Regulatory CD8+ T cells fine-tune the myelin basic protein-reactive T cell receptor V beta repertoire during experimental autoimmune encephalomyelitis.

A significant number of self-reactive T cell clones escape thymic negative selection and are released into the periphery, where some are potentially pathogenic. The clonal expansion of self-reactive T cells is known to be limited during initial antigen encounter by apoptotic or anergic mechanisms, regulatory CD4+ T cells, and cytokines. Here we report that superimposed on these mechanisms, during the evolution of autoimmunity in experimental autoimmune encephalomyelitis (EAE), CD8+ T cells are induced, which fine-tune the peripheral self-reactive T cell receptor (TCR) repertoire. We assayed the myelin basic protein-reactive TCR repertoire in naive, EAE-recovered mice as well as EAE-recovered mice depleted of CD8+ T cells by TCRV beta surface expression, complementarity-determining region 3 length distribution, and complementarity-determining region 3 sequencing analysis. In EAE-recovered mice, certain myelin basic protein-reactive CD4+V beta 8.2+ clones are significantly decreased and this decrease is not observed if CD8+ T cells were depleted from these mice. The clones that persist in CD8+ T cell-intact mice are highly diverse in contrast to the clones expanded in CD8+ T cell-depleted mice, which are dominated by the significant outgrowth of a few clones. Importantly, the T cell clones that expand in the absence of CD8+ T cell control are enriched in potentially pathogenic self-reactive T cell clones capable of inducing EAE in vivo.

Mechanisms of cell-mediated myocytotoxicity in the peripheral blood of patients with inflammatory myopathies.

Cell-mediated cytotoxicity is thought to play an important role in the immunopathogenesis of inflammatory myopathies. We determined whether lymphocytes circulating in patient peripheral blood contain automyocytotoxic precursors. Peripheral blood mononuclear cells, sheep red blood cell rosetting (E+) and nonrosetting (E-) cells, were isolated from patients with polymyositis or dermatomyositis and tested for their ability to kill autologous-cultured myotubes derived from diseased muscle biopsies. Patient-derived as well as normal allogeneic mononuclear cells lysed both polymyositis-dermatomyositis and nonrelated myotubes. However, whereas patient E+ cells were preferentially cytotoxic to autologous myotubes, their E-cells did not discriminate autologous from allogeneic targets. Furthermore, cultures of patient E+ cells triggered by phytohemagglutinin and interleukin-2 maintained myocytotoxic potential. In these cultures, virtually all autologous but only 50% of allogeneic killing was mediated by CD3+ T cells. Moreover, autologous cell-mediated killing was abrogated by anti-CD3 monoclonal antibodies. In conclusion, both myocytotoxic CD3+ T-cell clones specific for autologous myotubes, as well as non-T cells, which are nonspecifically myocytotoxic, are present in the peripheral blood of patients with inflammatory myopathies.

Induction of TCR Vbeta-specific CD8+ CTLs by TCR Vbeta-derived peptides bound to HLA-E.

Previous studies have identified murine and human regulatory CD8+ T cells specific for TCR-Vbeta families expressed on autologous activated CD4+ T cells. In the mouse, these regulatory CD8+ T cells were shown to be restricted by the MHC class Ib molecule, Qa-1. In the present study, we asked whether HLA-E, the human functional equivalent of Qa-1, binds Vbeta peptides and whether the HLA-E/Vbeta-peptide complex induces and restricts human CD8+ CTLs. We first created stable HLA-E gene transfectants of the C1R cell line (C1R-E). Two putative HLA-E binding nonapeptides identified in human TCR Vbeta1 and Vbeta2 chains (SLELGDSAL and LLLGPGSGL, respectively) were shown to bind to HLA-E. CD8+ T cells could be primed in vitro by C1R-E cells loaded with the Vbeta1 (C1R-E/V1) or Vbeta2 (C1R-E/V2) peptide to preferentially kill C1R-E cells loaded with the respective inducing Vbeta peptide, compared with targets loaded with the other peptides. Priming CD8+ T cells with untreated C1R-E cells did not induce Vbeta-specific CTLs. Of perhaps more physiological relevance was the finding that the CD8+ CTLs primed by C1R-E/V1 also preferentially killed activated autologous TCR Vbeta1+. Similar results were observed in reciprocal experiments using C1R-E/V2 for priming. Furthermore, anti-CD8 and anti-MHC class I mAbs inhibited this Vbeta-specific killing of C1R-E and CD4+ T cell targets. Taken together, the data provide evidence that certain TCR-Vbeta peptides can be presented by HLA-E to further induce Vbeta-specific CD8+ CTLs.

