Killer T cells
One of the most important roles of the immune system is to clear the body of viruses and cancer cells. This job is performed by killer T cells which hunt down and destroy tumors and virally-infected cells. In this immunofluorescence image, a killer T cell (blue) is engaging a target cell. A patch of signaling molecules (pink) that gathers at the site of cell-cell contact indicates that the CTL has identified a target. Lytic granules (red) that contain cytotoxic components then travel along the microtubule cytoskeleton (green) to the contact site and are secreted, thus killing the target.
Credit: Alex Ritter, Jennifer Lippincott Schwartz and Gillian Griffiths, National Institutes of Health