HUMORAL IMMUNITY TO COMMENSAL ORAL BACTERIA IN HUMAN INFANTS - SALIVARY ANTIBODIES REACTIVE WITH ACTINOMYCES-NAESLUNDII GENOSPECIES-1 AND GENOSPECIES-2 DURING COLONIZATION

The secretory immune response in saliva to colonization by Actinomyces naeslundii genospecies 1 and 2 was studied in 10 human infants from b irth to 2 years of age. Actinomyces species were not recovered from th e mouths of the infants until approximately 4 months after the eruptio n of teeth. However, low levels of secretory immunoglobulin Al (SIgA1) and SIgA2 antibodies reactive with whole cells of A. naeslundii genos pecies 1 and 2 were detected within the first month after birth, Altho ugh there was a fivefold increase in the concentration of SIgA between birth and age 2 years, there were no differences between the concentr ations of SIgA1 and SIgA2 antibodies reactive with A. naeslundii genos pecies 1 and 2 over this period, When the concentrations of SIgA1 and SIgA2 antibodies reactive with whole cells of A. naeslundii genospecie s 1 and 2 were normalized to the concentrations of SIgA1 and SIgA2 in saliva, the A. naeslundii genospecies 1- and 2-reactive SIgA1 and SIgA 2 antibodies showed a significant decrease from birth to 2 years of ag e. The fine specificities of A, naeslundii genospecies 1- and 2-reacti ve SIgA1 and SIgA2 antibodies were examined by Western blotting of env elope proteins. Similarities in the molecular masses of proteins recog nized by SIgA1 and SIgA2 antibodies, both within and between subjects over time, were examined by cluster analysis and showed considerable v ariability. Taken overall, our data suggest that among the mechanisms Actinomyces species employ to persist in the oral cavity are the induc tion of a limited immune response and clonal replacement with strains differing in their antigen profiles.