Evolutionary Regression and Species-Specific Codon Usage of TLR15. Voogdt CGP, Merchant ME, Wagenaar JA, van Putten JPM. Front Immunol. 2018 Nov 13;9:2626. Toll-like receptors (TLRs) form an ancient family of innate immune receptors that detect microbial structures and activate the host immune response. Most subfamilies of TLRs (including TLR3, TLR5, and TLR7) are highly conserved