A protein inhibitor, extracted from Hela cells, which recognises a cell surface protease on preneoplastic cells obtained from cervical smears.

Hela cells originate from a clone of cervical carcinoma cells. The cytoplasm of Hela cells contains a protein which recognises and inhibits a proteolytic enzyme (guanidino-benzoatase) on the surface of Hela cells. This same protease is present on the surface of abnormal epithelial cells obtained from cervical smears, enabling a rhodamine labelled inhibitor extracted from Hela cells to locate abnormal cervical cells in monolayer spreads.