Role of the gut as a primary lymphoid organ

► CD8αα intraepithelial T lymphocytes located in the gut mucosa of the small intestine have unique characteristics. ► Origin and differentiation of these cells has been the subject of much debate. ► Identification of early thymus precursors responsible for their generation led to a unifying concept. ► These precursors leave the thymus, colonize the gut and complete differentiation while migrating to the epithelium. ► The gut epithelium behaves as a primary lymphoid organ.