(1/8823) Crystal structure of an MHC class I presented glycopeptide that generates carbohydrate-specific CTL.
T cell receptor (TCR) recognition of nonpeptidic and modified peptide antigens has been recently uncovered but is still poorly understood. Immunization with an H-2Kb-restricted glycopeptide RGY8-6H-Gal2 generates a population of cytotoxic T cells that express both alpha/beta TCR, specific for glycopeptide, and gamma/delta TCR, specific for the disaccharide, even on glycolipids. The crystal structure of Kb/RGY8-6H-Gal2 now demonstrates that the peptide and H-2Kb structures are unaffected by the peptide glycosylation, but the central region of the putative TCR binding site is dominated by the extensive exposure of the tethered carbohydrate. These features of the Kb/RGY8-6H-Gal2 structure are consistent with the individual ligand binding preferences identified for the alpha/beta and gamma/delta TCRs and thus explain the generation of a carbohydrate-specific T cell response. (+info)
(2/8823) T cell subsets in experimental lupus nephritis: modulation by bacterial superantigen.
Chronic graft-vs-host disease (GvH), induced by injection of DBA/2 lymphocytes into (C57BL/6 x DBA/2)F1 hybrids, is a murine model for lupus nephritis, associated with a Th2-dependent polyclonal B cell activation. The development of glomerulosclerosis in this model is preceded by a glomerular influx of LFA-1+ T cells. We investigated whether exposure to bacterial superantigen would modulate the course of this autoimmune syndrome. Injection of the bacterial superantigen staphylococcal enterotoxin B (SEB) in mice has been shown to induce the activation of TcRVbeta8+ T cells. Within 2 weeks after GvH induction, mice were injected twice with 20 microg of SEB and the following parameters were examined: cytokine and Ig profile, proteinuria and renal pathology. The second SEB injection induced in GvH mice an increased release of both interferon-gamma (IFN-gamma) and interleukin-10 (IL-10) as compared with control F1 mice. No differences were observed in IL-2 production. SEB-treated GvH mice demonstrated a delayed onset of proteinuria. Histological analysis of the kidney showed that SEB-challenged GvH mice displayed significantly more interstitial inflammation and mesangial proliferation together with more IgG2a deposits in glomeruli than non-injected GvH mice. From these results, we conclude that GvH mice are more responsive to SEB in terms of cytokine production and that bacterial infection can modulate the course of this renal disease from a membranous to a more proliferative type of nephropathy. (+info)
(3/8823) Melanoma cells present a MAGE-3 epitope to CD4(+) cytotoxic T cells in association with histocompatibility leukocyte antigen DR11.
In this study we used TEPITOPE, a new epitope prediction software, to identify sequence segments on the MAGE-3 protein with promiscuous binding to histocompatibility leukocyte antigen (HLA)-DR molecules. Synthetic peptides corresponding to the identified sequences were synthesized and used to propagate CD4(+) T cells from the blood of a healthy donor. CD4(+) T cells strongly recognized MAGE-3281-295 and, to a lesser extent, MAGE-3141-155 and MAGE-3146-160. Moreover, CD4(+) T cells proliferated in the presence of recombinant MAGE-3 after processing and presentation by autologous antigen presenting cells, demonstrating that the MAGE-3 epitopes recognized are naturally processed. CD4(+) T cells, mostly of the T helper 1 type, showed specific lytic activity against HLA-DR11/MAGE-3-positive melanoma cells. Cold target inhibition experiments demonstrated indeed that the CD4(+) T cells recognized MAGE-3281-295 in association with HLA-DR11 on melanoma cells. This is the first evidence that a tumor-specific shared antigen forms CD4(+) T cell epitopes. Furthermore, we validated the use of algorithms for the prediction of promiscuous CD4(+) T cell epitopes, thus opening the possibility of wide application to other tumor-associated antigens. These results have direct implications for cancer immunotherapy in the design of peptide-based vaccines with tumor-specific CD4(+) T cell epitopes. (+info)
(4/8823) Peripheral autoantigen induces regulatory T cells that prevent autoimmunity.
Previous studies have shown that autoimmune thyroiditis can be induced in normal laboratory rats after thymectomy and split dose gamma-irradiation. Development of disease can be prevented by reconstitution of PVG rats shortly after their final irradiation with either peripheral CD4(+)CD45RC- T cells or CD4(+)CD8(-) thymocytes from syngeneic donors. Although the activity of both populations is known to depend on the activities of endogenously produced interleukin 4 and transforming growth factor beta, implying a common mechanism, the issue of antigen specificity of the cells involved has not yet been addressed. In this study, we show that the regulatory T cells that prevent autoimmune thyroiditis are generated in vivo only when the relevant autoantigen is also present. Peripheral CD4(+) T cells, from rats whose thyroids were ablated in utero by treatment with 131I, were unable to prevent disease development upon adoptive transfer into thymectomized and irradiated recipients. This regulatory deficit is specific for thyroid autoimmunity, since CD4(+) T cells from 131I-treated PVG.RT1(u) rats were as effective as those from normal donors at preventing diabetes in thymectomized and irradiated PVG.RT1(u) rats. Significantly, in contrast to the peripheral CD4(+) T cells, CD4(+)CD8(-) thymocytes from 131I-treated PVG donors were still able to prevent thyroiditis upon adoptive transfer. Taken together, these data indicate that it is the peripheral autoantigen itself that stimulates the generation of the appropriate regulatory cells from thymic emigrant precursors. (+info)
(5/8823) Selective recruitment of CCR4-bearing Th2 cells toward antigen-presenting cells by the CC chemokines thymus and activation-regulated chemokine and macrophage-derived chemokine.
