NO production of granulocytes associated with antibacterial immune response in Tegillarca granosa

Nitric oxide (NO) is a signaling molecule and immune effector produced by the nitric oxide synthases (NOS), which involved to various physiological processes of animals. In marine bivalves, hemocytes play important roles in antimicrobial innate immune response. Although hemocyte-derived NO has been detected in several bivalves, the immune function of hemocyte-derived NO is not well understood. Here, we investigated the antibacterial response of hemocyte-derived NO in the blood clam Tegillarca granosa. Two types of hemocytes including erythrocytes and granulocytes were isolated by Percoll density gradient centrifugation, their NO production and TgNOS expression level were analyzed. The results showed that NO was mainly produced in granulocytes and almost no detected in erythrocytes. The granulocytes showed significantly higher NO level and TgNOS expression level than the erythrocytes. And the TgNOS expression level was significantly increased in granulocytes after Vibro parahemolyticus challenge. In addition, the NO donor sodium nitroprusside (SNP) significantly increased the NO production of hemocytes to kill pathogenic bacteria. In summary, the results revealed that granulocytes-derived NO play vital roles in the antimicrobial immune response of the blood clam.