Study of humoral immunity to commensal oral bacteria in human infants demonstrates the presence of secretory immunoglobulin A antibodies reactive with Actinomyces naeslundii genospecies 1 and 2 ribotypes

Abstract

The mouths of three human infants were examined from birth to age 2 years to detect colonization of Actinomyces naeslundii genospecies 1 and 2. These bacteria did not colonize until after tooth eruption. The diversity of posteruption isolates was determined by ribotyping. Using immunoblotting and enzyme-linked immunosorbent assay, we determined the reactivity of secretory immunoglobulin A (SIgA) antibodies in saliva samples collected from each infant before and after colonization against cell wall proteins from their own A. naeslundii strains and carbohydrates from standard A. naeslundii genospecies 1 and 2 strains. A. naeslundii genospecies 1 and 2 carbohydrate-reactive SIgA antibodies were not detected in any saliva sample. However, SIgA antibodies reactive with cell wall proteins were present in saliva before these bacteria colonized the mouth. These antibodies could be almost completely removed by absorption with A. odontolyticus, a species known to colonize the human mouth shortly after birth. However, after colonization by A. naeslundii genospecies 1 and 2, specific antibodies were induced that could not be removed by absorption with A. odontolyticus. Cluster analysis of the patterns of reactivity of postcolonization salivary antibodies from each infant with antigens from their own strains showed that not only could these antibodies discriminate among strains but antibodies in saliva samples collected at different times showed different reactivity patterns. Overall, these data suggest that, although much of the salivary SIgA antibodies reactive with A. naeslundii genospecies 1 and 2 are directed against genus-specific or more broadly cross-reactive antigens, species, genospecies, and possibly strain-specific antibodies are induced in response to colonization.

FIG. 1.

Ribotype patterns of the strains of A. naeslundii genospecies 1 and 2 isolated from the infants. The ribotypes were produced by separate digestion of genomic DNA with the restriction endonucleases BamHI and BbrPI.

FIG. 2.

Cluster analysis of protein profiles of isolates of A. naeslundii genospecies 1 and 2 obtained from infants 18, 20, and 21. The genospecies are separated at 57.5% similarity. Genospecies 2 isolates form the upper cluster and genospecies 1 isolates form the lower cluster.

FIG. 3.

Cluster analysis of immunoblots from infant 18. Wall extracts of autochthonous strains of A. naeslundii genospecies 1 were incubated with saliva collected at 2, 4, and 10 months (visits 4, 5, and 8) and probed to detect SIgA antibodies.

FIG. 4.

Separation and internal similarities among Western blot patterns produced by reaction of SIgA antibodies in saliva from infants 18, 20, and 21 with cell wall antigens of autochthonous strains of A. naeslundii genospecies 1. Superscripts: a, percentage similarity separating the cluster; b, internal similarity of the cluster.

FIG. 5.

Separation and internal similarities among Western blot patterns produced by reaction of SIgA antibodies in saliva from infant 20, with cell wall antigens of autochthonous strains of A. naeslundii genospecies 2. Superscripts: a, percent similarity separating the cluster; b, internal similarity of the cluster.