A T cell receptor V beta segment that imparts reactivity to a class II major histocompatibility complex product

Staphylococcal Enterotoxins: Description and Importance in Food

Staphylococcus aureus stands out as one of the most virulent pathogens in the genus Staphylococcus. This characteristic is due to its ability to produce a wide variety of staphylococcal enterotoxins (SEs) and exotoxins, which in turn can cause staphylococcal food poisoning (SFP), clinical syndromes such as skin infections, inflammation, pneumonia, and sepsis, in addition to being associated with the development of inflammation in the mammary glands of dairy cattle, which results in chronic mastitis and cell necrosis. SEs are small globular proteins that combine superantigenic and emetic activities; they are resistant to heat, low temperatures, and proteolytic enzymes and are tolerant to a wide pH range. More than 24 SE genes have been well described (SEA-SEE, SEG, SEH, SEI, SEJ, SElK, SElL, SElM, SElN, SElO, SElP, SElQ, SElR, SElS, SElT, SElU, SElV, SElW, SElX, SElY, and SElZ), being a part of different SFP outbreaks, clinical cases, and isolated animal strains. In recent years, new genes (sel26, sel27, sel28, sel31, sel32, and sel33) from SEs have been described, as well as two variants (seh-2p and ses-3p) resulting in a total of thirty-three genes from Ses, including the nine variants that are still in the process of genetic and molecular structure evaluation. SEs are encoded by genes that are located in mobile genetic elements, such as plasmids, prophages, pathogenicity islands, and the enterotoxin gene cluster (egc), and housed in the genomic island of S. aureus. Both classical SEs and SE-like toxins (SEls) share phylogenetic relationships, structure, function, and sequence homology, which are characteristics for the production of new SEs through recombination processes. Due to the epidemiological importance of SEs, their rapid assessment and detection have been crucial for food security and public health; for this reason, different methods of identification of SEs have been developed, such as liquid chromatography coupled with high-resolution mass spectrometry (LC-HRMS), molecular methods, and whole-genome sequencing; providing the diagnosis of SEs and a better understanding of the occurrence, spread, and eradication of SEs. This review provides scientific information on the enterotoxins produced by S. aureus, such as structural characteristics, genetic organization, regulatory mechanisms, superantigen activity, mechanisms of action used by SEs at the time of interaction with the immune system, methods of detection of SEs, and recent biocontrol techniques used in food.

Induction of Immunosuppressive CD8+CD25+FOXP3+ Regulatory T Cells by Suboptimal Stimulation with Staphylococcal Enterotoxin C1

Superantigens (SAgs) produced by Staphylococcus aureus at high concentrations induce proliferation of T cells bearing specific TCR Vβ sequences and massive cytokinemia that cause toxic shock syndrome. However, the biological relevance of SAgs produced at very low concentrations during asymptomatic colonization or chronic infections is not understood. In this study, we demonstrate that suboptimal stimulation of human PBMCs with a low concentration (1 ng/ml) of staphylococcal enterotoxin C1, at which half-maximal T cell proliferation was observed, induced CD8⁺CD25⁺ T cells expressing markers related to regulatory T cells (Tregs), such as IFN-γ, IL-10, TGF-β, FOXP3, CD28, CTLA4, TNFR2, CD45RO, and HLA-DR. Importantly, these CD8⁺CD25⁺ T cells suppressed responder cell proliferation mediated in contact-dependent and soluble factor-dependent manners, involving galectin-1 and granzymes, respectively. In contrast, optimal stimulation of human PBMCs with a high concentration (1 μg/ml) of staphylococcal enterotoxin C1, at which maximal T cell proliferation was observed, also induced similar expression of markers related to Tregs, including FOXP3 in CD8⁺CD25⁺ cells, but these T cells were not functionally immunosuppressive. We further demonstrated that SAg-induced TCR Vβ-restricted and MHC class II-restricted expansion of immunosuppressive CD8⁺CD25⁺ T cells is independent of CD4⁺ T cells. Our results suggest that the concentration of SAg strongly affects the functional characteristics of activated T cells, and low concentrations of SAg produced during asymptomatic colonization or chronic S. aureus infection induce immunosuppressive CD8⁺ Tregs, potentially promoting colonization, propagation, and invasion of S. aureus in the host.

Cross-Reactivity of TCR Repertoire: Current Concepts, Challenges, and Implication for Allotransplantation

Being able to track donor reactive T cells during the course of organ transplantation is a key to improve the graft survival, to prevent graft dysfunction, and to adapt the immunosuppressive regimen. The attempts of transplant immunologists have been for long hampered by the large size of the alloreactive T cell repertoire. Understanding how self-TCR can interact with allogeneic MHC is a key to critically appraise the different assays available to analyze the TCR Vβ repertoire usage. In this report, we will review conceptually and experimentally the process of cross-reactivity. We will then highlight what can be learned from allotransplantation, a situation of artificial cross-reactivity. Finally, the low- and high-resolution techniques to characterize the TCR Vβ repertoire usage in transplantation will be critically discussed.

Toward a Molecular Understanding of Adaptive Immunity: A Chronology, Part III

Early reports on T cell antigen receptor (TCR) signaling uncovered a rapid increase in intracellular calcium concentration and the activation of calcium-dependent protein kinase as necessary for T cell activation. Cytolytic T cell clones were instrumental in the discovery of intracellular cytolytic granules, and the isolation of the perforin and granzyme molecules as the molecular effectors of cell-mediated lysis of target cells via apoptosis. Cytolytic T cell clones and TCR cDNA clones were also instrumental for the generation of TCR transgenic animals, which provided definitive evidence for negative selection of self-reactive immature thymocytes. In addition, studies of TCR complex signaling of immature thymocytes compared with mature T cells were consistent with the interpretation that negative selection occurs as a consequence of the incapacity of immature cells to produce IL-2, resulting in cytokine deprivation apoptosis. By comparison, taking advantage of cloned TCRs derived from T cell clones reactive with male-specific molecules, using TCR transgenic mice it was possible to document positive selection of female thymocytes when the male-specific molecules were absent. Focusing on the molecular mechanisms of T cell "help" for the generation of antibody-forming cells following the path opened by the elucidation of the IL-2 molecule, several groups were successful in the identification, isolation, and characterization of three new interleukin molecules (IL-4, IL-5, and IL-6) that promote the proliferation and differentiation of B cells. In addition, the identification of a B cell surface molecule (CD40) that augmented B cell antigen receptor-stimulated proliferation and differentiation led to the discovery of a T cell activation surface molecule that proved to be the CD40-ligand, thus finally providing a molecular explanation for "linked or cognate" recognition when T cells and B cells interact physically. Accordingly, the decade after the generation of the first T cell clones saw the elucidation of the molecular mechanisms of T cell cytotoxicity and T cell help, thereby expanding the number of molecules responsible for adaptive T cell immunity.

