The T-cell repertoire is heavily influenced by tolerance to polymorphic self-antigens

No evidence for TCR V beta repertoire changes influencing disease protection in E-transgenic NOD mice

In order to study whether positive selection of T cells plays any role in the MHC-dependent protection from diabetes in the non-obese-diabetic (NOD) mouse, the T cell V beta repertoire has been studied in NOD mice and in NOD mice either transgenic for the wildtype MHC class II E alpha gene, or for delta Y, a promotor-mutagenized E alpha gene with a restricted tissue expression. The E alpha transgenic line is protected from both insulitis and diabetes. The delta Y transgenic line is neither protected from insulitis nor from diabetes, although it can perform both positive and negative E-mediated selection in the thymus. The V beta repertoire was studied in the pancreatic lymph nodes as these drain the area which is the target for the autoimmune attack. We see no evidence for E alpha TCR V beta repertoire differing from both nontransgenic NOD mice and delta Y mice despite its striking difference in susceptibility to autoimmunity. We conclude that none of the differences in the TCR V beta repertoire of E alpha-transgenic NOD mice hitherto observed are likely to explain the protective effect of E molecule expression in NOD mice.

Susceptibility to tumors induced by polyoma virus is conferred by an endogenous mouse mammary tumor virus superantigen

A dominant gene carried in certain inbred mouse strains confers susceptibility to tumors induced by polyoma virus. This gene, designated Pyvs, was defined in crosses between the highly susceptible C3H/BiDa strain and the highly resistant but H-2k-identical C57BR/cdJ strain. The resistance of C57BR/cdJ mice is overcome by irradiation, indicating an immunological basis. In F1 x C57BR/cdJ backcross mice, tumor susceptibility cosegregates with Mtv-7, a mouse mammary tumor provirus carried by the C3H/BiDa strain. This suggests that Pyvs might encode the Mtv-7 superantigen (SAG) and abrogate polyoma tumor immunosurveillance through elimination of T cells bearing specific V beta domains. DNA typing of 110 backcross mice showed no evidence of recombination between Pyvs and Mtv-7. Strongly biased usage of V beta 6 by polyoma virus-specific CD8+ cytotoxic T lymphocytes in C57BR/cdJ mice implicates T cells bearing this Mtv-7 SAG-reactive V beta domain as critical anti-polyoma tumor effector cells in vivo. These results indicate identity between Pyvs and Mtv-7 sag, and demonstrate a novel mechanism of inherited susceptibility to virus-induced tumors based on effects of an endogenous superantigen on the host's T cell repertoire.

Antigen-specific development of primary and memory T cells in vivo

The expansion and contraction of specific helper T cells in the draining lymph nodes of normal mice after injection with antigen was followed. T cell receptors from purified primary and memory responder cells had highly restricted junctional regions, indicating antigen-driven selection. Selection for homogeneity in the length of the third complementarity-determining region (CDR3) occurs before selection for some of the characteristic amino acids, indicating the importance of this parameter in T cell receptor recognition. Ultimately, particular T cell receptor sequences come to predominate in the secondary response and others disappear, showing the selective preservation or expansion of specific T cell clones.

T cell receptor V beta repertoire in mice lacking endogenous mouse mammary tumor provirus

When endogenous mouse mammary tumor virus (MMTV) superantigens (SAg) are expressed in the first weeks of life an efficient thymic deletion of T cells expressing MMTV SAg-reactive T cell receptor (TcR) V beta segments is observed. As most inbred mouse strains and wild mice contain integrated MMTV DNA, knowing the precise extent of MMTV influence on T cell development is required in order to study T cell immunobiology in the mouse. In this report, backcross breeding between BALB.D2 (Mtv-6, -7, -8 and -9) and 38CH (Mtv-) mice was carried out to obtain animals either lacking endogenous MMTV or containing a single MMTV locus, i.e. Mtv-6, -7, -8 or -9. The TcR V beta chain (TcR V beta) usage in these mice was analyzed using monoclonal antibodies specific for TcR V beta 2, V beta 3, V beta 4, V beta 5, V beta 6, V beta 7, V beta 8, V beta 11, V beta 12 and V beta 14 segments. Both Mtv-8+ mice and Mtv-9+ mice deleted TcR V beta 5+ and V beta 11+ T cells. Moreover, we also observed the deletion of TcR V beta 12+ cells by Mtv-8 and Mtv-9 products. Mtv-6+ and Mtv-7+ animals deleted TcR V beta 3+ and V beta 5+ cells, and TcR V beta 6+, V beta 7+ and V beta 8.1+ cells, respectively. Unexpectedly, TcR V beta 8.2+ cells were also deleted in some backcross mice expressing Mtv-7. TcR V beta 8.2 reactivity to Mtv-7 was shown to be brought by the 38CH strain and to result from an amino acid substitution (Asn-->Asp) in position 19 on the TcR V beta 8.2 fragment. Reactivities of BALB.D2 TcR V beta 8.2 and 38CH TcR V beta 8.2 to the exogenous infectious viruses, MMTV(SW) and MMTV(SHN), were compared. Finally, the observation of increased frequencies of TcR V beta 2+, V beta 4+ and V beta 8+ CD4+ T cell subsets in Mtv-8+ and Mtv-9+ mice, and TcR V beta 4+ CD4+ T cells in Mtv-6+ and Mtv-7+ mice, when compared with the T cell repertoire of Mtv- mice, is consistent with the possibility that MMTV products contribute to positive selection of T cells.

T cell and non-T cell compartments can independently determine resistance to Leishmania major

In experimental murine cutaneous leishmaniasis caused by Leishmania major (Lm), the cellular determinants governing development of protective or exacerbative T cells are not well understood. We, therefore, attempted to determine the influence of T cell and non-T cell compartments on disease outcome. To this end, T cell chimeric mice were constructed using adult thymectomized lethally irradiated, bone marrow-reconstituted (ATXBM) animals of genetically resistant, C57BL/6, or susceptible, BALB/c, backgrounds. These hosts were engrafted with naive T cell populations from H-2-congenic susceptible, BALB.B6-H-2b, or resistant, C57BL/6.C-H-2d, animals, respectively. Chimeric mice were then infected with Lm, and disease outcome was monitored. BALB/c T cell chimeric mice, BALB/c ATXBM hosts given naive C57BL/6.C-H-2d T cells, resolved their infections as indicated by reductions in both lesion size and parasite numbers. Furthermore, the mice developed typical Th1 (interferon[IFN]-gamma hiinterleukin[IL]-4lo) cytokine patterns. In contrast, both sham chimeric, BALB/c ATXBM hosts given naive BALB/c T cells, and control irradiated euthymic mice succumbed to infection, producing Th2 profiles (IFN-gamma loIL-4hiIL-10hi). C57BL/6 T cell chimeras, C57BL/6 ATXBM hosts given naive BALB.B6-H-2b T cells, resolved their infections as did C57BL/6 sham chimeras and euthymic controls. Interestingly, whereas C57BL/6 control animals produced Th1 cytokines, chimeric animals progressed from Th0 (IFN-gamma hiIL-4hiIL-10hi) to Th2 (IFN-gamma loIL-4hiIL-10hi) cytokine profiles as cure ensued. Both reconstitution and chimeric status of all mice were confirmed by flow cytometry. In addition, T cell receptor V beta usage of Lm-specific blasts was determined. In all cases, V beta use was multiclonal, involving primarily V beta 2, 4, 6, 8.1, 8.2, 8.3, 10, and 14, with relative V beta frequencies differing between H-2b and H-2d animals. Most importantly, however, these differences did not segregate between cure and noncure outcomes. These findings indicate that: (a) genetic traits determining cure in Lm infection can direct disease outcome from both T cell and non-T cell compartments; (b) the presence of the curing genotype in only one compartment is sufficient to confer cure; (c) curing genotype T cells autonomously assume a Th1 cytokine profile-mediating cure; (d) noncuring genotype T cells can mediate cure in a curing environment, despite the onset of Th2 cytokine production; and lastly, (e) antigen specificity of responding T cells, as assessed by V beta T cell receptor diversity, is not a critical determinant of disease outcome.

