Previous studies showed 30 to 60% of patients with disseminated neoplastic disease excrete in their urine 100 to 500 mg/day of a novel glycoprotein, m.w. 27,000, labeled EDC1. Normal urine contains <1 mg/day. Both normal and cancer plasmas contain a large m.w. factor that cross-reacted with antiserum to EDC1.

Immunoelectrophoresis (IEP) of normal plasma versus rabbit antiserum to EDC1 shows one precipitin line that is of slower mobility than EDC1. Gel filtration of plasma on Sephadex G-150, and analysis of the effluent by double immunodiffusion (DID), IEP, and radioimmunoassay (RIA) with antiserum to EDC1, reveal that the plasma EDC1-immunoreactive component has a m.w. of about 150,000.

Among antisera to 45 purified plasma proteins, only that to inter-α trypsin inhibitor (IATI) m.w. 170,000, reacts with EDC1. This finding suggests that the large EDC1-immunoreactive component is IATI. This is confirmed by the following observations with purified IATI: EDC1 and IATI give a reaction of partial identity in DID versus anti-EDC1 and versus anti-IATI; IATI and plasma give a line of identity in DID versus anti-EDC1; IATI and the immunoreactive component in plasma have the same mobility in IEP versus anti-EDC1. Furthermore, EDC1 possesses an antiproteolytic property closely similar to that of IATI (both proteins inhibit trypsin and chymotrypsin but not plasmin, pepsin, elastase, or exopeptidases).

We conclude that cancer-related urinary glycoprotein EDC1 is related antigenically and chemically to IATI and may be a cleavage product of the latter.

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