"The macrophages and the neutrophils arrive. The macrophages engulf the invading organism and digest them by a process called phagocytosis. Macrophages are like scavengers, ridding the body of worn-out cells, debris and other foreign invaders. Macrophages are able to display a part of the invading organism on its surface as a signal to other cells that the body is infected. This process is called antigen presentation."