Effects of oral and systemic immunization on nasopharyngeal clearance of nontypeable Haemophilus influenzae in BALB/c mice.

BALB/c mice were immunized orally or subcutaneously with formalin-killed nontypeable Haemophilus influenzae (NTHi). Salivary immunoglobulin A (IgA) antibody titers against NTHi were significantly increased by oral immunization, but not by subcutaneous immunization. Both immunization procedures remarkably increased the levels of serum antibody activities of both IgA and immunoglobulin G. Live NTHi were then inoculated into the naso-pharynx, and the clearance of the pathogen from the nasopharynx was observed. Significantly fewer bacteria were present in the nasopharynx of the orally immunized mice than in the control mice. However, there was no significant difference between the subcutaneously immunized mice and the control mice. The results indicate that oral immunization can enhance the ability of mice to clear NTHi from the nasopharynx.