Endogenous mouse mammary tumor viruses (mtv): new roles for an old virus in cancer, infection, and immunity

Mouse Mammary Tumor Viruses are beta-retroviruses that exist in both exogenous (MMTV) and endogenous (Mtv) forms. Exogenous MMTV is transmitted via the milk of lactating animals and is capable of inducing mammary gland tumors later in life. MMTV has provided a number of critical models for studying both viral infection as well as human breast cancer. In addition to the horizontally transmitted MMTV, most inbred mouse strains contain permanently integrated Mtv proviruses within their genome that are remnants of MMTV infection and vertically transmitted. Historically, Mtv have been appreciated for their role in shaping the T cell repertoire during thymic development via negative selection. In addition, more recent work has demonstrated a larger role for Mtv in modulating host immune responses due to its peripheral expression. The influence of Mtv on host response has been observed during experimental murine models of Polyomavirus- and ESb-induced lymphoma as well as Leishmania major and Plasmodium berghei ANKA infection. Decreased susceptibility to bacterial pathogens and virus-induced tumors has been observed among mice lacking all Mtv. We have also demonstrated a role for Mtv Sag in the expansion of regulatory T cells following chronic viral infection. The aim of this review is to summarize the latest research in the field regarding peripheral expression of Mtv with a particular focus on their role and influence on the immune system, infectious disease outcome, and potential involvement in tumor formation.

Challenging the Tritope Model of T cell receptor structure-function relationships with classical data on 'super' and 'allo-MHC' antigens

The response of the immune system to allo-MHC-encoded antigens and Mls 'superantigens' has been experimentally analysed in detail, but the data have not been coupled to a theoretical framework. It should therefore be instructive to see how well the newly proposed Tritope Model of TCR structure-function relationships deals with the signalling interactions between the TCR and the above antigens. We will pay heed to William Bateson's admonition, 'treasure the exceptions', by showing how a meaningful theory interrogates the data with the same validity that the data interrogate the theory. The concordances, as well as the contradictions, with the Tritope Model are a test of its heuristic value.

Stability of regulatory T-cell lineage

Regulatory T (Treg) cells expressing the transcription factor Foxp3 constitute a unique T-cell lineage committed to suppressive functions and play a central role in maintaining self-tolerance and immune homeostasis. While their differentiation state is remarkably stable in the face of various perturbations from the extracellular environment, recent studies have also revealed their adaptability to the changing environment; in response to extrinsic cues, Treg cells differentiate further into distinct substates to regulate different classes of immune responses effectively. In contrast, some other recent studies have challenged this notion of a committed Treg cell lineage and suggested that Treg cells might lose their identity and be reprogrammed to various effector helper T cells under certain circumstances, although this issue of environment-induced Treg cell reprogramming remains highly controversial. This review will focus on recent advances in our understanding of how the stability and adaptability of Treg cell lineage is regulated and how it might be perturbed in a changing environment.

Hematopoietic chimerism and transplantation tolerance: a role for regulatory T cells

The immunosuppressive regimens currently used in transplantation to prevent allograft destruction by the host's immune system have deleterious side effects and fail to control chronic rejection processes. Induction of donor-specific non-responsiveness (i.e., immunological tolerance) to transplants would solve these problems and would substantially ameliorate patients' quality of life. It has been proposed that bone marrow or hematopoietic stem-cell transplantation, and resulting (mixed) hematopoietic chimerism, lead to immunological tolerance to organs of the same donor. However, a careful analysis of the literature, performed here, clearly establishes that whereas hematopoietic chimerism substantially prolongs allograft survival, it does not systematically prevent chronic rejection. Moreover, the cytotoxic conditioning regimens used to achieve long-term persistence of chimerism are associated with severe side effects that appear incompatible with a routine use in the clinic. Several laboratories recently embarked on different studies to develop alternative strategies to overcome these issues. We discuss here recent advances obtained by combining regulatory T cell infusion with bone-marrow transplantation. In experimental settings, this attractive approach allows development of genuine immunological tolerance to donor tissues using clinically relevant conditioning regimens.

Junctional diversity prevents negative selection of an antigen-specific T cell repertoire

Endogenous mouse mammary tumor proviruses (MMTV; Mtv loci) deletes Vbeta6 expressing T cells in the thymus of Mtv-7(+) DBA/2 (H2(d)) mice through negative selection. We found that in Mtv-7(-) BALB/c (H2(d)) mice, Vbeta6 is a dominant V gene used in T cell responses to an 18 amino acid long peptide antigen: EYKEYAEYAEYAEYAEYA [abbreviated as K5 or EYK(EYA)(5)]. It was therefore surprising to find that despite the deletion of Vbeta6+ T cells, vigorous K5 specific T cell responses that use Vbeta6 can be raised in DBA/2 mice. Sequence analysis of Vbeta6 junctional diversity in K5 specific T cell lines revealed that the DBA/2 K5 repertoire compensates for the loss of most Vbeta6 T cells by overusing and amplifying Vbeta6+ T cells escaping central deletion and peripheral tolerization. In order to address the inability of some Vbeta6 T cells to recognize Mtv-7(+) we analyzed a panel of BALB/c Vbeta6 expressing T cell hybridomas. This data supported the argument that certain Vbeta6 junctional sequences preclude Mtv recognition and allows their escape from central deletion in DBA/2 mice. These cells are not anergic and can be activated with cognate peptide antigen in periphery. We suggest that junctional diversity at the V region of some of the T cell receptors does not allow these cells to recognize self-superantigens with high enough affinity and thus they escape negative selection in the thymus. These results for the first time provide a molecular explanation of how the immune system compensates for "hole in the repertoire" caused by deletion of the majority of T cells carrying certain V region segments.

Mls: A Link Between Immunology and Retrovirology

The nature of the mysterious minor lymphocyte stimulating (Mls) antigens has recently been clarified. These molecules which were key elements for our current understanding of immune tolerance, have a strong influence on the mouse immune system and are encoded by the open reading frame (orf) of endogenous and exogenous mouse mammary tumor viruses (MMTV's). The knowledge that these antigens are encoded by cancerogenic retroviruses opens an interdisciplinary approach for understanding the mechanisms of immune responses and immune tolerance, retroviral carcinogenesis, and retroviral strategies for infection.

Age-associated decline in T cell repertoire diversity leads to holes in the repertoire and impaired immunity to influenza virus

A diverse T cell repertoire is essential for a vigorous immune response to new infections, and decreasing repertoire diversity has been implicated in the age-associated decline in CD8 T cell immunity. In this study, using the well-characterized mouse influenza virus model, we show that although comparable numbers of CD8 T cells are elicited in the lung and lung airways of young and aged mice after de novo infection, a majority of aged mice exhibit profound shifts in epitope immunodominance and restricted diversity in the TCR repertoire of responding cells. A preferential decline in reactivity to viral epitopes with a low naive precursor frequency was observed, in some cases leading to “holes” in the T cell repertoire. These effects were also seen in young thymectomized mice, consistent with the role of the thymus in maintaining naive repertoire diversity. Furthermore, a decline in repertoire diversity generally correlated with impaired responses to heterosubtypic challenge. This study formally demonstrates in a mouse infection model that naturally occurring contraction of the naive T cell repertoire can result in impaired CD8 T cell responses to known immunodominant epitopes and decline in heterosubtypic immunity. These observations have important implications for the design of vaccine strategies for the elderly.

