and its use to analyze cofactors required for the expression of suppressor T cell function. Activation of primed MLR-Ts (alloantigen-activated suppressor T cells suppressive of mixed leukocyte reaction) to suppressor T cell factor (TsF) production typically fails in the presence of glutaraldehyde- fixed rather than irradiated allogeneic stimulator cells. However, MLR- TsF production was restored by the addition of 48-h primary MLR supernates; MLR-derived Ts costimulator neither activated primed MLR-Ts in the absence of fixed allogeneic stimulators nor directly suppressed assay MLR. Lack of antigen specificity or genetic restriction and failure to activate unprimed MLR-Ts precursors suggested that Ts costimulator activity differed from previously described Ts inducer functions and was more closely aligned with the lymphocyte- or monocyte- derived interleukins (IL). Three findings distinguished Ts costimulator from IL-2. Depletion of IL-2 activity from MLR supernates by HT2 adsorption failed to affect Ts costimulator function. In addition, MLR supernates prepared in the presence of cyclosporin A contained no IL-2 but expressed Ts costimulator activity. Finally, gel chromatography demonstrated Ts costimulator in peaks of 21,000 and 43,000 mol wt that were largely distinct from the IL-2-containing fractions. Ts costimulator activity was also identified in phorbol myristate acetate (PMA)-induced EL4 supernates and was retained in those supernates after IL-2 depletion by HT2 adsorption. In preliminary functional characterization, MLR supernate-derived Ts costimulator triggered MLR- TsF production from irradiated MLR-Ts in the absence of proliferation. Thus a differentiative rather than proliferative stimulus required for primed MLR-Ts function appears to be provided by this Ts costimulator and has been provisionally termed Ts differentiative factor ( TsDF ). This initial characterization may thus identify one of a possibly distinctive family of interleukins required in the alloantigen-driven activation of suppressor T cells to effector function.