CD8+ T cells control the TH phenotype of MBP-reactive CD4+ T cells in EAE mice.

Trimolecular interactions between the T cell antigen receptor and MHC/peptide complexes, together with costimulatory molecules and cytokines, control the initial activation of naive T cells and determine whether the helper precursor cell differentiates into either T helper (TH)1 or TH2 effector cells. We now present evidence that regulatory CD8(+) T cells provide another level of control of TH phenotype during further evolution of immune responses. These regulatory CD8(+) T cells are induced by antigen-triggered CD4(+) TH1 cells during T cell vaccination and, in vitro, distinguish mature TH1 from TH2 cells in a T cell antigen receptor Vbeta-specific and Qa-1-restricted manner. In vivo, protection from experimental autoimmune encephalomyelitis (EAE) induced by T cell vaccination depends on CD8(+) T cells, and myelin basic protein-reactive TH1 Vbeta8(+) clones, but not TH2 Vbeta8(+) clones, used as vaccine T cells, protect animals from subsequent induction of EAE. Moreover, in vivo depletion of CD8(+) T cells during the first episode of EAE results in skewing of the TH phenotype toward TH1 upon secondary myelin basic protein stimulation. These data provide evidence that CD8(+) T cells control autoimmune responses, in part, by regulating the TH phenotype of self-reactive CD4(+) T cells.

Analysis of CD154 and CD40 expression in native coronary atherosclerosis and transplant associated coronary artery disease.

T cells have roles in the pathogenesis of native coronary atherosclerosis (CA) and transplant-associated coronary artery disease (TCAD). The mechanisms by which T cells interact with other cells in these lesions are not fully known. CD154 is an activation-induced CD4+ T cell surface molecule that interacts with CD40+ target cells, including macrophages and endothelial cells, and induces the production of pro-inflammatory molecules, including CD54 (ICAM-1) and CD106 (VCAM-1). To investigate whether CD154-CD40 interactions might be involved in the pathogenesis of CA or TCAD we performed immunohistochemical studies of CD154 and CD40 expression on frozen sections of coronary arteries obtained from cardiac allograft recipients with CA (n=10) or TCAD (n=9). Utilizing four different anti-CD154 mAb we found that CD154 expression was restricted to infiltrating lymphocytes in CA and TCAD. CD40 expression was markedly up-regulated on intimal endothelial cells, foam cells, macrophages and smooth muscle cells in both diseases. Dual immunolabeling demonstrated many CD40+ cells co-expressed CD54 and CD106. The extent of CD40, CD54 and CD106 expression showed statistical significant correlation with the severity of disease and the amount of intimal lymphocytes. Together these studies demonstrate the presence of activated CD154+ and CD40+ cells in both CA and TCAD lesions and suggest that CD154-mediated interactions with CD40+ macrophages, foam cells, smooth muscle cells and/or endothelial cells may contribute to the pathogenesis of these diseases.

The specific regulation of immune responses by CD8+ T cells restricted by the MHC class Ib molecule, Qa-1.

