A cell culture model for T lymphocyte clonal anergy

Mechanism of self-tolerance of gamma/delta T cells in epithelial tissue

The present study examined mechanisms of tolerance for T cell receptor gamma/delta (TCR-gamma/delta) cells. Using a transgenic (Tg) model, we demonstrate that although alloantigen (Ag)-specific TCR-gamma/delta cells are deleted in the thymus and spleen of Ag-bearing mice, intraepithelial lymphocytes (IELs) expressing normal levels of the Tg TCR were present. However, Tg+ IELs from Ag-bearing mice were unresponsive to activation. Furthermore, self-reactive Tg+ IELs decreased in number over time. Thus, in epithelial tissue, Tg TCR-gamma/delta cells are eliminated subsequent to and most likely as a result of the induction of clonal anergy.

Antigen-specific therapy of experimental allergic encephalomyelitis by soluble class II major histocompatibility complex-peptide complexes

Experimental allergic encephalomyelitis is a T-cell-mediated, major histocompatibility complex (MHC) class II gene-linked autoimmune demyelinating disease of the central nervous system. To develop therapies that will specifically inactivate only the autoantigen-reactive T cells, mice were treated with soluble MHC class II molecules that had been complexed with encephalitogenic peptides. Intravenous injections of 300 micrograms of complexes consisting of encephalitogenic peptide 91-103 of myelin basic protein plus I-As protein on day 0, 4, and 7 were effective in preventing experimental allergic encephalomyelitis. Similarly, administration of 45 micrograms of I-As protein complexed to peptide 139-151 from proteolipoprotein on day 1, 4, and 7 prevented mortality and significantly reduced paralysis induced by immunization with the encephalitogenic proteolipoprotein peptide. Histological examination of sections of animal brains revealed that treatment with I-As protein plus myelin basic protein 91-103 peptide prevents the development of inflammatory lesions characteristic of experimental allergic encephalomyelitis. Thus, treatment with MHC-self-peptide complexes could serve as a highly specific therapeutic modality in treating autoimmune disease when the putative autoantigen and the MHC restricting elements are known.

The majority of cells infected with the defective murine AIDS virus belong to the B-cell lineage

Murine AIDS (MAIDS) is caused by a defective retrovirus which encodes a gag fusion protein (Pr60gag). We previously reported that this virus induced an oligoclonal proliferation of infected cells and suggested that this cell expansion was an important event in the pathogenesis of MAIDS. To identify these target cells, we constructed novel defective viruses whose genomes could be detected with specific probes. Helper-free stocks of these viruses induced MAIDS. Using in situ hybridization and immunocytochemistry and Southern analysis, we found that most infected cells belong to the B-cell lineage. Transformation of these B cells appears to be the primary event responsible for the development of immunodeficiency. This animal model may be relevant to our understanding of AIDS, of the immunodeficiencies associated with B-cell lymphoproliferative disorders, and of the role of B-cell proliferation and transformation in the effects of superantigens, since Pr60gag appears to be a superantigen.

Cytokines and autoimmune disease

A wide array of cytokines are locally present in autoimmune lesions where they are produced by inflammatory cells or by the target cell of the autoimmune attack. The presence of cytokines at the site of autoaggression reflects ongoing inflammatory and activation processes. These mediators exert proinflammatory effects, contribute to the activation and stimulation of the effector function of T or B lymphocytes, directly participate in target cell destruction, and mediate accompanying local reactions, including fibrotic processes. The release of cytokines into the circulation may explain certain systemic reactions, including fever or changes in the profile of plasma proteins. Many, especially systemic, autoimmune diseases are accompanied by a dysregulation of lymphokine secretion at the level of circulating leukocytes or cells situated outside of the local inflammatory event, thus reflecting regulatory disorders that may either have a genetic or an acquired basis. Decreased production of lymphokines in vitro in response to nonspecific stimuli may be accompanied by an elevated spontaneous release in vivo resulting in an increase of circulating cytokine levels (interleukin 2, tumor necrosis factor-alpha). Secretion of interleukin 1, interleukin 2, and tumor necrosis factors-alpha or -beta, in part, is determined by genetic factors and it is possible that a particular secretor phenotype may predispose to the development of autoimmune lesions. Probably due to their pleiotropic nature, systemic administration of cytokines such as interleukin 1, interleukin 2, tumor necrosis factor, and interferon-gamma may exert either accelerating or suppressive effects on autoimmune diseases. Conversely, agents that block the function of the lymphokine interleukin 2 exert an unequivocal autoimmune disease-inhibiting effect.

Control of self-reactivity in the intestine

In the intestine maintenance of self-tolerance may involve tissue-specific self-Ags, APCs, 'second signals', and extrathymic pathways of T cell maturation. These factors combine to create a unique environment where autoimmune tissue destruction is prevented despite local inflammatory influences. In this review we summarize our findings using a TCR-gamma delta transgenic model where self-tolerance was maintained by clonal deletion for cells localizing to peripheral lymphoid tissue and by clonal anergy for cells localizing to the intraepithelial compartments. Several possible explanations exist for these results but in general, these findings have implications for the maintenance of self-tolerance of normal TCR-alpha beta and TCR-gamma delta IELs in epithelial tissues such as the intestine.

Autoantigen-induced self lysis of human myelin basic protein-specific T lymphocytes

Cytotoxic T cells reactive with myelin basic protein (MBP) may be isolated from most human subjects. Since activated T cells express major histocompatibility complex (MHC) class II antigens, we assessed whether MBP-specific, CD4+ T cells could present MBP or synthetic MBP peptides to themselves and whether this provoked self lysis. We examined two MBP-specific cell lines and eight T cell clones recognizing four different MBP epitopes. All T cell populations presented MBP as well as synthetic peptides to themselves eliciting self lysis of the T cell clones. CD4+ T cell populations recognizing another central nervous system (CNS) protein, proteolipid protein (PLP), or the recall antigen, Candida, did not exhibit this antigen-induced, autocytolytic activity. However, activated, PLP-reactive T cells were susceptible to lysis by cytotoxic MBP-specific T cells in the presence of MBP. These results suggest that antigen-induced self lysis of activated human T cells might limit an autoimmune response within a target organ independent of other immunoregulatory mechanisms.

The fail-safe paradigm of immunological self-tolerance

Immunological self-tolerance is guaranteed by several complementary mechanisms arranged in a fail-safe hierarchy--namely, clonal deletion, inactivation, and suppression. Only failure of all these self-tolerance-preserving systems allows autoimmune disease to develop. The notion of such a fail-safe organisation of the immune system is compatible with several features of autoimmune disease: its multicausal nature, its slowly progressive and relapsing course, and the diverse range of interventions available to restore autotolerance. This hypothesis has practical implications for the understanding of both the pathogenesis of iatrogenic autoimmune disease and the design of strategies to re-establish self-tolerance.