High frequency of the TCRBV20S1 null allele in the Sardinian population

Single nucleotide polymorphisms (SNPs) in the T-cell receptor (TCR) gene segments might play a role in shaping the TCR repertoire. Three polymorphisms have been described for the TCRBV20S1 gene segment, one of which is responsible for a nucleotide substitution at position 524, resulting in the introduction of a stop codon. Individuals homozygous for this inactivating polymorphism ("null allele") are unable to express TCRBV20 gene products. Using DNA restriction digestion analysis, we investigated the frequency of this polymorphism in 111 healthy Sardinian subjects. Inhabitants of the Mediterranean island of Sardinia are considered to represent a genetically isolated population. Our analyses revealed an incidence of 19.8% of homozygosity for the null allele, corresponding to an allele frequency of 0.45. Such an incidence, significantly higher than the one detected in 83 non-Sardinian Caucasians (6%), is the most elevated so far reported in the literature. BV20 is a single member subfamily and the null allele produces a gap in the potential TCR repertoire. Therefore, it is possible that an undetermined selective pressure could have played a role in determining the high frequency of this inactivating polymorphism in Sardinians. Alternatively, this finding could be related to a founder effect in this ancient island population.

Analysis of T cell receptor (TCR) BV-gene clonotypes in NC/Nga mice developing dermatitis resembling human atopic dermatitis

BACKGROUND

Our previous study showed that T cells in skin lesions of human atopic dermatitis (AD) had oligoclonal accumulation, indicating the involvement of antigen-specific immune reactions at those sites. Recently, NC/Nga mice, which develop skin lesions similar to AD, have been proposed as a model for that disease.

OBJECTIVE

To clarify whether NC/Nga mice are suitable as a model for human AD from the viewpoint of their antigen-specific immune responses.

METHODS

Reverse transcription-polymerase chain reaction (RT-PCR) and single strand conformation polymorphism (SSCP) analyses were conducted to detect TCR BV genes of clonally expanded T cells derived from NC/Nga mice at an early phase of the AD-like dermatitis, at a late phase of the dermatitis, and with no AD-like dermatitis.

RESULTS

(1) T cells with TCR BV 7, 10 and 17 reside in the skin of NC/Nga mice without the AD-like dermatitis. (2) T cells with these BV genes contain oligoclonal accumulations, however, expanded T cell clonotypes are also detected in the spleen and exist constantly during the course of the AD-like dermatitis. (3) Development of the AD-like dermatitis is associated with additional oligoclonal expansion/accumulation of T cells with TCR BV 2, 4 and 6 genes. (4) Progression of the AD-like dermatitis is associated with further oligoclonal expansion/accumulation of T cells with the TCR BV 14 gene. (5) Some of the expanded TCR clonotypes are common between the individual mice and between early and late phases.

CONCLUSIONS

Taking these data together with the previous human AD studies, NC/Nga mice seem to be an appropriate model for human AD.

On natural and artificial vaccinations

This review summarizes the general parameters of cell- and antibody-mediated immune protection and the basic mechanisms responsible for what we call immunological memory. From this basis, the various successes and difficulties of vaccines are evaluated with respect to the role of antigen in maintaining protective immunity. Based on the fact that in humans during the first 12-48 months maternal antibodies from milk and serum protect against classical acute childhood and other infections, the concept is developed that maternal antibodies attenuate most infections of babies and infants and turn them into effective vaccines. If this "natural vaccination" under passive protective conditions does not occur, acute childhood diseases may be severe, unless infants are actively vaccinated with conventional vaccines early enough, i.e., in synchronization with the immune system's maturation. Although vaccines are available against the classical childhood diseases, they are not available for many seemingly milder childhood infections such as gastrointestinal and respiratory infections; these may eventually trigger immunopathological diseases. These changing balances between humans and infections caused by changes in nursing habits but also in hygiene levels may well be involved in changing disease patterns including increased frequencies of certain autoimmune and degenerative diseases.

Donor-specific antigen transfusion-mediated skin-graft tolerance results from the peripheral deletion of donor-reactive CD8+ T cells

BACKGROUND

The mechanism of donor-specific transfusion (DST)-induced long-term skin-graft survival is examined in 2CF1 (2C x dm2) transgenic and B6F1 (C57BL/6 x dm2) nontransgenic mice in which CB6F1 (Balb/c x B6) DST and donor skin grafts differ from 2CF1 or B6F1 recipients only at major histocompatibility complex class I Ld.

METHODS

Saline (control) or allogeneic CB6F1 spleen cells were injected intravenously into 2CF1 and B6F1 mice. One week later, CB6F1 tail skin was transplanted onto the dorsum of these mice. Fluorescence-activated cell sorter analysis (flow cytometric analysis) of peripheral blood was performed 2 days before DST, 5 days after DST, and 7, 14, 21, 28, and 75 days after skin grafting. Splenocyte responsiveness was measured by in vitro mixed lymphocyte culture and cytotoxic T lymphocyte. Cytokine protein production (interleukin [IL]-2 and interferon-gamma) was measured by enzyme-linked immunosorbent assay.

RESULTS

Whereas all CB6F1 skin grafts in control saline-treated 2CF1 and B6F1 mice were rejected, 100% of 2CF1 and B6F1 pretreated with CB6F1 DST accepted the class I Ld disparate donor skin indefinitely. DST followed by a CB6F1 skin graft led to a significant deletion of donor-reactive CD8+ T cells by fluorescence-activated cell sorter analysis and decreased production of the inflammatory cytokines IL-2 and interferon-gamma. The hyporesponsiveness of residual CD8+ T cells in mixed lymphocyte culture and cytotoxic T lymphocyte to Ld after DST was restored to normal by IL-2.

CONCLUSION

These findings demonstrate that administration of DST uniformly results in long-term Ld+ skin-allograft acceptance. This tolerance induction is related to both a significant decrease in donor-reactive CD8+ transgenic T cells and anergy of the residual CD8+ T cells.

Mechanism of portal venous tolerant long-term MHC Class I L(d)-specific skin graft survival in transgenic 2CF1 mice

BACKGROUND

Administration of alloantigen via the portal vein (PV) in non-transgenic animals has been shown to promote immunologic tolerance and enhance transplant allograft survival. The underlying mechanisms remain unclear. In 2C x dm2 F1 (2CF1) transgenic mice, the monoclonal antibody, 1B2, identifies specific 2C TCR transgenic CD8+ T cells that are cytotoxic against Class I MHC L(d). In these mice, the specific response by these cells to L(d+) skin grafts after PV administration of L(d+) antigen was determined.

