Cytotoxic T-cells or CTLs are specialized immune cells that play a critical role in protecting the body against infections and diseases. Their main function is to kill cancerous or infected cells, including those containing intracellular pathogens like viruses or bacteria. CTLs are a type of T lymphocyte and work alongside other types of immune cells, such as helper T cells and natural killer cells, to respond to threats in the body. These killer cells function by interacting and communicating with their targets, and are essential components of both the innate and adaptive immune system. CTLs are also responsible for eliminating substances deemed harmful by the immune system, making them a vital part of the body's defense mechanism.