Transmission electron micrograph (TEM) of the ultrastructure of a macrophage containing lysosomes (grey, dark grey) and many vesicles, both representing the phagocytic and digestive functions of this cell. These cells are common in connective tissues and extracellular spaces. Motile and phagocytic, they engulf and digest dead or dying cells, or extracellular debris. They are important in immune responses where they may destroy pathogens, or act as antigen-presenting cells. Magnification: x4,400 when width printed at 10 cm wide.