MATERIALS AND METHODS

Saline (control) or allogeneic C57BL/6 x BALB/c F1 (CB6F1) spleen cells (25 x 10(6)), which differ from 2CF1 only at L(d), were injected PV into 2CF1 mice. One week later, CB6F1 tail skin was transplanted onto the dorsum of these 2CF1 mice. Skin graft rejection was defined as >50% loss of the graft. Parallel experiments were performed in non-transgenic littermates [B6F1 (C57BL/6 x dm2)]. FACS analysis of 2CF1 peripheral blood for 1B2+, CD4+, and CD8+ T cells was performed 2 days before PV injection (9 days prior to skin grafting), 5 days after PV injection (2 days prior to skin grafting), and 7, 14, 21, 28, and 60 days after skin grafting. FACS analysis of nai;ve, saline control, and CB6F1 PV-treated 2CF1 thymocytes was also performed. Responsiveness of saline (control)-treated and PV-treated 2CF1 splenocytes was measured by in vitro cytotoxic T lymphocyte (CTL).

RESULTS

All CB6F1 skin grafts were rejected in <14 days by PV saline controls. However, a single PV injection of donor L(d+) CB6F1 cells was sufficient to induce indefinite CB6F1 (L(d+)) skin allograft survival in 100% of non-transgenic B6F1 and transgenic 2CF1 (anti-L(d)) TCR transgenic recipients. FACS analysis of 1B2+ T cells demonstrated that PV injection of donor antigen followed by a CB6F1 skin graft led to a 70% decrease in peripheral donor-reactive 1B2+ CD8+ T cells by day 7, while central thymocytes were unchanged. CTL of 2CF1 splenocytes following PV CB6F1 demonstrated that they were hyporesponsive to L(d) compared to saline-treated 2CF1 splenocytes. Despite recovery of peripheral CD8+ T cells to near normal levels by 60 days post-transplantation, skin graft survival persisted indefinitely.

CONCLUSIONS

Administration of specific PV antigen results in exquisite long-term L(d+) skin allograft acceptance. This tolerance induction is related to a significant peripheral deletion of donor-reactive 1B2+ CD8+ transgenic T cells and anergy of the residual T cells.

Molecular identification of pathogenetic IdLNF+1 autoantibody idiotypes derived from the NZBxSWR F1 model for systemic lupus erythematosus

The acceleration of nephritis in SNF(1) mice by CD4(+) T-cell clones reactive with a nephritogenic idiotype, Id(LN)F(1) [1], as well as the ability of anti-Id(LN)F(1) antisera to down-regulate the production of Id(LN)F(+)(1) immunoglobulin (Ig) in vivo and delay nephritis [2], suggests that dysregulation of this idiotype may contribute to the development of SNF(1) nephritis. Herein, we show that a monoclonal Id(LN)F(1)-expressing antibody, 540, significantly (P< or = 0.01) stimulated Id(LN)F(1)-reactive T-cell clones B6 and D2 to proliferate, while other Id(LN)F+1 antibodies did not. Further, injection of 540-producing hybridoma cells into nonautoimmune (SWRxBalb/c)F(1) mice resulted in the deposition of Id(LN)F(+)(1) Ig in the kidneys, in a pattern indicative of early nephritis. To identify the pathogenetic Id(LN)F(1) epitope(s) at the molecular level, we compared the deduced amino acid sequences of the heavy and light chain variable regions of pathogenetic and non-pathogenetic Id(LN)F(1)-expressing Igs 540, 317, and 533. Two overlapping peptides derived from the V(H) sequence of 540 (aa 54-66 and 62-73), which both contain the triple basic amino acid motif K(X)K(X)K, stimulated SNF(1) T cells and T-cell clones B6 and D2. These results further support the involvement of a subset of Id(LN)F(1)-expressing Ig in SNF(1) nephritis.

Lack of evidence for superantigen activity of Toxoplasma gondii towards human T cells

Toxoplasma gondii is an obligatory intracellular parasite whose life cycle may include man as an intermediate host. More than 500 million people are infected with this parasite worldwide. It has been previously reported that T. gondii contains a superantigen activity. The purpose of the present study was to determine if the putative superantigen activity of T. gondii would manifest towards human T cells. Peripheral blood mononuclear cells (PBMC) from individuals with no previous contact with the parasite were evaluated for proliferation as well as specific Vbeta expansion after exposure to Toxoplasma antigens. Likewise, PBMC from individuals with the congenital infection were evaluated for putative Vbeta family deletions in their T cell repertoire. We also evaluated, over a period of one year, the PBMC proliferation pattern in response to Toxoplasma antigens in patients with recently acquired infection. Some degree of proliferation in response to T. gondii was observed in the PBMC from individuals never exposed to the parasite, accompanied by specific Vbeta expansion, suggesting a superantigen effect. However, we found no specific deletion of Vbeta (or Valpha) families in the blood of congenitally infected individuals. Furthermore, PBMC from recently infected individuals followed up over a period of one year did not present a reduction of the Vbeta families that were originally expanded in response to the parasite antigens. Taken together, our data suggest that T. gondii does not have a strong superantigen activity on human T cells.

Mouse xenoantigens contribute to rat T-cell Vbeta repertoire generation in mixed xenogeneic bone marrow chimeras

We previously demonstrated that rat bone-marrow-derived cells in mixed xenogeneic chimeras (rat + mouse --> mouse) contribute to peripheral selection of mouse T-cell receptor (TCR) variable betas (Vbetas) repertoire. In this study, we analysed rat T cells that developed in the chimeras to assess the contribution of mouse xenoantigens to the development of rat TCR repertoire. The expression of rat Vbetas was analysed using flow cytometry and a reverse transcription-polymerase chain reaction (RT-PCR) method that allows for both semiquantitative analysis of rat Vbeta gene expression and size heterogeneity of the complementarity determining region 3 (CDR3) domain. Three distinct patterns of Vbeta expression were detected. Partial deletion was observed for Vbeta5, 7, 12, 14, 16, 17 and 20 that exhibited reduced levels of peripheral expression by 3.4-, 1.8-, 8.7-, 2.0-, 7.8-, 9.5- and 1.8-fold, respectively, compared with the levels of Vbetas in naYve rats. Higher levels of peripheral expression were detected for three rat Vbeta genes; Vbeta6 (2.2-fold), Vbeta8.2 (3.2-fold), and Vbeta9 (1.7-fold). The relative expression of the other 10 known rat Vbeta families in chimeras was unchanged as compared with that of normal rats. We did not observe detectable changes in the pattern of CDR3 expression in chimeras, suggesting that the mouse xenogeneic environment exerted its influence on the development of rat T cells via the Vbeta-encoded CDR1/2 domains. Our data demonstrate that the rat T-cell repertoire in chimeras is shaped by both contractions as well as expansions of selected Vbetas and suggest that mouse xenoantigens and/or superantigens of endogenous mouse retroviruses may contribute as ligands for these selection processes

Oligoclonal T cell expansions in atherosclerotic lesions of apolipoprotein E-deficient mice

