Peripheral Thy1+ lymphocytes rearranging TCR‐γδ genes in LAT‐deficient mice

Linker for activation of T cells (LAT) is an adaptor molecule indispensable for development of αβ and γδ T lymphocytes. Surprisingly, using a new model of LAT‐deficient mice we found that despite arrested thymic development, a discrete population of cells with active Lat promoter, expressing Thy1 molecules, accumulated in peripheral lymphoid organs of homozygous (Lat^Inv/Inv) mutant mice. By measuring frequencies of TCR gene rearrangements in conjunction with a panel of cell surface Ag, we dissected two subsets of these Thy1⁺ cells. Thy1^dull cells expressed markers of NK lymphocytes and contained low frequency of TCR‐γ gene rearrangements without detectable TCR‐δ rearrangements. Thy1^high cells resembled immature CD44⁺CD25⁺ thymocytes and contained high frequency of non‐productive TCR‐γ and TCR‐δ rearrangements, indicating that cells displaying molecular signatures of commitment toward γδ T‐cell lineage can develop and populate lymphoid tissues of LAT‐deficient mice. Phenotypically similar Thy1^high cells were also found in lymph nodes of lymphocyte‐deficient (Rag2^?/?) mice but not in T lymphocyte proficient, heterozygous Lat^+/Inv mice suggesting that Thy1^high cells of LAT‐deficient mice identified in this study accumulate in peripheral lymphoid organs as a result of congenital lymphopenia.