Single-positive CD8 Thymocytes Research Articles

Thymic expression of IL-4 and IL-15 after systemic inflammatory or infectious Th1 disease processes induce the acquisition of "innate" characteristics during CD8+ T cell development.

Innate CD8+ T cells express a memory-like phenotype and demonstrate a strong cytotoxic capacity that is critical during the early phase of the host response to certain bacterial and viral infections. These cells arise in the thymus and depend on IL-4 and IL-15 for their development. Even though innate CD8+ T cells exist in the thymus of WT mice in low numbers, they are highly enriched in KO mice that lack certain kinases, leading to an increase in IL-4 production by thymic NKT cells. Our work describes that in C57BL/6 WT mice undergoing a Th1 biased infectious disease, the thymus experiences an enrichment of single positive CD8 (SP8) thymocytes that share all the established phenotypical and functional characteristics of innate CD8+ T cells. Moreover, through in vivo experiments, we demonstrate a significant increase in survival and a lower parasitemia in mice adoptively transferred with SP8 thymocytes from OT I—T. cruzi-infected mice, demonstrating that innate CD8+ thymocytes are able to protect against a lethal T. cruzi infection in an Ag-independent manner. Interestingly, we obtained similar results when using thymocytes from systemic IL-12 + IL-18-treated mice. This data indicates that cytokines triggered during the acute stage of a Th1 infectious process induce thymic production of IL-4 along with IL-15 expression resulting in an adequate niche for development of innate CD8+ T cells as early as the double positive (DP) stage. Our data demonstrate that the thymus can sense systemic inflammatory situations and alter its conventional CD8 developmental pathway when a rapid innate immune response is required to control different types of pathogens.

Neurokinin 1 receptor-signaling sustains T-cell survival during thymus development and following T-cell activation in secondary lymphoid organs

Abstract T-cell receptor (TCR)-signaling triggers intracellular Ca2+ increase required for NFAT1/2-mediated IL-2 secretion. This pathway is necessary for thymocyte maturation and survival of activated T cells in secondary lymphoid organs (SLOs). In T cells, cellular Ca2+ levels are regulated by TCR- and G-protein coupled receptor (GPCR)-signaling via the PLCγ and PLCβ subunits, respectively. Nevertheless, the GPCR(s) involved in this phenomenon has not been identified. The neurokinin-1 receptor (NK1R) is a GPCR that induces Ca2+ flux in neurons, and NK1R-signaling by the neuropetides substance P (SP) and hemokinin 1 (HK1) promotes T-cell immunity. We studied the role of NK1R-signaling in T-cell development in the thymus and after T-cell priming in SLOs. By Imagestream, we found that the NK1R and its ligands localize at the site of dendritic cell (DC)-T cell contact. Following CD3-signaling, the NK1R was required for optimal Ca2+flux and NFAT-mediated IL-2 secretion in T cells, effects that were abrogated in NK1RKO or SP/HK1double KO T cells. In the thymus, absence of NK1R resulted in decreased maturation and survival of TCR+ double positive CD4 CD8, single positive CD4, and single positive CD8thymocytes. In SLOs, the NK1R was required for survival of Ag-activated CD4 Th1 and CD8 T cells. In vivo, in a skin model of Th1-DTH induced in NK1RKO T-cell or HK-1/SPdouble KOT-cell bone marrow chimeras, 73±5% of activated CD4 and CD8 T cells died during priming in skin-draining SLOs, and the remaining T cells died in the skin following elicitation. We conclude that the NK1R cooperates with the TCR to increase intracellular Ca2+ necessary for thymocyte maturation and survival of activated T cells in SLOs. NIH R01 AR068249 and AR071277 to ATL and LDF.

Structural and Mechanistic Implications of Rearrangement Frequencies within Human TCRBV Genes.

The T cell repertoire is a function of thymic V(D)J rearrangement and of peripheral selection. The mature repertoire embodies TCR sequences that are important for survival and can identify important structural aspects of the TCR. Analysis of the circulating TCRBV19 CD8 T cell repertoire showed that a majority of NDN-encoded CDR3 amino acid motifs start at CDR3 position four, well within the V region. Rearrangement at this position indicates that the DNA hairpin loop is not opened at the position adjacent to the recombination signal sequence, but rather is trimmed back three or more bases. In this article, we show that the rearrangement frequency distribution within the V region reveals selection on CDR3 position four. The selection is already established in single-positive CD8 thymocytes. Crystal structures reveal a possible basis for this selection due to the location of this residue in a bend that positions the remaining portion of CDR3 to interact with the peptide and MHC. Examination of other TCRBV families also shows selection for rearrangement within the V region of a number of genes and for CD8 and CD4 cells. The exact profile of rearrangement within the V region appears to be V gene specific. The frequent observation of side chains associated with turn motifs at CDR3 positions three and four fits with the structural need for a bend. The data are discussed in terms of the generation of a structural turn motif, the rearrangement mechanism, and selection of the repertoire on the peptide and MHC.

Developmental control of antigen-induced thymic transcription factors.

Antigen engagement of the TCR may lead to activation of mature T cells while inducing deletion or positive selection of immature thymocytes. Using thymocytes from TCR transgenic mice recognizing the allo-antigen H-2Kb we investigated whether double-positive CD4+CD8+ (DP) thymocytes constitute a particular developmental stage where signals originating from surface receptor engagement will lead to distinct nuclear signaling. We show that the developmental control of transcription factors is apparent, at least at two levels. First, NF-AT binding activity was not induced in response to either antigen or phorbol myristate acetate (PMA)/lonomycin in DP thymocytes, whereas it was induced in single-positive CD8 thymocytes. Second, antigen induced a different pattern of transcription factor binding activities than PMA/lonomycin in DP thymocytes, AP-1 activity being selectively induced by antigen and NF-kappa B by PMA/lonomycin. Further we show that the transcription factors found to be induced in the DP thymic population were not susceptible to the inhibitory effect of cyclosporin A.