Even though further studies are needed to mechanistically explain how dietary amino acids can control macrophage activity, it has been demonstrated that (1) they stimulate the replenishment of intestinal macrophages and their IL-10 secretion [51]; (2) arginine, glutamine and tryptophan are able to promote macrophages phagocytic activity [52]; and (3) in IL-10−/− mice, histidine inhibits the production of pro-inflammatory cytokines (TNF-α and IL-6), through the suppression of NF-κB activation, thus counteracting colitis development [50,53,54]. The gene discussed is IL10; the disease is colitis.