Nonresponsiveness to an immunodominant Epstein-Barr virus-encoded cytotoxic T-lymphocyte epitope in nuclear antigen 3A: implications for vaccine strategies

An immunodominant Epstein-Barr virus (EBV)-encoded cytotoxic T lymphocyte (CTL) epitope has been mapped to the EBV nuclear antigen 3A. The epitope, represented by the peptide sequence AWNAGFLRGRAYGLD (hereafter termed AWNA), is restricted through the HLA-B8 allele and is expressed by type A but not type B-infected transformants. Herein, we show that EBV-specific memory CTLs from an HLA-B8+ healthy virus carrier, JS, did not respond in vitro to AWNA, even though that individual's endogenously infected transformants processed and presented the natural equivalent of this peptide to AWNA-specific CTLs from another B8+ individual. Instead, an epitope, represented by the peptide sequence QLSDTPLIPLTIFVGENTGV, was the dominant EBV-specific CTL epitope in donor JS. This epitope mapped to EBV nuclear antigen 2A, was restricted by an HLA-A2 subtype, and specifically associated with type A strains of EBV. No AWNA-specific CTL precursors were detected by limiting dilution analysis of peripheral blood mononuclear cells from donor JS whereas the precursor frequency of AWNA-specific CTLs from a responder donor, LC, was estimated at 1:4500. The presentation in vivo of an immunogenic epitope-HLA antigen complex is clearly insufficient to guarantee an effective memory CTL response to that foreign epitope. Thus, vaccination strategies based on peptides inducing CTL responses may need to take into account not only the polymorphism of HLA antigens but also possible allelic variation in the repertoires of T-cell receptors.

A single amino acid change in a myelin basic protein peptide confers the capacity to prevent rather than induce experimental autoimmune encephalomyelitis

Experimental autoimmune encephalomyelitis (EAE) is an experimental demyelinating disease of rodents. In (PL/J x SJL) F1 mice, it is induced by immunization with the myelin basic protein peptide Ac1-11. Ac1-11 [4A], a myelin basic protein peptide analog with a single amino acid substitution, (i) binds to class II major histocompatibility complex molecules and stimulates encephalitogenic T cells in vitro better than Ac1-11, (ii) is nonimmunogenic and nonencephalitogenic in vivo in (PL/J x SJL)F1 mice, (iii) prevents EAE when administered before or at the time of immunization with Ac1-11, and (iv) prevents EAE when administered later, near the time of disease onset. Initial studies suggest that Ac1-11 [4A] does not prevent EAE by competitive inhibition or by activation of regulatory cells. Thus, substitution of a single amino acid in a myelin basic protein peptide confers the capacity to prevent rather than induce EAE, even after peptide-specific encephalitogenic T cells have been activated.

The thymus leukemia antigen binds human and mouse CD8

The thymus leukemia antigen (TLA) is a class Ib, or 'nonclassical' class I molecule, one of several encoded within the Tla locus of the mouse major histocompatibility complex (MHC). It structurally resembles the H-2K, D, and L class I transplantation antigens, which present processed peptides to cytotoxic T lymphocytes (CTLs). Although their function(s) are unknown, there has been recent speculation concerning the possibility that class Ib molecules may present antigens to T cells that express gamma delta T cell antigen receptors (TCRs). In this report, using both a cell-cell adhesion assay and adhesion of T lymphocyte clones to purified plate-bound TLA, we provide evidence that TLA can bind to both human and mouse CD8. We also show that a chimeric class I molecule containing the peptide antigen binding site of Ld and the alpha 3 domain, transmembrane, and cytoplasmic segments of TLA, can support a CD8-dependent immune response by CTLs. These results demonstrate for the first time binding of a class Ib molecule to CD8 with a functional outcome, as is observed for the class I transplantation antigens. The capacity to interact with CD8 has been conserved despite the extensive sequence divergence of TLA in the peptide antigen binding site, suggesting this interaction is highly significant. TLA is expressed by epithelial cells in the mouse small intestine. As these epithelial cells are in close contact with intestinal intraepithelial lymphocytes that are nearly all CD8+, and many of which express the gamma delta TCR, the data are consistent with the hypothesis that TLA is involved in antigen presentation, perhaps to gamma delta-positive lymphocytes in this site.

Pretransplantation blood transfusion revisited

BACKGROUND

Blood transfusion before organ transplantation has a beneficial effect on allograft survival; the mechanism of this effect has remained a mystery. In murine models, the presence of common histocompatibility antigens in the blood donor and the recipient favors the induction of allograft tolerance.

METHODS

To investigate the effect of HLA compatibility between blood donor and recipient on the induction of allograft tolerance, we determined the relative frequency of cytotoxic T-lymphocyte precursors specific for donor cells before and at several times after blood transfusion in 23 patients awaiting a first renal transplant. We correlated the results with the presence of shared HLA antigens.

RESULTS

T-cell nonresponsiveness against donor cells developed after blood transfusion in 10 of the 23 patients. Tolerance developed only if the blood donor and the recipient had one HLA haplotype or at least one HLA-B and one HLA-DR antigen in common (as was observed in 9 of these 10 patients). Tolerance developed relatively late after blood transfusion (one to two months) and was long-lasting. No decline in the T-cell response against donor alloantigens was observed in any of the 13 patients who received transfusions without having HLA-antigen compatibility with the donor.

CONCLUSIONS

Blood transfusion in which there is a common HLA haplotype or shared HLA-B and HLA-DR antigens induces tolerance to donor antigens. This finding may lead to the development of new strategies with which to induce tolerance for transplantation after blood transfusion. Perhaps transplant donors will be selected not only by HLA-antigen matching, but also on the basis of acceptable HLA-antigen mismatches associated with T-cell non-responsiveness induced by selected blood transfusion.

