Interleukin II (60-70) is a peptide with the sequence NH2-LEU-THR-PHE-LYS-PHE-TYR-MET-PRO-LYS-LYS-ALA-COOH and a molecular weight of 1373.7. Interleukin 2 (IL-2) is a cytokine signaling molecule that regulates leukocytes (often lymphocytes) responsible for immunity, and was the first interleukin molecule identified and characterized.