Characterization of protective mucosal and systemic immune responses elicited by pneumococcal surface protein PspA and PspC nasal vaccines against a respiratory pneumococcal challenge in mice

Pneumococcal surface protein A (PspA) and PspC are virulence factors that are involved in the adhesion of Streptococcus pneumoniae to epithelial cells and/or evasion from the immune system. Here, the immune responses induced by mucosal vaccines composed of both antigens as recombinant proteins or delivered by Lactobacillus casei were evaluated. None of the PspC vaccines protected mice against an invasive challenge with pneumococcal strain ATCC 6303. On the other hand, protection was observed for immunization with vaccines composed of PspA from clade 5 (PspA5 or L. casei expressing PspA5) through the intranasal route. The protective response was distinguished by a Th1 profile with high levels of immunoglobulin G2a production, efficient complement deposition, release of proinflammatory cytokines, and infiltration of neutrophils. Intra- nasal immunization with PspA5 elicited the highest level of protection, characterized by increased levels of secretion of interleukin-17 and gamma interferon by lung and spleen cells, respectively, and low levels of tumor necrosis factor alpha in the respiratory tract.