Phagocytes in Inflammation

Neutrophils and macrophages are phagocytic cells that comprise the cellular components of the mammaLian innate immune system. Phagocytes are bone marrow-derived cells that respond to pathogen-derived chemoattractants to migrate to sites of infection within the tissue. Phagocytes utiLize immune receptors on their plasma membranes to recognize pathogens coated with immunoglobuLin G antibody molecules or complement. Cross-Linking of these receptors initiates the internaLization of the pathogens into an intracellular compartment. The process of internaLization is called phagocytosis, and the intracellular compartment is termed a phagosome. Phagosomes fuse with subcellular granular structures that contain the phagocyte's kilLing armamentarium, which includes a variety of toxic acid hydrolases, proteins, and peptides that destroy the internaLized pathogens. Additionally, phagocytes produce several reactive oxygen intermediates, including superoxide, hydrogen peroxide, and hypochlorous acid, that have deleterious effects on the ingested microbes. These antimicrobial substances can cause tissue injury in inflammatory-based diseases when they leak from the forming phagosome. This leakage may occur when subcellular vacuoles containing the toxic agents fuse with the forming phagosome before it has fully enclosed its target. Thus, phagocytes serve an essential protective role but also can exacerbate disease when their antimicrobial constituents are released inappropriately or excessively.