Peripheral blood T lymphocytes in systemic vasculitis: increased T cell receptor Vβ2 gene usage in microscopic polyarteritis

Antigen recognition by T lymphocytes is mediated by cell surface receptors. T cell specificity depends on the variable, diversity and junctional (VDJ) regions of the α and β polypeptide chains of the T cell receptor (TCR). The expression of the variable region genes of the β chain (Vβ) has been analysed to study the involvement of peripheral blood T cells in systemic vasculitis. RNA was extracted from peripheral blood lymphocytes of 12 patients with microscopic polyarteritis, 10 with Wegener's granulomatosis, six with unclassified vasculitis, and 28 healthy age- and sex-matched individuals. Complementary DNA was made from RNA and amplified by the anchored polymerase chain reaction (PCR) using redundant oligonucleotide primers for the TCR Vβ genes. To determine if the dominant usage of a Vβ gene family reflected the presence of particular T cell clones, cDNA was amplified with primers for the specific Vβ gene family. The product was screened for sequence homogeneity by single-stranded conformational polymorphism (SSCP) and cloned to sequence the adjoining TCR (Dβ)Jβ region. A significant increase in the mean percentage expression of the Vβ 2.1 gene was seen in vasculitis patients (11·4+1·0% (mean + s.e.m.)) compared with controls (6·6 + 0·6%; P < 0·003). The most marked increase was seen in microscopic polyarteritis (13·9 + 1·7%; P < 0·0001). There were also increases in the expression of Vβ3, 13 and 14 in peripheral blood of vasculitis patients compared with controls. SSCP analysis of Vβ 2.1 amplified products indicated the presence of oligoclonal bands in a smaller proportion of patients (8/27) than controls (12/28). There was no strong evidence for the conservation of the TCR Vβ 2.1 junctional region sequence data from a sample group of three patients with oligoclonal bands. Thus, a subset of patients with systemic vasculitis, particularly those with microscopic polyarteritis, have increased TCR Vβ 2.1 gene expression in their peripheral blood T cell repertoire. As superantigens binding Vβ 2.1 are postulated to activate T cells with diverse CDR3 sequences, it is proposed that a superantigen is involved in the immunopathogenesis of vasculitis.     

The homogeneity of the TCRδ repertoire expressed by the Thy-1dull γ δ T cell population is due to cellular selection

Thy-1^dull γ δ T cells are an unusual subset of mature TCRγ δ T cells characterized by their highly restricted TCR repertoire. In DBA/2 mice, they predominantly express the product of the Vγ1 gene together with that of a member of the Vδ6 subfamily (the Vδ6.4 gene) and their junctional sequences show very little diversity. To address the mechanisms underlying the expression of the restricted TCRγ δ repertoire, we have cloned all Vδ6 subfamily members present in DBA/2 mice and studied their frequency of expression in Thy-1^dull and Thy-1^bright γ δ thymocyte populations. Furthermore, we have also cloned non-functional Vδ6DδJδ1 rearrangements present in the Thy-1^dull γ δ T cell population and compared their Vδ6 gene utilization and their junctional sequences with those expressed by this population. Our results indicate that the restricted TCRδ repertoire expressed by the Thy-1^dull γ δ thymocytes results from cellular selection, rather than molecular constraints suggesting the existence of a limited set of self-ligands. Finally, phenotypic, functional and TCRγ δ repertoire analysis of Thy-1^dull γ δ T cells in β2 -microglobulin (β₂m)-deficient mice indicated that these putative ligands are not β₂m-dependent major histocompatibility complex class I or class I-like molecules.     

T cell receptor-γδ-expressing fetal mouse thymocytes are generated without T cell receptor Vβ selection

We investigated whether fetal mouse T cell receptor (TCR) γδ cells have been subjected to so-called TCRβ selection at the CD25 stage of thymus development. To this end, we carried out a comparative three-color flow microfluorimetric analysis of TCRβδ cells developing in the fetal, neonatal and adult thymus using monoclonal antibodies to CD2, CD8, CD24, CD25 and CD44. Day-15 fetal TCRγδ cells were CD2⁺, suggesting an origin at a post-CD25 stage. Molecular analysis of TCRβ rearrangements were also carried out. Thus, by semi-quantitative polymerase chain reaction (PCR) amplification of Vβ6 and Vβ8 to Jβ2 rearrangements day-15 fetal TCRγδ showed extensive TCRβ rearrangements, a finding confirmed by PCR amplification from single micromanipulated cells. Finally, sequencing analysis of 104 PCR-amplified TCR VDJβ2 fragments showed that the majority (58%) were rearranged out of frame. Taken together, these phenotypic and molecular analyses suggest that fetal TCRγδ cells have not been subject to TCRβ selection.     

