Natural killer T cells, computer illustration. Natural killer T cells are a group of T cells that share properties of both T cells and natural killer (NK) cells. NK cells and T cells are both types of white blood cell (leukocyte) and are part of the immune system. NK cells provide rapid responses to virus-infected cells. T cells recognise a specific site (antigen) on the surface of a pathogen or foreign object, bind to it, and attract antibodies or cells to eliminate it.