Lipopolysaccharide interferes with the induction of peripheral T cell death

In mice injected with superantigens, T cells specific for that antigen proliferate and then die. It has been suggested that the target cells die because they encounter superantigen on the surfaces of nonprofessional presenting cells, such as B cells, which cannot deliver costimulatory signals to T cells. A number of reagents that induce costimulatory molecules on B cells were tested. Lipopolysaccharide very effectively prevented T cell death driven by superantigen. Perhaps surprisingly, the action of lipopolysaccharide was not mediated through the expected costimulatory molecule, B7. Rather, the effects of lipopolysaccharide involved the production of inflammatory cytokines, in particular TNF alpha. The rescued cells survived in vitro culture and were resistant to Fas-induced killing. These data demonstrate that LPS can block antigen-induced T cell death perhaps by interfering with Fas signaling.

The T cell response of HLA-DR transgenic mice to human myelin basic protein and other antigens in the presence and absence of human CD4

Analysis of HLA class II transgenic mice has progressed in recent years from analysis of single chain HLA class II transgenes with expression of mixed mouse/human heterodimers to double transgenic mice expressing normal human heterodimers. Previous studies have used either HLA transgenic mice in which there is a species-matched interaction with CD4 or mice which lack this interaction. Since both systems are reported to generate HLA-restricted responses, the matter of the requirement for species-matched CD4 remains unclear. We have generated triple transgenic mice expressing three human transgenes, DRA, DRB, and CD4, and compared HLA-restricted responses to peptide between human-CD4+ (Hu-CD4+) and Hu-CD4- littermates. We saw no difference between Hu-CD4+ and Hu-CD4- groups, supporting the notion that for some responses at least the requirement for species-matched CD4 may not be absolute. Evidence for positive selection of mouse T cell receptors in HLA-DR transgenic mice came both from the acquisition of new, HLA-restricted responses to various peptides and from an increased frequency of T cells using the TCR V beta 4 gene segment. An important goal with respect to the analysis of function in HLA transgenic mice is the clarification of mechanisms which underpin the recognition of self-antigens in human autoimmune disease. As a first step towards 'humanized' disease models in HLA transgenic mice, we analyzed the responses of HLA-DR transgenic mice to the human MPB 139-154 peptide which has been implicated as an epitope recognized by T cells of multiple sclerosis patients. We obtained T cell responses to this epitope in transgenic mice but not in nontransgenic controls. This study suggests that HLA transgenic mice will be valuable in the analysis of HLA-restricted T cell epitopes implicated in human disease and possibly in the design of new disease models.

Programmed differentiation of murine thymocytes during fetal thymus organ culture

Fetal thymus organ culture (FTOC) has become widely used to investigate the impact of immunomodulators on T cell development. However, these studies have given variable results among different laboratories. In this study, we have found that fetal tissue age and mouse strain differences can affect the development of T cell phenotypes in this system. T cell development in FTOC occurred in two 'waves', defined as peaks of cell recovery. The first wave consisted initially of CD4-CD8- double negative (DN) cells and CD4-CD8+ single positive (SP) T cells expressing gamma delta T cell receptor (TCR). CD4+CD8+ double positive (DP) cells expressing low levels of alpha beta TCR were produced soon thereafter; and these cells dominated the cultures for the balance of the first wave. Prolonged FTOC resulted in the production of another wave of T cells which were relatively enriched for CD4 or CD8 SP cells expressing high levels of alpha beta TCR, as well as DN cells and CD4-CD8+ SP T cells expressing high levels of gamma delta TCR. As defined by cell number and differentiation of alpha beta TCR SP cells, development was delayed in FTOC using fetal thymus tissue from younger fetuses relative to that observed when older fetal thymus tissue was used. The degree of development of T cells in FTOC was also strain dependent. Organ cultures derived from 14 gestation days (gd) C.B-17 scid/scid fetal thymus did not generate TCR-bearing mature SP cells, but they did produce TCR-negative CD4 and CD8 SP cells likely to be precursors of DP thymocytes. Such cultures made from 18 gd tissue did not produce SP cells. Negative selection in FTOC was also evaluated. Mtv-specific V beta 3 cells were deleted in FTOC of C3H/HeN tissue. Deletion occurred only in late FTOC, suggesting a late encounter between the Mtv deleting elements and susceptible T cells during ontogeny. These results show that while FTOC recapitulates normal thymic development by a variety of criteria, results can be influenced by the length of culture, as well as by the age and strain of fetal thymus tissue utilized.

Structure and biological activity of the subgenomic Mtv-6 endogenous provirus

The Mtv-6 provirus has an incomplete genome, but retains a functional superantigen gene (sag) which directs the thymic deletion of CD4+ T cells expressing T cell receptors containing the V beta 3 or V beta 5 chains. To better understand the Mtv-6 superantigen, the structure and biological activity of the Mtv-6 provirus was analyzed. First, the complete nucleotide sequence was determined, and the mutation producing the subgenomic provirus was identified. Second, the nucleotide sequence of the 5' end of the sag gene transcript (including the splice junction) was determined by sequence analysis of a cDNA clone. Third, the superantigen activity of Mtv-6 was analyzed in mice carrying the Mtv-6 provirus isolated by selective breeding on a genetic background free of endogenous and exogenous mouse mammary tumor virus (MMTV). These studies demonstrate that (i) the Mtv-6 provirus contains a 6.2-kb deletion between two 12-bp direct repeats encompassing the central portion of the provirus but not affecting sag gene splicing or translation, (ii) the sag gene transcript has the structure predicted from previous S1 nuclease mapping studies, and (iii) the Mtv-6 superantigen can direct thymic deletion of target V beta 3+ and V beta 5+ T cells in the absence of gene products from full-length MMTV proviruses.

Cross-reactive trinitrophenylated peptides as antigens for class II major histocompatibility complex-restricted T cells and inducers of contact sensitivity in mice. Limited T cell receptor repertoire

The induction of contact sensitivity in mice by hapten reagents such as trinitrochlorobenzene (TNCB) involves the activation of class II major histocompatibility complex (MHC)-restricted, hapten-specific, CD4+ T cells. Reports from different laboratories have indicated that the relevant antigenic epitopes in such reactions might include hapten-conjugated, MHC class II-associated peptides. This study for the first time directly demonstrates that hapten-peptides account for the majority of determinants recognized by trinitrophenyl (TNP)-specific CD4+ T lymphocytes. The sequences of those TNP carrier peptides do not have to be related to mouse proteins. Thus, we show that TNP-modified peptides derived from mouse IgG, pigeon cytochrome c or staphylococcal nuclease known to bind to I-Ab or from lambda repressor with specificity to I-Ad as well as TNP-proteins such as bovine serum albumin, ovalbumin or keyhole limpet hemocyanin all create class II-restricted hapten determinants for a number of TNP-specific T cell clones and hybridomas. All of these cells were induced with cells modified by trinitrobenzene sulfonic acid (TNBS). In addition, we present arguments indicating that individual TNP-specific helper T cells may cross-react with different TNP-peptides bound to identical class II molecules. Chemical treatment of antigen-presenting cells with TNCB or TNBS may thus result in a limited number of particularly repetitive immunodominant hapten epitopes. Immunodominant epitopes were also indicated by an overrepresentation of the TCR elements V beta 2 and V alpha 10 in I-Ab/TNP-specific T cells. Most importantly, however, we demonstrate that TNP attached to lysine 97 in the staphylococcal nuclease peptide 93-105 (i.e. a clearly "non-self" sequence) is able to prime mice for subsequent elicitation of contact sensitivity by TNCB in the absence of foreign protein. We take this to indicate that those TNP-peptide determinants defined by us as immuno-dominant are responsible for the induction of contact sensitivity to haptens.

