macròfags

Macrophages are versatile cells of the innate immune system that reside in virtually all tissues and originate from the myeloid lineage. In adults, tissue-resident macrophages come from embryonic progenitors or circulating monocytes that differentiate upon entering tissues. They perform housekeeping and defense roles, including surveillance, phagocytosis of pathogens and dead cells, and support of tissue remodeling.

Function and mechanisms. Macrophages are professional phagocytes that ingest bacteria, debris, and infected or dying cells. They destroy ingested material in phagolysosomes and generate reactive oxygen and nitrogen species. They also clear apoptotic cells in a process called efferocytosis, which helps prevent inflammation. Beyond killing, they process and present antigens to T cells via MHC class II molecules and secrete a broad spectrum of cytokines and chemokines that regulate inflammation and recruit other immune cells. They express a range of receptors, including scavenger receptors, toll-like receptors, and Fc receptors, and respond to signals in the tissue microenvironment.

Development and diversity. Macrophages include tissue-resident populations such as Kupffer cells in the liver, microglia in the brain, alveolar macrophages in the lungs, and Langerhans cells in the skin, as well as monocyte-derived macrophages that infiltrate tissues during inflammation. Phenotypic activation is influenced by local cues; they can adopt pro-inflammatory (often termed M1) or anti-inflammatory/tissue-remodeling (often termed M2) programs, though the in vivo spectrum is more nuanced than a strict binary.

Clinical relevance. Macrophages defend against infections and help with tissue repair, but they can contribute to disease when dysregulated, including chronic inflammatory conditions, atherosclerosis, obesity, and cancer through tumor-associated macrophages. Their functions and markers (such as CD14, CD68, CD163, and CD206 in humans) reflect their diverse roles across tissues.