Phosphoantigen activation induces surface translocation of intracellular CD94/NKG2A class I receptor on CD94− peripheral Vγ9 Vδ2 T cells but not on CD94− thymic or mature γ δ T cell clones

Most adult peripheral blood γ δ T cells express Vγ9/Vδ2-encoded TCR that recognize a restricted set of nonpeptidic phosphorylated compounds, referred to as phosphoantigens. They also express various MHC class I-specific inhibitory receptors (IR), in particular CD94/NKG2-A heterodimers, which participate in the fine tuning of their TCR-mediated activation threshold. Most mature Vγ9/Vδ2 T cells express surface CD94 receptors, unlike cord blood or thymus-derived Vγ9/Vδ2 clones, thus suggesting a role for the microenvironment in IR expression. In the present study we show that most CD94⁻ Vγ9Vδ2 PBL ex vivo express an intracellular pool of CD94/NKG2-A receptors that is translocated to the cell surface upon activation by phosphoantigens or IL-2. In stark contrast, intracellular CD94/NKG2-A complexes are undetectable in CD94⁻ thymus or PBL-derived mature Vδ2 T cell clones, and no surface induction is observed following phosphoantigen activation of T cell clones. Altogether these results provide new insights into the regulation of CD94/NKG2-A expression on T lymphocytes and suggest the existence of distinct mechanisms controlling in vivo and in vitro induction of IR on these cells.     

The Jβ segment of the T cell receptor contributes to the Vβ-specific T cell expansion caused by staphylococcal enterotoxin B and Urtica dioica superantigens

We have used a new polymerase chain reaction-based technique to analyze at the clonal level the CDR3 diversity and the Jβ usage associated with the Vβ-dependent T cell receptor (TCR) recognition of two superantigens: the staphylococcal enterotoxin B and the Urtica dioica agglutinin. Our results show that a subset of Jβ elements is preferentially expanded in a given Vβ family, independently of the nature of the superantigen. By contrast, the CDR3 loop does not contribute significantly to the T cell expansion induced by the superantigens. We conclude that the Jβ segment of the TCR β chain, but not the CDR3 region, participates in superantigen binding, presumably by influencing the quaternary structure of the TCR β chain.     

T cell receptor γδ repertoire is skewed in cerebrospinal fluid of multiple sclerosis patients: molecular and functional analyses of antigen-reactive γδ clones

To study the relevance of γδ T cells in multiple sclerosis (MS) we analyzed the T cell receptor (TCR) γδ repertoire and the antigen reactivity of γδ clones isolated from cerebrospinal fluid (CSF). In T cell cultures derived from CSF we found an increased percentage of Vδ1⁺ cells as compared to peripheral blood of the same donors. Phenotypic analysis of cells from MS CSF with Vγ- and Vγ-specific monoclonal antibodies (mAb) showed that the Vγ1 chain is most frequently associated with γ chains belonging to the VγI family. Sequence analysis of TCR genes revealed heterogeneity of junctional regions in both δ and γ genes indicating polyclonal expansion. γδ clones were established and some recognized glioblastoma, astrocytoma or monocytic cell lines. Stimulation with these targets induced serine esterase release and lymphokine expression characteristic of the T_H0-like phenotype. Remarkably, these tumor-reactive γδ cells were not detected in the peripheral blood using PCR oligotyping, but were found in other CSF lines independently established from the same MS patient. Altogether, these results demonstrate that in the CSF there is a skewed TCR γδ repertoire and suggest that γδ cells reacting against brain-derived antigens might have been locally expanded.     

