Chapter 2 - Basic biology of macrophages

Abstract

Macrophages are the most numerous and professional tissue-resident phagocytes and are critical players in diverse functional activities to maintain tissue integrity and to regulate the inflammation or disease. Macrophages have the central role in immune defense mechanism. Studies on macrophage biology and differentiation explore the pleiotropic actions of these cells. The mononuclear phagocyte system is the key regulator of macrophage lineage development. The progenitors of macrophages are seeded within tissues during embryogenesis. Three distinct origins of macrophages include (1) yolk sac, (2) fetal liver, and (3) bone marrow. Differentiation of macrophages from monocytes occurs in different functional phenotypes of the tissue depending on microenvironmental stimuli. The polarized and activated phenotypes are responsible for the many and apparently opposed macrophage functions. Progress has now been made on versatile biological and functional phenomenon of macrophages but is still to be elucidated. To attain this, the basic biology of macrophages must be fully understood. The aim of this chapter is to highlight that context for the reader.