Mannose-modified chitosan microspheres enhance OprF-OprI-mediated protection of mice against Pseudomonas aeruginosa infection via induction of mucosal immunity

Pseudomonas aeruginosa is an opportunistic pathogen that localizes to and colonizes mucosal tissue. Thus, vaccines that elicit a strong mucosal response against P. aeruginosa should be superior to other vaccination strategies. In this study, to stimulate rapid and enhanced mucosal immune responses, mannose-modified chitosan microspheres loaded with the recombinant outer membrane protein OprF(190-342)-OprI(21-83) (FI) (FI-MCS-MPs) of P. aeruginosa were developed as a potent subunit vaccine for mucosal delivery. FI-MCS-MPs were successfully obtained via the tripolyphosphate ionic crosslinking method. Confocal and immunohistochemical analyses indicated that FI-MCS-MPs exhibited the ability to bind the macrophage mannose receptor (MMR, CD206) in vitro and in vivo. After intranasal immunization of mice with FI-MCS-MPs, FI-specific humoral immune responses were detected, measured as local IgM antibody titers in lung tissue slurry; IgA antibody titers in nasal washes, bronchoalveolar lavage (BAL), and intestinal lavage; and systemic IgA and IgG antibody titers in serum. FI-MCS-MPs induced early and high mucosal and systemic humoral antibody responses comparable to those in the group vaccinated with unmodified mannose. High levels of IFN-gamma and IL-4 in addition to T lymphocyte subsets induced a mixed Th1/Th2 response in mice immunized with FI-MCS-MPs, resulting in the establishment of cellular immunity. Additionally, when immunized mice were challenged with P. aeruginosa via the nasal cavity, FI-MCS-MPs demonstrated 75 % protective efficacy. Together, these data indicate that mannose-modified chitosan microspheres are a promising subunit delivery system for vaccines against P. aeruginosa infection.