Receptor Beta-chain Variable Region Research Articles

Correlation between clonotypic T-cell receptor beta chain variable region (TCR-V beta) gene expression and aberrant T-cell antigen expression in cutaneous T-cell lymphoma.

Immunohistochemical studies can augment the clinicopathologic diagnosis of cutaneous T-cell lymphoma (CTCL). Our goal was to determine whether a panel of 11 T-cell receptor (TCR) beta chain variable region (V beta) monoclonal antibodies (moAbs) could consistently identify clonal T-cell populations within CTCL skin infiltrates, and whether these cell exhibited aberrant T-cell antigen expression. Biopsies from 24 CTCL and 3 parapsoriasis patients were analyzed. Of the 27 patients, 4 (15%) demonstrated T-cell clonality by restricted TCR-V beta moAb staining. The V beta + restricted cells expressed aberrant antigen profiles. Overall, aberrant antigen profiles were detected in 18/24 (75%) CTCL. Patients. V beta 18 moAb crossreacted with a 85 kD protein produced by basal and suprabasal keratinocytes. We conclude: 1) Restricted TCR-V beta expression correlated with aberrant T-cell antigen profiles: 2) In the absence of a complete panel of TCR-V beta moAbs, localization of aberrant T-cell antigen expression can be useful in identifying malignant T-cells within CTCL skin infiltrates; 3) The detection sensitivity and specificity of the currently available TCR-V beta moAbs may limit their utility to consistently detect clonal T-cell populations in CTCL skin biopsies; 4) A 85 kD protein present on basal and suprabasal keratinocytes is recognized by V beta 18 moAb and may be related to immune function(s) of the epidermis.

Analysis of Germline and Expressed T Cell Receptor Variable Region Genes in Crohn's Disease

A possible role of the T cell receptor genes in the pathogenesis of Crohn's disease was investigated by 1) comparison of restriction fragment length polymorphisms at the T cell receptor beta chain locus in 64 Crohn's patients and 64 normal controls; 2) semi-quantitative polymerase chain reaction analysis of T cell receptor beta and alpha chain variable region gene expression by lamina propria lymphocytes from resected segments of diseased terminal ileum. We found no association between any of the restriction fragment length polymorphisms and Crohn's disease using polymorphic markers spanning the T cell receptor beta chain locus. Analysis of T cell receptor V beta and V alpha gene expression showed that expression of T cell receptor V region families in terminal ileum lymphocytes from patients with active Crohn's disease was indistinguishable from the lymphocytes found in normal terminal ileum. These data fail to support susceptibility to Crohn's disease being associated with the T cell beta chain antigen receptor genotype. No restricted or dominant T cell receptor variable region gene expression was found in Crohn's disease tissue, compared to normal terminal ileum.

The influence of a maternal chronic hepatitis B virus infection on the repertoire of transcribed T-cell receptor beta chain variable region genes in human cord blood

We used an anchor polymerase chain reaction method to compare the repertoires of transcribed T-cell receptor β chain variable region (Vβ) genes in cord blood T cells from neonates of hepatitis B surface antigen (HBsAg) positive (n = 40) and HBsAg negative (n = 40) women. Fifteen of the HBsAg positive women were hepatitis B e antigen (HBeAg) positive, and 25 were HBeAg negative. The percentage of Vβ.4 transcripts was lower in cord blood T cells from neonates of HBsAg-positive relative to HBsAg-negative women (9.7% ± 0.5% vs. 12.7% ± 0.6%, P = .002). The percent of Vβ5.1 transcripts was higher in cord blood T cells from neonates of HBeAg-positive relative to HBeAg-negative women (9.3% ± 0.7% vs. 7.0% ± 0.3%, P < .001). There were no correlations between neonatal maturity at birth and Vβ repertoire. In summary, a maternal chronic hepatitis B virus (HBV) infection is associated with changes in the repertoire of transcribed T-cell receptor genes in neonatal cord blood T cells. It is possible that the T-cell response to the HBV is associated with a limited repertoire of Vβ genes. The mechanism of vertical chronic HBV infection in human neonates may involve changes in the T-cell response to the virus that are induced in utero. (HEPATOLOGY 1995; 22:1034–1039.).