T cells are present in atherosclerotic lesions at all stages of development. They exhibit activation markers and are particularly prominent at sites of plaque rupture. This suggests that T-cell-mediated immune responses are involved in the pathogenesis of atherosclerosis. Antigen-specific T cells reactive with oxidized lipoproteins and heat shock proteins have been isolated from plaques, indicating that local activation and clonal expansion might occur. To analyze different stages of atherosclerosis, we have used a murine model. Targeted deletion of the apolipoprotein E gene results in severe hypercholesterolemia and spontaneous atherosclerosis, with lesions containing large numbers of T cells and macrophages. We have analyzed mRNA for T-cell antigen receptors (TCRs) from aortic fatty streaks, early fibrofatty plaques, and advanced fibrofatty plaques of such mice. Polymerase chain reaction amplification of complementarity-determining region 3 (CDR3 region) of TCRs was followed by spectratyping of fragment lengths. This analysis detected all types of variable (V) segments with a gaussian distribution of CDR3 in lymph nodes. In contrast, a restricted heterogeneity was found in atherosclerotic lesions, with expansion of a limited set of Vbeta and Valpha segments and a monotypic or oligotypic CDR3 spectrum in each lesion. Vbeta6 was expressed in all lesions; Vbeta5.2, Vbeta16, Valpha34s, and Valpha9, in the majority of lesions; and Vbeta6, Vbeta5.2, and Valpha34S, in lesions at all 3 stages of development. The strongly skewed pattern of the CDR3 region in the TCR is indicative of oligoclonal expansions of T cells and suggests the occurrence of antigen-driven T-cell proliferation in atherosclerosis.

In utero bone marrow transplantation induces donor-specific tolerance by a combination of clonal deletion and clonal anergy

BACKGROUND/PURPOSE

In utero bone marrow transplantation can induce donor-specific tolerance to postnatal solid organ transplantation, although the mechanisms remain poorly defined. In this study, we investigated the role of clonal deletion and clonal anergy in the maintenance of tolerance in a murine model of in utero bone marrow transplantation.

METHODS

DBA/2 mice (MIs(a+)) were used as donors of adult bone marrow, and 14-day-gestation fetal Balb/c mice (MIs(a-)) were used as recipients. Tolerance was defined by donor-specific skin graft survival for more than 8 weeks. Clonal deletion was assessed by flow cytometry for Vbeta6 T cell receptor usage. A tolerant animal demonstrating partial deletion of CD4+/Vbeta6+ T cells and a nontolerant animal were selected for analysis of clonal anergy by a proliferation assay using plate-bound anti-Vbeta6 antibody for stimulation with or without exogenous interleukin-2 (IL2).

RESULTS

Vbeta6+ splenocytes constituted 6.32% of CD4+ T cells in the tolerant animal compared with 9.19% in the nontolerant animal, demonstrating incomplete clonal deletion in the tolerant animal. Stimulation with plate-bound anti-Vbeta6 induced a good proliferative response in the nontolerant animal but a significantly attenuated response in the tolerant animal (P< .001), which was abrogated by the addition of IL2.

CONCLUSIONS

In this murine model of in utero bone marrow transplantation, the tolerant state is characterized by partial clonal deletion of donor reactive T cells and clonal anergy of nondeleted donor reactive T cells. The anergic state can be abrogated by exogenous IL2, suggesting that the mechanism of anergy is a deficiency of IL2 production.

T-cell clonal change after allo-kidney transplantation in humans

Whether T cells circulating peripherally express changes at a clonal level after renal transplantation is uncertain. To clarify this issue, we analyzed T-cell clonality of peripheral blood lymphocytes (PBLs) in 12 renal transplant recipients by a novel polymerase chain reaction-single-strand conformation polymorphism (PCR-SSCP) method that can discriminate T-cell clones with different T-cell receptor (TCR) Vbeta motifs. The PCR-SSCP study showed that after transplantation, only a few distinct T-cell clonotypes accumulated in the absence of clinical episodes, irrespective of the compatibility of HLA antigens. In contrast, various T-cell clones appeared in cases of acute rejection (AR) and infection. These subsided immediately after the AR was resolved; however, they remained long after the resolution of the infection. In a case of AR followed by an infectious episode, distinct T-cell clones appeared concomitantly with each episode. Several of them disappeared or remained thereafter. In one case, significant numbers of accumulating bands were observed by in-vitro stimulation by mixed lymphocyte reaction (MLR); several were identical to those found in vivo. However, some of those that did not appear in vitro were apparent in vivo. In conclusion, the appearance of T-cell clonotypes at a peripheral level indicates the existence of immunologically activated T-cell clones, which were significantly affected by immunosuppressive therapy. It was also determined that the T-cell immune system is much more complicated in vivo than in vitro.

Quantitative analysis of the T cell repertoire selected by a single peptide-major histocompatibility complex

The positive selection of CD4+ T cells requires the expression of major histocompatibility complex (MHC) class II molecules in the thymus, but the role of self-peptides complexed to class II molecules is still a matter of debate. Recently, it was observed that transgenic mice expressing a single peptide-MHC class II complex positively select significant numbers of diverse CD4+ T cells in the thymus. However, the number of selected T cell specificities has not been evaluated so far. Here, we have sequenced 700 junctional complementarity determining regions 3 (CDR3) from T cell receptors (TCRs) carrying Vbeta11-Jbeta1.1 or Vbeta12-Jbeta1.1 rearrangements. We found that a single peptide-MHC class II complex positively selects at least 10(5) different Vbeta rearrangements. Our data yield a first evaluation of the size of the T cell repertoire. In addition, they provide evidence that the single Ealpha52-68-I-Ab complex skews the amino acid frequency in the TCR CDR3 loop of positively selected T cells. A detailed analysis of CDR3 sequences indicates that a fraction of the beta chain repertoire bears the imprint of the selecting self-peptide.

Anti-T-cell receptor therapy in murine experimental systemic lupus erythematosus

Experimental systemic lupus erythematosus (SLE), similar to that observed after immunization with the human anti-DNA mAb 16/6 Id+, could be induced in mice by injection of 16/6 Id specific T-cell lines. The above T-cell lines were exclusively CD4+ CD8- and the majority of cells expressed the Vbeta8 T-cell receptor (TCR) gene products. Furthermore, lymph node cells of mice immunized with the 16/6 Id were enriched with CD4+ Vbeta8+ T-cells. The TCR used by 16/6 Id-specific T-cells showed a limited homology in their CDR3 junctional regions. Nevertheless, mice injected with the anti-Vbeta8 mAb developed autoantibody titers that were not significantly different from those found in the non-treated, 16/6 Id-injected group.

