Sequential development of intraepithelial γδ and αβ T lymphocytes expressing CD8αβ in neonatal rat intestine: Requirement for the thymus

Abstract

Previous studies in congenitally athymic nude rats have suggested that the thymus is important for the development of intestinal T cells. Here we have examined the effect of the nude mutation on intraepithelial lymphocyte (IEL) development from the perinatal period. By immunohistochemistry it was shown that CD3-CD8αα+ putative IEL precursors colonized the epithelium of both normal and athymic neonatal rats. Mature T cells, however, did not develop in athymic neonates. In normal rats, γδ T cells were present at birth and αβ T cells appeared within 8 days of postnatal life. At this age, the composition and relative number of intraepithelial T cells were similar to that in normal adult rats, with the exception that most neonatal T-cell receptor-γδ+ and -αβ+ IEL expressed CD8β. By contrast, extrathymic T- cell maturation in the gut of congenitally athymic rats occurred slowly, as CD3+ IEL did not appear until 4-6 months of age. These intraepithelial T cells displayed variable phenotypes and appeared to be induced by environmental antigens as they were not found in isolator-kept old nudes. In conclusion, the present results indicate that the major colonization of the gut epithelium with γδ and αβ T cells expressing CD8αβ takes place perinatally and requires the presence of the thymus. The developmental relationship between these neonatal T cells and more immature CD3-CD8αα(+/- ) IEL remains elusive.