IL2 and inborn error of immunity: It was developed as a method to quantitatively assess cytotoxicity of the NK cells and CTL (after overnight activation of PBMCs with IL-2) by measuring the expression of CD107α on the cell membrane, which appeared to be an effective and rapid screening test for cytotoxic defects-related diseases such as familial hemophagocytic lymphopro-liferative syndrome and other hemophagocytic lymphohistiocytosis secondary to primary immunodeficiency [56].