Neutralizing antibodies against Escherichia coli and Vibrio cholerae enterotoxins in human milk from a developing country.
By means of the adrenal cell assay and the rabbit small-bowel loop technique enterotoxin-neutralizing antibodies were demonstrated in all investigated milk samples from severely undernourished Pakistani women but, with a single exception, not in milk from Swedish mothers. The antibodies belonged to the IgA and IgG classes as observed in an enzyme-linked immunosorbent assay, which also revealed secretory component on specific enterotoxin antibodies, showing that the IgA antibodies were primarily of the secretory type. The epidemiological stituation and experimental data strongly indicate that Escherichia coli enterotoxin rather than immunologically cross-reactive Vibrio cholerae toxin in most cases constituted the antigenic stimulus for the milk antibodies. The presence in the milk of the Pakistani mothers of secretory IgA antibodies against an important diarrheogenic agent may have practical importance for protection of the breast-fed baby and probably also illustrates the frequent intestinal exposure of these women to enterotoxinogenic bacteria. Since enterotoxin antigen is presumed not to enter deeper tissues, the demonstration of secretory antibodies in milk agrees with a proposed homing of intestinally triggered lymphocytes to the mammary gland.