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(1/2820) 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)

(2/2820) Differential effects of manipulating signaling in early T cell development in intestinal intraepithelial lymphocytes and thymocytes.

A pre-TCR-CD3 signal is required for the efficient maturation of CD4- CD8- thymocytes to the CD4+ CD8+ stage. This study addressed whether a similar signal is required for maturation of intestinal intraepithelial lymphocytes (IEL) that may develop extrathymically. We have shown previously that IEL from mice deficient for CD3- associated zeta chains include an immature population of CD3- CD8alphaalpha+ cells expressing cytoplasmic TCR beta chains but lacking detectable surface TCRalphabeta, CD16 and B220. Here we stimulated the appearance of such IEL in epsilon+/- zeta-/- mice by expression of an activated Lck transgene or in vivo treatment with anti-CD3epsilon. Anti-CD3epsilon treatment of RAG-deficient animals also yielded CD16- B220- IEL. In contrast, expression of a TCRbeta transgene in rag-1(-/-) mice did not stimulate the appearance of CD3- CD8alphaalpha+ CD16- B220- cells. Taken together these data indicate that although anti-CD3epsilon treatment and LckF505 assist in catalyzing a CD16+ B220+ --> CD16- B220- transition, these manipulations are not equivalent to a pre-TCR signal in IEL lymphocytes.  (+info)

(3/2820) T cell receptor and coreceptor CD8 alphaalpha bind peptide-MHC independently and with distinct kinetics.

The T cell surface glycoprotein CD8 enhances T cell antigen recognition by binding to MHC class I molecules. We show that human CD8 alphaalpha binds to the MHC class I molecule HLA-A2 with an extremely low affinity (Kd approximately 0.2 mM at 37 degrees C) and with kinetics that are between 2 and 3 orders of magnitude faster than reported for T cell receptor/peptide-MHC interactions. Furthermore, CD8 alphaalpha had no detectable effect on a T cell receptor (TCR) binding to the same peptide-MHC class I complex. These binding properties provide an explanation as to why the CD8/MHC class I interaction is unable to initiate cell-cell adhesion and how it can enhance TCR recognition without interfering with its specificity.  (+info)

(4/2820) Oligoclonality of rat intestinal intraepithelial T lymphocytes: overlapping TCR beta-chain repertoires in the CD4 single-positive and CD4/CD8 double-positive subsets.

Previous studies in humans and mice have shown that gut intraepithelial lymphocytes (IELs) express oligoclonal TCR beta-chain repertoires. These studies have either employed unseparated IEL preparations or focused on the CD8+ subsets. Here, we have analyzed the TCR beta-chain repertoire of small intestinal IELs in PVG rats, in sorted CD4+ as well as CD8+ subpopulations, and important differences were noted. CD8alphaalpha and CD8alphabeta single-positive (SP) IELs used most Vbeta genes, but relative Vbeta usage as determined by quantitative PCR analysis differed markedly between the two subsets and among individual rats. By contrast, CD4+ IELs showed consistent skewing toward Vbeta17 and Vbeta19; these two genes accounted collectively for more than half the Vbeta repertoire in the CD4/CD8 double-positive (DP) subset and were likewise predominant in CD4 SP IELs. Complementarity-determining region 3 length displays and TCR sequencing demonstrated oligoclonal expansions in both the CD4+ and CD8+ IEL subpopulations. These studies also revealed that the CD4 SP and CD4/CD8 DP IEL subsets expressed overlapping beta-chain repertoires. In conclusion, our results show that rat TCR-alphabeta+ IELs of both the CD8+ and CD4+ subpopulations are oligoclonal. The limited Vbeta usage and overlapping TCR repertoire expressed by CD4 SP and CD4/CD8 DP cells suggest that these two IEL populations recognize restricted intestinal ligands and are developmentally and functionally related.  (+info)

(5/2820) Reduced generation but efficient TCR beta-chain selection of CD4+8+ double-positive thymocytes in mice with compromised CD3 complex signaling.

