The development of IgA-specific antibodies to Escherichia coli O antigen in children.

One hundred and sixty-five infants were studied longitudinally from birth to 5 years of age. One hundred and twenty-three school-age children and 27 adults were examined cross-sectionally. Total salivary IgA levels and IgA antibodies against Escherichia coli O antigens were measured. Total IgA levels were low (less than 20 mg/l) from birth to 4 years of age. At 5 years of age there was a dramatic increase in the total IgA level (geometric mean = 100.7 mg/l), after which the levels fell to values similar to those observed in adults (adult geometric mean = 53.2 mg/l). Low levels of IgA-specific E. coli antibodies were observed for the first 4 years of life (less than 1.0 ELISA units). There was a gradual increase in specific antibodies between 5 and 9 years of age (geometric men at 9 years = 4.66 ELISA units) to levels similar to those observed in adults (adult geometric mean = 8.20 ELISA units). It is suggested that the patterns of development for these variables reflect a balance between antigenic exposure and immune control mechanisms.