CD8+ recent thymic emigrants home to and efficiently repopulate the small intestine epithelium

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Abstract
Prevailing knowledge dictates that naive αβ T cells require activation in lymphoid tissues before differentiating into effector or memory T cells capable of trafficking to nonlymphoid tissues. Here we demonstrate that CD8+ recent thymic emigrants (RTEs) migrated directly into the small intestine. CCR9, CCL25 and α4β7 integrin were required for gut entry of CD8+ RTEs. After T cell receptor stimulation, intestinal CD8+ RTEs proliferated and acquired a surface phenotype resembling that of intraepithelial lymphocytes. CD8+ RTEs efficiently populated the gut of lymphotoxin-α-deficient mice, which lack lymphoid organs. These studies challenge the present understanding of naive αβ T cell trafficking and suggest that RTEs may be involved in maintaining a diverse immune repertoire at mucosal surfaces. *Note: In the version of this article initially published, the vertical axis label ‘FITC’ is missing from the right column in Figure 1a. The correct figure is presented here. The error has been corrected in the PDF version of the article.