Macrophage engulfing bacterium. Artwork of a section through a macrophage (center) engulfing a bacterium (bottom). The macrophage pseudopod is seen here extending over the bacterial cell wall (green) and flagellum. Within the bacterium can be seen its cytoplasm (purple) and nucleus (red and orange). Above is the blood serum (yellow and brown). Macrophages are a type of white blood cell (leucocyte) which defends the body against invading micro-organisms. When a macrophage encounters a pathogen, it engulfs and destroys it, a process called phagocytosis. This image is the third in a series of three. See also P276/201 & P276/202.