Cells of the immune system protect the body against pathogens. If cells in our bodies are infected by viruses, or become cancerous, then killer cells of the immune system identify and destroy the affected cells. Cytotoxic T cells are very precise and efficient killers. They are able to destroy infected or cancerous cells, without destroying healthy cells surrounding them…Cytotoxic T cells are just 10 microns in length: approximately one-tenth the width of a human hair. These movies are 92 times real time.