Abstract: An enzymatic protein hydrolysate from Cyclina sinensis was prepared by treatment with pepsin. The hydrolysate was fractionated by ultrafiltration into five fractions (CSP-1–CSP-5). CSP-5 was found to be most effective in promoting cell proliferation as determined by methyl thiazolyltetrazolium (MTT) assay. To further evaluate its immunomodulatory activity, the effects of CSP-5 on the growth and proliferation, morphology, phagocytic activity, nitric oxide (NO) and cytokines secretion of RAW264.7 macrophages were detected by MTT assay, inverted microscope observation, neutral red phagocytosis assay, nitric acid reductase method and enzyme-linked immunosorbent assay (ELISA), respectively. The effects on the cell cycle distribution of macrophages were also observed. Our results showed that CSP-5, with molecular mass less than 3 kDa, could significantly promote the growth and proliferation of RAW264.7 macrophages, mainly at the G0/G1 phase. The cell phagocytosis, and NO and cytokine secretion capacity were also enhanced by CSP-5. Furthermore, morphological observation showed that macrophages became larger with more pseudopods after treatment with CSP-5. It is clear that the peptide obtained in this study has the potential to activate macrophages and enhance immune function.

Key words: enzymatic hydrolysis, Cyclina sinensis peptides, RAW264.7 macrophages, immunomodulatory effects