Over the last three decades considerable evidence has accumulated that CD8(+) T cells regulate peripheral immune responses, in part, by specifically controlling the outgrowth of antigen-triggered CD4(+) T cells. This regulatory function of CD8(+) T cells has been shown, in vivo, to control the emergence of autoreactive CD4(+) T cells as well as CD4(+) T cells reactive to conventional antigens, including alloantigens. In this review, we summarize the evidence that this immune suppression mediated by CD8(+) T cells is dependent, in part, on specific cognate interactions between MHC class I-restricted regulatory CD8(+) cells and antigen-activated CD4(+) T cells. Moreover, we review the evidence that regulatory CD8(+) T cells recognize antigen-activated CD4(+) T cells in a TCR specific manner restricted by the MHC class Ib molecule, Qa-1. The Qa-1 molecule may be uniquely qualified to serve this MHC restrictive function because, unlike conventional MHC molecules, it is preferentially and transiently expressed on activated and not resting CD4(+) T cells. This may assure that only recently antigen-activated CD4(+) T cells expressing Qa-1/TCR peptide complexes will induce regulatory CD8(+) T cells and subsequently become susceptible to regulation. Because Qa-1 also binds to self Qdm peptides that trigger NK (CD94/ NKG2) receptors on CD8(+) T cells, the machinery for homeostatic regulation of regulatory CD8(+) T cells can be envisioned. Finally, we propose a model by which these TCR specific, Qa-1-restricted regulatory CD8(+) T cells selectively downregulate antigen-activated T cells expressing TCRs of certain affinities. Ultimately these regulatory CD8(+) T cells control the peripheral TCR repertoire during the course of immune responses to both self and foreign antigens.

A novel 26 kilodalton antigen expressed on the surface membrane of activated T cells.

We have identified and characterized the tissue distribution of the antigen recognized by a novel monoclonal antibody (mAb) 1B10, raised against an activated gammadelta T cell clone. Immunohistochemistry of tissue sections, and analysis of single cell suspensions by flow cytometry revealed that mAb 1B10 weakly reacted with <6% of normal human peripheral blood mononuclear cells (PBMC). After 5-6 days of in vitro culture of PBMC activated with phytohemagglutinin (PHA), 55% of the CD4+ and 25% of the CD8+ T cells became 1B10+. 1B10 expression was maintained on long term cultured interleukin 2 (IL-2)-dependent T cell receptor (TCR) alphabeta+ and gammadelta+ clones, and importantly, in contrast to resting T cells, the majority of in vivo activated synovial T lymphocytes from a patient with rheumatoid arthritis were 1B10+. In addition, myelo-monocytic U927 cells, tissue macrophages and some epithelia and fibroblasts were found to react with mAb 1B10. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) of molecules immuno-precipitated by mAb 1B10 from radio-iodinated cell surface membrane lysates of T lymphocyte and U937 cells revealed 26 and 29 kiloDalton (kDa) glycoproteins respectively. In conclusion, mAb 1B10 recognizes a novel <> appearing 26 kDa T cell activation antigen that may be useful for further studies of activated T cells in health and disease.

T cell vaccination induces T cell receptor Vbeta-specific Qa-1-restricted regulatory CD8(+) T cells.

