Proc. Natl. Acad. Sci. USA https://doi.org/10.1073/pnas.1805268115 (2018)

Immune responses can be strongly influenced by biological sex; however, this is rarely considered as a variable in vaccine responses. Klein and colleagues, in the Proceedings of the National Academy of Sciences, use a mouse model of influenza virus challenge and vaccination to systematically compare responses in males and females. Female mice show more-robust humoral and cellular immunity than that of male mice after infection with influenza virus, although vaccination serves to protect both sexes equivalently. Passive transfer of serum, however, demonstrates that antibodies in female mice mediate more-potent protection. B cells from female mice have higher expression of TLR7, and knockout of this receptor impairs their more-potent antibody response. Therefore, TLR7 might, at least in part, underpin sex differences in vaccine efficacy.