THYMIC EPITHELIUM INDUCES NEITHER CLONAL DELETION NOR ANERGY TO MLS 1A ANTIGENS

Grafting of thymic anlagen from day-10 DBA/2 (H-2d; Mls-1a) embryos to newborn athymic BALB/c (H-2d; MlS-1b) mice leads to reconstitution of T cell populations in the recipients. Analysis of adult chimeras shows that their V-beta T cell receptor (TcR) repertoires, particularly V(beta)6 and V(beta)8.1, do not significantly differ in most animals (10 out of 13) from those scored in control chimeras that received syngeneic thymic anlagen. In all cases analyzed, such MlS-1a-reactive T cells could be stimulated at levels comparable to control responses, both in vitro and in vivo.The few cases in which Mls-1a reactive V(beta) TcR were reduced seem to reflect the variability in TcR V(beta) repertoires found in this experimental system. In contrast, BALB/c mice, injected at birth with DBA/2 spleen cells show a marked, albeit variable, reduction in the frequencies of V(beta)6- and V(beta)8.1-bearing CD4+ T cells, and lower frequencies of Mls-1a-reactive T cells in limiting dilution analyses. It appears, however, that V(beta)6- and V(beta)8.1-bearing T cells remaining in these mice are functionally competent. We conclude that Mls-1 antigens are not expressed by thymic epithelium.