Vaccination With the Commensal Expressing Pneumococcal Serotype 5 Capsule Elicits IgG/IgA and Th17 Responses Against .

Recent studies have identified a clinical isolate of the commensal that expresses serotype 5 capsule ( serotype 5) and shows serospecificity toward pneumococcal serotype 5. However, it remains unknown whether serotype 5 induces protective immunity against pneumococcal serotype 5. In this study, we evaluated the ability of serotype 5 to generate protective immunity in a mouse model of lung infection with pneumococcal serotype 5. Upon challenge infection with serotype 5, mice intranasally immunized with serotype 5 exhibited reduced pneumococcal loads in the lungs, nasal wash, and bronchoalveolar lavage fluid compared with those receiving PBS (control). The immunized mice displayed significantly higher levels of IgG and IgA antibodies reactive to serotype 5, serotype 5 or serotype 4 than the antibody levels in control mice. In vaccinated mice, the IgG/IgA antibody levels reactive to serotype 5 or S. serotype 5 were higher than the levels reactive to serotype 4. Furthermore, restimulation of the lung-draining mediastinal lymph node cells and splenocytes from immunized mice with killed serotype 5, serotype 5 or serotype 4 showed enhanced Th17, but not Th1 and Th2, responses. Overall, our findings show that mucosal immunization with serotype 5 protects against serotype 5 infection and induces Th17 and predominant serotype-specific IgG/IgA antibody responses against pneumococcal infection.