Vaccination of mice with activated autoantigen-reactive CD4(+) T cells (T cell vaccination, TCV) has been shown to induce protection from the subsequent induction of a variety of experimental autoimmune diseases, including experimental allergic encephalomyelitis (EAE). Although the mechanisms involved in TCV-mediated protection are not completely known, there is some evidence that TCV induces CD8(+) regulatory T cells that are specific for pathogenic CD4(+) T cells. Previously, we demonstrated that, after superantigen administration in vivo, CD8(+) T cells emerge that preferentially lyse and regulate activated autologous CD4(+) T cells in a T cell receptor (TCR) Vbeta-specific manner. This TCR Vbeta-specific regulation is not observed in beta2-microglobulin-deficient mice and is inhibited, in vitro, by antibody to Qa-1. We now show that similar Vbeta8-specific Qa-1-restricted CD8(+) T cells are also induced by TCV with activated CD4(+) Vbeta8(+) T cells. These CD8(+) T cells specifically lyse murine or human transfectants coexpressing Qa-1 and murine TCR Vbeta8. Further, CD8(+) T cell hybridoma clones generated from B10.PL mice vaccinated with a myelin basic protein-specific CD4(+)Vbeta8(+) T cell clone specifically recognize other CD4(+) T cells and T cell tumors that express Vbeta8 and the syngeneic Qa-1(a) but not the allogeneic Qa-1(b) molecule. Thus, Vbeta-specific Qa-1-restricted CD8(+) T cells are induced by activated CD4(+) T cells. We suggest that these CD8(+) T cells may function to specifically regulate activated CD4(+) T cells during immune responses.

Endogenous production of beta-chemokines by CD4+, but not CD8+, T-cell clones correlates with the clinical state of human immunodeficiency virus type 1 (HIV-1)-infected individuals and may be responsible for blocking infection with non-syncytium-inducing HIV-1 in vitro.

Recent studies have demonstrated that the beta-chemokines RANTES, MIP-1alpha, and MIP-1beta suppress human immunodeficiency virus type 1 (HIV-1) replication in vitro and may play an important role in protecting exposed but uninfected individuals from HIV-1 infection. However, levels of beta-chemokines in AIDS patients are comparable to and can exceed levels in nonprogressing individuals, indicating that global beta-chemokine production may have little effect on HIV-1 disease progression. We sought to clarify the role of beta-chemokines in nonprogressors and AIDS patients by examination of beta-chemokine production and HIV-1 infection in patient T-lymphocyte clones established by herpesvirus saimiri immortalization. Both CD4+ and CD8+ clones were established, and they resembled primary T cells in their phenotypes and expression of activated T-cell markers. CD4+ T-cell clones from all patients had normal levels of mRNA-encoding CCR5, a coreceptor for non-syncytium-inducing (NSI) HIV-1. CD4+ clones from nonprogressors and CD8+ clones from AIDS patients secreted high levels of RANTES, MIP1alpha, and MIP-1beta. In contrast, CD4+ clones from AIDS patients produced no RANTES and little or no MIP-1alpha or MIP-1beta. The infection of CD4+ clones with the NSI HIV-1 strain ADA revealed an inverse correlation to beta-chemokine production; clones from nonprogressors were poorly susceptible to ADA replication, but clones from AIDS patients were highly infectable. The resistance to ADA infection in CD4+ clones from nonprogressors could be partially reversed by treatment with anti-beta-chemokine antibodies. These results indicate that CD4+ cells can be protected against NSI-HIV-1 infection in culture through endogenously produced factors, including beta-chemokines, and that beta-chemokine production by CD4+, but not CD8+, T cells may constitute one mechanism of disease-free survival for HIV-1-infected individuals.

Immunohistologic analysis of renal CD40 and CD40L expression in lupus nephritis and other glomerulonephritides.