Murine nursing thymic epithelial cell lines capable of inducing thymocyte apoptosis express the self-superantigen Mls-1a

Two cloned thymic epithelial cell (TEC) lines, D2.TEC-A3 and AKR TEC-K1, were established from minor lymphocyte-stimulating (Mls)-1a-positive normal, 4-week-old DBA/2 (H-2d, Mls-1a2a) mice and AKR (H-2k, Mls-1a2b) mice, respectively. Both cell lines were MHC class I and class II (both I-A and I-E) positive without stimulation by interferon-gamma. They were capable of infolding immature thymocytes to form thymic nurse cells (TNC; we call this type of TEC "nursing TEC") and induced apoptosis with DNA fragmentation in immature thymocytes. Using a primary Mls mixed lymphocyte reaction (MLR) we demonstrated that self-superantigen Mls-1a was expressed on these cloned nursing TEC lines. D2.TEC-A3 cells stimulated nylon-wool-purified splenic T cells obtained from H-2d-compatible BALB/c (Mls-1b2a) and B10.D2 (Mls-1b2b) mice with a maximal response at a stimulator:responder ratio of 1:40 after 4 days of the coculture. AKR TEC-K1 cells also stimulated purified T cells from H-2k-compatible C3H/He mice (Mls-1b2a) in a similar manner. The Mls MLR induced by the nursing TEC lines was completely inhibited in the presence of anti-mouse I-A and anti-mouse I-E monoclonal antibodies. These results suggest that nursing TEC/TNC could be involved in negative selection due to apoptosis.

Molecular analysis of the helper T cell response in murine interstitial nephritis. T cells recognizing an immunodominant epitope use multiple T cell receptor V beta genes with similarities across CDR3

Anti-tubular basement membrane disease (alpha TBM disease) produces T cell-mediated interstitial nephritis in SJL mice after immunization with renal tubular antigen. Initial mononuclear infiltrates appear in vivo after several weeks, with the subsequent progression to renal fibrosis and end stage renal disease over many months. We have analyzed the fine specificity of the autoreactive helper T cell repertoire in alpha TBM disease through the isolation and characterization of a panel of CD4+ Th1 clones harvested after 1-2 wk from animals immunized to produce disease. All clones capable of mediating alpha TBM disease are directed towards a 14-residue immunodominant epitope (STMSAEVPEAASEA) contained within the target antigen, 3M-1. Evaluation of the T cell receptor (TCR) V beta repertoire used by these autoreactive T cells reveals the use of several V beta genes, but with some preference for V beta 14. Sequencing across the putative CDR3 region of the TCR beta chains suggests that common amino acids at the V beta(N)D beta junction and the D beta(N)J beta junction may contribute to the specific ability of these cells to recognize the immunodominant epitope.

Transfer of Sjögren's syndrome-like autoimmune lesions into SCID mice and prevention of lesions by anti-CD4 and anti-T cell receptor antibody treatment

We describe the successful transfer of murine Sjögren's syndrome-like autoimmune lesions from MRL/lpr mice (H-2k) to severe combined immunodeficiency (SCID) mice (H-2d) and prevention of lesions by anti-CD4 and -T cell receptor V beta 8 antibody treatment. Mononuclear cells (1 x 10(6)) isolated from the inflamed submandibular salivary gland tissues of MRL/lpr mice were transferred intraperitoneally into SCID mice. Autoimmune lesions resembling those seen in Sjögren's syndrome developed in the salivary and lacrimal glands of SCID mice 8 weeks after the injection, whereas other organs did not show any lesion. This pathology resembles Sjögren's syndrome in humans involving both the salivary and lacrimal glands. Immunohistochemically, a major proportion of these infiltrating cells in transferred SCID mice were CD4+ and V beta 8+. When the spleen cells from MRL/lpr mice were injected, severe inflammatory lesions, probably resulting from a graft-versus host reaction, were observed in multiple organs of SCID mice. The disease could not be induced by intraperitoneal administration of the sera from MRL/lpr mice, or of the spleen cells from C3H/He (H-2k) and BALB/c (H-2d) mice. We detected autoantibody production specific for the salivary gland tissue in sera from transferred SCID mice. Moreover, we found that the lesions were prevented by administration of the isolated cells treated in vitro with anti-CD4 and anti-V beta 8 monoclonal antibodies. These results suggest that CD4- and V beta 8-bearing T cells are involved in recognizing an autopeptide and triggering autoimmunity in the salivary and lacrimal glands, and therapies designed with anti-CD4 and anti-V beta 8 antibodies may prove effective in treating the murine autoimmune disease.

Dichotomy between the T and the B cell epitopes of the synthetic polypeptide (T,G)-A--L

Studies with the well-characterized, synthetic, random-multichain polypeptide poly(LTyr,LGlu)-poly(DLAla)-poly(LLys) (T,G)-A-L) led to the discovery of determinant-specific genetic control of the immune response, as well as to other immunological phenomena. Moreover, the tetrapeptide TyrTyrGluGlu built on the same backbone ("(T-T-G-G)-A--L") was found to represent its major B cell epitope. We have recently shown that for interaction with major histocompatibility complex class II molecules and stimulation of T cells, (T,G)-A--L requires proteolytic processing and the resulting T cell epitopes are close to the N termini of the branched polymer's side chains. Thus, we were interested to elucidate the major T cell epitope of (T,G)-A--L, by using the ordered polypeptides (T-T-G-G)-A--L and (T-G-T-G)-A--L, in which only the two internal amino acids of the tetrapeptide attached to the side chains are switched. We established T cell lines to these antigens, and found that the ordered analog (T-T-G-G-)-A--L, which was defined as the B cell epitope of (T,G)-A--L, did not represent its T cell epitope, whereas (T-G-T-G)-A--L, to which only a minor anti-(T,G)-A--L Ab response was directed, was found to be its major T cell epitope. In addition, there was no cross-reaction between (T-G-T-G)-A--L and (T-T-G-G)-A--L at the T cell level, similar to the lack of cross-reaction of their antibodies. Analysis of the repertoire of the T cell receptors used by these lines revealed that the (T,G)-A--L and the (T-T-G-G)-A--L specific T cell lines were not restricted in their V alpha and V beta TCR usage, whereas the (T-G-T-G)-A--L-specific line was restricted by both V alpha and V beta T cell receptor gene products. This difference might be due to the thymus-independent characteristics previously described for the latter antigen.

CD4+V beta 8+ T cells mediate herpes stromal keratitis

T lymphocytes are critical in mediating herpes simplex stromal keratitis (HSK). Using immunohistologic methods, we studied the T cell subsets and the T cell receptor variable region (TCR V beta) repertoire of T cells in the eye after corneal infection with HSV (KOS strain). We investigated the possibility that there might be differential V beta preferential usage in HSK resistant and susceptible BALB/c congenic mice that differ only in a small region associated with the Igh-1 gene locus. The inflamed corneas of HSK susceptible C.AL-20 mice were mainly infiltrated by CD4+ cells and by V beta 8 expressing cells. Such T cells were not seen in the corneas of resistant C.B-17 mice. Our results indicate that CD4+V beta 8+ cells are involved in mediating HSV-1 stromal keratitis.

Neonatal deletion and selective expansion of mouse T cells by exposure to rabies virus nucleocapsid superantigen

The nucleocapsid (NC) of the rabies virus behaves as an exogenous superantigen (SAg) in humans. In the present report, we analyzed whether it is also a SAg in mice by studying the effect of NC on T cell receptor (TCR) V beta expression in BALB/c mice. Repeated injection of NC in newborn BALB/c mice led to a marked reduction by two- to sixfold of V beta 6 expressing CD4+ T cells in spleen and in peripheral blood. Decrease of V beta 6-expressing CD3+ mature T cells was also observed in thymus. Single NC injection in footpad resulted in a three- to sixfold expansion of V beta 6 CD4+ T cells, but not of CD8+ T cells, in the draining lymph nodes of BALB/c mice. The intensity of the stimulation was dose dependent and was maximal 3 d after the NC injection. The clonal deletion of T cells bearing a particular V beta demonstrates that NC is a SAg in mice. T cells, especially CD4+ T cells, are an essential factor in host resistance to rabies virus and also in the pathophysiology of paralysis; thus, we postulate that a rabies virus component, which stimulates T cells, such as a SAg, may increase virus immunopathogenicity. To evaluate this hypothesis, we compared the course of rabies in adult BALB/c lacking V beta 6, 7, 8.1, and 9 T cells and in normal BALB/c. Immune-related paralysis was decreased in BALB/c missing the NC target V beta T cells. Transfer of V beta 6 but not of V beta 8.1-3 T cells into recipient mice lacking V beta 6, 7, 8.1, and 9 allowed the immune-related paralysis to evolve. Taken together, these results strongly support the hypothesis that T cells expressing rabies SAg-specific V beta 6 T cells, are involved in the genesis of the immunopathology that is characteristic of paralytic rabies.

