Humoral immunity to commensal oral bacteria in human infants: Salivary secretory immunoglobulin A antibodies reactive with Streptococcus mitis biovar1, Streptococcus oralis, Streptococcus mutans, and Enterococcus faecalis during the first two years of life

Secretory immunoglobulin A (SIgA) antibodies reactive with the pioneer oral streptococci Streptococcus mitis biovar 1 and Streptococcus oralis, the la te oral colonizer Streptococcus mutans, and the pioneer enteric bacterium E nterococcus faecalis in saliva samples from 10 human infants from birth to age 2 years were analyzed. Low levels of salivary SIgA1 and SIgA2 antibodie s reactive with whole cells of all four species were detected within the fi rst month after birth, even though S. mutans and E. faecalis were not recov ered from the mouths of the infants during the study period. Although there was a fivefold increase in the concentration of SIgA between birth and age 2 Sears, there were no differences between the concentrations of SIgA1 and SIgA2 antibodies reactive with the four species over this time period. Whe n the concentrations of SIgA1 and SIgA2 antibodies reactive with all four s pecies were normalized to the concentrations of SIgA1 and SIgA2 in saliva, SIgA1 and SIgA2 antibodies reactive with these bacteria showed a significan t decrease from birth to 2 gears of age. Adsorption of each infant's saliva with cells of one species produced a dramatic reduction of antibodies reco gnizing the other three species. Sequential adsorption of saliva samples re moved all SIgA antibody to the bacteria, indicating that the SIgA antibodie s were directed to antigens shared by all four species. The induction by th e host of a limited immune response to common antigens that are likely not involved in adherence may be among the mechanisms that commensal streptococ ci employ to persist in the oral cavity.