OBJECTIVE: To investigate potential mechanisms by which CD40L-mediated signals may be involved in the pathogenesis of lupus glomerulonephritis (GN). METHODS: Renal in situ CD40L and CD40 expression was examined in patient biopsy specimens. Immunohistochemical studies were performed on frozen sections utilizing anti-CD40L monoclonal antibody (MAb), anti-CD40 MAb, or control MAb. As controls, we analyzed normal kidney specimens and specimens obtained from patients with IgA nephropathy, focal segmental glomerulosclerosis, minimal change disease, idiopathic membranous GN, and antineutrophil cytoplasmic antibody-positive pauci-immune GN. Staining distribution was noted and staining intensity scored on a semiquantitative scale of 0 (no staining) to 3+ (intense staining). RESULTS: In normal kidney, CD40 was expressed on parietal epithelial cells, mesangial cells, endothelial cells, and distal tubules but not proximal tubules. Glomerular and tubular CD40 expression was markedly up-regulated in class III and class IV lupus GN, where there was intense staining of crescents, proximal and distal tubules, and interstitial mononuclear cells. In contrast, CD40 expression in class V lupus GN was similar to that in normal kidney. Interstitial mononuclear cells expressing CD40L were present in class IV lupus GN. However, these findings were not unique to lupus GN: up-regulation of CD40 and CD40L expression was similarly observed in other inflammatory renal diseases. CONCLUSION: This study shows that CD40 is expressed on a variety of renal parenchymal and non-parenchymal cells in normal kidney. Renal CD40 expression is up-regulated in class III and class IV lupus nephritis, as well as in other inflammatory renal diseases, and is associated with the presence of CD40L+ mononuclear cells.

Herpesvirus saimiri-transformed human CD4+ T cells can provide polyclonal B cell help via the CD40 ligand as well as the TNF-alpha pathway and through release of lymphokines.

We have developed human CD4+ T cell lines from the PBL of normal donors by infection with Herpesvirus saimiri (HVS), to evaluate functional properties of these immortalized lymphocytes. In this report, we characterize two such CD4+ T cell lines, CHCD4 and MHCD4, which were derived from two different donors. These cells grew independent of exogenous IL-2 stimulation for over 1 yr, and expressed surface markers (CD25+, CD69+, HLA-DR+, and B7+) associated with an activated T cell phenotype. Both lines constitutively produced and released IFN-gamma, but no IL-2 or IL-4. However, the surface expression of the two cell lines differed in that CHCD4 constitutively expressed CD40 ligand (CD40L) and membrane TNF-alpha, but MHCD4 did not. Also, CHCD4, but not MHCD4, potently induced polyclonal B cell activation and differentiation in the absence of PWM, in an MHC-unrestricted fashion. The B cell help afforded by CHCD4 included contact-dependent and soluble components. Contact-dependent help was strongly inhibited by mAb against CD40L (5C8) and to a lesser extent, by anti-TNF-alpha Ab. The CD40L-dependent helper function of CHCD4 contrasts with the recent description of other HVS-transformed CD4+ T cells that provide B cell help primarily via the membrane TNF-alpha and TNF-alphaR pathways. Furthermore, CHCD4 cells also secreted soluble factors that could mediate CD40-linked B cell differentiation into Ab-producing cells. Interestingly, this factor is not likely to be IL-2, IL-4, IL-6, IL-10, IL-15, TNF-alpha, or IFN-gamma as Abs against these cytokines were not able to inhibit the contact-independent B cell help by CHCD4. These results indicate that HVS-immortalization of CD4+ lymphocytes may produce T cell clones with a spectrum of important contact-dependent, as well as contact-independent, B cell helper function capacities.

The central role of the CD40-ligand and CD40 pathway in T-lymphocyte-mediated differentiation of B lymphocytes.

This review summarizes recent findings concerning the role of CD40-ligand and CD40 interactions in B-cell differentiation. CD40-ligand on helper CD4+ T lymphocytes interacts with CD40 on B cells and directs the selection and differentiation of clones of B lymphocytes to generate specific antibody-dependent immune responses. CD40-ligand is necessary for normal B-cell differentiation and plays several distinctive roles in this multistage process. The CD40 signaling pathway that normally regulates B-cell death appears to be usurped by the Epstein-Barr virus to mediate B-cell transformation.

Functional interactions of T cells with endothelial cells: the role of CD40L-CD40-mediated signals.

