Immunomodulatory activity of low molecular-weight peptides from Nibea japonica skin in cyclophosphamide-induced immunosuppressed mice

In this study, a low molecular weight peptides fraction (<3 kDa, named NJSP) was isolated and purified from the skin protein hydrolysate of Nibea japonica by ultrafiltration. The in vivo immunomodulatory effects of NJSP were investigated in cyclophosphamide (CY)-induced immunosuppressed mice. The intragastric administration of NJSP (100, 200, 400 mg/kg/d) upregulated the immune organ indexes, restored the pathological histomorphology of immune organs, and improved the body weight of CY-treated mice in a time and dose-dependent manner. NJSP treatment also remarkably promoted the proliferation of splenocyte, enhanced phagocytosis of macrophages, restored delayed-type hypersensitivity (DTH). Moreover, NJSP administration dramatically improved hemolysin, tumor necrosis factor α (TNF-α), immunoglobulin (Ig) A, IgG and IgM levels in blood serum in a dose-dependent manner. Besides, NJSP also significantly increased the activities of superoxidase dismutase (SOD) and catalase (CAT), improved the total antioxidant capacity (T-AOC), and decreased malondialdehyde (MDA) levels in blood serum. These findings confirm that NJSP can protect the immune system against oxidative damage to maintain homeostasis. Finally, NJSP can serve as a promising immunomodulator with potential application in functional food and nutraceutical industry.