Characterization and expression analysis of chemokine-like receptor 3 gene in rainbow trout Oncorhynchus mykiss

Chemokine-like receptors (CMKLRs) are multi-functional receptors with roles in regulating leukocyte and inflammation. Currently, two members of the CMKLRs, CMKLR1 and CMKLR2, have been found in salmonids, indicating that the CMKLRs had expanded from an ancestor gene in teleost fish. In the present study, the third member of the CMKLRs, defined as CMKLR3, was identified and cloned in rainbow trout. The trout CMKLR3 possessed conserved features of the CMKLR family including seven transmembrane regions, a dynein regulatory complex (DRC) motif, and two cysteine residues, but shared low sequence identities with fish CMKLR1 and CMKLR2 (24aEuro'38 %), which was confirmed by phylogenetic tree analysis. Trout CMKLR3 was highly expressed in body kidney, head kidney, and IgM(+) B cells, indicating its functional role in regulating leukocytes. We were able to modulate the expression of trout CMKLR3 in vivo by bacterial and parasitic infections but it remained apathetic to virus infection, and it was also successfully modulated in vitro by peptidoglycan and cytokines (IFN-gamma and IL-6). Our results suggest that trout CMKLR3 is regulated in a complex way and has an important regulatory role in inflammatory responses.