A dominant V beta bias in the CTL response after HSV-1 infection is determined by peptide residues predicted to also interact with the TCR beta-chain CDR3

Many T cell responses are dominated by restricted TCR expression and can range from repeated usage of particular TCR Vbeta- and/or Valpha-elements, to the preferential usage of both V- and J-elements, often in conjunction with conserved V-D-J or V-J junctional sequences. Cytotoxic T lymphocytes specific for a Kb-restricted determinant from the herpes simplex virus glycoprotein B (gB) preferentially express a dominant TCRBV10 beta-chain with sequence conservation of a tryptophan-glycine located in the V-D junction. Here we have examined whether immunisation of C57BL/6 mice with the gB-peptide can mimic the CTL response seen after HSV-1 infection. Immunisation with the gB-peptide resulted in the generation of gB-specific CTL that showed a similar TCRBV10 bias to that observed after HSV-1 infection. When the gB-determinant was expressed as a part of a fusion protein, immunised mice again exhibited the TCRBV10 bias with the junctional sequence conservation in the responding CTL. C57BL/6 mice were then immunised with variants of the gB-peptide that contained amino acid substitutions at positions previously predicted to contact the TCR beta-chain CDR3. Analysis of the TCRBV usage of variant specific CTL lines showed that substitutions at the TCR-contact positions 4, 6 and 7 of the gB-peptide resulted in a loss of the TCRBV10 bias. These results suggest that the TCRBV10 bias seen in gB-specific CTL after HSV-1 infection is due to antigenic selection by the minimal peptide and is determined by residues proposed to contact the TCR beta-chain CDR3.

Immune response to mouse mammary tumor virus in mice lacking the alpha/beta interferon or the gamma interferon receptor

Mouse mammary tumor virus (MMTV) is a retrovirus which induces a strong immune response and a dramatic increase in the number of infected cells through the expression of a superantigen (SAg). Many cytokines are likely to be involved in the interaction between MMTV and the immune system. In particular, alpha/beta interferon (IFN-alpha/beta) and gamma interferon (IFN-gamma) exert many antiviral and immunomodulatory activities and play a critical role in other viral infections. In this study, we have investigated the importance of interferons during MMTV infection by using mice with a disrupted IFN-alpha/beta or IFN-gamma receptor gene. We found that the SAg response to MMTV was not modified in IFN-alpha/betaR(0/0) and IFN-gammaR(0/0) mice. This was true both for the early expansion of B and T cells induced by the SAg and for the deletion of SAg-reactive cells at later stages of the infection. In addition, no increase in the amount of proviral DNA was detected in tissues of IFN-alpha/betaR(0/0) and IFN-gammaR(0/0) mice, suggesting that interferons are not essential antiviral defense mechanisms during MMTV infection. In contrast, IFN-gammaR(0/0) mice had increased amounts of IL-4 mRNA and an altered usage of immunoglobulin isotypes with a reduced frequency of IgG2a- and IgG3-producing cells. This was associated with lower titers of virus-specific antibodies in serum early after infection, although efficient titers were reached later.

Enhanced prevalence of T cells expressing TCRBV8S2 and TCRBV8S3 in hearts of chronically Trypanosoma cruzi-infected mice

We have analysed the relative T cell receptor (TCR) BV gene usage in T cells from hearts and spleens of CBA/HJ mice chronically infected with the Tulahuén strain of Trypanosoma cruzi. During chronic infection, CBA/HJ mice recruit T cells at the major site of inflammation (i.e. the heart), with over-representation of certain TCRBV gene subfamilies (TCRBV8S2 and TCRBV8S3). In contrast, no signal or a very weak message from a limited number of T cells was recorded from one heart of the control group. No alteration of TCRBV distribution was recorded in spleens of chronically infected CBA/HJ. Our findings indicate that there is a preferential TCRBV gene usage in the T cell response in the hearts of chronically infected mice. Furthermore, the pattern of CDR3 lengths in inflammatory T cells was altered.

Mechanisms of Long-Term Donor-Specific Allograft Survival Induced by Pretransplant Infusion of Lymphocytes

Pretransplantation donor-specific transfusion (DST) can enhance allograft survival in man and animals. However, due to the lack of a specific marker to identify donor-reactive cells in vivo in man and normal (nontransgenic) animals, the underlying mechanism remains unknown. In this study, we use 2CF1 transgenic mice expressing a transgenic T-cell receptor (TCR) specifically recognizing Ld, a major histocompatibility complex (MHC) class I molecule, to delineate the role of DST in long-term skin allograft survival and its underlying mechanisms. Our main findings include: (1) in the absence of any other immunosuppressive treatment, a single dose pretransplantation infusion of viable splenocytes from an Ld+ donor is sufficient to induce permanent donor-specific skin allograft survival in 2CF1anti-Ld TCR transgenic mice; (2) DST leads to a deletion of the majority (>60%) of donor-reactive T cells in the periphery of the recipient. However, deletion does not necessarily result in tolerance; (3) remaining donor-reactive T cells from DST-treated mice are fully responsive to Ld in vitro, and can suppress the antidonor response of naive T cells in vitro only when exogenous interleukin (IL)-4 is provided; and (4) the sera level of IL-4 in DST-treated tolerant mice is significantly increased. These results suggest that the generation of a subset of T cells with the potential to specifically inhibit antidonor responses, together with promotion of IL-4 production in recipients, may be important mechanisms for the induction and maintenance of antigen-specific tolerance.

Mechanisms of Long-Term Donor-Specific Allograft Survival Induced by Pretransplant Infusion of Lymphocytes

Pretransplantation donor-specific transfusion (DST) can enhance allograft survival in man and animals. However, due to the lack of a specific marker to identify donor-reactive cells in vivo in man and normal (nontransgenic) animals, the underlying mechanism remains unknown. In this study, we use 2CF1 transgenic mice expressing a transgenic T-cell receptor (TCR) specifically recognizing Ld, a major histocompatibility complex (MHC) class I molecule, to delineate the role of DST in long-term skin allograft survival and its underlying mechanisms. Our main findings include: (1) in the absence of any other immunosuppressive treatment, a single dose pretransplantation infusion of viable splenocytes from an Ld+ donor is sufficient to induce permanent donor-specific skin allograft survival in 2CF1anti-Ld TCR transgenic mice; (2) DST leads to a deletion of the majority (>60%) of donor-reactive T cells in the periphery of the recipient. However, deletion does not necessarily result in tolerance; (3) remaining donor-reactive T cells from DST-treated mice are fully responsive to Ld in vitro, and can suppress the antidonor response of naive T cells in vitro only when exogenous interleukin (IL)-4 is provided; and (4) the sera level of IL-4 in DST-treated tolerant mice is significantly increased. These results suggest that the generation of a subset of T cells with the potential to specifically inhibit antidonor responses, together with promotion of IL-4 production in recipients, may be important mechanisms for the induction and maintenance of antigen-specific tolerance.