Monoclonal antibody-targeted superantigens: a different class of anti-tumor agents

The bacterial superantigen staphylococcal enterotoxin (SE) A (SEA) directs cytotoxic T lymphocytes (CTLs) expressing particular sequences of the T-cell receptor (TCR) beta chain to lyse tumor cells expressing major histocompatibility complex (MHC) class II molecules, which serve as receptors for SEs. We now report that chemical conjugates of SEA and the colon carcinoma-reactive monoclonal antibodies (mAbs) C215 or C242 mediate T cell-dependent destruction of colon carcinoma cells lacking MHC class II molecules. SEA was covalently linked to the mAbs C215 and C242 via a PEG-based hydrophilic spacer. The C215-SEA conjugate targeted CD4+ as well as CD8+ CTLs to lyse a panel of colon carcinoma cells lacking MHC class II molecules. T-cell recognition of mAb-SEA conjugates was SEA specific, since SEB-selective T-cell lines with potent cytotoxic activity towards Raji cells coated with SEB did not respond to the C215-SEA conjugate. Unconjugated SEA did not induce T-cell lysis of MHC class II- colon carcinoma cells but efficiently directed CTLs against MHC class II+ Raji cells and certain interferon-treated MHC class II+ colon carcinoma cells. These results suggest that SEA-mAb conjugates retain the SEA-related selectivity for certain TCR beta-chain variable region (V beta) sequences but, in contrast to unconjugated SEA, mediate the TCR interaction in a MHC class II-independent manner. The cytotoxic activity mediated by C215-SEA and C242-SEA conjugates was blocked by excess of C215 mAb and C242 mAb, respectively, showing that the specificity in the targeting of mAb-SEA conjugates is defined by the antigen reactivity of the mAb. These results demonstrate that bacterial superantigens may be successfully conjugated to mAb with preserved T cell-activating capacity. The circumvention of MHC class II binding of SEs by conjugation to mAb suggests that such conjugates may find general application as antitumor agents, taking advantage of the extreme T cell-activating potency of superantigens.

Staphylococcus aureus enterotoxin mediated specific non-responsiveness of human T cells

Exotoxins produced by certain strains of Staphylococcus aureus are able to both stimulate and induce non-responsiveness in T cells expressing specific T cell antigen receptor V beta gene elements. The exposure of human CD4+ T cells to the appropriate enterotoxin rendered them anergic to restimulation with their natural ligand, although responsiveness to exogenous IL-2 remained intact. The loss of antigen-dependent proliferation was associated with the down-regulation of the TCR complex that was paralleled by enhanced cell surface CD2 and CD25. Further analysis of the phenotypic changes revealed that membrane levels of CD28 were increased only on activation, suggesting a differential expression of this protein on activated and anergic T cells. During the induction of anergy it was observed that the synthesis of the lymphokines IL-2, IL-4 and IFN-gamma was differentially regulated. IL-4 and IFN-gamma, but not IL-2 were detected in the supernatants of overnight cultures of T cells exposed to tolerising concentrations of toxin. Transcription of IL-4, as determined by polymerase chain reaction at selected intervals, was elevated during the induction of anergy and accounted for the presence of the protein in the supernatants. In contrast, no tight coupling was observed between protein and mRNA levels for IL-2, suggesting post-translational regulation.

Analysis of T cell stimulation by superantigen plus major histocompatibility complex class II molecules or by CD3 monoclonal antibody: costimulation by purified adhesion ligands VCAM-1, ICAM-1, but not ELAM-1

Many ligands of adhesion molecules mediate costimulation of T cell activation. The generality of this emerging concept is best determined by using model systems which exploit physiologically relevant ligands. We developed such an "antigen-specific" model system for stimulation of resting CD4+ human T cells using the following purified ligands: (a) major histocompatibility complex class II plus the superantigen Staphylococcus enterotoxin A, to engage the T cell receptor (TCR); (b) adhesion proteins vascular cell adhesion molecule 1 (VCAM-1), intercellular adhesion molecule 1 (ICAM-1), and endothelial leukocyte adhesion molecule 1 (ELAM-1), to provide potential cell surface costimulatory signals; and (c) recombinant interleukin 1 beta (rIL-1 beta)/rIL-6 as costimulatory cytokines. In this biochemically defined system, we find that resting CD4+ T cells require costimulation in order to respond to TCR engagement. This costimulation can be provided by VCAM-1 or ICAM-1; however adhesion alone is not sufficient since ELAM-1 mediates adhesion but not costimulation. The cytokines IL-1 beta and IL-6 by themselves cannot mediate costimulation, but augment the adhesion ligand-mediated costimulation. Direct comparison with the model of TCR/CD3 engagement by CD3 monoclonal antibody demonstrated comparable costimulatory requirements in both systems, thereby authenticating the commonly used CD3 model. The costimulation mediated by the activation-dependent interaction of the VLA-4 and LFA-1 integrins with their respective ligands VCAM-1 and ICAM-1 leads to increased IL-2R alpha (CD25) expression and proliferation in both CD45RA+ CD4+ and CD45RO+ CD4+ T cells. The integrins also regulate the secretion of IL-2, IL-4, and granulocyte/macrophage colony-stimulating factor. In contrast the activation-independent adhesion of CD4+ T cell to ELAM-1 molecules does not lead to T cell stimulation as measured by proliferation, IL-2R alpha expression, or cytokine release. These findings imply that adhesion per se is not sufficient for costimulation, but rather that the costimulation conferred by the VLA-4/VCAM-1 and LFA-1/ICAM-1 interactions reflects specialized accessory functions of these integrin pathways. The new finding that VLA-4/VCAM-1 mediates costimulation adds significance to observations that VCAM-1 is expressed on a unique set of potential antigen-presenting cells in vivo.

Structure, expression, and T cell costimulatory activity of the murine homologue of the human B lymphocyte activation antigen B7

Following occupancy of the T cell receptor by antigen, T cell proliferation and lymphokine production are determined by a second costimulatory signal delivered by a ligand expressed on antigen presenting cells. The human B cell activation antigen B7, which is expressed on antigen presenting cells including activated B cells and gamma interferon treated monocytes, has been shown to deliver such a costimulatory signal upon attachment to its ligand on T cells, CD28. We have cloned and sequenced the murine homologue of the human B7 gene. The predicted murine protein has 44% amino acid identity with human B7. The greatest similarity is in the Ig-V and Ig-C like domains. Murine B7 mRNA was detected in murine hematopoietic cells of B cell but not T cell origin. Cells transfected with murine B7 provided a costimulatory signal to human CD28+ T lymphocytes. These results demonstrate the costimulatory activity of murine B7 and provide evidence that the ligand attachment site is conserved between the two species.

CTLA-4 is a second receptor for the B cell activation antigen B7

Functional interactions between T and B lymphocytes are necessary for optimal activation of an immune response. Recently, the T lymphocyte receptor CD28 was shown to bind the B7 counter-receptor on activated B lymphocytes, and subsequently to costimulate interleukin 2 production and T cell proliferation. CTLA-4 is a predicted membrane receptor from cytotoxic T cells that is homologous to CD28 and whose gene maps to the same chromosomal band as the gene for CD28. It is not known, however, if CD28 and CTLA-4 also share functional properties. To investigate functional properties of CTLA-4, we have produced a soluble genetic fusion between the extracellular domain of CTLA-4 and an immunoglobulin C gamma chain. Here, we show that the fusion protein encoded by this construct, CTLA4Ig, bound specifically to B7-transfected Chinese hamster ovary cells and to lymphoblastoid cells. CTLA4Ig also immunoprecipitated B7 from cell surface 125I-labeled extracts of these cells. The avidity of 125I-labeled B7Ig fusion protein for immobilized CTLA4Ig was estimated (Kd approximately 12 nM). Finally, we show that CTLA4Ig was a potent inhibitor of in vitro immune responses dependent upon cellular interactions between T and B lymphocytes. These findings provide direct evidence that, like its structural homologue CD28, CTLA-4 is able to bind the B7 counter-receptor on activated B cells. Lymphocyte interactions involving the B7 counter-receptor are functionally important for alloantigen responses in vitro.

