L-Theanine Modulates Intestine-Specific Immunity by Regulating the Differentiation of CD4+ T Cells in Ovalbumin-Sensitized Mice.

Ovalbumin (OVA), a common food protein, can cause deadly allergies with intestine-specific immune reactions. L-Theanine (LTA) shows great potential for regulating intestinal immunity. To investigate the regulatory effect of LTA intervention on intestine-specific immunity, a 41 day experiment was performed on BALB/c OVA-sensitized mice. The results show that injecting female mice intraperitoneally with 50 μg of OVA and administering 30 mg of OVA 4 times can successfully establish an OVA-sensitized mouse model. LTA intervention significantly increased weight gain and thymus index ( p < 0.05), decreased allergy and diarrhea scores ( p < 0.05), and improved jejunum structure. Meanwhile, the histological score and degranulation of mast cells decreased. LTA intervention increased Clostridiales , Lachnospiraceae , Lactobacillus , Prevotella , and Ruminococcus abundance while decreasing Helicobacter abundance . Flow cytometry and Western blotting results indicated that 200 and 400 mg/kg of LTA upregulated the expression of T-bet and Foxp3 proteins ( p < 0.05), thus promoting the differentiation of jejunum CD4+ T cells to Th1 and Tregs and increasing the cytokines IFN-γ, IL-10, and TGF-β ( p < 0.05). We found that 200 and 400 mg/kg of LTA downregulated the expression of RORγt and GATA3, thus inhibiting the differentiation of Th2 and Th17 cells and decreasing cytokines IL-4, IL-5, IL-13 TNF-α, IL-6, and IL-17A ( p < 0.05). LTA inhibited the degranulation of mast cells and significantly decreased the serum levels of OVA-IgE, HIS, and mouse MCPT-1 ( p < 0.05). Therefore, LTA intervention alleviated OVA allergy by improving intestine-specific immunity.