Figure 1.

Pathogen recognition in trout. Toll-like receptors, Nod1, and downstream factors as known from trout are listed with their GenBank accession numbers. Different colors of the LRR regions factors indicate the membership to individual Tlr families (TLR1 (blue), Tlr3 (orange), Tlr5 (black), Tlr7 (green), and Tlr11 (red)). Notably, a Tlr4 ortholog is absent in salmonid fish (marked with a flash). The Myddosome consisting of Myd88, Irak4a, and Irak1 (inside the green box) binds to the activated Tlr and recruits Traf6 and further downstream factors (indicated with a broken arrow), which in turn activate NF-κB. Tollip functionally inhibits Irak1 by preventing its recruitment into the Myddosome complex.