Breakdown of self-tolerance in anergic B lymphocytes

Production of autoantibodies, which characterizes most autoimmune diseases, is normally avoided by active elimination or functional inactivation (anergy) of B and T lymphocytes bearing receptors for self antigens. The mechanisms leading to the escape of self-reactive clones from these normal tolerance mechanisms in autoimmune diseases nevertheless remain obscure. Here, we demonstrate that clonal anergy in B lymphocytes is a reversible process, and that silenced self-reactive B cells can be reactivated under particular conditions to give rise to vigorous antibody responses. Reactivation of anergic lymphocytes may explain many examples of transient autoimmune reactions in normal individuals, and may under pathological conditions be important in the development of chronic autoimmune disease.

B-cell surface antigen B7 provides a costimulatory signal that induces T cells to proliferate and secrete interleukin 2

Occupancy of the T-cell receptor complex does not appear to be a sufficient stimulus to induce a T-cell-mediated immune response. Increasing evidence suggests that cognate cell-cell interaction between an activated T cell and an antigen-presenting cell may provide such a stimulus. A candidate T-cell surface molecule for this costimulatory signal is the T-cell-restricted CD28 antigen. Following crosslinking with anti-CD28 mAb, suboptimally stimulated CD28+ T cells show increased proliferation and markedly increased secretion of a subset of lymphokines. Recently, the B-cell surface activation antigen B7 was shown to be a natural ligand for the CD28 molecule, and both B7 and CD28 are members of the immunoglobulin superfamily. Here we report that B7-transfected CHO cells can induce suboptimally activated CD28+ T cells to proliferate and secrete high levels of interleukin 2. The response is identical whether T cells are submitogenically stimulated with either phorbol myristate acetate or anti-CD3 to activate the T cells. This response is specific and can be totally abrogated with anti-B7 monoclonal antibody. As has previously been observed for anti-CD28 monoclonal antibody, B7 ligation induced secretion of interleukin 2 but not interleukin 4. We have previously demonstrated that B7 expression is restricted to activated B lymphocytes and interferon gamma-activated monocytes. Since these two cellular populations are involved in antigen presentation as well as cognate interaction with T lymphocytes, B7 is likely to represent a central constimulatory signal that is capable of amplifying an immune response.

T-cell tolerance to viruses

T-cell tolerance to self antigens is maintained by events that occur within the thymus and in the periphery. Mechanisms that operate on immature T cells within the thymus are effective in induction of tolerance to viruses, but mechanisms of tolerizing mature T cells are likely to break down. This failure of peripheral mechanisms to induce T-cell tolerance to viruses has implications for autoimmunity and for treatment of chronic viral infections.

Components of an antigen-/T cell receptor-independent pathway of lymphokine production

The general way to induce the synthesis of lymphokines by T cells is the stimulation through the T cell receptor (TcR) complex which results in an increase of intracellular [Ca2+] and in the activation of a tyrosine kinase as well as of protein kinase C. Lymphokine production induced via the TcR is inhibited by the immunosuppressive drug cyclosporin A (CsA). However, an alternative pathway of lymphokine production exists. Several T lymphocyte clones can synthesize interferon-gamma (IFN-gamma), granulocyte-monocyte colony-stimulating factor, and small amounts of interleukin (IL3) when stimulated with syngeneic or allogeneic accessory cells (AC) plus IL2. In contrast to the TcR pathway the alternative pathway does not require a rise of intracellular [Ca2+] and is insensitive to the effects of CsA. In this report we provide evidence for the involvement of T cell-stimulating factor (TSF)--a probably novel murine cytokine--in the alternative pathway of lymphokine production. It is shown that fixation of the AC with carbodiimide or treatment of the AC with UV light greatly reduces their capacity to induce (in combination with IL2) the synthesis of IFN-gamma by T cells. This function is restored by addition of TSF. Moreover, TSF alone (without IL2) in combination with fixed AC can induce the synthesis of substantial amounts of IFN-gamma. Furthermore, TSF in combination with IL2 can stimulate freshly isolated spleen cells to produce IFN-gamma. The target cell resides probably in the non-B cell, non-T cell population.

Interferon-beta specifically inhibits interferon-gamma-induced class II major histocompatibility complex gene transcription in a human astrocytoma cell line

We established cultures of human astrocytes and astrocytoma cells from surgical specimens, to study regulation of class II major histocompatibility (MHC) complex antigen expression by interferons. Using these cultures we previously showed that expression of the class II MHC determinant HLA-DR could be induced by interferon-gamma and this induction was inhibited by interferon-beta. In this report, we extend these observations by showing that the inhibitory effect of interferon-beta on interferon-gamma induction of the class II MHC gene HLA-DR alpha was exerted at the transcriptional level, as documented by nuclear run-on experiments and confirmed with blot hybridization analysis. Astrocyte expression of intercellular adhesion molecule-1 (ICAM-1) was induced efficiently by interferon-gamma, but not by interferon-beta, and induction of ICAM-1 expression by interferon-gamma could not be impaired by interferon-beta, suggesting that the suppressive effect on induction of HLA-DR was relatively gene-specific. Furthermore, interferon-beta did not antagonize interferon-gamma induction of HLA-DR expression in human monocytes, suggesting that the inhibition observed in astrocytes was relatively tissue-specific.

Altered antigen receptor signaling in anergic T cells from self-tolerant T-cell receptor beta-chain transgenic mice

T-cell tolerance to the minor lymphocyte-stimulating antigen Mls-1a in a T-cell receptor (TcR) V beta 8.1 transgenic line of mice is maintained by both clonal deletion and clonal anergy. Approximately 20-50% of peripheral CD4+ (but not CD8+) T cells isolated from these mice are anergic and fail to proliferate following TcR ligation. We have examined key events in T-cell signaling in peripheral T cells isolated from these mice. In this report, we show that the anergic CD4+ T cells did not mobilize calcium or express receptors for interleukin 2 (IL-2) following TcR ligation. However, the cells retained viability and functional potential because stimulation with phorbol 12-myristate 13-acetate and ionomycin bypassed the block in receptor-mediated signaling and induced IL-2 receptor expression and proliferation of the anergic cells.

