Classically activated macrophage (M1-like macrophage) (M1)

M1-like macrophages, also known as classically activated macrophages, represent a pro-inflammatory phenotype of the monocyte-macrophage lineage that is essential for host defense against pathogens and tumor cells (Murray, 2017). These cells are typically induced by Th1-type cytokines such as interferon-gamma (IFN-γ) or by recognition of pathogen-associated molecular patterns (PAMPs) like lipopolysaccharide (LPS) through Toll-like receptors (TLRs) (Shapouri-Moghaddam et al., 2018). Once polarized, M1-like macrophages exhibit high microbicidal and tumoricidal activity, characterized by the secretion of pro-inflammatory cytokines (e.g., TNF-α, IL-12, IL-1β) and the production of reactive oxygen and nitrogen species, such as nitric oxide via inducible nitric oxide synthase (iNOS) (Yunna et al., 2020). In oncology, M1-like macrophages are generally associated with anti-tumor immunity and improved patient prognosis, as they can present antigens to T cells and promote a Th1-polarized immune response (Vitale et al., 2019). Therapeutic strategies often aim to repolarize immunosuppressive M2-like tumor-associated macrophages (TAMs) toward an M1-like state using TLR agonists, CD40 antibodies, or cytokine-based therapies to enhance the efficacy of immunotherapies. However, excessive or chronic M1 activation can lead to significant tissue damage and is a key driver in the pathogenesis of various autoimmune and chronic inflammatory diseases (Shapouri-Moghaddam et al., 2018).

Other names

M1 macrophagePro-inflammatory macrophageM1-polarized macrophageClassically activated macrophage

Induction of pro-inflammatory polarization and activation via TLR, CD40, or cytokine receptor signaling pathways