Mucosal immunization with PsaA protein, using chitosan as a delivery system, increases protection against acute otitis media and invasive infection by Streptococcus pneumoniae.

As infection with Streptococcus pneumoniae (mainly via the mucosal route) is a leading cause of acute otitis media, sinus and bacterial pneumonia, the mucosal immunity plays an important role in the prevention of pneumococcal diseases. Therefore, intranasal vaccination may be an effective immunization strategy, but requires appropriate mucosal vaccine delivery systems. In this work, chitosan was used as a mucosal delivery system to form chitosan-PsaA nanoparticles based on ionotropic gelation methods and used to immunize BALB/c mice intranasally. Compared to mice immunized with naked PsaA, levels of IFN-γ, IL-17A and IL-4 in spleen lymphocytes, the systemic (IgG in serum) and mucosal (IgA in mucosal lavage) specific antibodies were enhanced significantly in mice inoculated with chitosan-PsaA. Furthermore, increased protection against acute otitis media following middle ear challenge with pneumococcus serotype 14, and improved survival following intraperitoneal challenge with pneumococcus serotype 3 or serotype 14, was found in the mice immunized with chitosan-PsaA nanoparticles. Thus, intranasal immunization with chitosan-PsaA can successfully induce mucosal and systemic immune responses and increase protection against pneumococcal acute otitis media and invasive infections. Hence, intranasal immunization with PsaA protein, based on chitosan as a delivery system, is an efficient immunization strategy for preventing pneumococcal infections.