The immunomodulation of inducible nitric oxide in scallop Chlamys farreri

Nitric oxide (NO) is an important signalling molecule which plays an indispensable role in immunity of all vertebrates and invertebrates. In the present study, the immunomodulation of inducible NO in scallop Chlamys farreri was examined by monitoring the alterations of haemocyte behaviours and related immune molecules in response to the stimulations of LPS and/or with S-Methylisothiourea Sulphate (SMT), an inhibitor of inducible NO synthase (NOS). The total activity of NOS and NO concentration in the haemolymph of scallop C. farreri increased significantly at 3, 6 and 12 h after LPS stimulation respectively, whereas their increases were fully repressed when scallops were treated in the collaborating of LPS and SMT. Meanwhile, some cellular and humoral immune parameters were determined after the stimulation of LPS and SMT to investigate the role of inducible NO in innate immunity of scallop. After LPS stimulation, the highest levels of haemocytes apoptosis and phagocytosis were observed at 24 h (38.5 ± 2.5%, P < 0.01) and 12 h (38.6 ± 0.2%, P < 0.01), respectively, and the reactive oxygen species (ROS) level (5.88 ± 0.90%, P < 0.01) of haemocytes and anti-bacterial activity of haemolymph (10.0 ± 2.2%, P < 0.01) all elevated dramatically at 12 h. Although the activity of lysozyme and phenoloxidase (PO) in haemolymph both declined at 48 h (93.0 ± 6.3 U mgprot−1, 0.40 ± 0.06 U mgprot−1, P < 0.01), superoxide dismutase (SOD) activity and GSH concentration both increased to the highest level at 24 h post treatment (99.2 ± 8.1 U mgprot−1, 93.0 ± 6.3 nmol mgprot−1, P < 0.01). After the collaborating treatment of LPS and SMT, the apoptosis index increased much higher from 48 h, while the increase of haemocytes phagocytosis, ROS level and haemolymph anti-bacteria activities were suppressed completely at 12 h. The declines of lysozyme and PO activity in haemolymph were reversed at 48 h, and the rise of SOD activity and GSH concentration started earlier from 3 h. These results indicated clearly that NO could participate in the scallop immunity and play a crucial role in the modulation of immune response including haemocytes apoptosis and phagocytosis, anti-bacterial activity and redox homeostasis in the haemolymph of scallop.