Cytotoxic T lymphocytes (CTLs) are a type of white blood cell that play a crucial role in the immune system. They are primarily responsible for identifying and destroying infected or cancerous cells. CTLs recognize specific antigens presented on the surface of these target cells, which are often derived from viruses or abnormal proteins. Once activated, CTLs release toxic substances that induce apoptosis, or programmed cell death, in the infected or malignant cells. This process helps to eliminate threats to the body and maintain overall health. CTLs are a vital component of the adaptive immune response, working alongside other immune cells like helper T cells and B cells.