A null cell is a large agranular lymphocyte without surface markers or membrane-associated proteins from B lymphocytes or T lymphocytes. Natural killer cells are usually null cells with surface marker CD 16 which bind to the Fc portion of the IgG, and thereby destroy it. NK-cells do immune surveillance, attack pathogens and abnormal cells. Members of null cells are NK cells, antigen dependent cytotoxic cells(ADCC), and the lymphokine activated killer(LAK)cells. In 75% of the cases of ALL, the lymphocytes are neither B nor T-cells and are called Null cells.