Effects of interferon-α on cytokine profile,T cell receptor repertoire and peptide reactivity of human allergen-specific T cells

A large panel of T cell clones (TCC) specific for the recombinant form of Poa pratensis allergen (rKBG7.2 or Poa p9) were established from the peripheral blood of a grass pollen-sensitive donor in the absence or presence of recombinant interferon-α (IFN-α) in bulk culture and their pattern of cytokine secretion, peptide reactivity and TCR Vβ repertoire was examined. The majority of allergen-specific TCC derived in absence of IFN-α produced high amounts of interleukin-4 (IL-4) and IL-5 but not IFN-γ (Th2 cells), while most of TCC derived in presence of IFN-α produced IFN-γ but not, or limited amounts of, IL-4 and IL-5 (Th1 or Th0 cells). Of 24 TCC established in the presence of IFN-α, 22 were able to recognize a single allergen peptide, p26, while none of the clones established in the absence of IFN-α showed a similar specificity. The majority of both clones expressed the Vβ2 element regardless of whether they were established in the presence of IFN-α, but the presence of IFN-α favored the expansion of Vβ2⁺, Vβ17⁺ and Vβ22⁺ Poa p9-specific T cells, whereas in the absence of IFN-α, other TCR Vβ-bearing T cells (Vβ5, Vβ6.7 and Vβ14) were expanded in addition to Vβ2⁺ T cells. None of Vβ2⁺ clones established in the absence of IFN-α reacted with p26, whereas all the Vβ2⁺ clones established in its presence responded to this peptide. IFN-α also shifted the TCR Vβ repertoire of both Poa p9- and Lolium perenne group 1 (Lol p1)-specific T cell lines generated from the same patient and from a different grass-sensitive individual. These data demonstrate that IFN-α modulates the development of allergen-specific T cells in vitro, and suggest that IFN-α may represent an useful tool for novel immunotherapeutic approaches in allergic disorders.     

The expansion and selection of T cell receptor αβ intestinal intraepithelial T cell clones

In conventional mice, the T cell receptor (TCR)αβ⁺ CD8αα⁺ and CD8αβ⁺ subsets of the intestinal intraepithelial lymphocytes (IEL) constitute two subpopulations. Each comprise a few hundred clones expressing apparently random receptor repertoires which are different in individual genetically identical mice (Regnault, A., Cumano, A., Vassalli, P., Guy-Grand, D. and Kourilsky, P., J. Exp. Med. 1994. 180: 1345). We analyzed the repertoire diversity of sorted CD8αα and CD8αβ⁺ IEL populations from the small intestine of individual germ-free mice that contain ten times less TCRαβ⁺ T cells than conventional mice. The TCRβ repertoire of the CD8αα and the CD8αβ IEL populations of germ-free adult mice shows the same degree of oligoclonality as that of conventional mice. These results show that the intestinal microflora is not responsible for the repertoire oligoclonality of TCRαβ⁺ IEL. The presence of the microflora leads to an expansion of clones which arise independently of bacteria. To evaluate the degree of expansion of IEL clones in conventional mice, we went on to measure their clone sizes in vivo by quantitative PCR in the total and in adjacent sections of the small intestine of adult animals. We found that both the CD8αα and the CD8αβ TCRαβ IEL clones have a heterogeneous size pattern, with clones containing from 3 × 10³ cells up to 1.2 × 10⁶ cells, the clones being qualitatively and quantitatively different in individual mice. Cells from a given IEL clone are not evenly distributed throughout the length of the small intestine. The observation that the TCRαβ IEL populations comprise a few hundred clones of very heterogeneous size and distribution suggests that they arise from a limited number of precursors, which may be slowly but continuously renewed, and undergo extensive clonal expansion in the epithelium.     

Analysis of TCR β chains in Lewis rats with experimental allergic encephalomyelitis. II. Vβ8.2+ T cells with limited CDR3 N region additions derive from the adult thymus

