SEQUENTIAL DEVELOPMENT OF INTRAEPITHELIAL GAMMA-DELTA AND ALPHA-BETA T-LYMPHOCYTES EXPRESSING CD8-ALPHA-BETA IN NEONATAL RAT INTESTINE - REQUIREMENT FOR THE THYMUS

Previous studies in congenitally athymic nude rats have suggested that the thymus is important for the development of intestinal T cells. He re we have examined the effect of the nude mutation on intraepithelial lymphocyte (IEL) development from the perinatal period. By immunohist ochemistry it was shown that CD3(-) CD8 alpha alpha(+) putative IEL pr ecursors colonized the epithelium of both normal and athymic neonatal rats. Mature T cells, however, did not develop in athymic neonates. In normal rats, gamma delta T cells were present at birth and alpha beta T cells appeared within 8 days of postnatal life. At this age, the co mposition and relative number of intraepithelial T cells were similar to that in normal adult rats, with the exception that most neonatal T- cell receptor-gamma delta(+) and -alpha beta(+) IEL expressed CD8 beta . By contrast, extrathymic T-cell maturation in the gut of congenitall y athymic rats occurred slowly, as CD3(+) IEL did not appear until 4-6 months of age. These intraepithelial T cells displayed variable pheno types and appeared to be induced by environmental antigens as they wer e not found in isolator-kept old nudes. In conclusion, the present res ults indicate that the major colonization of the gut epithelium with g amma delta and alpha beta T cells expressing CD8 alpha beta takes plac e perinatally and requires the presence of the thymus. The development al relationship between these neonatal T cells and more immature CD3(- ) CD8 alpha alpha(+/-) IEL remains elusive.