NK cells are cytotoxic lymphocytes that patrol the body, identifying and eliminating harmful cells lacking normal "self" markers. They recognize and kill tumor or infected cells using activating and inhibitory receptors, serving as a fast-acting, non-specific immune response. https://www.edocr.com/v/lpnglm6o/xelleratherapeutics/natural-killer-cells-the-bodys-frontline-defenders