Immunization of Lewis (LEW) rats with guinea pig myelin basic protein (MBP) induces a population of encephalitogenic CD4 T cells having specificity for the dominant immunogenic peptide of MBP, 68 – 86. The TCR β chains of these disease-causing T cells show three distinct features: they are almost exclusively Vβ8.2, they use AspSer as the first two amino acid residues of the third complementarity-determining region (CDR3) and these junctional region sequences show few if any non-germline N-region nucleotide additions. This last feature raises the possibility that these autoimmune T cell precursors derive from TCR gene rearrangements occurring during early, perinatal ontogeny, a period when the enzyme terminal deoxynucleotidyl transferase (TdT), responsible for N region additions, is not expressed. An alternative possibility is that these features of the TCR of MBP 68 – 86-reactive T cells are dictated by considerations of antigen selection throughout ontogeny both in the thymus and in the periphery – i.e., that such β chains are conformationally the most appropriate for triggering by an epitope of 68 – 86 complexed to class II RT1.B^l MHC molecules. We show here that active experimental allergic encephalomyelitis, while delayed in onset, occurs in heavily irradiated animals, but not in the absence of a thymus, a finding indicating that this autoimmune disease is caused by a T cell subpopulation derived from the post-irradiation adult thymus. These disease-causing T cells are heavily Vβ8.2⁺ , CDR3 AspSer⁺ and use few N region additions. We conclude that T cells with these TCR β chain features can be generated in the adult thymus and most likely reflect requirements imposed by antigen selection.     

Restricted T cell receptor expression by human T cell clones specific for mycobacterial 65-kDa heat-shock protein: Selective in vivo expansion of T cells bearing defined receptors

We have examined the T cell receptor (TcR) expression of clones specific for epitopes of mycobacterial 65-kDa heat-shock protein (hsp65) in the context of two different HLA molecules, and used this system as a model to assess the selection of T cells responsive to this antigen in vivo. DR3-restricted clones were raised from both the synovial fluid (SF) and peripheral blood (PB) of a patient with reactive arthritis in three separate cloning events. Five of five SF-derived clones tested expressed either Vβ5.2 or a closely related β chain, Vβ5.6.The α chains expressed by Vβ5.2⁺ and Vβ5.6⁺ clones were from different families, Vα2.4 and Vα23.2, respectively. Nine of ten clones derived from two cloning procedures on PB taken 3 years later also expressed either Vβ5.2 or Vβ5.6. This suggests that the TcR repertoire for recognizing this major histocompatibility complex/peptide complex is relatively restricted and favors the use of Vβ5. Conservation of the β chain third complementarity-determining region (CDR3) sequence was not evident, however. Sequencing α and β chains of representative Vβ5.2⁺ and Vβ5.6⁺ PB-derived clones revealed TcR which were identical to those utilized by the SF-derived clones, showing that the repertoire for recognition of this antigen is stable over time. Similar studies of TcR expression were carried out on hsp65-specific, DP4-restricted clones derived from the SF of a patient with rheumatoid arthritis by two independent cloning procedures. There was conservation of a chain usage, since all clones expressed a member of the Vαl family, but again CDR3 sequence conservation was not apparent, β chain usage was not restricted since different clones expressed Vβ6.7, Vβ22.3 and Vβ12. Subtle differences in epitope specificity were detected for two clones with differing TcR. Once more, T cell clones with identical α and β TcR chains were obtained from the separate cloning procedures, suggesting oligoclonalty of T cells with this defined specificity in the patient's SF.     

Helper activity of CD4+ αβ T cells is required for the avian γδ T cell response

We have studied the in vitro activation of chicken γδ T cells. Both splenic αβ and γδ T cells obtained from complete Freund's adjuvant-primed chickens proliferated in vitro when stimulated with mycobacterial sonicate or purified protein derivative of Mycobacterium tuberculosis. When CD4⁺ cells or αβ T cell receptor (TcR)-positive cells were removed, both the proliferation and the blast formation of γδ T cells in response to mycobacterial antigens were abrogated. The response was restored if supernatant from concanavalin A (Con A)-activated lymphocyte cultures (CAS) as a source of helper factors was added together with the specific antigen purified protein derivative. The CD4- or αβ TcR-depleted cells still proliferated in response to Con A, although a decrease of the response was observed. To analyze the γδ T cell response more specifically we stimulated peripheral blood cells with immobilized monoclonal antibodies against T cell receptor. Anti-γδ TcR antibody alone did not induce significant proliferation. When CAS was added together with the anti-γδ TcR monoclonal antibody, a strong proliferation of γδ T cells was observed. In contrast, both Vβ1- and Vβ2-expressing αβ T cells proliferated in vitro in response to stimulation with the relevant anti-TcR monoclonal antibody alone. Depletion of either Vβ1⁺ or Vβ2⁺ T cell subset alone had no negative effect on the proliferation or blast formation of γδ T cells stimulated with mycobacterial antigens. Taken together our results suggest that CD4⁺ αβ T cells (both Vβl- and Vβ2-expressing) play a role in the activation and response of chicken γδ T cells.     

