Orange-spotted grouper (Epinephelus coioides) NADPH oxidase: Cloning and expression analysis after Cryptocaryon irritans infection.

Phagocytic cells are activated to produce a large amount of reactive oxygen species (ROS) that kill pathogens quickly and efficiently through oxidation. NADPH oxidase is the main source of intracellular ROS. In the present study, five subunits of the phagocytic NADPH oxidase complex were identified in orange-spotted grouper (Epinephelus coioides). The open reading frame of grouper gp91phox, p22phox, p67phox, p47phox, and p40phox were 1,698 bp, 564 bp, 1,497 bp, 1,290 bp, and 1,050 bp, respectively, and encoded 565, 187, 498, 429, and 349 amino acids. Evolutionary analysis indicated that these proteins are evolutionarily homologous to the corresponding proteins of other fish and mammals, and contain conserved functional domains and sites that are important in mammals. In addition, real-time polymerase chain reaction analysis showed that the expression of these five genes was higher in immune-related tissues in normal grouper, and that these genes were up-regulated in gill and spleen after C. irritans infection, which suggests that these genes may be involved in the defense against C. irritans infection.