title: Role of the gut as a primary lymphoid organ.
abstract: The TCR-αβ/γδ CD8αα intraepithelial T lymphocytes (T-IEL) located in the gut mucosa of the small intestine are an abundant population believed to have a major role in ensuring the integrity of the gut wall. Here, we describe their unique characteristics and the controversies regarding the origin and differentiation of these T-IELs. We show how accumulated experimental evidence has finally arrived at a unifying concept, which demonstrates that these cells originate from early thymus precursors that have not yet undergone TCR rearrangement and TCR-αβ/γδ commitment. These precursors colonize the gut lamina propria during the perinatal period and complete rearrangements and TCR-αβ/γδ commitment while migrating to the epithelium. Therefore, the gut epithelium, which shares the same embryonic origin as the thymus epithelium, behaves as a primary lymphoid organ responsible for the differentiation of a major local T cell set.
authors.affiliation: INSERM, U1020, Medical Faculty Descartes Paris V, 75015 Paris, France. laetitia.peaudecerf@inserm.fr
authors.forename: Laetitia
authors.initials: L
authors.lastname: Peaudecerf
authors.forename: Benedita
authors.initials: B
authors.lastname: Rocha
mesh_terms: D000818:Animals; D002454:Cell Differentiation; D019070:Cell Lineage; D015321:Gene Rearrangement; D006801:Humans; D007107:Immune System / Q000196:embryology / Q000254:growth & development; D007413:Intestinal Mucosa / Q000196:embryology / Q000276:immunology / Q000378:metabolism*; D008221:Lymphoid Tissue / Q000276:immunology; D011948:Receptors, Antigen, T-Cell / Q000235:genetics / Q000276:immunology*; D016176:T-Lymphocyte Subsets / Q000276:immunology*; D013601:T-Lymphocytes / Q000276:immunology*; D013950:Thymus Gland / Q000196:embryology / Q000276:immunology / Q000378:metabolism*
chemical_list: D011948:Receptors, Antigen, T-Cell