γδ T cells are secondary participants in acute graft-versus-host reactions initiated by CD4+ αβT cells

To examine the role of T cell subpopulations in an acute graft-versus-host (GVH) reaction, γδ T cells and αβ T cells expressing one of the two prototypic Vβ gene families were negatively isolated from adult blood samples and injected into allogeneic chick embryos. CD4⁺ αβ T cells expressing either Vβ1 or Vβ2 receptors were equally capable of inducing acute GVH reactions, consistent with the idea that αβ T cell alloreactivity is determined by CDR3 variability. By themselves, the γδ T cells were incapable of inducing GVH reactions. However, host γδ T cells were recruited into the donor αβ T cell-initiated lesions, where they were activated and induced to proliferate. The data suggest that γβ T cells may play a secondary role in GVH reactions.     

Characteristics of fetal thymus-derived T cell receptor γδ intestinal intraepithelial lymphocytes

We have previously demonstrated that grafting of CBF1(H-2^b/d) fetal thymus (FTG) under the kidney capsule of congenitally athymic nude mice of BALB/c background (H-2^d) generates a substantial number of T cell receptor (TCR) γδ intestinal intraepithelial lymphocytes (IEL) that were of FTG origin (H-2^b+) (see accompanying report). Here we investigated the characteristics of these FTG-derived TCR γδ IEL and compared them to the extrathymically derived TCR γδ IEL found in nude mice. Phenotypically, FTG-derived TCR γδ IEL were similar to their extrathymically derived counterparts in that most were Thy-1 ^?, CD5^? and CD8αα (homodimer). Vγ and Vδ gene usage in thymus-derived and extrathymically derived TCR γδ IEL were found to be virtually the same. Functionally, FTG-derived TCR γδ IEL were similar to the TCR γδ IEL found in euthymic mice as both were relatively anergic to TCR cross-linking in vitro. However, FTG-derived TCR γδ IEL differed slightly from extrathymically derived TCR γδ IEL, which were completely nonresponsive to the same in vitro stimulation. Overall, these findings support the view that FTG-derived and extrathymically derived TCR γδ IEL are almost indistinguishable. Lastly, we demonstrate that despite their thymic origin, development of FTG-derived TCR γδ IEL partially takes place extrathymically; that is positive selection of FTG-derived Vδ4 IEL occurs extrathymically. In addition, we demonstrate that the CD8 molecule is not necessary for development and homing of FTG-derived TCR γδ IEL. This later finding suggests that the CD8αα molecule develops extrathymically for FTG-derived CD8αα TCR γδ IEL.     

Clonal expansion of myelin basic protein-reactive T cells in patients with multiple sclerosis: Restricted T cell receptor V gene rearrangements and CDR3 sequence

Myelin basic protein (MBP)-reactive T cells are thought to play an important role in the pathogenesis of multiple sclerosis (MS). In some patients with MS, these autoreactive T cells display a limited heterogeneity in their epitope recognition and T cell receptor (TCR) variable (V) gene usage. These individual-dependent properties of MBP-reactive T cells have led to the speculation that they may represent clonal expansion in vivo in some MS patients. In the present study, 51 MBP-reactive T cell clones derived from patients with MS and healthy individuals were examined for their epitope recognition and the TCR Vα and Vβ gene rearrangements. The V gene junctional region sequences of identified α and β genes were further analyzed to probe their clonal origins, as the sequences are unique for individual clones. Our data showed that 26 clones derived from nine patients with MS shared a predominant reactivity to the immunodominant regions of MBP, 84–102, 110–129 and 143–168, and used various TCR Vα and Vβ rearrangements. The V gene usage of the clones was restricted to certain Vα Vβ combination(s) in a given MS patient, but varied among different patients. The sequence analysis revealed that the clones generated from a given patient shared a limited or a single junctional region sequence pattern(s), indicating their oligoclonal or monoclonal origin(s). In contrast, 25 MBP-reactive T cell clones derived from normal individuals exhibited unfocused epitope recognition and V gene usage. Thus, the limited heterogeneity of MBP-reactive T cells in their structural and functional charactertistics reflects their clonal expansion in vivo in some patients with MS.     

