Natural killer (NK) cells, also known as large granular lymphocytes (LGL), are defined as a type of cytotoxic lymphocyte which is critical to the innate immune system in the human body. NK cells belong to the innate lymphoid cells (ILC) which is a rapidly expanding family in the world of biological cells. They represent 5% to 20% of all circulating lymphocytes in humans. They are useful in the...