The role of secretory immunoglobulin (Ig) A in nasopharyngeal secretions in the adherence of Streptococcus pneumoniae and Hemophilus influenzae to nasopharyngeal epithelial cells was investigated in vitro. The adherence was remarkably reduced by treating bacteria with nasopharyngeal secretions, and the antiadhesive activity was significantly greater in nasopharyngeal secretions having secretory IgA antibody activity against bacteria than in those having no activity. Noticeable changes were not observed in the antiadhesive activity caused by absorption of IgG from nasopharyngeal secretions. Results suggest that secretory IgA in nasopharyngeal secretions is related to bacterial adherence and adds to the prevention of nasopharyngeal infections.
Nontypeable Hemophilus influenzae organisms were inoculated into the nasopharynx of BALB/c mice immunized by oral administration of formalin-killed bacteria. Salivary antibodies and the colonization of H influenzae in the nasopharynx were investigated in order to clarify the effect of oral immunization. Salivary immunoglobulin A antibody titers against H influenzae were significantly increased by oral immunization, but salivary immunoglobulin G antibody titers were not. The bacteria inoculated into the nasopharynx were more rapidly eliminated in immunized mice than in control mice. The results suggest that oral immunization might be useful in preventing otitis media with effusion by inhibiting the colonization of the nasopharynx by pathogenic bacteria.
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