Macrophages are phagocytic cells capable of engulfing dead cells and foreign substances. Macrophage cells are key players in the immune response, by ridding the body of worn-out cells, foreign substances, microbes and cancer cells, and alerting the immune system to the presence of invaders. Because human macrophages possess the ability to eliminate pathogens and recruit and instruct other immune cells, they play a central role in protecting the body and contribute to the pathogenesis of inflammatory and degenerative diseases.