Two types of TNF-α and their receptors in snakehead (Channa argus): Functions in antibacterial innate immunity

Tumor necrosis factor-alpha (TNF-alpha) is a pluripotent mediator of pro-inflammatory and antimicrobial defense mechanisms and a regulator of lymphoid organ development. Although two types of TNF-alpha have been identified in several teleost species, their functions in pathogen infection remain largely unexplored, especially in pathogen clearance. Herein, we cloned and characterized two types of TNF-alpha, termed shTNF-alpha 1 and shTNF-alpha 2, and their receptors, shTNFR1 and shTNFR2, from snakehead (Channa argus). These genes were constitutively expressed in all tested tissues, and were induced by Aeromonas schubertii and Nocardia seriolae in head kidney and spleen in vivo, and by lipoteichoic acid (LTA), lipopolysaccharides (LPS), and Polyinosinic-polycytidylic acid [Poly (I:C)] in head kidney leukocytes (HKLs) in vitro. Moreover, recombinant shTNF-alpha 1 and shTNF-alpha 2 upregulated the expression of endogenous shTNF-alpha 1, shTNF-alpha 2, shTNFR1, and shTNFR2, and enhanced intracellular bactericidal activity, with shTNF-alpha 1 having a greater effect than shTNF-alpha 2. These findings suggest important roles of fish TNF alpha 1, TNF alpha 2, and their receptors in bacterial infection and pathogen clearance, and provide a new insight into their function in antibacterial innate immunity.