A glycoprotein secreted by lung cancer cells is present in human serum as an immunoglobulin-binding protein

Identification and purification of a toxic component to B cell hybridoma cells in fetal calf serum

A component exhibiting toxicity to B cell hybridoma cells was isolated and purified from fetal calf serum (FCS) by immunoaffinity chromatography using a monoclonal antibody (mAb) which reacted with the high-molecular-weight glycoprotein (6B3.Ag) recognized by a mAb, 6B3, to human large cell lung carcinoma cells (HLC-2). The component (FCS-6B3.Ag) was a high-molecular-weight antigen (approximately 1,000,000), consisting mainly of 76,000 subunits. FCS-6B3.Ag showed the same mobility in the pre-beta globulin region as that of 6B3.Ag on electrophoresis in 1.2% agarose gel. When FCS-6B3.Ag was analyzed by double immunodiffusion, it reacted with anti-6B3.Ag antiserum and the precipitin line fused partially with that formed between 6B3.Ag and anti-6B3.Ag antiserum. FCS-6B3.Ag was found to be toxic to hybridoma cells (anti-6B3.Ag, anti-alpha-fetoprotein, anti-carcinoembryonic antigen or anti-C-reactive protein mAb producing cells) specifically in vitro at 5 micrograms/ml. The antigen also strongly suppressed their growth. The toxic effect of FCS-6B3.Ag appeared immediately after addition, and death of the target cells was complete only after 36-48 h. However, the antigen exhibited only weak suppression of Ig-non-secretory mouse myeloma (P3U1), thymic lymphoma (EL4) of mastocytoma (P815) cell growth. Five lots of FCS contained 2.1 to 4.1 micrograms/ml of FCS-6B3.Ag.