Antibody-independent, CD4+ T-cell-dependent protection against pneumococcal colonization elicited by intranasal immunization with purified pneumococcal proteins

Immunity to pneumococcal colonization in mice by exposure to live or killed pneumococci has been shown to be antibody independent but dependent on CD4+ T cells. Here we show that intranasal immunization with pneumococcal proteins (pneumococcal surface protein C, adhesin A, and a pneumolysoid) can elicit a similar mechanism of protection. Colonization could be significantly reduced in mice congenitally deficient in immunoglobulins after intranasal immunization with this mixture of proteins; conversely, the depletion of CD4+ T cells in immunized wild-type mice at the time of challenge eliminated the protection afforded by immunization. Overall, our results show that intranasal immunization with a mixture of pneumococcal proteins protects against colonization in an antibody-independent, CD4+ T-cell-dependent manner.