A transgenic approach to the study of peripheral T-cell tolerance

There is now convincing evidence for the imposition of self tolerance by means of the clonal deletion of self-reactive T cells operating within the thymus. Since not all self components may be encountered there, the question must be asked whether tolerance can occur post-thymically. To test this, we and other investigators have used transgenic technology to direct expression of a known "nonself" gene to a given extrathymic tissue. No lymphocytic infiltration was ever seen in transgene-expressing tissues, even if the mice were given normal syngeneic (nontransgenic) spleen cells intravenously or were stimulated with H-2Kb spleen cells. Infiltration did, however, occur in irradiated transgenic recipients of H-2Kb immune spleen cells. In MET-Kb mice, this infiltrate diminished with time, raising the possibility that peripheral tolerance may even have been induced in immune cells. H-2Kb-bearing skin was accepted in young RIP-Kb mice but rejected in older mice, which had lost more than 75% of their beta cells as a result of the overexpression of H-2Kb. This loss of tolerance thus occurred when the concentration of the tolerogen, H-2Kb, fell below some critical threshold. Following in vitro stimulation, spleen cells from young RIP-Kb mice could not kill H-2Kb-bearing targets, but could respond to third party targets. Thymus cells, on the other hand, could be stimulated to kill both targets, clearly indicating that tolerance was not imposed intrathymically. Spleen cells from older RIP-Kb mice (those that had lost most of their beta cells) killed both targets, which is in agreement with the in vivo data. Reactivity to H-2Kb was restored to young spleen cells by providing them with IL-2. Two hypotheses were proposed to account for the above findings: tolerance results either from the deletion or functional silencing of high-affinity effector cells or of regulatory, IL-2-producing helper T cells. As it is difficult to distinguish between these, we have produced a second series of transgenic mice (F3+) with rearranged TCR genes encoding an anti-H-2Kb TCR and derived "double-transgenic" (F3+RIP+) offspring by mating these mice with RIP-Kb mice. The transgenic TCR utilized the V beta 11 segment which can be detected by a monoclonal antibody. There were in the thymus very few CD4+ and very few CD4+8+ cells in both F3+ and F3+RIP+ mice and, in the double-transgenic mice, there was no evidence of deletion of CD8+V beta 11+ cells in the periphery although they showed tolerance to H-2Kb-bearing skin.(ABSTRACT TRUNCATED AT 400 WORDS)

Non-deletional mechanisms of peripheral and central tolerance: studies with transgenic mice with tissue-specific expression of a foreign MHC class I antigen

The studies described here reveal a surprising variety of non-deletional manifestations of tolerance (anergy and unresponsiveness) in both the thymus and peripheral lymphoid organs. This can be observed in anti-Kb TCR transgenic mice crossed with normal Kb positive mice, and in TCR mice crossed with transgenic mice expressing Kb in restricted tissues, such as liver, epithelial cells, cells of neuroectodermal origin etc. Thymic induction of unresponsiveness: Transgenic mice were prepared with the a, beta TCR genes from a CD8-dependent and Kb-specific CTL clone. In homozygous H-2b mice clonotype+ cells were found in the thymus but none or few in the periphery, suggesting that deletion occurs in the thymus although lack of migration to the periphery has not been ruled out. In H-2 heterozygous mice (TCR.H-2kxb) deletion was incomplete in the thymus and clonotype+ cells accumulated substantially in the periphery. Most of them had downregulated their CD8 molecules. The clonotype+ cells in both the thymus and periphery were unresponsive to the Kb antigen in vitro, suggesting the induction of anergy in the thymus. The inefficient negative selection in H-hkxb heterozygous mice is probably due to the lower Kb expression in comparison to H-2b homozygous mice. We then further reduced the amount of Kb expression in the thymus by constructing Kb transgenic mice using the 0.8 Kb fragment of the keratin IV promoter. In the thymus expression was only observed on a subset of medullary epithelial cells. When these mice were crossed with the TCR transgenic mice than no deletion was observed in the thymus. However, the clonotype+ CD8+ thymocytes could not respond to Kb in vitro, indicating that they had been rendered anergic in the thymus. These data show that unresponsiveness can be induced in the thymus, that the extent of clonal deletion can vary greatly owing to a change in antigen expression by a factor of two as in H-2 heterozygous versus homozygous mice, and that expression of Kb on a few medullary thymic epithelial cells is sufficient to induce anergy. Peripheral induction of unresponsiveness: To study the consequence of tissue-specific tolerogen expression we have generated transgenic mice expressing Kb exclusively in cells of neuroectodermal origin (GFAP.Kb mice) in the liver (alumin.Kb mice), or in certain epithelial cells outside the thymus (2.4 keratin IV.Kb mice). Consistent with the absence of Kb expression in the thymus there was no deletion of clonotype+ CD8+ cells in the thymus, and the thymocytes were fully functional.(ABSTRACT TRUNCATED AT 400 WORDS)

Differential regulation of lymphokine production in mitogen-stimulated murine spleen cells

Activation of murine spleen cells in vitro with soluble anti-CD3 monoclonal antibody and phorbol 12-myristate 13-acetate (PMA) induced an initial production of interleukin 2 (IL2), interferon-gamma (IFN-gamma), IL4 and IL5, followed by a refractory state during which the T cells did not produce lymphokines when stimulated with some common mitogens. The refractory state was long-lasting, depended on the presence of anti-CD3 and PMA but could be reverted by incubation in fresh medium. Pokeweed mitogen (PWM) differed from other mitogens tested, since stimulation by PWM and PMA induced lymphokine production and proliferation also in the refractory cells. Furthermore, PWM stimulation selectively induced IL4 and IFN-gamma production but not IL2 and IL5, as detected by intracellular cytokine-specific immunofluorescence and in situ hybridization for mRNA. The results indicate differential regulation of lymphokine production in primary lymphocytes.

Remote T cell co-stimulation via LFA-1/ICAM-1 and CD2/LFA-3: demonstration with immobilized ligand/mAb and implication in monocyte-mediated co-stimulation

Proliferative response of resting T cells generally requires not only cross-linking of the T cell receptor (TcR) but also co-stimulatory signals from accessory molecules. We here have used a "three-cell" model consisting of: (a) resting human CD4+ T cells as responders; (b) CD3 monoclonal antibody (mAb) OKT3 on latex beads as surrogate stimulators; (c) autologous monocytes as source of co-stimulation. As described by Kawakami et al. (J. Immunol. 1989, 142: 1818), T cell proliferation in this system is observed with paraformaldehyde-fixed monocytes if they have been activated and interleukin (IL) 1 beta/IL 6 is supplied. Since this three-cell system provides TcR cross-linking at a site spatially "remote" from co-stimulation, they help distinguish adhesion from signal transduction but the molecules that mediate co-stimulation in this system have not been identified. Our studies now demonstrate that co-stimulation by the monocytes is dependent on each of two receptor/ligand pathways CD2/LFA-3 and LFA-1/ICAM-1 since it is inhibited by each relevant mAb but not a variety of control mAb. The hypotheses that CD2 and LFA-1 could each mediate co-stimulation was tested in simplified model systems in which the monocyte was replaced with immobilized CD2 mAb or purified ICAM-1 presented on a separate surface from the CD3 mAb. The results in these simplified models demonstrate that on resting T cells either CD2 or LFA-1 molecules alone can mediate "remote" co-stimulation unlike most other T cell surface molecules. Co-stimulation requires IL 1 beta/IL6 both in the weaker LFA-1 ligand-mediated co-stimulation and at lower CD2 mAb concentrations in the stronger CD2 mAb-mediated co-stimulation. Thus: (a) the accessory cell function of stimulated fixed monocytes in T cell proliferation requires both the LFA-1/ICAM-1 and CD2/LFA-3 pathways; and (b) the T cell molecules CD2 and LFA-1 can give co-stimulatory signals that can act in a "remote" fashion.