The influence of a maternal chronic hepatitis B virus infection on the repertoire of transcribed T-cell receptor beta chain variable region genes in human cord blood

We used an anchor polymerase chain reaction method to compare the repertoires of transcribed T-cell receptor β chain variable region (Vβ) genes in cord blood T cells from neonates of hepatitis B surface antigen (HBsAg) positive (n = 40) and HBsAg negative (n = 40) women. Fifteen of the HBsAg positive women were hepatitis B e antigen (HBeAg) positive, and 25 were HBeAg negative. The percentage of Vβ7.4 transcripts was lower in cord blood T cells from neonates of HBsAg-positive relative to HBsAg-negative women (9.7% ± 0.5% vs. 12.7% ± 0.6%, P = .002). The percent of Vβ5.1 transcripts was higher in cord blood T cells from neonates of HBeAg-positive relative to HBeAg-negative women (9.3% ± 0.7% vs. 7.0% ± 0.3%, P < .001). There were no correlations between neonatal maturity at birth and Vβ repertoire. In summary, a maternal chronic hepatitis B virus (HBV) infection is associated with changes in the repertoire of transcribed T-cell receptor genes in neonatal cord blood T cells. It is possible that the T-cell response to the HBV is associated with a limited repertoire of Vβ genes. The mechanism of vertical chronic HBV infection in human neonates may involve changes in the T-cell response to the virus that are induced in utero.

PCR-based genotyping and haplotype analysis of human TCRBV gene segment polymorphisms.

There are at least 63 tandemly arranged human T-cell receptor (Tcr) beta-chain variable region (BV) gene segments, which have presumably arisen by repeated gene duplication events. The 5'-most half of the TCRBV gene loci is particularly complex in organization due to the presence of multiple interspersed members of the largest BV subfamilies, BV5, BV6, and BV13. Polymorphism and linkage relationships among these genes has been poorly characterized in part due to the high similarity of these duplicands. Germline DNA polymorphisms were specifically examined in the exons and introns of these and other BV gene segments distributed across 240 kilobases (kb) in this 5'-most region. Polymerase chain reaction restriction enzyme-based assays were used to genotype ten point mutations in seven of the BV gene segments. Eight of these polymorphisms altered an amino acid of the BV gene segment. In addition, length polymorphisms due to simple sequence repeats were noted in the introns of six BV6 subfamily members. Approximately 250 unrelated haplotypes were constructed by segregation analyses of fifteen of these TCRBV polymorphisms. Linkage disequilibrium analyses indicated that haplotypic relationships are not detectable over a distance of more than 55 kb in this genomic region. These TCRBV polymorphisms, and the haplotypic analysis, provide important resources and guidance for future attempts to associate Tcr germline DNA differences in the human population with immune response differences, such as might occur in some autoimmune diseases.

T-cell receptor (TCR) usage in Lewis rat experimental autoimmune encephalomyelitis: TCR beta-chain-variable-region V beta 8.2-positive T cells are not essential for induction and course of disease.

Predominant usage of V beta 8.2 gene segments, encoding a T-cell receptor (TCR) beta chain variable region, has been reported for pathogenic Lewis rat T cells reactive to myelin basic protein (MBP). However, up to 75% of the alpha/beta T cells in a panel of MBP-specific T-cell lines did not display TCR V beta 8.2, V beta 8.5, V beta 10, or V beta 16 elements. To further investigate TCR usage, we sorted the T-cell lines for V beta 8.2- and V beta 10-positive T cells or depleted the lines of cells with these TCRs. V beta 8.2-positive T cells and one of the depleted T-cell lines strongly reacted against the MBP peptide MBP-(68-88). The depleted T-cell line caused marked experimental autoimmune encephalomyelitis (EAE) even in Lewis rats in which endogenous V beta 8.2-positive T cells had been eliminated by neonatal treatment with anti-V beta 8.2 monoclonal antibodies. T-cell hybridomas generated from this line predominantly used V beta 3 TCR genes coexpressed with TCR V alpha 2 transcripts, which were also used by V beta 8.2-positive T cells. Furthermore, V beta 10-positive T cells reactive to MBP-(44-67) were encephalitogenic when injected immediately after positive selection. After induction of EAE by sorted V beta 8.2- or V beta 10-positive T-cell lines, immunocytochemical analysis of the spinal cord tissue showed a predominance of the injected TCR or of nontypable alpha/beta T cells after injection of the depleted line. Our results demonstrate heterogeneity of TCR beta-chain usage even for a single autoantigen in an inbred strain. Moreover, V beta 8.2-positive T cells are not essential for the induction and progression of adoptive-transfer EAE.

