Sex differences in vaccine-induced neuraminidase cross-recognition and protection against H5N1 in mice

Despite concerns about the spread and pandemic potential of H5N1, there is no commercial H5N1 vaccine. Seasonal influenza vaccines offer some cross-protection against H5N1, but to date there has been no consideration of whether protection differs between the sexes. We investigated immune responses and protection in adult male and female C57BL/6 mice following vaccination with either inactivated H1N1 or H5N1 (LAIV backbone) virus vaccines. Vaccination induced strong homologous antibody responses, with females generating greater total IgG than males against both H1N1 and H5N1 vaccine, which was primarily mediated by greater IgG responses to neuraminidase (NA) than hemagglutinin (HA) protein. IgG cross-recognition of H1N1 also was greater among H5N1 vaccinated females and was primarily caused by greater IgG responses to N1. IgG2b and IgG2c were the primary isotypes generated in response to these vaccines, with females having greater IgG2b responses and greater binding to Fc{gamma}RIV for avian and human NA than males in response to both homologous and heterologous vaccination. Antibody-dependent complement deposition was measured as an FcR-mediated non-neutralizing response against HA and NA and was robust in both sexes. Vaccinated females had greater neutralizing antibody titers than males against the homologous vaccine virus, with limited cross-neutralizing antibodies detected in either sexes. Neuraminidase inhibition titers were greater in vaccinated females than males against the heterologous virus following H1N1 vaccination and against both the vaccine and heterologous viruses following H5N1 vaccination. When H1N1 and H5N1 vaccinated mice were challenged with a lethal dose of A/Texas/37/2024 H5N1, all H5N1 vaccinated mice were protected, regardless of sex. Among H1N1 vaccinated mice, while both sexes were protected against disease, H1N1 vaccinated females cleared virus faster than their male counterparts. These findings highlight that female-biased NA-specific antibodies result in greater cross-protection and should be considered in studies of influenza vaccines. HighlightsO_LIFemales mount stronger IgG responses than males to both H1N1 and H5N1 vaccines C_LIO_LISex differences in vaccine responses are driven by immunity to neuraminidase (NA) C_LIO_LINA inhibition titers are greater in females, supporting broader cross-protection C_LIO_LIH5N1 vaccination confers full protection in both sexes against lethal H5N1 challenge C_LIO_LIH1N1-vaccinated females clear H5N1virus faster than males after lethal challenge C_LI