7.3.2　Microbial Products (TLR agonists)

Many immune-enhancing substances besides alum have been reported, and most of these have been collectively referred to as pattern molecules of microbes.Hence, microbial components as well as minerals can be immune enhancers.Moreover, immune adjuvants can be synthesized based on the structures of microbial patterns, and functionally identified as an agonist for receptors such as TLR in innate immunity.Microbial products contain inflammatory “danger” signals, such as those known as “pathogen-associated molecular patterns” (PAMP).The host senses PAMPs as danger molecules, eliciting the release of cytokines and chemokines that initiate an inflammatory defensive response.Immune system cells have special receptors for PAMPs known as PRRs (pattern recognition receptors), including Toll-like receptors (TLRs), Nod-like receptors (NLRs), RIG-I-like receptors (RLRs), and C-type lectin receptors (CLRs).One of the main PAMPs is lipopolysaccharide (LPS) found in Gram negative bacteria, a TLR4 agonist.Both natural and synthetic derivatives of LPS with reduced toxicity are currently being developed [12, 13].(https://www.daowen.com)