Identical T Cell Clones Are Located within the Mouse Gut Epithelium and Lamina Propria and Circulate in the Thoracic Duct Lymph

Murine gut intraepithelial (IEL) T cell receptor (TCR)-α/β¹ lymphocytes bearing CD8α/β or CD8α/α coreceptors have been shown previously to express different oligoclonal TCR β chain repertoires in the same mouse, in agreement with other evidence indicating that these two populations belong to different ontogenic lineages, with only CD8α/β¹ IELs being fully thymus dependent. CD8α/β¹, but not CD8α/α¹, T lymphocytes are also present in the lamina propria. Here, we show that CD8α/β⁺ lymphocytes from the lamina propria and the epithelium are both oligoclonal, and that they share the same TCR-β clonotypes in the same mouse, as is also the case for CD4⁺ T cells. Furthermore, identical T cell clones were detected among CD8α/β¹ IELs and CD8α/β¹ blasts circulating into the thoracic duct (TD) lymph of the same mouse, whereas TD small lymphocytes are polyclonal. These findings must be considered in light of previous observations showing that T blasts, but not small T lymphocytes, circulating in the TD lymph have the capacity of homing into the gut epithelium and lamina propria. These combined observations have interesting implications for our understanding of the recirculation of gut thymus-dependent lymphocytes and their precursors, and of the events leading up to the selection of their restricted TCR repertoire.