Early expression of cytokines in lymph nodes after treatment in vivo with Staphylococcus enterotoxin B

Excessive cytokine expression induced by superantigen may be one aspect of the pathophysiology associated with Gram positive bacteremia. We have undertaken a study of the kinetics of cytokine production in lymph nodes obtained from in vivo Staphylococcus enterotoxin B (SEB) treated animals. This study was designed to evaluate the short term cytokine profile observed using immunohistochemistry (IHC) in BALB/c mice injected intraperitoneally (i.p.). The observed immunohistochemical kinetic profiles were corroborated using reverse transcription-polymerase chain reaction (RT-PCR) RNA analysis. We report here that TNF, IL-2, and IFN-gamma are the principal cytokines which were detected within hours of SEB administration, and that other cytokines such as IL-3, IL-4, IL-5, IL-6, IL-10, GM-CSF and M-CSF were undetectable. TNF and IL-2 appeared very early following SEB priming, and were observed by 1 h. IFN-gamma which appeared later (maximally at 14 h) was produced predominantly by CD8+ cells. In contrast, the TNF and IL-2 were produced primarily by CD4+ cells. Identical results were obtained by IHC and RT-PCR; the kinetics of mRNA expression slightly preceded the appearance of protein. The TNF and IFN-gamma staining patterns observed in lymph node sections were indicative of Golgi-localized cytokine. The IL-2 staining pattern observed in lymph node sections was distinctive, covering a significant local area of cells. This local regional concentration of IL-2, which may result from cytokine attached to extracellular binding components, may be an important aspect of the activation phase of a developing immune response. Rapid induction and excessive cytokine production elicited by superantigen in vivo, may ultimately help to explain the shock and death associated with SEB.

Pathogenesis of Sjögren's syndrome-like autoimmune lesions in MRL/lpr mice

Sjögren's syndrome in humans is a chronic inflammatory disease with a presumed autoimmune etiology of the exocrine organs, involving in particular the salivary and lacrimal glands. The pathogenesis of this syndrome remains unclear, but the majority of infiltrating cells in the salivary glands are CD4+ T cells both in humans and rodents. Since many cytokines are involved in the development of T cell-mediated autoimmunity, local cytokine gene expression was analyzed in vivo using an animal model for Sjögren's syndrome in MRL/lpr mice. Overexpression of interleukin-1 (IL-1)beta and tumour necrosis factor (TNF) was detected before the onset of inflammatory lesions in the salivary gland, and the upregulation of IL-6 mRNA was also found in accordance with autoimmune sialadenitis in MRL/lpr mice. The inflammatory cytokines such as IL-1 beta, TNF, and IL-6 have proved to play important roles as regulatory proteins inducing autoimmune phenomena. In addition, the expression of T cell antigen receptor beta (TCR) beta transcripts in the salivary gland tissues was analyzed. Transcript for V beta 8 was predominantly detected in the T cells infiltrating sialadenitis from the onset of the disease, suggesting that CD4+ T cells bearing TCR V beta 8 play an essential role in recognizing unknown autopeptide in the autoimmune sialadenitis of MRL/lpr mice. Furthermore, Sjögren's syndrome-like autoimmune lesions were successfully transferred into severe combined immunodeficiency (SCID) mice, and these lesions were prevented by administration of anti-CD4, and anti-V beta 8 monoclonal antibodies. This article will review recent observations of these pathogenetic analyses of autoimmune sialadenitis as it occurs in MRL/lpr mice.

Stoichiometry of the T cell antigen receptor (TCR) complex: each TCR/CD3 complex contains one TCR alpha, one TCR beta, and two CD3 epsilon chains

The stoichiometry of the subunits that comprise the T cell antigen receptor (TCR) complex is not completely known. In particular, it is uncertain whether TCR alpha and TCR beta proteins are present in the TCR complex as one or multiple heterodimeric pairs. In this study we have used mice transgenic for two different TCR alpha and two different TCR beta proteins to determine the number of TCR alpha and TCR beta chains in a single TCR complex. Individual thymocytes and splenic T cells from double TCR transgenic mice simultaneously expressed all four transgenic TCR proteins on their surfaces. Because the individual TCR alpha and individual TCR beta proteins were biochemically distinguishable, we were able to examine association among the transgenic TCR products. We found that each TCR alpha chain paired with each TCR beta chain, but that each TCR complex contained only one TCR alpha and one TCR beta protein. Furthermore, quantitative immunofluorescence revealed that T cells expressed twice as many CD3 epsilon as TCR beta proteins. These findings demonstrate that there are precisely one TCR alpha, one TCR beta, and two CD3 epsilon chains in each TCR/CD3 complex expressed on the surfaces of both thymocytes and mature T cells.

Anchored polymerase chain reaction based analysis of the V beta repertoire in the non-obese diabetic (NOD) mouse

We have performed extensive analyses of T cell receptor V beta usage in the thymus, the spleen and the infiltrated islets of preclinical non-obese diabetic (NOD) mice. A semiquantitative anchored polymerase chain reaction (An-PCR) protocol has been developed for this purpose. The validity of the method has been first assessed by antibody staining with a panel of anti-V beta monoclonal antibodies (mAb). The results obtained by An-PCR are accurate, reproducible, and in good agreement with cell surface protein staining. A strict comparison between thymus and spleen repertoires reveals no major V beta-specific deletion except the already reported V beta 3 deletion due to Mtv-3. Certain V beta such as V beta 15, 18, 20 are found with a low frequency in the spleen, but the fact that they are also scarce in the thymus probably reflects a poor availability of these genetic elements during beta chain rearrangement rather than negative selection. Other V beta, such as V beta 2, V beta 12 and V beta 14 are significantly more abundant in the spleen than in the thymus. This finding was confirmed by mAb staining for V beta 2 and V beta 14. The expansion asymmetrically affects the CD4+ subset and can be traced back to the mature, single-positive thymocyte subset, suggesting an intrathymic positive selection event. V beta repertoires in infiltrated islets of 13- and 18-week-old, non-diabetic mice are polymorphic. Practically all the V beta found in the peripheral lymphoid tissues are present in the islets, in similar proportions. The major exception is V beta 12, one of the V beta which is subject to expansion during intrathymic differentiation and which is further augmented in the islets, both at 13 and 18 weeks. This increase probably reflects further peripheral amplification of the V beta 12-bearing subset due to encounter with the same ligand as in the thymus or with a cross-reactive motif. Finally, the nucleotide sequencing of all the V beta segments in usage in the NOD strain confirms the absence of allelic polymorphism of V beta-coding regions.

Flexibility of the T cell receptor repertoire

Alternative T cell receptor (TcR) gene usage between mice of different Mls alleles has been demonstrated in a number of T cell responses. A clear illustration of a flexible TcR V beta usage in the same strain of mice remains to be established. Using a model system in which I-Ek-restricted T cells recognizing lambda repressor cI protein (cI) 12-26 and pigeon cytochrome c (pcc) 81-104 predominantly use V beta 3 in B10.A and B10.BR mice, and V beta 1 in Mls-2a-bearing A/J and C3H mice, we have first demonstrated that the hierarchy of TcR V beta usage can not be inferred from one strain of mice to the other. The presumed flexibility of V beta 3 to V beta 1 did not exist in B10.BR mice in the given responses. Instead, a switch of dominant TcR from V beta 1/V beta 3 to V beta 8 was identified in C3H and B10.BR mice. In contrast, there was an absolute rigidity in TcR repertoire usage in some mouse strains such as A/J. The lack of flexibility was not due to slow generating kinetics of replacing T cells; since A/J mice treated with staphylococcal enterotoxin A from birth on still responded poorly to cI 12-26 and pcc 81-104. Therefore, whether TcR V beta usage in a T cell response would be flexible or rigid is highly dependent on each strain of mice. However, even the plasticity seen in B10.BR mice is very limited and further tolerance of the V beta 8+ population results in non-responsiveness toward the given antigens.

