Intestinal Microbiota as Modulators of the Immune System and Neuroimmune System: Impact on the Host Health and Homeostasis

Figure 1

The functional interaction between microbiota and intestinal immune system. The evolutionary balance is formed over time, being modulated by the environmental pressure. Gut microbiota and gut environment are developed together, fitting for the benefit of both or tolerating each other. The immune system monitors the interaction to ensure homeostasis and contributes to symbiosis. However, the unbalance caused when dysbiosis is installed may cause the immune system reaction. Symbiosis and dysbiosis depend on balance between commensal and pathogenic bacteria. Commensal bacteria promote an anti-inflammatory environment. In a symbiosis context, MAMPs continuously stimulate IECs to secrete molecules that act protecting the epithelium and producing a tolerogenic environment. In dysbiosis, there is a significant liberation of MAMPs that can induce IECs, activated DCs, and macrophages to secrete inflammatory cytokines. Consequently, a development of immune effectors is generated. IL-22 is produced in both situations, but its contribution to epithelial barrier improvement is controlled by immune regulation. M: macrophage; Comm: commensal bacteria; Patho: pathogenic bacteria.