KILR cell lines are engineered to express an enhanced Prolabel (ePL) tagged housekeeping gene and may sometimes overexpress an untagged version of a receptor. Once the cells have been lysed the ePL-tagged protein is released into the media. Addition of enzyme acceptor (EA) will cause the complementation of the β-galactosidase enzyme fragments, EA and ePL. The resulting functional enzyme will hydrolyze its substrate to generate a chemiluminescent signal.