Regulation of growth, survival, and differentiation during T lineage development by the (gamma)c-dependent cytokines and prostaglandin E(2)
Date of Award
Doctor of Philosophy (Ph.D.)
Microbiology and Immunology
First Committee Member
Thomas R. Malek, Committee Chair
The common gamma chain (gammac) is a shared subunit of the receptors for interleukin (IL)-2, IL-4, IL,-7, IL-9, and IL-15. Of this group, IL-7 has the greatest influence on lymphocyte development, as only IL-7-/- and IL-7Ralpha-/- mice exhibit markedly hypocellular T and B cell compartments and a virtual absence of TCR gammadelta cells. gammac-/- mice also display profound abnormalities in thymic and intestinal intraepithelial lymphocyte (iIEL) development, but these defects are not equivalent to IL-7Ralpha-/- mice. Thus, other gammac-dependent cytokines also function in T cell development. During the course of experiments to identify novel gammac-dependent cytokines affecting T cell survival, a soluble thymic stromal activity which antagonized activation-induced cell death was identified as PGE2. Prostanoids are known to be pro- or anti-apoptotic depending on the maturation stage and tissue localization of target cells, but the mechanism by which PGE2 inhibits T cell apoptosis is unestablished. We show this protection involves the downregulation of Fas-Ligand (Fas-L) mRNA in T cells. Modulation of Fas-L surface expression by physiologic concentrations of PGE2 was both anti-apoptotic and inhibitory of Fas-L-mediated cellular cytotoxicity, providing direct evidence of the likely biological means by which PGE2 downregulates T cell apoptosis.We also assessed whether the T cell developmental defects associated with gammac-deficiency were due to currently defined gammac-dependent cytokines by crossbreeding IL-7Ralpha-/- mice to mice lacking either IL-2, IL-4, or IL-2Rbeta. IL-2/IL-7Ralpha and IL-4/IL-7Ralpha double knock-out (DKO) mice display equivalent thymic development to IL-7Ralpha-/- mice, whereas IL-2Rbeta/IL-7Ralpha DKO mice, which lack IL-2, IL-7, and IL-15 signaling, have thymic T cell defects identical to gammac-/- mice. Thus, these data indicate that of the gammac-dependent cytokines, only IL-7 and IL-15 contribute to the progression and production of thymic T cells. In the iIEL, IL-7Ralpha-/- mice selectively lack CD8alphaalpha TCR gammadelta cells, whereas IL-2Rbeta-/- mice show a significant reduction in all CD8alphaalpha cells. IL-2-/- and IL-2/IL-7Ralpha DKO mice demonstrate reduced CD8alphaalpha iIEL to nearly the same extent as IL-2Rbeta-/- mice, indicating IL-2 functions in CD8alphaalpha iIEL development. Moreover, IL-2Rbeta/IL-7Ralpha DKO mice lack all TCR-bearing iIEL, again recapitulating the phenotype of gammac-/- mice. These data designate IL-2, IL-7, and IL-15 as the essential gammac-dependent cytokines for iIEL development.As the pre-eminent gammac-dependent cytokine in T lineage development, IL-7 exerts a pleiotropic effect, functioning in both T lineage growth and differentiation. In this study, we examined the extent these activities were controlled by signaling associated with distinct IL-7Ralpha cytoplasmic domains by transgenic expression of wildtype or cytoplasmic deletion mutants of IL-7Ralpha in the thymi of IL-7Ralpha-/- mice. We show an essential requirement for the tyrosine-containing carboxy-terminal T domain in restoring thymic cellularity, pro-T cell progression, survival, and functional differentiation of TCR alphabeta cells. In contrast, the development of TCR gammadelta cells is largely independent of the T domain, as rearrangements of the TCR gamma chain locus were readily detectable in mice lacking this domain. Thus, separate cytoplasmic domains of IL-7Ralpha control distinct functions during T cell development, while normal IL-7R-dependent thymic development requires the integrated activity of all these domains.
Biology, Cell; Health Sciences, Immunology
Porter, Brian Oscar, "Regulation of growth, survival, and differentiation during T lineage development by the (gamma)c-dependent cytokines and prostaglandin E(2)" (2000). Dissertations from ProQuest. 3880.