L-theanine improves immunity by altering th2/th1 cytokine balance, brain neurotransmitters, and expression of phospholipase c in rat hearts

Abstract

Background: This study aimed to investigate the regulatory effects of L-theanine on secretion of immune cytokines, hormones, and neurotransmitters, and mRNA expression of phospholipase C (PLC) in rats, and to explore its regulatory mechanism in immune function. Material/Methods: Sixty-four Sprague-Dawley rats received daily intragastric infusion of different doses of L-theanine solution [0, 50 (LT), 200 (MT), and 400 (HT) mg/kg BW]. Cytokines, immunoglobulins, and hormones in the serum, neurotransmitters, and mRNA expression of PLC in the relevant tissues were assayed. Results: L-theanine administration increased the splenic organ index and decreased the contents of ILs-4/6/10 and the ratio of IL-4/IFN-g in the serum. High-dose L-theanine administration increased the levels of dopamine and 5-hydroxytryptamine in the pituitary and hippocampus, resulting in decrease in corticosterone level in the serum. L-theanine administration decreased the mRNA expressions of PLC isomers in the liver and PLC-g1 and PLC-d1 in the spleen. Interestingly, mRNA expressions of PLC-b1 in the spleen and PLC isomers mRNA in the heart were up-regulated by L-theanine administration. Conclusions: Administration of 400 mg/kg BWL-theanine improved immune function of the rats by increasing the splenic weight, altering the Th2/Th1 cytokine balance, decreasing the corticosterone level in the serum, elevating dopamine and 5-hydroxytryptamine in the brain, and regulating the mRNA expression of PLC isomers in the heart.