A V beta 8.2-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.

Are primed CD4+ T lymphocytes different from unprimed cells?

Primed and unprimed lymphocytes are usually classified as separate subsets of cells, based on phenotypic and functional distinctions. In the case of CD4+ T lymphocytes, primed cells are thought to proliferate more vigorously, quickly and easily, and to release a different profile of cytokines, than their naive equivalent. However, most of these data were obtained from studies in which populations of lymphocytes were compared before and after antigenic stimulation, and therefore did not distinguish between the effects resulting from the clonal expansion of specific precursor cells within such populations and those due to cell differentiation per se. We have investigated the contribution of precursor cell frequency to some of the functional changes observed in populations of CD4+ T cells following antigenic stimulation, using approaches in which antigen-specific precursor frequencies are high in both primary and secondary stimulations: mixed leukocyte reaction responses and cells from alpha beta T cell receptor transgenic mice. Our data suggest that when equivalent numbers of antigen-specific naive and previously primed CD4+ responder T cells are compared, there is no difference in their potency to proliferate but only the previously activated subset can generate cytokines such as interferon-gamma.

Clonal expansion of T lymphocytes causes arthritis and mortality in mice infected with toxic shock syndrome toxin-1-producing staphylococci

Erosive arthritis is a common and feared complication of staphylococcal infection. The reason(s) for the progressive course of the arthritis is unknown. It has been recently established that enterotoxins produced by Staphylococcus aureus display superantigen properties leading to stimulation of T cells carrying distinct T cell receptor V beta elements. This finding provides a potential connection between staphylococcal exoproteins and endogenous immune mechanisms participating in the infectious process. We have recently describe successful induction of infections arthritis in mice after intravenous inoculation of a toxic shock syndrome toxin-1 (TSST-1)-producing S. aureus LS-1 strain. Using this model we have now found a clonal expansion of T cells expressing V beta 11+ T cell receptor in the synovial tissue of arthritic mice. The role of TSST-1 as a superantigen inducing oligoclonal expansion was confirmed in an in vitro culture system. The expansion of V beta 11+ T cells proved to be of arthritogenic significance since mice genomically deleted of the V beta 11+ T cells did not develop arthritis and since pretreatment of healthy mice with anti-CD4 or anti-V beta 11 monoclonal antibodies inhibited arthritis. In addition, CD4+ and V beta 11+ T cells showed themselves to be of pathogenic significance in staphylococcal-induced mortality, since mice depleted of such populations showed increased survival. We propose that in hematogenously spread S. aureus-induced arthritis the TSST-1-dependent clonal expansion of CD4+ V beta 11+ T cells is a driving pathogenic force.

The human T cell antigen receptor repertoire: skewed use of V beta gene families by CD8+ T cells

The TCR repertoire of human CD8+ peripheral blood lymphocytes has been determined using MoAbs to the V beta 2, 3, 5.1, 5.2/5.3, 6.7, 8, 12 and 19(17)V beta gene families. The CD8T cell repertoire for V beta 2 and V beta 3 is shown to be skewed, with an excess of individuals having higher values than are consistent with a normal distribution. A significant majority of these individuals are over the age of 40. High values of V beta CD8+ cells were found for each V beta family studied except for 6.7a. Individual high values are stable for at least 12 months. In addition, the total percentage of CD4 and CD8 cells reacting with this panel of reagents was determined. There is a significant excess of V beta + CD4+ cells (33%) over CD8+V beta + cells (21.9%). Thus the human CD8 V beta repertoire differs from the human CD4 repertoire in a number of important ways.

Combined activation of murine lymphocytes with staphylococcal enterotoxin and interleukin-2 results in additive cytotoxic activity

This report demonstrates that in vitro activation of murine spleen cells with interleukin-2 (IL-2) or the bacterial superantigen staphylococcal enterotoxin A (SEA) results in different patterns of activation and function of cytotoxic cells. Lymphokine-activated killer activity and antibody-dependent cellular cytotoxicity (ADCC) are mainly mediated by IL-2 activated natural killer (NK) cells. SEA is the most powerful T cell mitogen known so far and retargets cytotoxic T lymphocytes (CTL) to tumors expressing major histocompatibility complex (MHC) class II in staphylococcal-enterotoxin-dependent cellular cytotoxicity (SDCC). Culture of mouse spleen cells with SEA led to expansion and activation of T cells, which demonstrated strong SDCC activity and some NK-like cytotoxicity after 5 days in culture. Cell sorting revealed that both CD8+ and CD4+ T cells mediated SDCC but the former were more effective. Phenotypic analysis showed that SEA preferentially stimulated and expanded T cells expressing T cell receptor V beta 11, in particular CD8+ T cells. Combined activation with SEA and IL-2 resulted in simultaneous induction of T and NK cell cytotoxicity. Moreover, IL-2 had additive effects on SEA-induced SDCC. Combined treatment with SEA and IL-2 might therefore be an approach to induce maximal cytotoxicity against tumors and to recruit both T and NK cells in tumor therapy.

T cell costimulation by B7/BB1 induces CD8 T cell-dependent tumor rejection: an important role of B7/BB1 in the induction, recruitment, and effector function of antitumor T cells

A successful antitumor T cell immune response involves induction, recruitment, and effector function of T cells. While B7/BB1 is known as a major costimulatory molecule in the induction of T cell responses, its role in T cell recruitment and effector function is still unclear. In this study, we show that introducing a major costimulatory molecule B7/BB1 into a major histocompatibility complex class II-negative tumor cell line, J558, results in a drastic reduction of its tumorigenicity. The tumor rejection depends on CD8 T cells but not CD4 T cells. However, unlike the previous reports on melanoma cell lines, B7/BB1-transfected J558 cells fail to induce cross-protection against parental J558 cells. The B7/BB1-transfected (J558-B7), but not untransfected J558 cells (J558-Neo) induce a CD8 T cell-dominant inflammatory response, and the T cells isolated from the tumor infiltrating lymphocytes (TIL) are polyclonal in terms of their T cell receptor V beta usage. Most surprisingly, the freshly prepared TIL have a potent, CD8 T cell-mediated cytotoxicity on tumor cells without any in vitro stimulation. The cytotoxic T lymphocyte (CTL) activity can be blocked by anti-CD8 monoclonal antibody (mAb). Interestingly, the CTL lyse J558-B7 about 10- to 80-fold more efficiently than untransfected J558-Neo cells. This preferential lysis cannot be attributed to recognition of B7/BB1-derived antigen by the T cells. This finding, together with the lack of the cross-protection between the J558-B7 and J558-Neo, suggests that B7/BB1 can also function at the effector phase of CTL responses. This notion is confirmed by our findings that the lysis of J558-B7 can be blocked by anti-B7 mAbs. Taken together, our results indicate that not only can the B7/BB1 molecule function as a costimulatory molecule at the initiation of immune response, it can also play a major role in T cell recruitment and effector function. This conclusion has significant implications for immunotherapy of tumors.

Processing and major histocompatibility complex binding of the MTV7 superantigen

Mouse mammary tumor viruses produce superantigens (vSAGs) which interact with class II major histocompatibility complex (MHC) proteins and stimulate T cells. vSAGs are synthesized as Type II membrane proteins, but at least one of these proteins (vSAG7) is found on the cell surface in a proteolytically processed form. Monoclonal antibodies (MAbs) were used to characterize vSAG7 and its binding to class II molecules. vSAG7 is synthesized in the endoplasmic reticulum (ER) as a 45 kd glycoprotein containing N-asparagine-linked oligomannosyl carbohydrates. vSAG7 transits the golgi complex, where it is modified by the addition of complex-type glycans and proteolysed at three positions. After proteolysis, the amino and carboxyl termini remain noncovalently associated. The ER, golgi, and surface forms of vSAG7 are stably bound to class II, but one of the proteolysed forms comprises the majority of the class II-bound material.