T-Cell Receptor α and β Chain Gene Expression in Cells Infiltrating Human Cardiac Allografts

Intragraft T-cell receptor (TCR) alpha and beta chain variable region gene expression was analyzed in human cardiac allograft biopsies by reverse transcription polymerase chain reaction. Rearranged TCR alpha and beta chain gene transcripts were detected in all biopsies examined (N = 23), indicating the presence of T cells bearing the alpha/beta TCR even in the absence of microscopically apparent leukocyte infiltration. In this analysis, a broad TCR alpha/beta repertoire in actively rejecting lesions was demonstrated, whereas fewer TCR alpha and beta chain gene families were detected in nonrejecting lesions. The number of expressed TCR V beta chain gene families typically was two- to sixfold higher than that of V alpha chain families in all biopsies tested. This asymmetric relation was present throughout the histologic grading spectrum of the biopsies. Based on these data, the TCR repertoire is heterogenous even in the early stages of mononuclear cell infiltration of the allograft. Also based on the data, the presence of T cells in grafts with minimal cellular infiltrates is not a specific marker of subsequent rejection episode, because T cells were identified in all allograft biopsies.

Correlation between cellular rejection of cardiac allografts and quantitative changes among T-cell subsets identified by V beta epitope expression.

Cellular rejection of an allograft is mediated in part by peripheral blood T cells. We tested the hypothesis that quantitative changes in T-cell subsets can be detected in the peripheral blood and that these changes correlate with rejection. T-cell subset analysis was performed by flow cytometry using monoclonal antibodies recognizing six isotypic epitopes of the T-cell receptor beta-chain variable (V) region. These analyses were done at 7-day (mean) time intervals. Fluctuations within a given subset were determined by dividing the number of positive cells observed by the number of positive cells found on the previous analysis. For healthy volunteers observed over a period of 30 days, 119 of 120 subset ratios (99.2%) fell between 0.5 and 2.0. For patients, 57 of 240 subset ratios (23.8%) fell outside of this range (P < .004, chi 2). The occurrence of the abnormal ratios coincided more closely with cellular rejection (mean +/- SD, 7.7 +/- 6.2 days from a positive biopsy; median, 5 days; range, 0 to 28 days) than did the occurrence of normal subset ratios (mean +/- SD, 14.4 +/- 10.9 days from a positive biopsy; median, 11 days; range, 0 to 44 days; P < .005 by Mann-Whitney U test). Regression analysis confirmed a significant (P < .001, R = .91) temporal association between cellular rejection and abnormal subset fluctuations. No correlation was found between abnormal subset ratios and either vascular rejection or use of high-dose prednisone. T-cell subset measurement may be a method of noninvasive monitoring of cellular rejection after transplantation and may provide insights into the physiology of graft rejection with the potential for the development of more specific immunosuppressive therapy.

A Vβ.2‐specific superantigen from exogenous mouse mammary tumor virus carried by FM mice

A number of endogenous mouse mammary tumor virus (MMTV) proviruses encode superantigen that have the ability to stimulate T cells with a certain T cell receptor (TCR) beta-chain variable region (V beta) and to mediate the V beta-specific clonal deletion. The tumorigenic milk-borne MMTV carried by C3H and GR mice also have superantigenic properties in vivo. In the present study we identified and characterized a novel V beta 8.2-specific superantigen of exogenous MMTV carried by FM mice. The open reading frame (ORF) in the 3' long terminal repeat of the MMTV was cloned by polymerase chain reaction with primers corresponding to conserved regions spanning the ORF coding region. Sequence analysis of the ORF revealed that there is no sequence identical to those in other known MMTV in the carboxy terminus implicated in TCR V beta recognition. Subcutaneous injection of the virus into adult BALB/c mice induced an approximately three- to fourfold enlargement of draining lymph nodes and a substantial increase of V beta 8.2+ CD4+ T cells in the lymph nodes within 6 days. The exposure of newborn BALB/c mice to the virus by foster nursing resulted in a marked deletion of V beta 8.2+ cells both in CD4+ and CD8+ T cells. Thus, a novel milk-borne MMTV in FM mice expresses strong superantigenic properties capable of stimulating V beta 8.2+ T cells. V beta 8.2+ T cells have been demonstrated to be frequently involved in recognition of conventional antigens and responsible for autoimmune diseases such as experimental allergic encephalomyelitis. Therefore, the MMTV (FM) may provide a new mouse model system for inducing immunodeficiency or autoimmune disease by retroviral infection.

Frequent occurrence of in vivo clonal expansion of CD4- CD8- T cells bearing T cell receptor alpha beta chains in adult humans.

