The human mucosal immune system seems to be structurally mature, having all the necessary cellular components to generate an immune response at birth. In the absence of dietary antigens and bacterial flora, there are no secondary follicles in the Peyer's patches and virtually no immunoglobulin A plasma cells in the lamina propria at birth. Reactive follicle centers develop soon after birth but it may take about 2 years for mucosal immunoglobulin A plasma cell density to reach adult levels. T cells are present in epithelium and lamina propria at birth, albeit in fewer numbers than later in life. Functional studies on mucosal immunity in the neonate are limited for clinical and ethical reasons. Salivary antibodies have been studied, but it is not clear whether reactivity in saliva reflects mucosal responses at other sites. Deficiencies in the ability of peripheral blood T cells of the neonate to produce interleukin-4 and interferon-γ may also occur in the intestine. The available data are contradictory and it is still not known whether it is better to try to prevent immunologic sensitization of the neonate by avoiding potential allergens (eg, cow's milk, gluten), or whether early exposure (as occurs when premature infants are given formula feeds) might tolerize the infant. It is also unclear whether events in the neonate have any role in the subsequent development of life-long diseases such as celiac disease or inflammatory bowel disease.
Current Opinion in Gastroenterology 1993, 9:946-952