Macrophages are large immune cells that play a crucial role in the body's defense against pathogens by engulfing and digesting them. These cells are derived from monocytes and are found throughout the body, particularly in tissues, where they help to identify and eliminate harmful microorganisms, dead cells, and debris through processes like phagocytosis. Their ability to both consume pathogens and present antigens makes them key players in coordinating the immune response.