Structure, function, and potential application of Toll-like receptor 22 from fish

Abstract

The innate immune system is initiated by the recognition of Pathogen-associated molecular patterns (PAMPs) through Pattern recognition receptors (PRRs). Among all the identified PRRs, the Toll-like receptors (TLRs) are the most extensive spectrum of pathogen recognition. TLR22 is a non-mammalian TLR that is found mostly in fish. In this review, we have briefly expounded on the structure and signaling pathways of TLR22 in several fish species, as well as how it kills pathogens. Similar to the other TLRs, TLR22 has a three-domain structure: the periplasmic extracellular domain (ectodomain – ECD) containing Leucine-rich repeats domain (LRR), transmembrane domain (TM), and cytoplasmic Toll/IL-1 receptor domain (TIR). The LRR motifs number, the choice of ligands, and signaling pathways are different from fish to fish. TLR22 recognizes dsRNA and LPS, signaling the immune system to kill pathogens. Currently, there are several reports of the application of TLRs, but there is no published report on the applications of TLR22. We presented several applications similar to other TLRs, suggesting new potential applications for TLR22. However, there are still many unresolved issues remaining, thus more research is needed to warrant the understanding of TLR22 functionality.