l-Theanine alleviates heat stress-induced impairment of immune function by regulating the p38 MAPK signalling pathway in mice

With the current trend of global warming, heat stress-induced impairment could seriously endanger human health. l-Theanine is a non-protein amino acid in tea with various biological activities, including immunoregulatory, anti-anxiety, and anti-oxidation. However, its effect on immune function under heat stress and the underlying mechanism are currently unclear. In this study, male BALB/c mice were used as experimental objects to explore the effect of l-theanine on heat stress-induced changes in immune function and its mechanism. Three doses of l-theanine were used: low (100 mg kg(-1) d(-1)), medium (200 mg kg(-1) d(-1)), and high (400 mg kg(-1) d(-1)). Treatment with l-theanine could attenuate the heat stress-induced reductions in body weight and feed intake in mice, alleviate damage in the liver and jejunum, and inhibit the inflammatory factors IL-6, IL-1 beta, and TNF-alpha. Aspartate aminotransferase and alanine transaminase activity levels and the malondialdehyde content decreased, while the IgA, IgM, and IgG contents increased in response to l-theanine. It is possible that l-theanine affects the P38 signalling pathway and inhibits the increase in p-P65/P65 caused by the overexpression of HSP27 and regulation of PPAR-gamma and Foxp3 proteins, thereby alleviating immune dysfunction caused by heat stress.