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Polyphosphazenes are synthetic, biodegradable, water-soluble polymers with a great versatility for vaccine and drug delivery applications. We previously observed that polyphosphazenes enhance immune responses in mice when injected subcutaneously against X:31 influenza antigens. Here, we investigated the potential of polyphosphazenes as mucosal adjuvants for enhancing influenza-specific immune responses. Vaccine combinations with soluble polyphosphazenes (PCPP or PCEP) and influenza X:31 antigen were administered to BALB/c mice intranasally. Antigen-specific antibody responses were assayed in serum and mucosal washes by ELISA, while antigen-specific cytokine production was assayed in spleen cells by ELISPOT assay. We observed that the formulation of either of the two polyphosphazenes with X:31 induced significant and prolonged serum IgG1 antibody responses as early as 2 weeks after primary immunization. Interestingly, only PCEP + X:31 induced a significant and prolonged serum IgG2a response. These results implied that the PCEP+X:31 formulation induced better Th1 immune responses, suggesting increased cell-mediated immunity. To confirm this, we determined that IFN-γ, a Th1 cytokine, was produced at significantly higher levels in spleens from mice that were vaccinated with the PCEP+X:31 formulation, while IL-4, a Th2 cytokine, was produced at higher levels from both vaccinated groups. Finally, we determined that these polyphosphazenes were indeed effective as adjuvants in inducing mucosal immune responses, as IgA and IgG antibodies were detected in lung and vaginal washes. We conclude that polyphosphazenes increase mucosal immune responses effectively, and can be used to modulate the quality of Th1 and Th2 immune responses.