TLR5 and influenza: In relation to the role of the activation of PRRs, mice deficient in Toll-like receptor 5 (TLR5) or in nucleotide-binding oligomerization domain-containing (Nod) 2 (both PRRs), and germ-free mice show impaired antibody responses to influenza, IPV and cholera toxin vaccines, with a restored response after bacterial reconstitution52,59.