Maturation to the CD4+8+ double-positive (DP) stage of thymocyte development is restricted to cells that have passed TCRbeta selection, an important checkpoint at which immature CD4-8- double-negative (DN) cells that express TCRbeta polypeptide chains are selected for further maturation. The generation of DP thymocytes following TCRbeta selection is dependent on cellular survival, differentiation, and proliferation, and the entire process appears to be mediated by the pre-TCR/CD3 complex. In this study, we investigate the signaling requirements for TCRbeta selection using mice single deficient and double deficient for CD3zeta/eta and/or p56lck. While the numbers of DP cells are strongly reduced in the single-deficient mice, a further drastic reduction in the generation of DP thymocytes is seen in the double-deficient mice. The poor generation of DP cells in the mutant mice is primarily due to an impaired ability of CD25+ DN thymocytes to proliferate following expression of a TCRbeta-chain. Nevertheless, the residual DP cells in all mutant mice are strictly selected for expression of TCRbeta polypeptide chains. DN thymocytes of mutant mice expressed TCRbeta and CD3epsilon at the cell surface and contained mRNA for pre-Talpha, but not for clonotypic TCRalpha-chains, together suggesting that TCRbeta selection is mediated by pre-TCR signaling in all cases. The data suggest differential requirements of pre-TCR signaling for cell survival on the one hand, and for the proliferative burst associated with TCRbeta selection on the other.  (+info)

(6/2820) Th1 and Th2 cytokine mRNA profiles in childhood nephrotic syndrome: evidence for increased IL-13 mRNA expression in relapse.

Idiopathic nephrotic syndrome of childhood is thought to be associated with T lymphocyte dysfunction often triggered by viral infections, with the production of circulating factor(s) resulting in proteinuria. In view of the conflicting evidence of T cell activation and Th1 or Th2 pattern of cytokine synthesis in this disease, this study examined the mRNA expression of interleukin-2 (IL-2), interferon-gamma, IL-4, and IL-13 from CD4+ and CD8+ T cells in steroid-responsive nephrotic patients in relapse and remission. Fifty-five children with steroid-responsive nephrotic syndrome were included in this study, together with 34 normal controls and 24 patient controls with viral infections. RNA was isolated from purified CD4+ or CD8+ cells from peripheral blood and subjected to reverse transcription-PCR. Cytokine mRNA expression was measured semiquantitatively, and a cytokine index was derived from densitometric readings, with cyclophilin as the housekeeping gene. Both cross-sectional and paired data showed an increased CD4+ and CD8+ IL-13 mRNA expression in patients with nephrotic relapse as compared to remission, normal, and patient controls (P < 0.008). This was also associated with increased cytoplasmic IL-13 expression in phorbol myristate acetate/ionomycin-activated CD3+ cells (6.66+/-3.39%) from patients with nephrotic relapse compared to remission (2.59+/-1.35%) (P < 0.0001). However, there was no significant difference in CD4+ or CD8+ IL-2, interferon-gamma and IL-4 mRNA expression. IL-13 is an important T cell cytokine with anti-inflammatory and immunomodulatory functions on B cells and monocytes. It is conceivable that IL-13 may act on monocytes to produce vascular permeability factor(s) involved in the pathogenesis of proteinuria in patients with relapse nephrotic syndrome.  (+info)

(7/2820) Functional differences between memory and naive CD8 T cells.

To determine how murine memory and naive T cells differ, we generated large numbers of long-lived memory CD8(+) T cells and compared them to naive cells expressing the same antigen-specific receptor (T cell receptor; TCR). Although both populations expressed similar levels of TCR and CD8, on antigen stimulation in vitro memory T cells down-regulated their TCR faster and more extensively and secreted IFN-gamma and IL-2 faster than naive T cells. Memory cells were also larger, and when freshly isolated from mice they contained perforin and killed target cells without having to be restimulated. They further differed from naive cells in requiring IL-15 for proliferation and in having a greater tendency to undergo apoptosis in vitro. On antigen stimulation in vivo, however, they proliferated more rapidly than naive cells. These findings suggest that, unlike naive T cells, CD8 memory T cells are intrinsically programmed to rapidly express their effector functions in vivo without having to undergo clonal expansion and differentiation.  (+info)

(8/2820) Demonstration of bovine CD8+ T-cell responses to foot-and-mouth disease virus.

The aim of this study was to investigate the importance of cellular immunity in foot-and-mouth disease in cattle, in particular to determine whether a CD8+ T-cell response could be detected, as these cells may play a role in both immunity and virus persistence. As attempts to characterize classical cytotoxic T cells had yielded non-reproducible results, largely due to high backgrounds in control cultures, a proliferation assay was developed that was demonstrated to detect antigen-specific, MHC class I-restricted bovine CD8+ cells responding to foot-and-mouth disease virus (FMDV). Proliferative CD8+ T-cell responses were detected consistently from 10 to 14 days following infection with FMDV and typically lasted 3-4 weeks. The role of CD8+ T cells in control of the disease, in particular their relevance for the establishment of persistence, may now be investigated.  (+info)