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  • Title: ICOS-mediated costimulation on Th2 differentiation is achieved by the enhancement of IL-4 receptor-mediated signaling.
    Author: Watanabe M, Watanabe S, Hara Y, Harada Y, Kubo M, Tanabe K, Toma H, Abe R.
    Journal: J Immunol; 2005 Feb 15; 174(4):1989-96. PubMed ID: 15699127.
    Abstract:
    ICOS is the third member of the CD28 family molecules and plays a critical role in many T cell-dependent immune responses. Although accumulated data suggest that ICOS costimulatory signals play an important role in Th2-mediated immune responses, the molecular basis for this selective differentiation mechanism is largely unknown. To clarify this mechanism, we used DO11.10 TCR transgenic ICOS-/- mice and evaluated the nature of ICOS costimulatory signals during the process of Ag-specific activation and differentiation of naive CD4+ T cells. Results obtained from these experiments demonstrated that Ag stimulation of naive CD4+ T cells in the absence of an ICOS signal resulted in impaired Th2 development. Unlike previous reports, we found that primary IL-4 production by these T cells was intact and that IL-4R sensitivity of these T cells was reduced as evidenced by a profound defect in IL-4-induced Stat6 phosphorylation and the early induction of GATA-3. The fact that ICOS ligation of wild-type T cells significantly enhanced IL-4-induced Stat6 phosphorylation and primary GATA-3 induction, but not IL-4 transcription, of naive CD4+ T cells was consistent with the results obtained from ICOS-/- T cell experiments. These observations led us to propose that the predominant effect of ICOS-mediated costimulation on Th2 differentiation is achieved by the enhancement of IL-4R-mediated signaling.
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