L-theanine can alleviate the immune stress response caused by LPS, maintain the α1-acid glycoprotein (α1-AGP) and IL-6 concentrations in serum, and the secretory immunoglobulin A (sIgA) content in the jejunal mucosa [75], inhibit the infection and survival of coccidia in vivo, and improve the non-specific immune response of chickens [76]. Here, IL6 is linked to infection.