Role of gut cryptopatches in early extrathymic maturation of intestinal intraepithelial T cells

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-1(high)CD4⁺ and Thy- 1(high)CD8αβ⁺ 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 α(E)β₇ 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-α(E)β₇⁺ 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 α(E)β₇ integrin, CD3ε gene transcription, and TCR gene rearrangements.