Humoral immunity to commensal oral bacteria in human infants: evidence that Streptococcus mitis biovar 1 colonization induces strain-specific salivary immunoglobulin A antibodies

Abstract

To define the relationship between salivary SIgA antibodies and commensal oral bacteria, we examined the reactivity of SIgA antibodies from the saliva of four infants with their own colonizing Streptococcus mitis biovar 1 (S. mitis bv 1) clones (ribotypes). Immunoblot analysis was used to examine reactivity of these antibodies with persistent ribotypes isolated from the mouths of the infants over the first year postpartum. Results showed that the pattern of SIgA antibody reactivity with the majority of clones increased in complexity after colonization but that most additional bands were common to other clones, indicating that they represented shared antigens. However, unique bands were identified in 75% of the selected persistent clones. We hypothesized that if strainspecific SIgA antibody was induced in response to colonization of a particular clone and contributed to its elimination from the mouth, then the appearance of unique bands would immediately precede the disappearance of the strain. Seventy-three percent of all unique bands identified in the study fulfilled this criterion. Because the mouth is an open, dynamic environment and multiple factors are believed to play a role in the immune response at mucosal surfaces, it may not be possible to conclusively define the relationship between SIgA antibody and commensal bacteria. However, our data provide evidence that SIgA antibody, reactive with unique antigens of their own colonizing strains, is produced in infants and may point to a role of this antibody in regulating colonization by S. mitis bv 1.

Streptococcus mitis: walking the line between commensalism and pathogenesis

“…However, these antibodies do not completely block adherence and subsequent colonization. In an interesting study by Wirth et al (2008) colonization of the oropharynx of human infants appeared to induce strain-specific sIgA, which appeared to clear the IgA targeted strain. However, S. mitis exhibits clonal and antigenic diversity resulting in frequent turnover of different strains of S. mitis in the oropharynx (Kirchherr et al, 2005(Kirchherr et al, , 2007.…”

“…However, these antibodies do not completely block adherence and subsequent colonization. In an interesting study by Wirth et al. (2008) colonization of the oropharynx of human infants appeared to induce strain‐specific sIgA, which appeared to clear the IgA targeted strain.…”

Exploring Host–Commensal Interactions in the Respiratory Tract

“…Moreover, it is worth exploring the immune responses against S. mitis and its relationship with S. pneumoniae in humans. Studies have shown that salivary IgA antibodies in infants react to S. mitis antigens, but it is unclear whether the antibodies are elicited by S. mitis or by cross-reactive streptococcal pathogens ( 53 – 55 ). Ongoing studies in our laboratory focus at the antibody-mediated cross-reactivity between S. mitis and pneumococcal antigens.…”

Antibodies Reactive to Commensal Streptococcus mitis Show Cross-Reactivity With Virulent Streptococcus pneumoniae Serotypes

“…On the other hand, how the host responds to S. mitis is poorly understood. Salivary IgA antibodies reactive to S. mitis antigens have been reported in human infants ( 15 – 17 ). Our recent study has shown that human CD4+ T cells, which express IL-17 (Th17 cells) and are reactive with S. mitis , also respond to pneumococcal proteins when cocultured with antigen-presenting cells pulsed with S. pneumoniae ( 18 ).…”