Cytotoxic T lymphocytes (CTLs) are a type of white blood cell that play a crucial role in the immune system. They are responsible for identifying and destroying infected or cancerous cells. CTLs recognize these harmful cells by detecting specific proteins, known as antigens, presented on their surfaces. Once activated, CTLs release toxic substances that induce cell death, effectively eliminating the threat. They are essential for controlling viral infections and preventing the spread of tumors. The activation and function of CTLs are influenced by other immune cells, such as helper T cells and dendritic cells.