Majority of antigen presenting cells (APCs) in intestine is derived from macrophages, which have very quick turnover. Macrophages are prevalent in lamina propria and submucosal deeper layers like muscularis layer. Macrophages can use their trans-epithelial dendrites (long cytoplasmic extensions) and directly contact epithelial layer and sample luminal bacteria. Under healthy conditions macrophages engulf commensal bacteria and surrounding cellular debris, secrete IL-10, drive maturation of Treg and contribute to tissue homeostasis. Because of low expression of innate response receptors and co-stimulatory surface molecules, intestinal macrophages do not initiate inflammation. But upon infection or inflammation, the profile of macrophages changes and they start to secrete large amounts of TNF-"α" and become proinflammatory effector cells.