We have previously reported 2 cases of healthy men showing in vivo monoclonal expansion of mature CD4- CD8- alpha beta T cells. In the present study, an additional 3 adults were found to exhibit such an expansion, among a total 464 adult donors studied. These 5 individuals were otherwise physiologically normal, with no history of severe illness and autoimmune disease at the time of examination. To investigate the mechanisms of the clonal expansion, further characterization of the clonal cells was attempted. No apparent preference for usage of the T cell receptor beta chain variable region was observed in the clonal T cells. These clonal T cells showed lectin-dependent or redirected antibody-dependent cell-mediated cytotoxicities, whereas they could not lyse autologous lymphoblastoid cell lines. Failure of Fas antigen expression was not observed for any of these clones. These results suggest that clonal expansion of CD4- CD8- alpha beta T cells frequently occurs in the periphery without any T cell abnormalities.

T cell receptor beta chain gene polymorphisms in Graves' disease.

Graves' disease, or subgroups of such patients with thyroglobulin antibodies or HLA-DR3, have been associated with a restriction fragment length polymorphism of the T cell receptor beta chain constant region gene but not all studies are in agreement. We have examined 58 patients with Graves' disease and found no abnormal distribution of this polymorphism compared to 33 controls. There was also no significant association with the presence of thyroglobulin antibodies or HLA-DR3, even when the results were pooled with previously collected data (N = 90 patients with TG antibody results and N = 128 patients with HLA-DR types). We also found no abnormal distribution of three polymorphisms of the T cell receptor beta chain variable region genes, using probes which span over 600 kb of this complex. These results argue against an association of these allelic variations of the T cell receptor beta chain with Graves' disease.

A T cell receptor beta chain variable region polymorphism associated with radiographic progression in rheumatoid arthritis.

In rheumatoid arthritis (RA) genetic factors influence susceptibility to disease and progression. Identifying these genetic factors may give more insight into the aetiology and pathogenesis of this disease. Furthermore, if these genetic markers can predict progression in an early stage of disease, timely institution of more aggressive treatment in patients with a bad prognosis may help to prevent joint damage. Several studies have shown that HLA-DRB1 alleles are associated with RA, whereas others have indicated that genes not linked to the HLA complex are also involved. Candidates for such genes are the T cell receptor (TCR) alpha/beta genes. The association of a polymorphism in a TCR beta chain variable region gene (TCR-V beta 8) with both risk for RA and radiographic progression of joint disease was analysed after a three year follow up. A cohort of 118 white patients with a duration of disease shorter than one year at entry, and 110 white controls were typed for this (BamHI) TCR-V beta 8 polymorphism. The distribution of the two alleles, 2.0 and 23.0 kb, was identical in patients and controls. Radiographic progression (modified Sharp method) after a three year follow up, studied in 111 patients, was significantly less in the group possessing the 2.0 kb allele (p = 0.03). This does not confirm the reported association of the (BamHI) TCR-V beta 8 2.0 kb allele with RA. By contrast with previous findings in smaller studies, in the present study this 2.0 kb allele was protective against radiographic progression. Because well known prognostic variables in RA were corrected for, the findings indicate that the TCR-V beta 8 polymorphism studied is a new prognostic marker for this disease.

The human T-cell receptor beta-chain repertoire: longitudinal fluctuations and assessment in MHC matched populations.

The influence of the environment and of the major histocompatibility complex (MHC) in shaping the human T-cell receptor beta-chain variable region (TCRBV) repertoire has not been systematically studied. Here, expression of TCRBV gene families was estimated by a sensitive polymerase chain reaction (PCR)-based method. Serial studies of peripheral blood, performed at 2-week intervals over a 3-month period, revealed that fluctuation in the expression of many TCRBV genes occurred in healthy individuals and in the absence of clinically evident infections. Fluctuation of TCRBV4, TCRBV5.2, TCRBV9, and TCRBV13.1 genes were present in all subjects. Additional TCRBV genes fluctuated in some but not in other individuals. Comparison of the TCRBV repertoire between these unrelated individuals indicated differences in the mean expression of TCRBV5.1, TCRBV9, TCRBV11, TCRBV15, TCRBV17, and TCRBV20 genes. For any TCRBV gene, intersubject differences were generally of a magnitude of twofold or less. Larger differences characterized the TCRBV repertoire of CD4 compared to CD8 cells. Some differences, for example over-representation of TCRBV2 and TCRBV5.1 on CD4, and TCRBV10, TCRBV14, and TCRBV16 on CD8 cells, were present in most subjects. Individuals homozygous for DR2- or DR3-bearing extended MHC haplotypes displayed similar individual variability of TCRBV expression. These data indicate that the circulating TCRBV repertoire in humans is both dynamic and diverse. Both environment and MHC effects contribute to the diversity of TCRBV expression.

