Presence of secretory IgA antibodies to an enteric bacterial pathogen in human milk and saliva.

The concept of a common mucosal immune system in man was tested by examining the concurrent presence of specific-secretory IgA (SIgA) antibodies in human milk and saliva from three groups of subjects: 64 Sri Lankan women living in Sri Lanka; 20 immigrant Asian women living in Birmingham (median duration of residence in the United Kingdom five years); and 75 Caucasian women living in Birmingham (controls). Enzyme linked immunosorbent assays (ELISA) were developed to detect enterotoxigenic Escherichia coli (ETEC) colonisation factor/1 (CFA/1) specific SIgA antibodies in milk and saliva. ETEC CFA/1 specific SIgA antibody activity was detectable in milk (37.5% and 25%) and saliva (42.1% and 35%) of Sri Lankan and immigrant Asian women, respectively, but not in any of the Caucasian controls. Eighty five point two per cent of subjects who were positive had specific antibodies detectable in both milk and saliva; 5% of all Sri Lankan women and 10% of all immigrant Asian women had detectable antibody only in saliva. These observations lend further strong support to the idea that a common mucosal immune system exists in man. The continuing presence of specific SIgA antibodies in Asian immigrants to previously encountered antigens suggests that there may be an 'immunological memory' in the human secretory immune system.