This study was conducted to investigate impacts of arginine supplementation on intestinal microbiota and innate immunity in mice.We studied the microbiota composition,as well as the activation of innate immunity,such as the expression of toll-likes receptors (TLRs),proinflammatory cytokines and Paneth antimicrobials,in the jejunum,ileum or colon in mice receiving arginine supplementation or a control diet for 14 d.Meanwhile,signal transduction pathway activation in the jejunum and ileum,including TLR4- nuclear factor kappa B (NF-kB),mitogen-activated protein kinases (MAPK),phosphoinositide-3-kinases (PI3K)/PI3K-protein kinase B (Akt),was analyzed.qPCR analysis of arginine supplemented mice showed a shift in the Firmicutes:Bacteroidetes ratio in favor of Bacteroidetes in the jejunum and ileum (P<0.05),compared with the control group.This finding coincided with greater innate immune activation,including TLRs signaling,proinflmmatory cytokines expression,and the expression of SIgA,mucins and Paneth antimicrobials in the jejunum and ileum (P<0.05).Finally,arginine supplementation inhibited the activation of NF-kB,MAPK,and PI3K-Akt signaling pathway,except p38 MAPK in the jejunum and JNK in the ileum (P<0.05).Collectively,arginine supplementation changed the intestinal microbiota,contributing to the activation of intestinal innate immunity,through NF-kB,MAPK,and PI3K-pAkt signaling pathways.