TLR5 and influenza: A study in mice showed that TLR5-mediated sensing of flagellin that was produced by the gut microbiota was necessary for antibody responses to the influenza vaccine, as mice deficient for TLR5 had substantially impaired responses to the vaccine at day 7 and 14 post-vaccination (63), while germ-free (GF) or antibiotic-treated mice had significantly impaired antibody responses to the influenza vaccine (62–64).