Helper T cells are classified into Th1 and Th2 subsets based on their profiles of cytokine production. Th1 cells are involved in cell-mediated immunity, whereas Th2 cells induce humoral responses. Selective recruitment of these two subsets depends on specific adhesion molecules and specific chemoattractants. Here, we demonstrate that the T cell-directed CC chemokine thymus and activation-regulated chemokine (TARC) was abundantly produced by monocytes treated with granulocyte macrophage colony stimulating factor (GM-CSF) or IL-3, especially in the presence of IL-4 and by dendritic cells derived from monocytes cultured with GM-CSF + IL-4. The receptor for TARC and another macrophage/dendritic cell-derived CC chemokine macrophage-derived chemokine (MDC) is CCR4, a G protein-coupled receptor. CCR4 was found to be expressed on approximately 20% of adult peripheral blood effector/memory CD4+ T cells. T cells attracted by TARC and MDC generated cell lines predominantly producing Th2-type cytokines, IL-4 and IL-5. Fractionated CCR4+ cells but not CCR4- cells also selectively gave rise to Th2-type cell lines. When naive CD4+ T cells from adult peripheral blood were polarized in vitro, Th2-type cells selectively expressed CCR4 and vigorously migrated toward TARC and MDC. Taken together, CCR4 is selectively expressed on Th2-type T cells and antigen-presenting cells may recruit Th2 cells expressing CCR4 by producing TARC and MDC in Th2-dominant conditions. (+info)
(6/8823) Development and function of autospecific dual TCR+ T lymphocytes.
Recent studies have challenged the long held concept that each T lymphocyte expresses on its surface only a single, unique alphabetaTCR. Dual TCR+ T cells have been recognized, however, their origin and potential to escape screening for self-reactivity remain obscure. We now report the thymic generation of dual alphabetaTCR+ T cells in the H-2Db/H-Y-specific TCR transgenic (Tg) mouse. Dual TCR+ thymocytes were positively selected less efficiently than single TCR+ thymocytes, although a subset attained maturity. Importantly, when TCR Tg mice were bred onto a negatively selecting background, auto-specific cells survived central deletion and matured as CD4+ dual TCR+ cells. These cells were autoreactive when CD8 expression was restored. The existence of autospecific, dual TCR+ T cells may have implications for the maintenance of self tolerance. (+info)
(7/8823) Patterns of A2A extracellular adenosine receptor expression in different functional subsets of human peripheral T cells. Flow cytometry studies with anti-A2A receptor monoclonal antibodies.
Signaling through A2A adenosine receptors (A2AR) regulates T lymphocyte expansion and modulates T cell receptor (TCR)-mediated effector functions in vitro. To understand the role of A2ARs in the regulation of immune response, we investigated the expression levels of this receptor in different functional lymphocyte subsets. Monoclonal anti-A2AR antibody was used to develop a flow cytometric assay to quantify the expression A2ARs on lymphocytes. We report that detectable levels of expression of A2ARs are much higher among T cells than B cells. More CD4(+) than CD8(+) T cells express A2ARs, but activation of T cells increases A2AR expression, predominantly in CD8(+) T cells. No significant differences were found in the proportion of A2AR+ cells between CD8(low) and CD8(high) T cells or between TCR/CD3(low) and TCR/CD3(high) T cells. Studies of T helper cell subsets (TH1 and TH2) reveal that lymphokine-producing cells are much more likely to express A2ARs than are cells that do not produce lymphokines. These results suggest that A2ARs are variably expressed on T cell subsets and may regulate cytokine production in activated T lymphocytes. (+info)
(8/8823) IgA production in MHC class II-deficient mice is primarily a function of B-1a cells.
Mice deficient in MHC class II expression (C2d mice) do not make antibody to protein antigens administered systemically, but their ability to produce IgA antibody to antigen administered at mucosal sites has not been described. We investigated IgA production by C2d mice and their IgA antibody response to antigen given orally. Young C2d mice had normal amounts of serum IgA, intestinal-secreted IgA and normal numbers of intestinal IgA plasma cells, compared to control C57BL/6 mice. IgA production by C2d mice increased with age. Following oral immunization with cholera toxin, C57BL/6 mice responded with IgA and IgG antibody, and had increased numbers of IgA plasma cells, but C2d mice gave no response. The Peyer's patch and mesenteric lymph node tissues of C2d mice contained very few CD4-expressing T cells. Thus, C2d mice have no typical mucosal CD4 Th cells and cannot respond to a strong oral immunogen, yet they still produced and secreted IgA. We hypothesized that B-1 lymphocytes could provide a source of IgA independent of antigen-specific T cell help. Young C2d mice had normal numbers of peritoneal B-1a cells and their frequency increased with age. To test the role of these B-1a cells, we bred C2d mice to obtain mice that had no MHC class II expression and expressed the Xid gene that confers deficiency in B-1a cells. These double-deficient mice had 10-fold less serum and secreted IgA than all other F2 littermates. We conclude that B-1a cells are essential for the majority of IgA production in C2d mice. Thus, the C2d mouse may provide a useful tool for analysis of the role of intestinal IgA provided by B-1a cells. (+info)