Stimulation with specific antigen can block superantigen-mediated deletion of T cells in vivo

The T-cell response to pigeon cytochrome c peptide, residues 88-104 (pcytC), in B10.BR mice is mediated largely by cells bearing both V beta 3 and V alpha 11 variable regions of the T-cell antigen receptor. These cells are, therefore, reactive with the superantigen staphylococcal enterotoxin A (SEA). Recent reports have shown that in vivo exposure to superantigen can lead to deletion of superantigen-reactive T cells from the pool of mature T cells in the periphery. Here we show that upon cotreatment of animals with both SEA and pcytC, bulk deletion of the population of SEA-reactive cells is maintained, while the subpopulation of SEA-reactive T cells that also responds to pcytC is not deleted but instead proliferates in response to pcytC. These results are discussed with regard to mechanisms regulating the balance between T-cell tolerance and T-cell activation in vivo.

Absence of peripheral clonal deletion and anergy in immune responses of T cell-reconstituted athymic mice

Superantigens induce clonal deletion of reactive T cells in the thymus and clonal deletion and anergy in the periphery of euthymic mice. In this report we have assessed the ability of Staphylococcal enterotoxin B (SEB) to induce peripheral tolerance in nude mice reconstituted with normal, syngeneic T cells. Immunization of reconstituted nude mice with SEB resulted in lethal toxic shock in a large fraction of the animals. Such lethality was never observed in the normal donor mouse strain. Analysis of lymphokine production in response to SEB showed that reconstituted nude mice produced higher levels of interleukin-2 and tumor necrosis factor-alpha, but lower levels of interleukin-4, than euthymic control mice. Furthermore, SEB was unable to promote either clonal elimination or induction of anergy in the SEB-responsive peripheral T cells, despite the fact that reconstituted nude mice did produce high levels of corticosterone upon treatment with SEB. These results imply a lack of control over immune responses to superantigen in T cell-reconstituted athymic mice.

Analysis of the T-cell receptor beta-chain variable-region (V beta) repertoire in monozygotic twins discordant for human immunodeficiency virus: evidence for perturbations of specific V beta segments in CD4+ T cells of the virus-positive twins

We analyzed the T-cell receptor (TCR) V beta repertoire in human immunodeficiency virus type 1 (HIV-1)-infected individuals at different stages of disease. To circumvent the effect of HLA and other loci on the expressed TCR repertoire, we compared the TCR repertoire in nine pairs of monozygotic twins who were discordant for HIV infection. A semiquantitative polymerase chain reaction (PCR) assay and flow cytometry enabled us to show distinct differences in the V beta repertoire in the HIV-positive twin compared with the HIV-negative twin. By combining PCR and cytofluorometry, these differences were restricted to a specific set of TCR V beta segments, with members of the V beta 13 family perturbed in six out of seven cases and those of the V beta 21 family perturbed in four out of seven cases studied. Most of the other V beta families remained unchanged. Our results provide direct evidence for a skewed TCR repertoire in HIV infection.

Positive and negative selection of T cells in T-cell receptor transgenic mice expressing a bcl-2 transgene

To explore the role of bcl-2 in T-cell development, a bcl-2 transgene was introduced into mice expressing a T-cell receptor (TCR) transgene encoding reactivity for the mouse male antigen HY presented by the H-2Db class I antigen of the major histocompatibility complex (MHC). Normal thymic development is contingent on the ability of immature thymocytes to interact with self-MHC molecules presented by thymic stroma (positive selection). Thus, thymocyte numbers are low in female anti-HY TCR transgenic mice with a nonselecting (H-2Dd) background. Expression of bcl-2 inhibited the death of nonselectable thymocytes since, strikingly, female H-2Dd bcl-2/TCR transgenic mice developed normal numbers of CD4+CD8+ thymocytes, although these did not mature further into functional T cells. Hence, TCR-MHC interaction may induce positive selection through two signals, one which saves cells from death by increasing Bcl-2 synthesis and another which promotes maturation. Male H-2Db anti-HY TCR transgenic mice normally have a very small thymus, due to deletion of the self-reactive T cells. Expression of bcl-2 reduced the efficiency of deletion, since bcl-2/TCR transgenic male mice accumulated 4- to 6-fold more thymocytes than did TCR transgenic male littermates. Anti-HY TCR-expressing cells were also more numerous in the peripheral lymphoid tissues, but these cells expressed abnormally low levels of CD8 co-receptor and were not responsive to the HY antigen. Thus, although bcl-2 expression hampers the deletion of immature self-reactive cells in the thymus, self-tolerance is maintained.

Radiation leukemia virus-induced thymic lymphomas express a restricted repertoire of T-cell receptor V beta gene products

We have investigated the phenotypic changes that take place during the process of neoplastic transformation in the thymocytes of C57BL/Ka mice infected by the radiation leukemia virus (RadLV). By the combined use of antibodies against the envelope glycoprotein gp70 of RadLV, the transformation-associated cell surface marker 1C11, and the CD3-T-cell receptor (TCR) complex, we found that in the RadLV-infected thymus, the earliest expression of viral gp70 is in 1C11hi cells; a small but significant percentage of these cells also express CD3. A first wave of viral replication, manifested by the expression of high levels of gp70 in thymocytes (over 70% positive), reaches a peak at 2 weeks; during this period, no significant changes are observed in the expression of 1C11 or CD3. The population of gp70+ cells is drastically reduced at 3 to 4 weeks after infection. However, a second cohort of gp70+ cells appears after 4 weeks, and these cells express high levels of 1C11 and TCR determinants as well. RadLV-induced lymphomas differ from normal thymocytes in their CD4 CD8 phenotype, with domination by one or more subsets. Characterization of TCR gene rearrangements in RadLV-induced lymphomas shows that most of these tumors are clonal or oligoclonal with respect to the J beta 2 TCR gene, while the J beta 1 TCR gene is rearranged in a minority (4 of 11) of lymphomas. TCR V beta repertoire analysis of 12 tumors reveals that 6 (50%) express exclusively the V beta 6 gene product, 2 (17%) are V beta 5+, and 1 (8%) each are V beta 8+ and V beta 9+. In normal C57BL/Ka mice, V beta 6 is expressed on 12%, V beta 5 is expressed on 9%, V beta 8 is expressed on 22%, and V beta 9 is expressed on 4% of TCRhi thymocytes. Thus, it appears that RadLV-induced thymic lymphomas are not randomly selected with respect to expressed TCR V beta type.

The T cell antigen receptor alpha and beta chains interact via distinct regions with CD3 chains

Selective pairwise interactions between CD3 chains and the clonotypic T cell antigen receptor (TCR)-alpha, -beta chains has recently been established. In this study, the region of interaction between clonotypic and CD3 chains involved with assembly was examined. To determine the site of protein interaction a variety of genetically altered TCR chains were constructed. These included: truncated proteins, lacking transmembrane and or cytosolic domains; chimeric proteins, in which extracellular, transmembrane or cytosolic domains were replaced with similar domains derived from either the Tac antigen or CD4; and point mutagenized TCR chains. COS-1 cells were transfected with cDNA, metabolically labeled, and immunoprecipitates analyzed using non-equilibrium pH gel electrophoresis (NEPHGE)-SDS/PAGE. The results demonstrated that assembly between TCR-alpha and TCR-beta chains occurred at the extracellular level. Assembly of the TCR-alpha chain with CD3-delta, and CD3-epsilon was localized to an eight-amino acid motif within the transmembrane domain of TCR-alpha. Site-specific mutations of the TCR-alpha charged residues within this motif (arginine, lysine) to leucine and similar point mutations of the transmembrane CD3-epsilon and CD3-delta charge groups resulted in the abrogation of assembly. In contrast, TCR-beta and CD3-epsilon binary complexes interacted via their extracellular domain. Analogous to TCR-alpha, the site of TCR-beta and CD3-delta assembly was at the transmembrane region. Despite multiple genetic manipulations on CD3-gamma and zeta these proteins failed to assemble with TCR-alpha. Similarly, there was no interaction between TCR-beta and zeta. These findings when coupled with the information on pairwise interactions and formation of higher order subcomplexes extend our model for the structure of the TCR complex.

Heavy-chain directed B-cell maturation: continuous clonal selection beginning at the pre-B cell stage

A number of laboratories have demonstrated a biased representation of certain V-region segments in the primary B-cell repertoire. This may reflect clonal selection at the pre-B cell stage of differentiation. Here, Robert Schwartz and David Stollar suggest that pre-B cells undergo positive selection directed by the presence of surface heavy chain with low affinity to autoantigen. This mechanism would account for the anti-self property of the pre-immune B-cell repertoire.

