Secretory IgA against enterotoxins in breast-milk.
A pool of colostrum from Guatemalan mothers (Guatemalan colostrum)) obtained 2-4 days post partum inhibited the induced fluid accumulation in rabbit ileal loops when incubated with Vibrio cholerae or Escherichia coli enterotoxin. There was a linear relationship between the quantity of colostrum used and the protection achieved. Pools of Guatemalan breast-milk obtained 15-30 days post partum and North American breast-milk had the same effect when tested with E. coli and V. cholerae enterotoxins, respectively. The antitoxic activity of a given pool correlated with its IgA content but not with the concentration of IgG or IgM. Guatemalan colostrum globulins were precipitated by ammonium sulphate. The globulins were filtered through a 'Biogel A5' column and fractions obtained. When tested in rabbit ileal loops the antienterotoxin activity in these fractions closely paralleled their IgA but not their detectable IgG or IgM content. We hypothesise that IgA antibody to enterotoxin, present in breast-milk of normal mothers, is probably a manifestation of natural immunity. The passive transfer of these antibodies to the infant may explain why breast-milk prevents E. coli diarrhoea in the neonate.