CD40 is expressed on a variety of cells, including B cells, monocytes, dendritic cells, and fibroblasts. CD40 interacts with CD40L, a 30-33-kD activation-induced CD4+ T cell surface molecule. CD40L-CD40 interactions are known to play key roles in B cell activation and differentiation in vitro and in vivo. We now report that normal human endothelial cells also express CD40 in situ, and CD40L-CD40 interactions induce endothelial cell activation in vitro. Frozen sections from normal spleen, thyroid, skin, muscle, kidney, lung, or umbilical cord were studied for CD40 expression by immunohistochemistry. Endothelial cells from all tissues studied express CD40 in situ. Moreover, human umbilical vein endothelial cells (HUVEC) express CD40 in vitro, and recombinant interferon gamma induces HUVEC CD40 upregulation. CD40 expression on HUVEC is functionally significant because CD40L+ Jurkat T cells or CD40L+ 293 kidney cell transfectants, but not control cells, upregulate HUVEC CD54 (intercellular adhesion molecule-1), CD62E (E-selectin), and CD106 (vascular cell adhesion molecule-1) expression in vitro. Moreover, the kinetics of CD40L-, interleukin 1-, or tumor necrosis factor alpha-induced CD54, CD62E, and CD106 upregulation on HUVEC are similar. Finally, CD40L-CD40 interactions do not induce CD80, CD86, or major histocompatibility complex class II expression on HUVEC in vitro. These results demonstrate that CD40L-CD40 interactions induce endothelial cell activation in vitro. Moreover, they suggest a mechanism by which activated CD4+ T cells may augment inflammatory responses in vivo by upregulating the expression of endothelial cell surface adhesion molecules.

Opposing roles of CD95 (Fas/APO-1) and CD40 in the death and rescue of human low density tonsillar B cells.

The regulation of B cell death plays roles in the selection of Ag-specific B cells in humoral immune responses, controlling B cell homeostasis and perhaps limiting transformation. The present work addresses whether CD95 induces tonsillar B cells to undergo apoptosis and, if so, whether contact-dependent CD40-L:CD40 signaling can rescue tonsillar B cells from CD95-induced apoptosis. CD95 triggering by anti-CD95 mAb (APO-1) was studied in human tonsillar B cell populations that were separated by density centrifugation into fractions enriched for either low density, CD38+ B cells or high density, resting B cells. Low density tonsillar B cells express CD95 and undergo anti-CD95-mediated apoptosis by analysis of cellular morphology or DNA fragmentation by TUNEL assay. The induction of apoptosis in low density tonsillar B cells by anti-CD95 mAb is inhibited by CD40 signals provided by stably transfected CD40-L+ 293 cells, but not by control transfected 293 cells (expressing CD8). In addition, the rescuing effect of CD40-L+ cells is inhibited specifically by anti-CD40-L (mAb 5c8). The counteracting effects of CD95 and CD40 signaling were also studied in Ramos 2G6, a homogeneous B cell tumor line of germinal center phenotype that expresses CD95 and CD40. Similar to the behavior of low density tonsillar B cells, Ramos 2G6 undergoes anti-CD95-mediated apoptosis, which is prevented by CD40-mediated rescue. These data show that CD95 induces apoptosis in low density tonsillar B cells and that CD40-L:CD40 interactions rescue low density tonsillar B cells or the B cell tumor Ramos 2G6 from CD95-induced apoptosis, and suggest roles for CD95 and CD40 in B cell death and selection, respectively.

2 A crystal structure of an extracellular fragment of human CD40 ligand.

BACKGROUND: The CD40 ligand (CD40L) is a member of the tumor necrosis factor (TNF) family of proteins and is transiently expressed on the surface of activated T cells. The binding of CD40L to CD40, which is expressed on the surface of B cells, provides a critical and unique pathway of cellular activation resulting in antibody isotype switching, regulation of apoptosis, and B cell proliferation and differentiation. Naturally occurring mutations of CD40L result in the clinical hyper-IgM syndrome, characterized by an inability to produce immunoglobulins of the IgG, IgA and IgE isotypes. RESULTS: We have determined the crystal structure of a soluble extracellular fragment of human CD40L to 2 A resolution and with an R factor of 21.8%. Although the molecule forms a trimer similar to that found for other members of the TNF family, such as TNF alpha and lymphotoxin-alpha, and exhibits a similar overall fold, there are considerable differences in several loops including those predicted to be involved in CD40 binding. CONCLUSIONS: The structure suggests that most of the hyper-IgM syndrome mutations affect the folding and stability of the molecule rather than the CD40-binding site directly. Despite the fact that the hyper-IgM syndrome mutations are dispersed in the primary sequence, a large fraction of them are clustered in space in the vicinity of a surface loop, close to the predicted CD40-binding site.

