THE NEONATAL DEVELOPMENT OF INTRAEPITHELIAL AND LAMINA PROPRIA LYMPHOCYTES IN THE MURINE SMALL-INTESTINE

During early neonatal life, important changes occur in the gut. The in testine is challenged by both milk and a microbial flora. Later on, at weaning, the diet of mice changes from milk to pelleted food leading to changes in microbial contents. This period seems essential for a co mplete development of the mucosal immune system. We investigated the d evelopment of both intraepithelial (IEL) and lamina propria lymphocyte s (LPL), from day 5, and every 5 days, up to day 30 after birth, IEL a nd LPL were isolated from the small intestine and the phenotype was as sessed by FAGS analyses, using antibodies for detection of T-cell mark ers CD3, TCR alpha beta, TCR gamma delta, CD4, CD8 alpha, CD8 beta, CD 5, CD18, CD54, and CD49d. Our data show a clear increase in the number of LPL just before weaning, while the number of IEL increased after d ay 15, A more mature pattern of membrane antigen expression of both IE L and LPL was observed at weaning. The adhesion molecules CD18, CD54, and CD49d, essential for cellular communication of lymphocytes, showed an expression peak at weaning. In conclusion, the mouse mucosal immun e system develops during the first 3 weeks of neonatal life leading to the formation of a more mature immune system at weaning.