makrophage

Macrophages are large phagocytic cells of the innate immune system that continually survey tissues for pathogens, dead cells, and debris. They originate from monocytes that exit the bloodstream and differentiate into resident macrophages in tissues. As a component of the mononuclear phagocyte system, macrophages are present in virtually all organs, including the liver (Kupffer cells), lungs (alveolar macrophages), brain (microglia), skin (Langerhans cells), and spleen.

Primary functions include phagocytosis and digestion of microbes, clearance of apoptotic cells (efferocytosis), and tissue remodeling during development, infection, and wound healing. Macrophages also function as antigen-presenting cells, expressing MHC class II and co-stimulatory molecules to activate CD4+ T cells, thereby linking innate and adaptive immunity. They secrete a variety of cytokines and chemokines and generate reactive oxygen and nitrogen species to kill ingested microbes.

Macrophages can adopt different functional states driven by signals in the microenvironment. Classical activation (M1) occurs in response to IFN-γ and microbial products such as lipopolysaccharide and is associated with pro-inflammatory and microbicidal activity. Alternative activation (M2) arises with IL-4 and IL-13 and supports tissue repair, anti-inflammatory responses, and resolution of inflammation. In vivo, macrophages often display continuous or mixed phenotypes.

Dysregulated macrophage function contributes to disease. They participate in chronic inflammation and tissue damage, involvement in atherosclerotic plaque formation, and influence tumor progression through tumor-associated macrophages that may promote angiogenesis and immune suppression. Because of their central role, macrophages are frequent targets in therapies aimed at modulating inflammation, infection, and cancer.