IgA antibodies in human milk: epidemiological markers of previous infections?
The concept of an enteromammary link in secretory IgA (SIgA) antibody production was tested by hypothesising that specific SIgA antibody profiles in human milk might be an epidemiological marker for enteropathogens in a community. Milk from three subject groups was studied: 64 Sri Lankan women living in poor suburbs of Colombo, 20 Asian immigrant women domiciled in Birmingham, for a median period of five years (range 14 days-16 years), and 75 white women living in Birmingham. An enzyme linked immunosorbent assay (ELISA) was developed for the detection and measurement of SIgA antibodies to a panel of 14 crude O and 10 pure lipopolysaccharide antigens of diarrhoeagenic Escherichia coli strains well known to be endemic in the Indian subcontinent. The number of Sri Lankan and Asian immigrant women with SIgA antibodies to all 14 diarrhoeagenic E coli antigens (except O127 in Asian women) was significantly higher than in the white controls. The amount of E coli O antigen specific SIgA antibody activity as a percentage of total SIgA also gave significantly higher median values in Sri Lankan (6%) and in Asian immigrant (4%) women than in white controls (0.7%). SIgA antibodies were highly O serogroup specific and showed excellent concordance between crude O and the corresponding purified lipopolysaccharide antigens. These results suggest that milk antibody profiles represent an epidemiological marker of exposure to enteral pathogens. The continuing specific milk antibody response in Asian women who have been domiciled in the United Kingdom for many years may indicate 'memory' in the human secretory immune system.