Positive selection of T-lymphocytes induced by intrathymic injection of a thymic epithelial cell line.

Tlymphocytes recognize antigens as peptide fragments associated with molecules encoded by the major histocompatibility complex (MHC) and expressed on the surface of antigen-presenting cells1. In the thymus, T cells bearing αβ receptors that react with the MHC molecules expressed by radioresistant stromal elements are positively selected for maturation2–5. In (A × B → A) bone marrow chimaeras, T cells restricted to the MHC-A haplotype are positively selected, whereas MHC-B-reactive thymocytes are not. We investigated whether the introduction of particular thymic stromal elements bearing MHC-B molecules could alter the fate of B-reactive T cells in these (A × B → A) chimaeras. Thymic epithelial cell (TEC) lines expressing H-2b were introduced by intrathymic injection into (H-2b/s → H2S) bone marrow chimaeras and we measured their ability to generate H-2b-restricted cytotoxic T-lymphocytes (CTLs). We report here that one TEC line, 427.1, was able positively to select CTLs specific for influenza and vesicular stomatitis virus antigens in association with class I H–2b molecules. In addition, line 427.1 can process cytoplasmic proteins for presentation to H–2Kb- and H-2Db-restricted CTLs. Thus, a TEC line capable of normal class I MHC antigen processing and presentation in vitro can induce positive selection after intrathymic injection.