Azithromycin Modulates Murine Immune Responses to Pneumococcal Conjugate Vaccine and Inhibits Nasal Clearance of Bacteria

Macrolide antibiotics, including azithromycin, have been implicated in the modulation of host immune responses, independently of their antimicrobial properties. The present work was designed to study the effect that azithromycin has on protective humoral immune responses induced by a 7-valent, polysaccharide, pneumococcal conjugate vaccine (PCV7). By use of a murine vaccination/challenge model, it was found that inoculation with azithromycin led to significantly lower primary antibody responses, decreased recall proliferative responses, and, in nasal cavities, impaired clearance of Streptococcus pneumoniae serotype 14 from the nasal cavities. The results demonstrate that azithromycin can be inhibitory with regard to protective immune responsiveness.