Studies on human milk III. Secretory IgA quantity and antibody levels against Escherichia coli in colostrum and milk from underprivileged and privileged mothers.

We studied the milk content of secretory IgA (SIgA) and of specific IgA antibodies to E. coli in relation to volume, in 24 h samples from mothers belonging to different socio-economic groups and living under different ecologic conditions in Ethiopia, Guatemala and Sweden. There were no statistically significant differences in the daily output of milk SIgA among the population groups investigated at different times after onset of lactation. There was, however, a certain trend towards lower SIgA levels among the Guatemalan poor women, compared to the corresponding privileged one (Tables 2 and 3). Three days after delivery the underprivileged Ethiopian mothers showed significantly lower antibody levels than the privileged Ethiopian. These differences were no longer seen when the values were corrected for differences in volume (Table 5). One month after delivery, the levels of SIgA antibodies in milk from Swedish women and Guatemalan privileged women, against a pool of eight E. coli somatic antigens were comparable; these two groups of mothers had significantly higher antibody levels than the Guatemalan rural and urban ones (Table 4). The same pattern was observed after correction for differences in 24 h volumes (Table 5). At 3 months after delivery, the Guatemalan urban privileged women, again showed higher levels and daily output of antibodies against the E. coli antigens than the urban poor and rural mothers (Tables 4 and 5). The milk samples taken from a population where malnutrition is evident, i.e., mothers from Santa María Cauqué, did not show any changes in the levels of SIgA and the anti-E. coli antibodies 3, 6, 9 months after initiation of lactation. The data presented here provide evidence that chronically malnourished mothers are able to produce SIgA and transfer it to their offspring via breast milk. Furthermore, they do so in quantities that are comparable to those observed in well-nourished populations. There was a wide range of concentrations and daily output of SIgA and of specific antibodies in all groups, suggesting that some of the infants get less than others. The observed differences in levels of antibodies against E. coli may be explained by differences in exposure to E. coli strains of the eight serogroups studied here. The possibility of a deficiency in the SIgA antibody response in the undernourished mothers still remains unanswered.