IMMUNOGLOBULIN-A SUBCLASSES IN INFANTS SALIVA AND IN SALIVA AND MILK FROM THEIR MOTHERS

We sought to determine (1) the ontogeny of secretary IgA subclasses in saliva of breast- and formula-fed infants and (2) the influence of br east-feeding on the maturation of secretary salivary IgA subclasses. S ecretory IgA and subclasses I and 2 concentrations were determined in saliva from 40 healthy, term infants from birth to age 18 months, and in parallel milk samples from the infants' mothers who were breast-fee ding during the first 6 months after birth. Secretary IgA was detected in the neonates' saliva as early as 3 days after birth, increased rap idly during the next 6 months, but then stabilized at a level approxim ately one-sixth that of the mothers' salivary secretory IgA. Secretory IgA2 represented less than 15% of secretary IgA in saliva collected 2 weeks after birth but by 6 months represented 24.4% of secretory IgA, a value approaching that of the mothers' salivary secretary IgA2 (30. 4%). This increase in the proportion of secretory IgA2 was temporally related to a reduction in the proportion of secretory IgA2 in milk thr oughout lactation. The secretory IgA concentration increased more rapi dly during the first 6 months after birth in infants exclusively breas t fed than in those exclusively bottle fed. We conclude that although secretary immunity is immature in infants, breast-feeding may aid in p rotection against pathogenic microorganisms by increasing the rate of mucosal IgA maturation.