Role of Gut Cryptopatches in Early Extrathymic Maturation of Intestinal Intraepithelial T Cells

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Abstract
Lympho-hemopoietic progenitors residing in murine gut cryptopatches (CP) have been shown to generate intestinal intraepithelial T cells (IEL). To investigate the role of CP in progenitor maturation, we analyzed IEL in male mice with a truncated mutation of common cytokine receptor γ-chain (CRγ−/Y) in which CP were undetectable. IEL-expressing TCR-γδ (γδ-IEL) were absent, and a drastically reduced number of Thy-1highCD4+ and Thy-1highCD8αβ+ αβ-IEL were present in CRγ−/Y mice, whereas these αβ-IEL disappeared from athymic CRγ−/Y littermate mice. Athymic CRγ−/Y mice possessed a small TCR- and αEβ7 integrin-negative IEL population, characterized by the disappearance of the extrathymic CD8αα+ subset, that expressed pre-Tα, RAG-2, and TCR-Cβ but not CD3ε transcripts. These TCR− IEL from athymic CRγ−/Y mice did not undergo Dβ-Jβ and Vδ-Jδ joinings, despite normal rearrangements at the TCR-β and -δ loci in thymocytes from euthymic CRγ−/Y mice. In contrast, athymic severe combined immunodeficient mice in which CP developed normally possessed two major TCR−αEβ7+ CD8αα+ and CD8− IEL populations that expressed pre-Tα, RAG-2, TCR-Cβ, and CD3ε transcripts. These findings underscore the role of gut CP in the early extrathymic maturation of CD8αα+ IEL, including cell-surface expression of αEβ7 integrin, CD3ε gene transcription, and TCR gene rearrangements.

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