Effects of interactions between intestinal microbiota and intestinal macrophages on health

Macrophages reside in every tissue of the body and play an important role in maintaining homeostasis. The intestinal mucosa is the largest immune organ and harbors macrophages in abundance. Dysfunction of intestinal macrophages is characteristic of patients with certain inflammatory bowel diseases. Although intestinal macrophages exhibit hyporesponsiveness to foreign substances, including various bacterial products, their physiological functions are unknown, but may be related to the contribution of intestinal bacteria to the maintenance of various physiological functions of the host. Moreover, recent reports suggest that there are associations between intestinal microbiota and the onset of pathologies, such as diverse metabolic syndromes, depression, and cancer. Evidence indicates that the host's immune response to intestinal microbiota may be etiologically-linked to these diseases; however, the mechanisms are poorly understood. In the present review, we discuss the possibility that intestinal microbiota influence health through the function of intestinal macrophages.