Macrophages are a type of white blood cell that eat foreign material in the body. These cells are involved in primary or innate immune response to a number of immune invaders , and that also form an important part of body acquired immune system . At one point , macrophages act in many corners of the body , quietly clean foreign debris , bacteria and viruses before they have a chance to cause a problem. Monocytes and macrophages are phagocytes .