Monocytes / Macrophages
Monocytes are white blood cells that originate in the bone marrow and travel through the bloodstream to tissues throughout the body where they mature and differentiate into tissue-specific macrophages. Monocytes and macrophages are phagocytes that act in both a non-specific defense mode (innate immunity) and help to initiate specific defense mechanisms (adaptive immunity). Macrophages are professional antigen-presenting cells (APCs). After digesting a pathogen, a macrophage displays a fragment of the antigen to a corresponding helper T cell. In addition, monocytes and macrophages release substances including enzymes, complement proteins and regulatory factors that stimulate other cells of the immune system.