Expression of pro-inflammatory cytokines by TCRαβ+ T and TCRγδ+ T cells in an experimental model of colitis

An inflammatory bowel disease (IBD) comparable to human ulcerative colitis is induced upon transfer of T cell-depleted wild-type (F1) bone marrow into syngeneic T cell-deficient (tgε26) mice (F1 → tgε26). Previously we have shown that activated CD4⁺ T cells predominate in transplanted tgε26 mice, and adoptive transfer experiments verified the potential of these cells to cause disease in immunodeficient recipient mice. Using flow cytometry for the detection of intracellular cytokine expression, we demonstrate in the present study that large numbers of CD4⁺ and CD8⁺ TCRαβ⁺ T cells from the intraepithelial region and lamina propria of the colon of diseased, but not from disease-free mice, produced interferon-γ (IFN-γ) and tumor necrosis factor-α (TNF-α). Large numbers of T cells from peripheral lymphoid tissues of these animals also expressed IFN-α and TNF-α, but few expressed interleukin-4, demonstrating g strong bias towards Th1-type T cell responses in these animals. TCRγδ⁺ T cells, typically minor constituents of the inflammatory infiltrate of the colon in F1 → tgε26 mice, also expressed IFN-γ at a high frequency upon CD3 stimulation. In light of these findings we examined the potential involvement of TCRγδ⁺ T cells by testing their ability to induce colitis in tgε26 mice. We report here that tgε26 mice transplanted with T cell-depleted bone marrow from TCRα^null and TCRβ^null animals developed IBD. Furthermore, disease in these mice correlated with the development of peripheral and colonic TCRαδ⁺ T cells capable of IFN-γ production. These results suggest that IFN-γ may be a common mediator of IBD utilized by pathogenic T cells of distinct phenotype.     

Fine antigen specificity of human γδ T cell lines (Vγ9+) established by repetitive stimulation with a serotype (KTH-1) of a gram-positive bacterium,Streptococcus sanguis

We have established human γδ T cell lines specific for Streptococcus sanguis (S. sanguis) KTH-1 present in normal oral cavity flora. The CD4^?CD8^? CD3⁺Vγ9⁺Vδ1^?CD45RO⁺ CD25⁺ T cell lines showed a proliferative response to the streptococcal antigen (Ag) in the presence of autologous antigen-presenting cells without apparent evidence of HLA restriction. The proliferative response of the γδ T cell lines was completely blocked by anti-TcRγδ monoclonal antibody (mAb) and anti-HLA class I mAb (W6/32), whereas anti-HLA classical class Ia mAb (B-H9; anti-HLA-A,B,C), anti-HLA class II mAb (anti-DR, anti-DQ, and anti-DP) and anti-CD4 mAb did not have any inhibitory effects. Surprisingly, the γδ T cell lines showed the proliferative response against the original bacterial Ag KTH-1 exclusively, and exhibited no cross-reactivity with nominal Ag such as purified protein derivative of tuberculin, tetanus toxoid and Mycobacterium tuberculosis, or the same species but different strain of S. sanguis, American Type Culture Collection (ATCC) standard strain (10556), or even with the same strain but different serotype of S. sanguis, KTH-3. Moreover, cytokine production of the γδ T cell lines was similar to the Th1 pattern [interferon-γ, tumor necrosis factor (TNF)-α and TNF-β]. They also produced interleukin-8 that functions as one of chemoattractants for polymorphonuclear cells. Using direct sequencing technique of the polymerase chain reaction products, we found that junctional diversity of the T cell receptor (TcR) used by the parental KTH-1 specific γδ T cell line and its subclones is rather limited. It is suggested that γδ T cells with canonical TcR could preferentially respond to KTH-1 Ag. Thus, in addition to a broad or cross-reactivity of γδ T cells against phylogenetically conserved stress/heat-shock protein, which is well characterized by others, some peripheral blood γδ T cells could recognize and kill exogenous agents with fine antigenic specificity to protect the body against them.     

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) β-chain variable region (Vβ) and to mediate the Vβ-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 Vβ8.2-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 Vβ 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 Vβ8.2⁺ 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 Vβ8.2⁺ cells both in CD4⁺ and CD8⁺ T cells. Thus, a novel milk-borne MMTV in FM mice expresses strong superantigenic properties capable of stimulating Vβ8.2⁺ T cells. Vβ8.2⁺ 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.