Figure 2.

Immunosensory detection of intestinal bacteria. Surface enterocytes secrete many immune mediators in response to antigens, including antibacterial peptides, immunoglobulin A (IgA) and chemokines. Specialized epithelial cells, termed M cells, transport and deliver antigens to antigen-presenting cells, which subsequently process antigens and present them to naïve T cells. Antigen-presenting dendritic cells (DCs) also survey and sample the mucosal microenvironment. Pattern recognition receptors (PRRs) expressed by DCs and enterocytes mediate the detection of bacterial antigens, and DCs modulate immune responsiveness or tolerance by promoting either effector or regulatory T cells.