Abstract: Objective: To investigate immune modulation and inflammatory inhibition of soybean protein and soybean oligopeptides on Staphylococcus aureus-induced epidermal trauma in aged mice with negative nitrogen balance. Methods: Mice were divided into four groups: blank control group (positive nitrogen balance), model group (negative nitrogen balance), soybean protein group (administration with soybean protein plus negative nitrogen balance), soybean oligopeptides group (administration with soybean oligopeptides plus negative nitrogen balance), among them, the total nitrogen content of the liquid in the soybean protein group and the soybean oligopeptides group was equal, calculated as body mass of 650 mg/kg. The mice were orally administered after back epidermal wound infection with Staphylococcus aureus. The effects of soybean protein and soybean oligopeptides on humoral immunity level, inflammation inhibition and rectus muscle mass were investigated. Results: Low protein diet significantly reduced body mass, nitrogen intake and total serum protein in mice (P < 0.05). Soybean protein and soybean oligopeptides significantly increased the serum levels of immunoglobulin (Ig) M, IgG and IgA (P < 0.05), and significantly reduced the contents of macrophage inflammatory protein-2 (MIP-2) and RANTES (P < 0.05), decreased the contents of interleukin (IL)-1β, IL-6 and TNF-α but without any significant difference, and significantly augmented the ratio of rectus femoris to body mass (P < 0.05). Compared with soybean protein, soybean oligopeptides significantly increased serum IgG level, and significantly reduced MIP-2 level (P < 0.05). Conclusion: Soybean protein and soybean oligopeptides can significantly enhance humoral immune function, inhibit inflammatory response and restore muscle atrophy. Soybean oligopeptides can enhance humoral immune function and inhibit early inflammatory response more significantly than soy protein.

Key words: soybean protein, soybean oligopeptides, negative nitrogen balance, Staphylococcus aureus, immunomodulatory effect, inflammation