Generation of mature T cell populations in the thymus: CD4 or CD8 down-regulation occurs at different stages of thymocyte differentiation

We have studied the differentiation and repertoire selection during the maturation of CD4+CD8+ (DP) thymocytes into CD4+CD8- (CD4SP) and CD8+CD4- (CD8SP) T cells, in normal mice, mice transgenic for T cell receptor (TcR)-alpha beta restricted by either class I or class II major histocompatibility (MHC), and in mice deficient in class I or class II MHC expression. Our data suggest that mature CD4 and CD8 T cells derive from different pathways of T cell differentiation in the thymus. Thus, interaction of DP thymocytes with MHC class II leads to the immediate down-regulation of CD8, which occurs simultaneously with an increase in TcR expression; DPTcR(lo)HSA(hi) thymocytes mature into a CD4+CD8(lo) TcR(hi)HSA(hi) intermediate population. This cell population generates CD4SP thymocytes, the majority of which are still HSA(hi). In contrast, interaction with MHC class I induces the up-regulation of TcR, which precedes the down-regulation of CD4; DPTcR(lo) generate DPTcR(hi) thymocytes, the majority of which are the committed precursors of CD8SP cells. Further differentiation results in CD4 down-regulation and the transition from DPTcR(hi) into CD8+CD4(lo) TcR(hi)HSA(lo) and +D8SPTcR(hi)HSA- T cells. Since down-regulation of CD4 and CD8 occurs at different stages of thymocyte differentiation, our results do not support a stochastic/selective model of lineage commitment in the thymus.

Superantigenic staphylococcal exotoxins induce T-cell proliferation in the presence of Langerhans cells or class II-bearing keratinocytes and stimulate keratinocytes to produce T-cell-activating cytokines

Several staphylococcal toxins are among a growing number of immunostimulatory molecules called "superantigens" because of their ability, when presented by appropriate major histocompatibility complex class II+ accessory cells, to activate essentially all T cells bearing particular T-cell receptor V beta gene segments. We have examined the ability of murine epidermal Langerhans cells and/or keratinocytes to act as accessory cells in the T-cell response to the superantigens staphylococcal enterotoxin B and exfoliative toxin, also known as epidermolysin. Purified murine splenic T cells were stimulated with staphylococcal enterotoxin B or exfoliative toxin in the presence of Langerhans cells--enriched epidermal cells from normal mice or epidermal cells isolated from mice pretreated with recombinant interferon-gamma, a procedure that induces the expression of major histocompatibility complex class II molecules on keratinocytes. The data show that both Langerhans cells and class II-bearing keratinocytes can act as accessory cells in the T-cell response to staphylococcal enterotoxin B and exfoliative toxin. We also observed that both human and murine keratinocytes cultured in the presence of staphylococcal enterotoxin B or exfoliative toxin produce increased amounts of cytokine(s) capable of stimulating thymocytes and D10 cells, and that this toxin activity is independent of the level of expression of class II on keratinocytes. Studies by enzyme-linked immunosorbent assay showed that staphylococcal enterotoxin B stimulates keratinocytes to produce tumor necrosis factor-alpha but not interleukin-1, suggesting tumor necrosis factor-alpha and perhaps other cytokines are responsible for the T-cell proliferative activity. These results demonstrate that two distinct epidermal constituents (i.e. Langerhans cells and keratinocytes) can serve as accessory cells in the responses of T cells to superantigenic bacterial toxins. It is possible that such toxins contribute to the pathogenesis of a variety of skin diseases by either locally activating T cells bearing particular V beta genes and/or enhancing keratinocyte production of immunomodulatory cytokines.

Development of T cells in SCID mice grafted with fetal thymus from AKR mice or F344 rats

To examine the development of T cells within an allogeneic or xenogeneic environment, we engrafted the fetal thymus from AKR mice or F344 rats under the kidney capsule of SCID mice (mTG and rTG mice). T lymphopoiesis developed in SCID mice 2 months after transplantation, although the ratio of CD4/CD8 in both experimental groups was different from that of normal control. T cells in mTG mice did not show in vitro proliferation or cytotoxicity against either host-type C.B-17 (H-2d) or donor-type AKR (H-2k) cells, while they exerted potent activities against third-party B10 (H-2b) cells. In contrast, T cells in rTG mice exhibited proliferation against both host-type C.B-17 and donor-type F344 rat cells. Consistently, graft-vs.-host disease symptoms developed in these mice and histological examination showed impressive infiltration of lymphocytes into the skin or into the mucosal layers of the stomach. Activated state of T cells in rTG mice was also evidence by the positive expression of interleukin-2 receptor. Taken together, fetal thymus appears to contain progenitor cells which are sufficient for in vivo reconstitution of T lymphopoiesis, but species-specific environment is important for the induction of tolerance. In mTG mice, V beta 6+ T cells reactive to donor Mlsa determinants and V beta 3+ T cells reactive to host Mlsc determinants were deleted, suggesting that tolerance was regulated mainly by clonal deletion. By contrast, V beta 11+ T cells reactive to Mlsf determinants were not deleted possibly due to the lack of their ligands.

Phenotypic characterization of splenic T cells from mice infected with Plasmodium chabaudi chabaudi

T cells from spleens of mice infected with the erythrocytic stages of Plasmodium chabaudi chabaudi have been analysed with respect to their expression of surface molecules CD3, CD4 and CD8 and T-cell receptor (TCR) alpha beta and gamma delta. The majority of T cells from infected mice were alpha beta TCR+. However, there was an increase of approximately 8-10-fold in the proportion and total number of gamma delta T cells. Immunocytochemical analysis of sections of spleens taken from infected C57BL/6 mice during a primary infection showed that this increase took place particularly in the non-lymphoid areas. Within the alpha beta TCR+ T-cell population, both CD4+ T cells and CD8+ T cells were represented in proportions similar to those observed in normal uninfected mice. Stimulation of splenic T cells from infected mice with P. chabaudi-infected erythrocytes in vitro resulted in a blasted cell population composed predominantly of alpha beta TCR+ T cells with no preferential expansion of gamma delta TCR+ T cells. There was no evidence of superantigen-like stimulation of T cells bearing particular V beta chains of the TCR. The representation of the different V beta chains within the population was not significantly different from that seen in uninfected mice.

Identification of an endogenous mammary tumor virus involved in the clonal deletion of V beta 2 T cells

Expression of V beta (beta-chain variable region) gene segments was investigated in the Mus m. domesticus DDO strain, which possesses a large genomic deletion encompassing 20 of the 29 V beta gene segments known in BALB/c. Stainings using V beta-specific monoclonal antibodies revealed that up to 60% of the peripheral T cells use 3 V beta gene segments. Variable frequencies of V beta 2 T cells were observed among DDO individuals. Segregation analyses of F2 crosses between V beta 2-deletor mice and mammary tumor virus (Mtv)-free mice led to the identification of a new endogenous Mtv, named Mtv-DDO, mediating V beta 2 T cell clonal deletion. Mtv-DDO structure is conserved with the exception of the carboxy-terminal region as compared to other Mtv. Comparison between Mtv sharing the same V beta specificity and isolated from laboratory or wild mice confirms that a stretch of 11 amino acids, defined as the V beta-specific region, is required for the V beta-specific interaction. Limited substitutions in this region account for the shift of the Mtv specificity towards different V beta.

