Acetylcholine modulates the immune response in Zhikong scallop Chlamys farreri

Acetylcholine (ACh) is an indispensable neurotransmitter and neuromodulator in the cholinergic nervous system and it is implicated in the dynamic modulation of immune response in vertebrates. Although ACh has also been identified in most invertebrates, the knowledge about its immunomodulation is still limited. In the present study, the immunoreactivities of ACh and acetylcholinesterase (AChE) were observed in all the tested tissues of scallop Chlamys farreri, including adductor muscle, mantle, gill, hepatopancreas, kidney and gonad. The ACh concentration in the supernate of scallop hemolymph increased from 11.59 ± 0.27 to 14.36 ± 0.17 μM L−1 at 6 h after LPS (0.5 mg ml−1) stimulation, and increased to 15.51 ± 1.20 μM L−1 at 3 h after the stimulation of tumor necrosis factor alpha (TNF-α) (50 ng ml−1). After LPS stimulation, the mRNA expression levels of superoxide dismutase (CfSOD), catalase (CfCAT) and lysozyme (CfLYZ) in hemocytes increased significantly at 3 h (P < 0.05), 6 h (P < 0.05) and 12 h (P < 0.05), respectively. Compared with the LPS treatment, the induction of CfSOD, CfCAT and CfLYZ expression in hemocytes was repressed effectively (P < 0.05) by the co-stimulation of LPS and ACh (5 × 10−7 M) at 3 h (P < 0.05), 6 h (P < 0.05) and 12 h (P < 0.05), respectively. Furthermore, the expression level of CfCAT in hemocytes increased significantly after 12 h by the co-stimulation with LPS and ACh (P < 0.05). These results indicated collectively that the scallop cholinergic nervous system could be activated by immune stimulations, and it might play an essential role in immunomodulation of scallops.