Major histocompatibility complex determinants select T-cell receptor alpha chain variable region dominance in a peptide-specific response.

Dominant expression of T-cell receptor (TCR) alpha or beta chain variable region (V alpha or V beta) gene families has been observed in the T-cell response to some conventional peptide antigens. Current models for the interaction of TCR V region elements with different determinants of a major histocompatibility complex (MHC)-peptide complex, the normal TCR ligand, suggest that the TCR V-J junctional region (CDR3, where J is joining) is the primary contact with a peptide epitope and that other TCR V region segments may interact directly with neighboring MHC determinants. This suggests that V alpha or V beta dominance in a specific response can be MHC-selected. In this case, if related peptides bind to an MHC molecule in a similar orientation, they could select for identical V alpha or V beta dominance even if they are noncrossreactive at the level of T-cell activation. We have screened for this possibility by introducing minimal conservative substitutions in a synthetic peptide, YYEELLKYYEELLK, that is presented to T cells in association with an uncommon A beta E alpha d mixed Ia isotype. We report here that the peptide variant FFEELLKFFEELLK is noncrossreactive with YYEELLKYYEELLK but appears to preserve the same MHC binding motif since T-cell responses are restricted to the same mixed A beta E alpha isotype. Although the two peptides are noncrossreactive in either direction, the same members of the V alpha 4 gene family are dominantly expressed in T cells specific for either peptide. We conclude that the similar topography of the two MHC-peptide complexes gives functional significance to a unique A beta E alpha determinant that selects for V alpha 4 dominance.

Superantigen staphylococcal enterotoxin B-induced T-helper cell activation is independent of CD4 molecules and phosphatidylinositol hydrolysis.

The role of the CD4 molecule in activation of T-helper cells was examined by investigating the effect of an anti-CD4 monoclonal antibody (Leu3a) in conventional peptide antigen-specific cloned T-helper cells that are also reactive to staphylococcal enterotoxin B (SEB). These T-helper cell clones are CD4+/CD45RO+/T-cell antigen receptor beta-chain variable region 12-positive and can respond to nominal peptide antigens and SEB by proliferation in the presence of class II major histocompatibility complex-expressing accessory cells. Although antigen and SEB were comparable in their ability to induce proliferative responses, interleukin 2 (IL-2) production, and IL-2 receptor alpha-chain expression, stimulation with SEB failed to trigger phosphatidylinositol hydrolysis or a rise in the intracellular free calcium ion concentration. Leu3a treatment inhibited antigen-induced proliferative responses of T cells with concomitant suppression of IL-2 production and IL-2 receptor expression. In contrast, SEB-induced responses were unaffected by Leu3a. These findings indicate that the functional consequences of binding (ligation) of conventional antigen and of superantigen with the T-cell receptor are distinct in the context of both signal transduction pathways and participation of CD4 molecules.

T-cell antigen receptor binding sites for the microbial superantigen staphylococcal enterotoxin A.

We have examined the interaction of the microbial superantigen staphylococcal enterotoxin A (SEA) with peptides corresponding to overlapping regions of the T-cell antigen receptor beta chain variable region V beta 3. SEA is known to stimulate murine T cells bearing certain V beta elements, among them V beta 3. Five peptides were synthesized representing amino acids 1-24, 20-44, 39-60, 57-77, and 74-95 of V beta 3. We demonstrate here that soluble V beta 3-bearing beta chains can bind to a complex of SEA and major histocompatibility complex class II and that the synthetic peptide V beta 3-(57-77) blocked this interaction. The peptide V beta 3-(57-77) also inhibited SEA-induced interferon-gamma production and SEA-induced proliferation of B10.BR spleen cells. Conversely, the peptide corresponding to amino acids 57-77 of V beta 8.2, a V beta element that is not recognized by SEA, decreased staphylococcal enterotoxin C-2-induced proliferation but did not affect SEA-induced proliferation. The peptide inhibition of SEA-induced function was due at least in part to inhibition of V beta 3-bearing T-cell activity, since the percentage of T cells reactive with an anti-V beta 3 monoclonal antibody was significantly reduced by V beta 3-(57-77). These data suggest that the region of V beta 3 encompassing amino acids 57-77 is an area that displays the appropriate sequence and conformation for binding of the SEA molecule and blocking of the resultant interaction with the T-cell antigen receptor.