Identification of two T-cell epitopes on the candidate Epstein-Barr virus vaccine glycoprotein gp340 recognized by CD4+ T-cell clones

Current efforts to develop an Epstein-Barr virus subunit vaccine are based on the major envelope glycoprotein gp340. Given the central role of CD4+ T cells in regulating immune responses to subunit vaccine antigens, the present study has begun the work of identifying linear epitopes which are recognized by human CD4+ T cells within the 907-amino-acid sequence of gp340. A panel of gp340-specific CD4+ T-cell clones from an Epstein-Barr virus-immune donor were first assayed for their proliferative responses to a series of truncated gp340 molecules expressed from recombinant DNA vectors in rat GH3 cells, by using an autologous B lymphoblastoid cell line as a source of antigen-presenting cells. The first four T-cell clones analyzed all responded to a truncated form of gp340 which contained only the first 260 N-terminal amino acids. These clones were subsequently screened for responses to each of a panel of overlapping synthetic peptides (15-mers) corresponding to the primary amino acid sequence of the first 260 N-terminal amino acids of gp340. One clone (CG2.7) responded specifically to peptides from the region spanning amino acids 61 to 81, while three other clones (CG5.15, CG5.24, and CG5.36) responded specifically to peptides from the region spanning amino acids 163 to 183. Work with individual peptides from these regions allowed finer mapping of the T-cell epitopes and also revealed the highly dose-dependent nature of peptide-induced responses, with inhibitory effects apparent when the most antigenic peptides were present at supraoptimal concentrations. Experiments using homozygous typing B lymphoblastoid cell lines as antigen-presenting cells showed that the T-cell clones with different epitope specificities were restricted through different HLA class II antigens; clone CG2.7 recognized epitope 61-81 in the context of HLA DRw15, whereas clones CG5.15, CG5.24, and CG5.36 recognized epitope 163-183 in the context of HLA DRw11. The present protocol therefore makes a systematic analysis of CD4+ T-cell epitopes within gp340 possible; it will be necessary to screen gp340-specific T-cell clones from a variety of donors to assess the wider influence of HLA class II polymorphism upon epitope choice.

Roles of multiple accessory molecules in T-cell activation

Accessory molecules expressed on T cells can mediate adhesion between T cells and other cells, or the extracellular matrix. The same T-cell accessory molecules participate in a dialogue with their ligands (counter-receptors) on the antigen-presenting cells, and elicit signals that determine the specifics of activation and subsequent differentiation of the T cells and antigen-presenting cells.

Interleukin 2 abrogates the nonresponsive state of T cells expressing a forbidden T cell receptor repertoire and induces autoimmune disease in neonatally thymectomized mice

Under physiological conditions, the vast majority of T cells differentiate in the thymus, an organ that provides an optimal microenvironment for T cell maturation and shapes the T cell repertoire via positive and negative selection processes. In the present report, we demonstrate that neonatal thymectomy of CBA/H mice results in a diminution of T cells in peripheral lymphoid organs (spleen, lymph nodes), but is followed by a marked transient (12 wk) increase in Thy-1+ CD3+ cells in the peritoneal cavity. These cells exhibit predominantly a double-negative (CD4-CD8-) phenotype among which products of the T cell receptor (TCR) V beta 11 gene family (i.e., an I-E-reactive TCR normally deleted in I-E-bearing CBA/H mice) are selectively overexpressed. This observation suggests that, under athymic conditions, T cell differentiation and/or accumulation may occur in the peritoneal cavity. Intraperitoneal inoculation of an interleukin 2 (IL-2) vaccinia virus construct that releases high titers of human IL-2 in vivo induces conversion of these double-negative T cells to either CD4+ CD8- or CD4- CD8+ single positives, and allows in vitro stimulation of TCR V beta 11-bearing cells with a clonotypic anti-V beta antibody. Since IL-2 induces autoimmune manifestations (DNA autoantibodies, rheumatoid factors, and interstitial nephritis) in thymectomized CBA/H mice, but not in sham-treated littermates, this lymphokine is likely to enhance the autoaggressive function of T cells that bear forbidden, potentially autoreactive TCR gene products and that are normally deleted in the thymus.

Separation of IL-4 production from Th cell proliferation by an altered T cell receptor ligand

In the presence of antigen presenting cells, a murine T helper (Th) cell specific for murine hemoglobin (Hb) responded to its immunogenic peptide by both cytokine (interleukin-4) secretion and proliferation. An altered Hb peptide with a single amino acid substitution induced only cytokine secretion and did not induce proliferation. Interleukin-1 costimulated and restored the Th proliferative response to normal levels. The altered peptide also supported cognate T cell-B cell interactions indicative of T cell helper function. Thus, this result suggests that the T cell receptor has the capacity of differential signaling.

Self-tolerance and autoimmunity

Studies of self-tolerance and autoimmunity have moved rapidly into new arenas. These include the definition of at least two mechanisms for tolerance induction in both T and B cells, the creation of new disease-susceptible strains such as the HLA-B27 transgenic rats, the creation of new disease-resistant strains such as I-E or I-Ak NOD transgenic mice, and the precise definition of both antigen and antigen receptor for pathogenic lymphocytes in some models. More effective therapies for autoimmune disease should result from the knowledge gained.