Defect in Th1-like cells of nonresponders to hepatitis B vaccine

Peripheral blood lymphocytes from nonresponders to hepatitis B vaccine (HBsAg) failed to undergo a proliferative response to recombinant HBsAg in vitro, whereas cells from responders proliferated vigorously. The lack of proliferative response was not due to defective antigen presentation in that MHC-identical responder and nonresponder antigen presenting cells were equally effective in stimulating responder T cells. Nonresponder T cells did not proliferate in response to antigen-pulsed MHC identical responder antigen presenting cells. The present study demonstrated that: 1) there were no detectable (1 in < 20 x 10(4) HBsAg-precursor T cells in any of the nonresponders, while in responders the frequency of HBsAg-precursor T cells ranged from 1 in 3.2 x 10(3) to 1 in 40 x 10(3); 2) nonresponder cell cultures did not secrete IL-2 in response to HBsAg stimulation; 3) exogenous recombinant IL-2 did not restore the proliferative response of the T cells in HBsAg-pulsed cultures of nonresponders. These results suggest that the cellular basis for the lack of response to HBsAg is a defect in HBsAg-specific Th1-like cells; either there is an absence of the Th1 cells or cells with TCR specificity for HBsAg are present but are unresponsive to the HBsAg peptide-MHC complex (i.e., anergy or tolerance).

T cell receptor expression and differential proliferative responses by T cells specific to a myasthenogenic peptide

Myasthenia gravis (MG) is a T-cell-regulated autoimmune disease in which a pathological autoantibody response is mounted against the nicotinic acetylcholine receptor of the neuromuscular junction. Our laboratory previously identified a T cell epitope, p195-212, derived from the human acetylcholine receptor alpha subunit, which triggered PBL to proliferate from about 70% of MG patients tested. p195-212 was also found to be an immunodominant T cell epitope in SJL mice and a cryptic epitope in C3H.SW mice. Inoculation of naive SJL mice with cells from a p195-212-specific syngeneic T cell line caused MG-related autoimmune manifestations in those mice. In these studies we analyzed TCR alpha and beta chain sequences used by T cell lines and clones from both high- and low-responder mouse strains in response to p195-212. T cell lines generated from either strain expressed single TCR V beta gene segments (V beta 17 in SJL mice and V beta 8 in C3H.SW mice). By deleting V beta 17-expressing T cells in p195-212-immunized SJL mice we established a T cell line that expressed the V beta 6 gene product, suggesting that SJL mice are not limited to using a single V beta gene segment in response to p195-212. In addition, we found that N- and/or C-terminal-truncated peptides of p195-212, presented under the same culture conditions to different clones bearing the same TCR alpha beta chain, could elicit very different proliferative responses from the clones. Thus, even within a constrained system, factors other than TCR sequence contribute to the differential stimulation of T cell responses.

Association of IgA nephropathy with T-cell receptor constant alpha chain gene polymorphism

T-cell receptor (TCR) proteins recognize a complex of an antigen-derived peptide bound to the cell surface products of the major histocompatibility complex (MHC) that could be of importance in the immunopathogenesis of IgA nephropathy (IgAN). Previous studies found no difference on TCR constant beta chain gene frequencies in IgAN compared with control. Yet no study on the TCR alpha gene in IgAN was reported. We studied the TCR C alpha gene polymorphisms by restriction fragment length polymorphism (RFLP) in 53 patients with IgAN and in comparison with 67 healthy controls. The patients were also classified into different histopathological grading (I, II, and III with increasing histological severity) and renal functions. The extracted DNA were digested with Taq I enzymes and probed with a full-length TCR-alpha cDNA clone p1.2alpha probe. A 7-kb C-alpha Taq 1 fragment is found in 32 of 53 patients (60.3%) compared with 26 of 67 controls (38.8%) (P < 0.05). There was no association of any polymorphic fragment, including the 7-kb fragment, with either the histological grading or renal function. It is concluded that the TCR C-alpha gene is associated with IgAN but not with the prognosis of the disease.

Predominant T-cell receptor Vbeta usage of intraepithelial lymphocytes during the immune response to enteric reovirus infection

Previous studies have found that intraepithelial lymphocytes (IEL) contain virus-specific cytotoxic T lymphocytes (CTL) that increase dramatically during the course of virus infection. In the present study, the T-cell receptor (TCR) V beta pattern used by IEL against reovirus enteric infection was investigated both in conventional and in germfree mice. IEL were isolated by a modified rapid method, and their expression of 13 TCR V betas was examined by flow cytometric analysis. The virus-specific CTL activity of each TCR V beta subset was assessed by subtraction with coated Dyna beads by a nonradioactive assay. There was a preferential perturbation of TCR V betas following virus challenge, including increases in cells expressing V beta7, -12, -14, and -17 in conventional mice and V beta2, -12, and -17 in germfree mice. In conventionally reared mice, IEL maintained and restimulated in culture had a preferential use of TCR V beta9, -12, and -17. TCR V beta2 and -17 subfamilies were found amplified in all conditions. Furthermore, TCR V beta12 and -17 accounted for 37 and 77% of the virus-specific CTL activity, respectively, after in vitro restimulation. This study provides evidence that virus-specific CTL activity may be due to the oligoclonal expansion of TCR V beta subfamilies in IEL. Our findings suggest that in vivo infection selectively presents few T-cell epitopes and that the correct identification of these T-cell epitopes would increase the likelihood of success when designing subunit vaccines.

Use of adoptive transfer of T-cell-antigen-receptor-transgenic T cell for the study of T-cell activation in vivo

Adoptive transfer of TCR-transgenic T cells uniformly expressing an identifiable TCR of known peptide/MHC specificity can be used to monitor the in vivo behavior of antigen-specific T cells. We have used this system to show that naive T cells are initially activated within the T-cell zones of secondary lymphoid tissue to proliferate in a B7-dependent manner. If adjuvants or inflammatory cytokines are present during this period, enhanced numbers of T cells accumulate, migrate into B-cell-rich follicles, and acquire the capacity to produce IFN-gamma and help B cells produce IgG2a. If inflammation is absent, most of the initially activated antigen-specific T cells disappear without entering the follicles, and the survivors are poor producers of IL-2 and IFN-gamma. Our results indicate that inflammatory mediators play a key role in regulating the anatomic location, clonal expansion, survival and lymphokine production potential of antigen-stimulated T cells in vivo.

Characteristics and maintenance of CD8+ T-cell clones found in old mice

Old mice, like old human beings, contain large clones of CD8+ T-cells. These cells grow poorly in tissue culture, therefore it is difficult to maintain the cells in vitro. The cells can be grown after transfer to sublethally irradiated mice. This technique will be useful in further studies on the properties of the cells. Based on observations from such transfer experiments, we conclude that: (1) expansion of the T-cell clones in recipients is dramatic but slow; (2) chance events caused by endogenous antigens or gene mutations rather than exogenous antigens may account for the expansion of these clones; and (3) the expanded T-cell clones are benign and do not cause malignancies.

