IT has been suggested that feeding infants with human milk reduces the incidence of gastrointestinal infections1. Although macrophages, lymphocytes and antibodies in the milk are probably important in this protection2,3, the mechanism for the development of specific immunity to enteric pathogens is not known. Human colostral cells synthesise IgA (ref. 4), and we have used the haemolysis-in-gel technique to demonstrate that human colostrum contains numerous cells which produce IgA antibodies against the O antigens of commonly encountered Escherichia coli bacteria5. This suggested that the sensitised lymphocytes had either undergone antigen-induced clonal proliferation within the mammary gland or had homed to that organ from another site after becoming sensitised. Because of reports that gastrointestinal immunisation of germ-free mice led to local6 and systemic 7 production of IgA antibodies, and that cells from Peyer's patches effectively repopulate the ileum of lethally-irradiated rabbits with IgA-producing cells8, we have examined the effect of gastrointestinal immunisation on the development of antibody-producing cells in colostrum of humans. We found that oral administration of a non-pathogenic strain of E. coli led to the rapid appearance of colostral cells producing antibodies against the O antigen of the organism.
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