Ontogeny of the Secretory Immune System in Man

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Abstract
Ig and albumin concentrations and Escherichia coli antibody levels were determined in a prospective study of saliva taken from 63 healthy infants during the 1st 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 2 mo. of age. IgA was detected by 3 wk of age. The IgA concentration fluctuated until 6 mo. 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 4 wk of age. No E. coli antibody was detected. There was no significant difference between breast-fed and formula-fed infants. Mucosal membrane permeability is apparently not restricted to the gut. Changes in mucosal permeability are nonspecific and not restricted to the uptake of specific food protein or ingestion of maternal milk. Maternal IgG may contribute to mucosal defense in the the neonate. Fluctuations in the concentration of IgA may reflect a balance between intense antigenic stimulation in the gut in the 1st weeks of life and immune regulatory mechanisms. Ingestion of maternal milk does not modify the pattern of ontogeny.