IMMATURITY, AGING AND ORAL TOLERANCE

Founding studies of cellular immunology emphasized that tolerance to a llografts could only be achieved early in the embryonic or neonatal pe riod, suggesting that the establishment of self-tolerance, a main even t in the organization of the immune system, would necessarily take pla ce in immature hosts. Contradicting these ideas, oral tolerance is a c ommon, daily phenomenon, easily achieved by a physiological route in a dult immunocompetent animals. Furthermore, there is solid evidence tha t, after the neonatal period, the susceptibility to oral tolerance ind uction also wanes and that it may be restored by adoptive transfer of cells from young hosts. These findings are briefly reviewed here to em phasize that immunological activity is a continuous and ongoing epigen esis extending throughout the entire life of the organism, far beyond the early phases of ontogenesis.