SHENTEK
https://www.shentekbio.com/products/shentek-e-coli-expression-strains-hcp-elisa-kit.html
This e coli hcp assay kit is designed to quantify and characterize host cell proteins (HCPs) in products manufactured by expression in E.coli originated from BL21, such as interleukin (IL), recombinant human interferon (rhIFN), recombinant human tumor necrosis factor (rhTNF), growth-promoting factor (EGF/FGF/PDGF), et.al.