Influence of a small number of mature T cells in donor bone marrow inocula on reconstitution of lymphoid tissues and negative selection of a T cell repertoire in the recipient

Allo-chimerism and clonal elimination of self antigen (Ag) (Ia + Mls-1a) reactive V beta 6+ T cells were analyzed and compared between allogeneic bone marrow (BM) chimeras reconstituted with BM cells which had been treated with anti-Thy-1 monoclonal antibody (mAb) plus complement (C) (T- chimeras) and BM chimeras which had been reconstituted with BM cells pretreated with anti-Thy-1 mAb alone (T+ chimeras). When lethally irradiated AKR (Mls-1a) mice were reconstituted with BM cells from B10 or B10 H-2 congenic mice, both T+ and T- chimeras were entirely free of signs of graft-versus-host reaction (GVHR). However, complete replacement of the AKR lymphoid tissues by donor BM cells was accomplished at an early stage in T+ chimeras but not in T- chimeras. On the other hand, clonal elimination of V beta 6+ T cells reactive to the recipient Ag (Mls-1a) was abolished in T+ chimeras but successfully induced in T- chimeras. The V beta 6+ T cells not eliminated in T+ chimeras showed depressed responses against Mls-1a antigens. The findings herein demonstrate that T cells which contaminate a BM inoculum survive in recipient mice after treatment with anti-Thy-1 mAb without C in vitro followed by BMT. The surviving T cells have been estimated to represent fewer than 0.5% of the BM cells inoculated. These cells appear to accelerate the full replacement of recipient lymphoid tissues by donor cells. Furthermore, the T cells which survive in the marrow inoculum influence eventually the development of a tolerant state in the T cell repertoire of the donor.

Characterization of monoclonal antibodies specific for the V beta 3 family of the human T cell receptor generated using soluble TCR beta-chain

A soluble, recombinant form of the human T cell receptor (TCR) beta-chain containing the V beta 3.1 sequence has been constructed, expressed in Chinese hamster ovary cells, amplified by dihydrofolate reductase selection, and purified in quantities appropriate for the generation of monoclonal antibodies (mAb). The V beta 3 sequence was chosen because of its reported elevated usage in the synovial T cells of rheumatoid arthritis patients but the approach described should be applicable to other known human V beta gene sequences. By this method, two mAb were prepared which reacted with up to 10% of normal, live peripheral blood T cells but with reactivity varying greatly among individual donors. Both mAb specifically bound to a murine T cell line transfected with a human TCR V beta 3.1 and immunoprecipitated a protein of the expected molecular weight for the TCR beta-chain. Both antibodies were mitogenic for T cells and analysis of peripheral blood lymphocyte cultures stimulated with the mAb suggested that both were specific for the V beta 3.1 subfamily and not D beta or J beta. Clones expressing V beta 3, which were derived from mAb-stimulated peripheral blood lymphocytes of a single individual, preferentially (8/13), but not exclusively, utilized the J beta 2.7 gene segment. The V beta 3.1 usage showed no preference for the CD8+ or CD4+ subpopulations of normal peripheral blood T cells.

The involvement of T cell receptor peptide-specific regulatory CD4+ T cells in recovery from antigen-induced autoimmune disease

Experimental allergic encephalomyelitis (EAE) is a prototype for CD4+ T cell-mediated autoimmune diseases. Immunization with myelin basic protein (MBP) in B10.PL mice results in EAE, and a majority of animals recover permanently from the disease. Most MBP-reactive encephalitogenic T cells recognize an immunodominant NH2-terminal peptide, Ac1-9, and predominantly use the T cell receptor (TCR) V beta 8.2 gene segment. Here we report that in mice recovering from MBP-induced EAE, peripheral T cells proliferate in response to a single immunodominant TCR peptide from the V beta 8.2 chain (amino acids 76-101), indicating natural priming during the course of the disease. Cloned T cells, specific for this TCR peptide, specifically downregulate proliferative responses to Ac1-9 in vivo and also protect mice from MBP-induced EAE. These regulatory T cells express CD4 molecules and recognize a dominant peptide from the TCR variable framework region of V beta 8.2, in the context of the major histocompatibility complex class II molecule, I-Au, and predominantly use the TCR V beta 14 gene segment. This is the first demonstration of the physiological induction of TCR peptide-specific CD4+ T cells that result from MBP immunization and that are revealed only during the recovery from disease. The downregulation of disease-causing T cells by TCR peptide-specific T cells offers a mechanism for antigen-specific, network-induced recovery from autoimmune disease.

The cytoplasmic tail of the T cell receptor zeta chain is dispensable for antigen-mediated T cell activation

The T cell antigen receptor consists of an antigen-binding alpha beta heterodimer and a group of invariant polypeptides denoted CD3-gamma, CD3-delta, CD3-epsilon and CD3-zeta. Whether antigen responsiveness is dependent on the expression of functional CD3-zeta subunit remains controversial. For instance, transfection of a zeta-/eta- variant of the 2B4.11. T cell hybridoma with mutated zeta cDNA that encoded a zeta protein truncated at residue 108, restored the surface expression of T cell antigen receptor complexes with, however, impaired antigen responsiveness [Frank, S. J., Niklinska, B. B., Orloff, D. G., Mercep, M., Ashwell, J. D. and Klausner, R. D., Science 1990. 249: 174.]. In marked contrast, BW5147 transfectants that expressed T cell antigen receptors devoid of functional zeta subunits were still able to trigger the production of interleukin-2 in response to antigen [Wegener, A.-M. K., Letourneur, F., Hoeveler, A., Brocker, T., Luton, F. and Malissen, B., Cell 1992. 68: 83.]. To assess if the above discrepancies may have resulted from the use of different recipient T cells, we transfected a zeta/eta-deficient variant of 2B4.11 (MA5.8) with the very same truncated zeta cDNA we previously used in BW5147. Consistent with our initial observations in BW5147, the cytoplasmic tail of the zeta polypeptide was found dispensable for antigenic responsiveness. Furthermore, a difference between the two recipient T cells was detected when cells were challenged via the Thy-1 and Ly-6 molecules. Once expressed in MA5.8, but not in BW5147, T cell antigen receptor complexes devoid of functional zeta subunits were able to sustain activation initiated via Thy-1 and Ly-6 molecules.

Regulation of T cell production in T cell receptor transgenic mice

The thymus produces many more cells than it releases into the periphery. According to generally accepted models of T cell development most of this loss occurs in the thymic cortex, among CD4+8+ thymocytes. An interesting situation arises in the case of T cell receptor (TcR) transgenic mice in which all cells can potentially be positively selected, leading to a theoretical increase of about 30-fold in the survival rate of CD4+8+ cells and in their transition to mature CD4+8- or CD4-8+ thymocytes. This in turn should lead to a 30-fold increase in the size of the thymic medulla, in the emigration rate and in the size of the peripheral T cell pool. Increases in medullary or peripheral pool sizes of this magnitude are not seen in TcR transgenic mice. The question was therefore asked whether some form of homeostatic process regulated the size of the mature T cell pool and at what level it might operate. In this report we demonstrate that the increased rate of double-positive to single-positive transition in the TcR transgenic mice is directly reflected in an increased emigration rate, and that the medulla seems to be relatively efficient regardless of the number of cells passing through it. However, the potential increases in emigrant numbers in TcR transgenic mice are offset by the reduced size of the CD4+8+ thymocyte pool. It would appear then that regulation of T cell production, if it occurs, probably does so through regulation of the size of the CD4+8+ thymocyte pool. Mechanisms for regulation of this kind are not yet known.

CD4+CD8+ cells lacking self-Mls reactive T cells are induced in mesenteric lymph nodes of Salmonella enteritidis-infected mice

The percentage of mesenteric lymph node (MLN) cells that co-expressed both CD4 and CD8 was found to be from 5 to 7% in BALB/c and AKR/N mice bred under conventional conditions. In mice maintained under specific pathogen-free (SPF) conditions, the percentage fell below 2%. When mice were infected with an attenuated strain of Salmonella enteritidis (SER), the percentage of CD4+CD8+ cells in MLN rose to 20-30% transiently. In these mice, the total cell number and the percentage of CD8+ cells were not changed, but the CD4+ cell percentage was decreased. The expression intensity of TCR-alpha beta on CD4+CD8+ cells in the infected mice was higher in the MLN than in the thymus, but was similar to that of mature peripheral T cells. Among the CD4+CD8+ cell population in MLN, TCR-V beta 3+ cells were deleted but V beta 6+ cells were present in BALB/c mice which possess endogenous superantigen Mls-2a, but lack Mls-la. In AKR mice with the inverse of the occurrence of the superantigens, TCR-V beta 3+ cells were present and V beta 6+ cells were absent. These data suggest that CD4+CD8+ cells in the MLN of SER-infected mice may belong to thymus-derived mature T cells undergoing negative selection and that they may appear following exogenous stimulation.