CD8 alpha alpha intraepithelial lymphocytes arise from two main thymic precursors

Abstract

TCR alpha b(+)CD4(-)CD8 alpha(+)CD8 beta-intestinal intraepithelial lymphocytes (CD8 alpha alpha IELs) are an abundant population of thymus-derived T cells that protect the gut barrier surface. We sought to better define the thymic IEL precursor (IELp) through analysis of its maturation, localization and emigration. We defined two precursor populations among TCR beta(+)CD4(-)CD8(-) thymocytes by dependence on the kinase TAK1 and rigorous lineage-exclusion criteria. Those IELp populations included a nascent PD-1(+) population and a T-bet(+) population that accumulated with age. Both gave rise to intestinal CD8 alpha alpha IELs after adoptive transfer. The PD-1(+) IELp population included more strongly self-reactive clones and was largely restricted by classical major histocompatibility complex (MHC) molecules. Those cells localized to the cortex and efficiently emigrated in a manner dependent on the receptor S1PR1. The T-bet(+) IELp population localized to the medulla, included cells restricted by non-classical MHC molecules and expressed the receptor NK1.1, the integrin CD103 and the chemokine receptor CXCR3. The two IELp populations further differed in their use of the T cell antigen receptor (TCR) alpha-chain variable region (V-alpha) and beta-chain variable region (V-beta). These data provide a foundation for understanding the biology of CD8 alpha alpha IELs