Ligation of CD40 on fibroblasts induces CD54 (ICAM-1) and CD106 (VCAM-1) up-regulation and IL-6 production and proliferation.

CD40 was originally described as a functionally significant B cell surface molecule. However, CD40 is also expressed on monocytes, dendritic cells, epithelial cells, and basophils. We now report that synovial membrane (SM) or dermal fibroblasts also express cell surface CD40 in vitro. Fibroblast CD40 expression declines with increasing time in culture and recombinant interferon-gamma (rINF-gamma) induces fibroblast CD40 up-regulation. This effect of rINF-gamma is augmented by recombinant interleukin-1 alpha or recombinant tumor necrosis factor-alpha. CD40 expression on fibroblasts is functionally significant because CD40L-CD40 interactions induce SM fibroblast CD54 (intercellular adhesion molecule-1) and CD106 (vascular cell adhesion molecule-1) up-regulation. Moreover, ligation of CD40 augments IL-6 production by SM fibroblasts and induces fibroblasts to proliferate. In addition, rINF-gamma enhances the effect of CD40L-CD40 interactions on fibroblast proliferation. Taken together, these studies show that fibroblasts can express CD40, cytokines can regulate fibroblast CD40 expression, and CD40 ligation induces fibroblast activation and proliferation.

Human CD8+ T lymphocyte clones specific for T cell receptor V beta families expressed on autologous CD4+ T cells.

CD8+ T cells control immune responses, and recent studies suggest that this regulation is, in part, specifically directed towards TCR structures expressed by CD4+ cells. To develop a system to study the role of the TCR in regulatory interactions, we isolated clones of CD4+ cells expressing identified TCR V beta chains. These CD4+ clones were used to stimulate and expand autologous CD8+ cells, which kill the inducing CD4+ clone as well as independently isolated autologous CD4+ clones sharing the same TCR V beta as the inducing cell but not CD4+ T cells expressing different V beta TCRs. This V beta-specific cytotoxicity is dependent on the state of activation of the target cells and is not inhibited by an anti-class I monoclonal antibody, W6/32. We envision that V beta-specific CD8+ T cells of this type may regulate immune responses by direct interaction with antigen-activated CD4+ cells.

Murine CD8+ T cells that specifically delete autologous CD4+ T cells expressing V beta 8 TCR: a role of the Qa-1 molecule.

Interactions mediated by TCRs expressed on different T cell subsets may play a role in immunoregulation. To investigate this idea, we studied the regulation of superantigen-induced TCR V beta-restricted responses. We asked whether the in vivo regulation of CD4+ V beta 8+ T cells following SEB injection is controlled by CD8+ T cells. We found that in mice deficient in CD8+ T cells, the down-regulation of CD4+ V beta 8+ T cells below baseline is not observed. Moreover, following SEB administration, CD8+ T cells emerge that preferentially kill subpopulations of activated CD4+ V beta 8+ but not CD4+ V beta 8- T cells in vitro. This TCR V beta-specific cytotoxicity is dependent on beta 2-microglobulin and is inhibited by antisera specific for Qa-1 but not by antibody to MHC class Ia. These data suggest the idea that the specificity of immune regulation may involve CD8+ T cell recognition of TCR V beta determinants and Qa-1 molecules expressed on CD4+ T cells.