IL4 and streptococcal pneumonia: It has been reported that Th17 cells play a role in immunity against nasal infection with Streptococcus pneumonia; protective immunity induced with a whole-cell vaccine was lost in Il17AR−/− mice, but not in Ifng−/− or Il4−/− mice, and was antibody-independent.30 Interestingly, acquired immunity did not prevent initial infection with S. pneumoniae, but rather accelerated clearance upon re-challenge and this was associated with infiltration of neutrophils into the nasopharyngeal mucosa.