Classically activated macrophage (M1 phenotype) (M1 macrophage)

The **M1 macrophage** or **classically activated macrophage** refers to a functional state of the innate immune cell known as the macrophage. This phenotype is induced by exposure to interferon-gamma, tumor necrosis factor, and microbial products such as lipopolysaccharide. M1 macrophages are characterized by their high production of pro-inflammatory cytokines—including IL‑6, IL‑12, TNF‑α—and reactive oxygen/nitrogen species. They play key roles in host defense against pathogens through phagocytosis and antigen presentation but can also contribute to tissue damage if their activity is excessive or uncontrolled[1][3][5]. The M1/M2 classification describes cellular states rather than discrete molecular targets; thus “Macrophage M1 phenotype” is not itself a druggable target like a receptor or enzyme[4]. **Note:** “Macrophage M1 phenotype” does *not* refer to a specific molecule or canonical drug target but rather describes one end of the spectrum of functional states that tissue-resident or recruited monocyte-derived cells can adopt in response to environmental cues[4]. Drugs may influence polarization toward this state indirectly via upstream signaling pathways such as TLRs, IFN receptors, NF‑κB pathway modulators etc., but there is no single “M1 receptor” or protein that defines this target for pharmacological intervention. (no direct drugs target the "M1 phenotype" as it is a cell state, but some agents modulate polarization; not applicable; drugs may shift polarization but do not bind to an "M1 receptor")

Other names

M1 phenotypeclassically activated macrophagepro-inflammatory macrophage