The Vo Repertoire of Mouse Gut Homodimeric a CD 8 + Intraepithelial T Cell Receptor a / o + Lymphocytes Reveals a Major Extrathymic Pathway of T Cell Differentiation

Gut intraepithelial lymphocytes (IEL) contain two independent T cell receptor a/#+ T cell populations, with different V# repertoires . In DBA/2 mice (Mlsa, IE'), the C1341 and heterodimeric alO CD8+ thymodependent T cell pool shows the same deletion of V#6, 8.1, and 11 + cells as found in peripheral lymphoid organs. In contrast, such deletions are not observed in the pool of IEL bearing homodimeric a CD8+ chains, in which these V(3 families are frequently observed in high amounts. The size of this gut homodimeric a CD8+ IEL pool and its different V(3 repertoire selection demonstrate the existence of a major extrathymic pathway of T cell differentiation with a gut-restricted localization . The large amount of the thymoindependent, homodimeric a CD8+ IEL found in the small bowel may contribute to a first line of defense against exogenous superantigens .