Abstract
Saliva contains essentially no IgA at birth. However, secretory immune responses to oral and non-oral microbial antigens emerge early in life. We have investigated the characteristics of these responses in salivas of infants less than 1 month through 4 years of age, using cross-sectional and longitudinal approaches. Antibody specificities (IgA, IgAl, and IgA2) were measured in ELISA and Western blot analysis to antigens of Streptococcus mitis and S. salivarius that colonize during the neonatal period. Antibodies reactive with S. sanguis and mutans streptococci, which colonize later in the infant's life, were also determined. Concurrent investigation of the oral flora of each infant was performed and related to the observed antibody specificities. The secretory nature of the immunoglobulins in these salivas was analyzed immunologically and chromatographically. The primary molecular form of salivary IgA was dimeric in all salivas tested. Both IgA subclasses were found, although a subset of infant salivas initially contained >90% IgAl. IgM (>1 μg/ml) was detected in 58% of 3- to 17-week-old infants. By 2 months of age, salivas from most infants contained IgA antibody reactive with at least two S. mitis components. Many salivas also contained antibody reactive with S. salivarius components. By the end of the first year, most salivas contained IgAl and IgA2 antibody to S. mitis antigens. Maturation of secretory responses in the second and third year was evidenced by the appearance of increased concentrations and additional specificities of salivary IgA antibodies to S. mitis antigens. Antibody to S. mitis, S. salivarius, and S. sanguis extracellular components was detected only after infection with the respective species. However, salivary IgA antibody to mutans streptococci occasionally was detected before colonization was demonstrated.