SELECTIVE GENE TRGETING OF TCR Vδ GENES AND ANALYSIS OF THE KNOCKOUT MICE

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In this Research project, we produced Vδ1 gene-deficient mice by selective gene targeting with Cre-1oxP system, followed by analyzing development of γδ T cells including fetal thymocytes, dendritic epidermal T cells (DETCs) and resident pulmonary T lymphocyrtes (RPLs) in the knockout mice.Murine DETCs localized in epidermis are derived from fetal thymocytes and overwhelmingly express Vγ5/Vδ1-TCR without junctional diversity. In Vδ1- deficient mice, the development of Vγ5^+ fetal thymocytes as precursors of DETC was markedly blocked. On the other hand, γδTCR^+ DETCs with a typical dendritic morphology were observed in Vδ1-deficient mice. Moreover, DETCs from Vδ1 deficient mice were predominantly Vγ5^+ but Vγ5^- DETCs were considerably detected in them. The Vγ5^+ DETCs showed mature phenotypes and age-associated expansion, while the Vγ5^- DETCs did immature phenotypes and no expansion in epidermis. These results suggest that optimal DETC development does not require a particular Vγ/Vδ usage but a limited diversity of of γδ TCRs is required for maturation and expansion of DETCs within the epidermal microenvironment.Murine RPLs contain γδ T cell subpopulation as a minority (ca. 5 %). The γδ RPLs are also derived from fetal thymocytes and predominantly express Vγ6/Vδ1-TCR without junctional diversity. However, a novel y6RPL subset expressing Vγ4/Vδ5 generate after birth and then they expand as a major population. In Vδ1-deficient mice, Vγ6^+ RPLs were virtually undetectable and the markedly decreased expression of Vγ1, Vγ4, Vδ4 and Vδ5 gene sements in RPL was also observed in comparison with RPLs from wild type mice. Therefore, the blocked development of fetus-type γδRPLs (Vγ6/Vδ1^+) may influence the development and/or migration of adult-type γδRPL (Vγ4/Vδ5^+).