Identification and functional analysis of Mannose receptor in Asian swamp eel (Monopterus albus) in response to bacterial infection.

Mannose receptor (MR), as a member of the C-type lectin (CLEC) family, plays an important role in the internalize pathogen-associated ligands and activate immune response. In the present study, MR was identified and characterized from Asian swamp eel (Monopterus albus) (namely Ma MR). The open reading frame of Ma MR was 4311 bp in length encoding 1437 amino acids of a ∼162.308 kDa protein, including a cysteine-rich (CR) domain, a fibronectin type II (FNII) domain, eight C-type lectin-like domains (CTLDs), a transmembrane domain and a short cytoplasmic domain. Phylogenetic analysis indicated that Ma MR shared the highest similarity with that of Paralichthys olivaceus. The expression of Ma MR was found in all the examined tissues, with the highest expression in the spleen and kidney. After injection with Edwardsiella tarda , the transcript level of Ma MR was initially reduced and then significantly elevated in the liver, spleen, foregut and hindgut. In the isolated peripheral blood leukocytes, the expression of Ma MR was significantly induced post stimulated with LPS and LTA. Then the Ma MR-CTLD4-8 recombinant protein was purified. Bacterial agglutination and binding assay showed that r Ma MR-CTLD4-8 could bind with both Gram-positive and Gram-negative bacteria and agglutinate bacteria in the presence of calcium in vitro. Further analysis revealed that Ma MR and TLR2 coordinately induced the expression of TRAF6 and promoted the phosphorylation level of p65, leading to the expression of proinflammatory cytokines il-1β and tnf-α in EPC cells. Taken together, these results reveal that Ma MR plays an important role in the immune response of fish to pathogen infections. • Mannose receptor (MR) was identified and characterized from Monopterus albus (namely Ma MR). • Ma MR was expressed in all examined tissues and could be induced by bacteria and PAMPs. • Ma MR can agglutinate and bind Gram-positive and -negative bacteria. • Ma MR induced the expression of proinflammatory cytokine with the assistance of TLR2. [ABSTRACT FROM AUTHOR]