Intestinal macrophages: differentiation and involvement in intestinal immunopathologies.
Intestinal macrophages, preferentially located in the subepithelial lamina propria, represent the largest pool of tissue macrophages in humans. As an adaptation to the local antigen- and bacteria-rich environment, intestinal macrophages exhibit several distinct phenotypic and functional characteristics. Notably, microbe-associated molecular pattern receptors, including the lipopolysaccharide (LPS) receptors CD14 and TLR4, and also the Fc receptors for IgA and IgG are absent on most intestinal macrophages under homeostatic conditions. Moreover, while macrophages in the intestinal mucosa are refractory to the induction of proinflammatory cytokine secretion, they still display potent phagocytic activity. These adaptations allow intestinal macrophages to comply with their main task, i.e., the efficient removal of microbes while maintaining local tissue homeostasis. In this paper, we review recent findings on the functional differentiation of monocyte subsets into distinct macrophage populations and on the phenotypic and functional adaptations that have evolved in intestinal macrophages in response to their antigen-rich environment. Furthermore, the involvement of intestinal macrophages in the pathogenesis of celiac disease and inflammatory bowel diseases is discussed.
Weber
Benjamin
B
Division of Experimental Pathology, Institute of Pathology, University of Bern, Bern, Switzerland.
Saurer
Leslie
L
Mueller
Christoph
C
D000818:Animals; D000942:Antigens, Bacterial / Q000276:immunology*; D001419:Bacteria / Q000276:immunology*; D002446:Celiac Disease / Q000276:immunology / Q000382:microbiology; D002454:Cell Differentiation / Q000276:immunology*; D016207:Cytokines / Q000276:immunology; D006706:Homeostasis / Q000276:immunology; D006801:Humans; D015212:Inflammatory Bowel Diseases / Q000276:immunology / Q000382:microbiology; D007413:Intestinal Mucosa / Q000276:immunology* / Q000382:microbiology / Q000473:pathology; D018950:Lipopolysaccharide Receptors / Q000276:immunology; D008264:Macrophages / Q000276:immunology* / Q000473:pathology; D010587:Phagocytosis / Q000276:immunology; D017452:Receptors, IgG / Q000276:immunology; D051197:Toll-Like Receptor 4 / Q000276:immunology
D000942:Antigens, Bacterial; D016207:Cytokines; D018950:Lipopolysaccharide Receptors; D017452:Receptors, IgG; C495345:TLR4 protein, human; D051197:Toll-Like Receptor 4