Regulation of growth, survival, and differentiation during T lineage development by the (gamma)c-dependent cytokines and prostaglandin E(2)

Date of Award




Degree Name

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

Link to Full Text