Ontogeny of the secretory immune system in man

Immunoglobulin and albumin concentrations and Escherichia coli antibody levels were determined in a prospective study of saliva taken from 63 healthy infants during the first year of life. Albumin and IgG were present in high concentrations at birth (57 +/- 6 and 35 +/- 8 mg/l respectively) and decreased in parallel to low values at two months of age. IgA was detected by three weeks of age. The IgA concentration fluctuated until six months of age, after which constant values were observed (14 +/- 3 mg/l). Low levels of salivary IgM (2.4 +/- 1.2 mg/l) were demonstrated in 37% of infants at four weeks of age. No E. coli antibody was detected. There was no significant difference between breast-fed and formula-fed infants. These findings suggest: (i) that mucosal membrane permeability is not restricted to the gut; (ii) that changes in mucosal permeability are non specific and not restricted to the uptake of specific food protein or ingestion of maternal milk; (iii) maternal IgG may contribute to mucosal defence in the neonate; (iv) fluctuations in the concentration of IgA may reflect a balance between intense antigenic stimulation in the gut in the first weeks of life and immune regulatory mechanisms and (v) ingestion of maternal milk does not modify the pattern of ontogeny.