I'm a Macrophage. I am a type of white blood cell that catches and kills foreign bodies, such as bacteria, and determines the type of antigens and information about the immune response. I also act as a cleaner, removing the remains of dead cells and bacteria. My second form is a Monocyte. Monocytes originate from the bone marrow and float in the blood, but turn into Macrophages as soon as they leave the blood vessel.