IL-2 IS stands for interleukin 2 "Improved Sequence", also termed aldesleukin, and is a variant of IL-2 with a serine to cysteine substitution. Human IL-2 IS is a recombinant protein optimized for use in cell culture, differentiation studies, and functional assays, and possesses the same properties as naturally occurring IL-2. Biological activity. Proliferation of CTLL-2 cells (NIBSC 86/504) premium grade: ≥ 5×10^6 IU/mg. Premium-grade cytokines offer the convenience of high and well-defined biological activities and allow exact unit dosing for demanding applications. The biological activity is determined after lyophilization and reconstitution, and normalized to WHO/NIBSC standards whenever available. In general, endotoxin levels are <0.01 ng/μg (<0.1 EU/μg), and purities are >97%. MSDS and lot-specific certificates of analysis are available on request (macs@miltenyibiotec.com.sg).