Abstract: Tyrosine-rich peptide of immunostimulating (Trpi) which is a novel casein-derived antimicrobial peptide with obvious antimicrobial and immunostimulating property was separated from tryptic casein hydrolysates. Antimicrobial activi- ties of rude and purified Trpi were proved by the agar diffusion test, and the purity of purified Trpi which was 86.45% was analyzed by the capillary electrophoresis (CE). The results about the effects of rude and purified Trpi on body weight, spleen index, thymus index and lymphoproliferation activity of mice, indicated that Trpi didn’t affect body weight, but enhanced observably the spleen index (p<0.01) and thymus index (p<0.01), and improved dramatically lymphoproliferation activity (p<0.001, SI=2.13). Compared to the control, Trpi promoted significantly the release of IL-1β(p<0.001), IL-6 (p <0.001)and IL-10 (p<0.01)and affected faintly the level of IL-4 by three different ways: oral, intraperitoneal injection and Caudal vein injection, however, it had no effect on TNF-α, IFN-γ and TGF-α. The order of intension on cytokines was intraperitoneal injection, cudal vein injection and oral. Therefore, it was possible that Trpi affected mainly the levels of mice’s cytokines through mucosal immune. In conclusion, the research revealed that antimicrobial peptide Trpi’s immunostimulating function was possibly associated with the cytokine network of mucosal system.

Key words: casein, tyrosine-rich peptide of immunostimulating (Trpi), immunomodulatory peptides, immune function