HRH2 and Allergy: For example, HEK293 cell-based biosensor with a synthetic histamine-responsive signal module (histamine receptor H2, HRH2) can detect allergies from blood samples of high-risk allergic patients by sensing the extracellular histamine levels and triggering the expression of cAMP-induced SEAP (secreted alkaline phosphatase).65 Such engineered mammalian cell systems can be used in high-throughput diagnostic applications such as testing novel drugs for allergic reactions.