monocytemacrophage

Monocyte/macrophage refers to a linked set of cells within the mononuclear phagocyte system that participate in innate immunity, tissue homeostasis, and antigen presentation. Monocytes are circulating white blood cells produced in the bone marrow from hematopoietic stem cells. In response to inflammatory cues, they migrate from blood into tissues where they differentiate into macrophages or dendritic cells. In many tissues, resident macrophages also originate from embryonic precursors and can self-renew, independently of circulating monocytes.

Macrophages are versatile phagocytes that engulf pathogens, dead cells, and debris. They act as antigen-presenting cells by expressing major histocompatibility complex class II molecules and costimulatory signals that help activate T cells. Macrophages secrete a broad repertoire of cytokines and chemokines, shaping inflammation and recruiting other immune cells. They also contribute to tissue remodeling, wound healing, and the clearance of apoptotic cells during homeostasis.

Functional diversity and activation states are influenced by the tissue environment. The classic M1/M2 polarization framework is commonly cited but can oversimplify in vivo phenotypes, which range along a spectrum depending on signals such as IFN-γ, lipopolysaccharide, IL-4, IL-13, and the local milieu.

Clinically, monocytes and macrophages play central roles in host defense and in various diseases. They participate in chronic inflammatory conditions, atherosclerosis, infections such as tuberculosis, and tumor biology. Researchers study monocyte-derived macrophages to understand innate immunity and to develop therapies targeting macrophage function.