TLR4 and infectious disease: The first is TLR agonist, which has been developed to activate TLR3, TLR4, TLR5, TLR7 and TLR9, most of which is still in clinical trials, among which MPLA as a TLR4 agonist and imiquimod as a TLR7 agonist has been approved by FDA for infectious diseases or cancer [112, 113].