Abstract

TLR3 and TRIF (adaptor protein for TLR3) are vital to the MyD88-independent pathway mediated by Toll-like receptors (TLRs). In order to identify the role of TLR3 and TRIF in Micropterus salmoides , the Ms _TLR3 and Ms _TRIF (Ms: abbreviation for M. salmoides ) were cloned and characterized in this study. The open reading frames (ORFs) of Ms _TLR3 and Ms _TRIF genes were 2736 bp and 1791 bp in length, encoding 911 and 596 amino acids, respectively. The protein structure of Ms _TLR3 includes a signal peptide, 18 LRR-related domains, a low complexity region, a transmembrane region, and a TIR domain. However, only a TIR domain and a coiled coil domain were found in Ms _TRIF. Both Ms _TLR3 and Ms _TRIF showed the highest homology to that of M. dolomieu . Ms _TLR3 and Ms _TRIF showed similar expression patterns in various tissues, with the highest expression level in the head kidney. After stimulation of Flavobacterium columnare , the mRNA expressions of Ms _TLR3 and Ms _TRIF were significantly up-regulated at 1 dpi in the gill, spleen and head kidney, and at 6 hpi in the trunk kidney. Furthermore, morphological changes in the gills of largemouth bass challenged with F. columnare suggested that F. columnare infection can destroy the gill filament. Taken together, Ms _TLR3 and Ms _TRIF are indeed involved in F. columnare infection and the subsequent immune response in largemouth bass. Moreover, Ms _TLR3 and Ms _TRIF might respectively play their potential roles in mucosal (mainly in the gill) and systemic (mainly in the head kidney) immune response to bacterial infection.