Measurement of ligand-induced activation in single viable T cells using the lacZ reporter gene

We have used the bacterial beta-galactosidase gene (lacZ) as a reporter gene for the rapid measurement of T-cell antigen receptor (TCR)-mediated activation of individual T cells. The reporter construct contained the lacZ gene under the control of the nuclear factor of activated T cells (NF-AT) element of the human interleukin 2 enhancer [Fiering, S., Northrop, J. P., Nolan, G. P., Matilla, P., Crabtree, G. R. & Herzenberg, L. A. (1990) Genes Dev. 4, 1823-1834]. The activity of the intracellular lacZ enzyme was analyzed by flow cytometric measurement of fluorescein accumulation in cells loaded with the fluorogenic beta-galactosidase substrate fluorescein di-beta-D-galactopyranoside. As a model system, the T-cell hybridoma BO4H9.1, which is specific for the lysozyme peptide (amino acids 74-88)/Ab complex, was transfected with the NF-AT-lacZ construct. lacZ activity was induced in 50-100% of the transfectant cells following exposure to pharmacological agents, to the physiological peptide/major histocompatibility complex ligand, or to other TCR-specific stimuli. Interestingly, increasing concentrations of the stimulus increased the fraction of lacZ+ cells, but not the level of lacZ activity per cell. Even under widely varying levels of stimulus, the level of lacZ activity in individual lacZ+ cells remained within a remarkably narrow range. These results demonstrate that TCR-mediated activation can be readily measured in single T cells and strongly suggest that, once committed to activation, the level of NF-AT transcriptional activity in individual T cells is independent of the form or concentration of stimulus. This assay is likely to prove useful for the study of early activation events in individual T cells and of TCR ligands.

Major histocompatibility complex-expressing nonhematopoietic astroglial cells prime only CD8+ T lymphocytes: astroglial cells as perpetuators but not initiators of CD4+ T cell responses in the central nervous system

The potential of cells within the central nervous system (CNS) to initiate T lymphocyte responses is not known and was the subject of this study. Using the ability of virgin T lymphocytes to proliferate in a primary response to allogeneic determinants on antigen-presenting cells (APC), we have examined the capacity of major histocompatibility complex (MHC)-expressing astroglial cells to act as stimulators of primary and secondary T cell responses. Neither freshly isolated astrocytes nor primary astrocyte cultures pretreated with interferon gamma (IFN-gamma) to upregulate MHC class I and II expression stimulated unfractionated lymph node (LN) cell populations in the primary mixed lymphocyte reaction. In mixing experiments, astrocytes did not inhibit the T cell response to allogeneic LN stimulators. Purified responder CD4+ T cells also were not stimulated to proliferate or secrete interleukin 2 (IL-2) by MHC class I- and II-expressing astrocytes. In contrast to their inability to stimulate virgin, alloreactive CD4+ T cells, astrocytes were able to specifically stimulate an alloreactive CD4+ T cell line. Unprimed CD8+ T cells, however, exhibited some weak autonomous proliferation to astrocyte stimulators but this response was only substantial in the presence of exogenous IL-2, the latter predominantly being a CD4+ T cell product. Those CD8+ T cells responding in the presence of IL-2 were mainly T cell receptor alpha/beta+ IL-2 receptor (alpha chain)+, and a majority had shifted from high to low CD45R expression. Given the virtual dependence of CD8+ T cells in these studies, on CD4+ T cell help, and the complete absence of activation of this latter subset by astrocytes, it is clear that in the context of this resident CNS cell, further activation of either T cell subset by astrocytes within the CNS can only follow priming by another type of APC. The implications of these results for the induction of T cell responses in the CNS are discussed.

Down-regulation of T cell receptors on self-reactive T cells as a novel mechanism for extrathymic tolerance induction

By generating two types of transgenic mice we have investigated how extrathymic events can contribute to self tolerance. The major histocompatibility complex class I gene Kb was expressed under the control of the glial fibrillary acidic protein promoter in cells of neuroectodermal origin outside the thymus. These mice were tolerant to Kb. When crossed to transgenic mice expressing a Kb-specific T cell receptor (TCR), clonotype+, CD8+CD4- mature T cells could be detected in normal numbers in the thymus of the double-transgenic mice but were strongly reduced in spleen and lymph nodes in comparison with TCR single-transgenic mice. After isolation of clonotype negative splenic T cells and activation in vitro, reappearance of the clonotype+, CD8+CD4- cells was observed. These results indicate that down-regulation of TCR and CD8 molecules on the antigen-specific T cells is a novel mechanism, by which peripheral tolerance to this antigen can occur.

Regulation of T cell receptor signaling by a src family protein-tyrosine kinase (p59fyn)

Engagement of the clonotypic antigen receptor (TCR) on T lymphocytes provokes an activation response leading to cell proliferation and lymphokine secretion. To examine the molecular basis of T cell signaling, we generated transgenic animals in which a lymphocyte-specific nonreceptor protein-tyrosine kinase p59fyn(T) is 20-fold overexpressed in developing T lineage cells. Thymocytes from these mice, analyzed using both cellular and biochemical assays, were remarkably hyperstimulable. Moreover, the responsiveness of normal thymocytes to TCR-derived signals correlated well with the extent to which p59fyn was expressed in these cells. Overexpression of a catalytically inactive form of p59fyn substantially inhibited TCR-mediated activation in otherwise normal thymocytes. These effects are unique to p59fyn; overexpression of a closely related T cell-specific tyrosine kinase, p56lck, elicits dramatically different phenotypes. Our results suggest that p59fyn is a critically important component of the TCR signal transduction apparatus.

Ablation of "tolerance" and induction of diabetes by virus infection in viral antigen transgenic mice

To address the mechanisms of tolerance to extrathymic proteins, we have generated transgenic mice expressing the lymphocytic choriomeningitis viral (LCMV) glycoprotein (GP) in the beta islet cells of the pancreas. The fate of LCMV GP-specific T cells was followed by breeding the GP transgenic mice with T cell receptor transgenic mice, specific for LCMV and H-2Db. These studies suggest that "peripheral tolerance" of self-reactive T cells does not involve clonal deletion, clonal anergy, or a decrease in the density of T cell receptors or accessory molecules. Instead, this model indicates that self-reactive cytotoxic T cells may remain functionally unresponsive, owing to a lack of appropriate T cell activation. Infection of transgenic mice with LCMV readily abolishes peripheral unresponsiveness to the self LCMV GP antigen, resulting in a CD8+ T cell-mediated diabetes. These data suggest that similar mechanisms may operate in several so-called "T cell-mediated autoimmune diseases."

Intercellular adhesion molecule (ICAM-1) inhibition can induce tolerance in vivo

Antigen specific unresponsiveness can be induced in vivo by administration of antibody against CD4, major histocompatibility complex (MHC) Class II or LFA-1 at the time of antigen exposure. Since target cell depletion is not necessary for this effect it was hypothesized that interference with intercellular interaction was responsible. To test this hypothesis, antibody against the ligand for LFA-1, ICAM-1, was administered during primary immunization with human gamma-globulin (HGG) and long-term secondary antibody responses monitored. It was found that HGG specific unresponsiveness resulted from this treatment (less than 10% of normal secondary antibody response). Delayed-type hypersensitivity responses to HGG were also suppressed suggesting unresponsiveness in some T cell subsets. These findings suggest a role for ICAM-1/LFA-1 interaction in determining the long-term outcome of contact with antigen.

