TY - CHAP M1 - Book, Section TI - Structure, Receptors, and Functions of Monocytes and Macrophages A1 - Douglas, Steven D. A1 - Douglas, Anne G. A2 - Kaushansky, Kenneth A2 - Lichtman, Marshall A. A2 - Prchal, Josef T. A2 - Levi, Marcel M. A2 - Press, Oliver W. A2 - Burns, Linda J. A2 - Caligiuri, Michael PY - 2015 T2 - Williams Hematology, 9e AB - SUMMARYThe monocyte is a spherical cell with prominent surface ruffles and blebs when examined by scanning electron microscopy. As the monocyte enters the tissue and differentiates into a macrophage, the cell volume and number of cytoplasmic granules increase. Cell shape varies, depending on the tissue in which the macrophage resides (e.g., lung, liver, spleen, brain). A characteristic feature of macrophages is their prominent electron-dense membrane-bound lysosomes, which can be seen fusing with phagosomes to form secondary lysosomes. The latter contain ingested cellular and noncellular material in different stages of degradation. A broad range of surface receptors for many ligands, including the Fc portion of immunoglobulin, complement proteins, cytokines, chemokines, lipoproteins, and others, are on the cell surface. Macrophages differ in appearance, biochemistry, and function based on the environment in which they mature from monocytes. These differences are exemplified by the diversity among dendritic cells of lymph nodes, histiocytes of connective tissue, osteoclasts of bone, Kupffer cells of liver, microglia of the central nervous system, and macrophages of the serosal surfaces, each fashioned to meet the local needs of the mononuclear phagocyte system, which plays a role in inflammation and host defense against microbes. Modern cell biologic methods refined our knowledge of surface receptors, endocytosis, and lysosomal degradation, with emphasis on membrane flow and secretion. These pioneering studies culminated in the discovery of dendritic cells as potent, specialized antigen-presenting cells. Subsequent development of monoclonal antibodies and molecular cloning of surface proteins and cytokines, followed by microarray analysis and genomics, provided the sensitive and specific tools to analyze macrophage functions in vitro and in vivo. These studies have brought insights into macrophage cytotoxic and antimicrobial activities and, to a lesser extent, their trophic, homeostatic functions in the body. Macrophages play a major role in innate as well as adaptive immunity. SN - PB - McGraw-Hill Education CY - New York, NY Y2 - 2024/10/15 UR - hemonc.mhmedical.com/content.aspx?aid=1121096305 ER -