Disease manifestations with immune alteration by bacterial neuraminidases in influenza virus infection with Streptococcus pneumoniae superinfection

Streptococcus pneumoniae often causes superinfection in influenza and exacerbates the disease with more severity and even mortality. In our influenza hemagglutinin (HA) antigen-specific transgenic mouse model, mice suffered from severe disease and died with increased virus titer and pathology in the lungs upon serotype-3 Streptococcus pneumoniae superinfection on day 4- post PR8 strain H1N1 influenza virus infection. Same dose viral or bacterial infection caused mild disease in control mice. Streptococcus pneumoniae supreinfection attenuated anti-influenza T cell immunity in the lungs. There was less clonotypic expansion, T-bet induction and effector cytokines IFN-γ and TNF-α production in HA-specific CD4+ T cells on day 2- and 3- post bacterial superinfection, with impaired viral clearance. Streptococcus pneumoniae strains with different combinations of bacterial neuraminidase (NA) demonstrated varied degrees of T cell immunity attenuation. Streptococcus pneumoniae with NA-B only was the most suppressive with up-regulated active TGF-β and down-regulated IFN-γ expression in HA-specific CD4+ T cells, followed by those with both NA-A and NA-B. Streptococcus pneumoniae with both NA-A and NA-B and inserted NA-C was least suppressive. With in vitro experiments, recombinant bacterial NA-A or NA-B augmented TGF-β and attenuated IFN-γ in HA-specific CD4+ T cells in overnight culture with PR8 virus. Recombinant bacterial NA-C mitigated TGF-β and increased IFN-γ in HA-specific CD4+ T cells. Our results demonestrates distinct immune alteration by different bacterial neuraminidases, which may play a significnt role of disease manifestation in influenza with bacterial superinfection.