NOS2 and Salmonella Infections: Exogenous IAA intervention significantly reduced Salmonella infection-induced intestinal pro-inflammatory responses, as evidenced by the decreased numbers of F4/80-positive macrophages (Figure 5I), the downregulated mRNA (Il1b, Il6, Il18, Tnfa, Nos2) expression (Figure 5H), and the reduced protein (Nos2, Il1b, Il6, Tnfa, markers of pro-inflammatory macrophages) expression (Figure 5I).