Loss of T cell receptor Vbeta repertoires in HIV type 1-infected SCID-hu mice

Late-stage HIV-1 disease in humans has been associated with perturbations of the T cell receptor (TCR) Vbeta repertoire. It is not known if the observed loss of certain Vbeta families is attributable directly to HIV-1 infection or whether this is a consequence of multiple opportunistic infections. Putative HIV-1-associated superantigens have been postulated to be the cause of the perturbed TCR Vbeta repertoire and the subsequent CD4+ T cell depletion in HIV-1-infected humans. In this study, we examined the human TCR Vbeta repertoire in SCID-hu mice, housed in a pathogen-free environment and infected with a molecularly cloned virus strain, to ascertain directly the effect of HIV-1 on the human TCR Vbeta repertoire in the absence of other infectious agents. We demonstrate that mock-infected human thymus/liver (Thy/Liv) implants in SCID-hu mice have complete TCR Vbeta repertoires, reflective of a normal human thymus. However, HIV-1-infected implants in SCID-hu mice had depleted TCR Vbeta repertoires, corresponding with thymocyte depletion. These results indicate that HIV-1-specific mechanisms are the cause of the TCR Vbeta repertoire depletion in infected implants. However, these thymocyte depletions were not restricted to specific TCR Vbeta subsets. These results are not consistent with the hypothesis that HIV-1 acts as a superantigen in vivo. The disruption of the TCR Vbeta repertoire in the human Thy/Liv implants of the SCID-hu mice suggests that HIV-1 infection may be influencing T cell development in the thymus, contributing to both the overall CD4+ T cell depletion in AIDS and limited TCR repertoire diversity.

Immunization with soluble BDC 2.5 T cell receptor-immunoglobulin chimeric protein:antibody specificity and protection of nonobese diabetic mice against adoptive transfer of diabetes by maternal immunization

The BDC 2.5 T cell clone is specific for pancreatic beta-cell antigen presented by I-Ag7, and greatly accelerates diabetes when injected into 10-21-d-old nonobese diabetic (NOD) mice. The BDC 2.5 T cell receptor (TCR) has been solubilized as a TCR-IgG1 chimeric protein. All NOD mice immunized against BDC 2.5 TCR-IgG1 produced antibodies recognizing TCR C alpha/C beta epitopes that were inaccessible on the T cell surface. 56% of the mice produced antibodies against the BDC 2.5 clonotype that specifically blocked antigen activation of BDC 2.5 cells. We have used the adoptive transfer model of diabetes to demonstrate that maternal immunization with soluble TCR protects young mice from diabetes induced by the BDC 2.5 T cell clone.

Characterization of T cell receptor beta chains of accumulating T cells in skin allografts in mice

The study of T cells involved in the immune reaction that occurs in engrafted organs should provide information that would be helpful in the regulation of allograft rejection in organ transplantation. Toward this end, we focused on detection and characterization of accumulating T cells in mouse skin allografts from B10.A(4R) to C57BL/6 mice in vivo. T cell receptor beta genes were amplified by reverse transcriptase-PCR from mRNA of the skin grafts, and accumulating T cell receptor beta gene clonotypes were identified by their single strand conformation polymorphism. Their joining region usage and the amino acid sequences of the complementarity-determining region-3 were then determined. The results were as follows: (1) Distinct oligoclonal accumulation of T cells was more prevalent in the skin allografts than in the syngenic skin grafts. (2) Although the accumulating T cell clonotypes appeared to use many different variable-region gene families, preferential combinations of variable region-joining region were found. (3) Several homologous amino acid sequences were found in these accumulating TCR beta genes in allografts, suggesting that these T cells are driven by the same or similar antigens. (4) In addition, little T cell accumulation was found in spleens from the mice with allografts or syngenic skin grafts. Taken together, accumulating T cells in the skin allografts were detected in vivo, and some appeared to have characteristics in common. This may lead to T cell clonotype-specific therapy in organ transplantation.

Role of the T cell receptor alpha-chain in superantigen recognition

Superantigens bind to antigen-presenting cells on the outside of the major histocompatibility complex (MHC) class II molecule and to T cells via the external face of the T cell receptor (TCR) V beta element. As a consequence, superantigens stimulate populations of T cells in a V beta-specific, non-MHC-restricted manner. However, accumulating evidence has shown an additional contribution of the TCR alpha-chain and polymorphic residues of the MHC molecule to superantigen recognition by some T cells. These data suggest that the TCR and MHC come into contact during superantigen engagement and indirectly modulate the superantigen reactivity. Thus, additional interactions between non-V beta elements of the TCR and MHC play a role in the overall stability of the superantigen/MHC/TCR complex, explaining the influence of the TCR alpha-chain. It is likely that this additional interaction is of greater consequence for weakly reactive T cells. This modulation of superantigen reactivity in individual T cells may have physiological consequences, for example, in the induction of autoimmunity.

A V beta 4-specific superantigen encoded by a new exogenous mouse mammary tumor virus

The superantigen (SAg) expressed by mouse mammary tumor virus (MMTV) has been shown to play an essential role in the course of the viral life cycle. In the present study, we describe a V beta 4-specific SAg encoded by a new exogenous MMTV carried by the SIM mouse strain. This is the first report of a viral or bacterial SAg reacting with mouse V beta 4+ T cells. Injection of MMTV(SIM) into adult BALB/c mice leads to a rapid and strong stimulation of V beta 4+ CD4+ T cells, followed by a slow deletion of these cells. Neonatal exposure to the virus also leads to a progressive deletion of V beta 4+ T cells. In contrast to other strong MMTV SAg, this new SAg requires the presence of major histocompatibility complex class II I-E molecules to be presented efficiently to T cells. Sequence analysis revealed a new predicted amino acid sequence in the C-terminal polymorphic region of this SAg. Furthermore, sequence comparisons to the most closely related SAg with different V beta specificities hint at the specific residues involved in the interaction with the T cell receptor.

Prophylactic intervention in radiation-leukemia-virus-induced murine lymphoma by the biological response modifier polysaccharide K

Polysaccharide K (PSK) is a biological response modifier used for adjuvant immunotherapy of malignant diseases. We studied the potential applicability of PSK for preventing tumor progression using an experimental model of murine lymphoma. Mice inoculated with the radiation leukemia virus (RadLV) develop thymic lymphomas after a latency of 3-6 months. However, 2 weeks after virus inoculation, prelymphoma cells can already be detected in the thymus. We found that PSK treatment induced hyperresponsiveness to concanavalin A and heightened production of interleukin-2 (IL-2) and IL-4 in spleen cells of both control and prelymphoma mice. The response was transient and was accompanied with a dominant usage of T cells expressing V beta 8, but other T cell subsets were also stimulated by PSK. T lymphoma cells expressing V beta 8.2 underwent apoptosis when incubated with PSK. Treatment of RadLV-inoculated mice with PSK delayed the onset of overt lymphoma (and mortality) but could not protect the mice from the disease. Combined treatment with PSK and a RadLV-specific immunotoxin prevented synergistically the progression of the prelymphoma cells to frank lymphoma. The results suggest that PSK contains a superantigen-like component that selectively activates V beta 8+ T cells. Its administration prelymphoma mice interfered with the process of lymphoma progression.