Split anergy in a CD8+ T cell: receptor-dependent cytolysis in the absence of interleukin-2 production

Engagement of the antigen-specific receptor (TCR) of CD4+ T lymphocytes without a second (costimulatory) signal prevents the subsequent production of interleukin-2 (IL-2) by these cells. Because IL-2 is a key immunoregulatory lymphokine and is also produced by a subset of CD8+ T cells that are able to kill target cells, the effect of engaging the TCR of one such clone in the absence of costimulatory signals was examined. The capacity for TCR-dependent IL-2 production was lost, indicating comparable costimulator-dependent signaling requirements for IL-2 production in CD4+ and CD8+ T cells. However, TCR-mediated cytotoxicity was not impaired, implying that costimulation is required for only certain TCR-dependent effector functions.

Functional inactivation of Dermatophagoides spp. (house dust mite) reactive human T-cell clones

Staphylococcal enterotoxins are able both to stimulate powerful polyclonal proliferative responses and to induce non-responsiveness of T lymphocytes expressing the appropriate T-cell antigen receptor V beta gene products. T-cell clones representative of the human response to house dust mite were identified that express either V beta 3 or V beta 6 gene products. The specificity of the latter was confirmed by serology. Pre-treatment of cloned V beta 3+ T cells with the Staphylococcus aureus enterotoxins B or C1 rendered them non-responsive to immunogenic challenge with their natural ligand, while retaining responsiveness to exogenous IL-2. Similarly, exposure of the V beta 6+ dust mite reactive T cells to the staphylococcal enterotoxin of the appropriate specificity, SEE, induced specific anergy. The development of non-responsiveness was associated with changes in the T-cell phenotypes. Downregulation of the T-cell receptor, Ti-CD3, was paralleled by enhanced expression of both CD2 and the IL-2 receptor, CD25. Differential co-modulation of CD4 and Ti-CD3 suggested that for some T cells CD4 may form part of the specific antigen recognition structure. Toxicity of the staphylococcal enterotoxins may be removed by chemical modification, thus their ability functionally to inactivate subpopulations of T cells expressing antigen-specific receptors with shared characteristics may be of potential value in the regulation of allergic diseases if the diversity of the T-cell repertoire proves to be limited.

Staphylococcal enterotoxin B as a potent suppressant of T cell proliferative responses in rats

The staphylococcal toxins are well known as stimulators of powerful T lymphocyte proliferative responses. Staphylococcal enterotoxin B (SEB) was found, in both humans and mice, to preferentially stimulate T cells bearing particular V beta gene products as part of their functional T cell receptor alpha/beta. In contrast to this reported stimulatory activity we demonstrate here that SEB is a poor stimulant of T lymphocyte proliferative responses in Lewis rats. Moreover, under appropriate conditions, SEB can serve as a powerful suppressant of Lewis rat T lymphocytes, capable of abolishing their antigen-specific or mitogen-stimulated proliferative responses. Suppression of mitogen-induced proliferative responses of rat T cell clones was effective in the presence of syngeneic or allogeneic accessory cells and similar to its stimulatory characteristics, SEB suppressed high proportions of rat T lymphocyte subsets. These data suggest that in certain circumstances SEB can be considered a "supersuppressogen" as well as a "superantigen". Whether SEB will be "superantigen" or "supersuppressogen" is likely to depend on the TcR elements of the lymphocytes as well as on the MHC molecules presenting SEB.

Binding of the B cell activation antigen B7 to CD28 costimulates T cell proliferation and interleukin 2 mRNA accumulation

A successful immune response requires intercellular contact between T and B lymphocytes. We recently showed that CD28, a T cell surface protein that regulates an activation pathway, could mediate intercellular adhesion with activated B cells by interaction with the B7 antigen. Here we show that CD28 is the primary receptor for B7 on activated peripheral blood T cells, that CD28 binds to B7 in the absence of other accessory molecules, and that interaction between CD28 and B7 is costimulatory for T cell activation. To characterize the binding of CD28 to B7, we have produced genetic fusions of the extracellular portions of B7 and CD28, and immunoglobulin (Ig) C gamma 1 chains. 125I-labeled B7 Ig bound to CD28-transfected Chinese hamster ovary (CHO) cells, and to immobilized CD28 Ig with a Kd approximately 200 nM. B7 Ig also inhibited CD28-mediated cellular adhesion. The function of CD28-B7 interactions during T cell activation was investigated with soluble fusion proteins and with B7-transfected CHO cells. Immobilized B7 Ig and B7+ CHO cells costimulated T cell proliferation. Stimulation of T cells with B7+ CHO cells also specifically increased levels of interleukin 2 transcripts. These results demonstrate that the CD28 signaling pathway could be activated by B7, resulting in increased T cell cytokine production and T cell proliferation. Cellular interactions mediated by B7 and CD28 may represent an important component of the functional interactions between T and B lymphoid cells.

Immobilized anti-CD5 together with prolonged activation of protein kinase C induce interleukin 2-dependent T cell growth: evidence for signal transduction through CD5

Monoclonal antibodies (mAb) identifying the CD5 antigen were used to stimulate human peripheral blood T lymphocytes. Three out of three anti-CD5 mAb, 10.2, OKT1 and anti-Leu-1 induced vigorous proliferation of purified T cells in the presence of 1.6 nM phorbol 12-myristate 13-acetate (PMA). Immobilization of anti-CD5 mAb on a solid support was necessary for the induction of a proliferative response. Neither 1.6 nM PMA, nor immobilized anti-CD5 mAb were mitogenic as a sole stimulus. mAb identifying CD4, CD7, CD11a, CD18, and major histocompatibility complex class I molecules were not comitogenic with PMA. Anti-CD5/PMA-induced cell proliferation proceeded by an interleukin 2 (IL 2)-dependent mechanism, as was demonstrated by the cell surface expression of the p55 chain of the IL 2 receptor (IL 2R), the production of IL 2 and the inhibition of the proliferative response by anti-IL 2R mAb anti-Tac. There was no strict requirement for detectable numbers of monocytes, although cell proliferation could be enhanced by the monocyte-derived cytokines IL 1 and IL 6. Phorbol 12,13-dibutyrate and mezerein could substitute for PMA in this activation pathway, but synthetic diacylglycerols and phorbol esters that do not activate protein kinase C (PKC) could not, indicating a need for prolonged activation of PKC. T cells activated by anti-CD5/PMA are sensitive to inhibition by cyclosporin A (CsA) and by prostaglandin E2 (PGE2). This contrasts with anti-CD28/PMA-induced T cell proliferation, which is resistant to CsA and PGE2. Cell surface expression of CD5 was strongly up-regulated by PMA, whereas CD3 expression was down-regulated. We conclude that T cell activation can be triggered by engagement of CD5 by immobilized anti-CD5 mAb, combined with prolonged activation of PKC. These data support a role for CD5 as an independent signal transducing molecule.