Identification of a limited T-cell receptor beta chain variable region repertoire associated with diabetes in the BB rat.

Diabetes-prone BB rats spontaneously develop type 1 diabetes due to a T-cell-dependent destruction of insulin-producing beta-islet cells. A number of T-cell abnormalities including lymphopenia, poor cell-mediated responsiveness to alloantigen, and an absence of an RT6+ T-cell subset are associated with disease susceptibility. Our previous studies have implicated the thymic antigen-presenting cell in influencing disease potential and responsiveness to alloantigen. Since this cell type is also known to influence T-cell receptor expression in developing thymocytes, we examined the thymic and peripheral T-cell receptor beta chain variable region repertoire in diabetes-prone and diabetes-resistant rats. Our findings indicate that animals susceptible to diabetes induction have a characteristic and limited peripheral beta chain variable region repertoire that differs markedly from that expressed in the thymus.

Identification of a T cell receptor beta chain variable region, V beta 20, that is differentially expressed in various strains of mice.

A cDNA library of TCR beta chain transcripts from BALB/c thymocytes was constructed using anchored polymerase chain reaction (PCR). Screening of this library led to the identification of a V beta gene segment, V beta 20, structurally related to V beta 3 and V beta 17. Genomic analysis of mice displaying deletions in their V beta loci, together with mapping of cosmid clones, situated V beta 20 2.5 kb beside V beta 17. The expression of V beta 20 was estimated by PCR in mice of different H-2 and Mls types. Peripheral T cells from H-2k and H-2d mice did not express V beta 20, whereas in I-E-negative mice (C57Bl/6 and SJL), V beta 20 transcripts were detected. The lack of V beta 20 transcripts in (C57Bl/6 x CBA/J)F1, (C57Bl/6 x BALB/c)F1, and in congenic B6.H-2k mice suggests that the differential use of V beta 20 is due to an I-E-mediated clonal deletion process. The involvement of the Mls super antigens was excluded by analysis of all Mls type combinations. The nature of the V beta 20-deleting element(s) is discussed in the context of the I-E/superantigen systems controlling the expression of V beta 11 and V beta 17.

A method for production of antibodies to human T-cell receptor beta-chain variable regions.

Mouse T-cell hybridomas bearing human V beta elements were produced by transfection of human/mouse hybrid T-cell receptor beta-chain genes into a mouse T-cell hybridoma lacking an endogenous beta-chain gene. These hybridomas were entirely mouse in origin except for the human V beta region. These cells were used to immunize mice against human V beta elements. Mouse monoclonal antibodies have thus been generated against human V beta 13.1 and -13.2. We expect that the method outlined in this paper will be useful in the production of monoclonal antibodies specific for other human V beta or V alpha elements.

Staphylococcal exotoxins deliver activation signals to human T-cell clones via major histocompatibility complex class II molecules.

We investigated whether staphylococcal exotoxins (SEs), in addition to their capacity to induce T-cell activation restricted by the T-cell receptor (TCR) beta-chain variable region, can deliver an activation signal to human T-cell clones through major histocompatibility complex (MHC) class II molecules. Eleven human T-cell clones (9 alpha beta TCR and 2 gamma delta TCR clones) of different antigenic specificities were tested for their capacity to proliferate in response to toxic shock syndrome toxin 1 (TSST-1) and two SEs, SEA and SEB. In the absence of accessory cells, only 4 alpha beta TCR clones were stimulated to proliferate, each by a single SE, and to mobilize intracellular free Ca2+ in response to that SE, events indicative of TCR engagement and, presumably, recognition restricted by the beta-chain variable region. In the presence of accessory cells, each of the 11 T-cell clones was stimulated to proliferate by any one of the three SEs tested. This apparently TCR-unrestricted SE-mediated polyclonal proliferation of T-cell clones occurred in the absence of an increase in intracellular free Ca2+ and was not dependent on the presence of MHC class II expression on accessory cells. In contrast, SE-mediated polyclonal proliferation did not occur in 3 alpha beta TCR clones derived from an MHC class II-deficient patient. Furthermore, all of the three SEs induced the proliferation of 4 natural-killer-cell clones, suggesting that expression of TCR/CD3 complex is not essential for SE-mediated polyclonal proliferation of activated lymphocytes. These results indicate that MHC class II molecules transduce activation signals to human T- and natural-killer-cell clones.