The specificity of human liver membrane lipoprotein: studies with monoclonal antibodies.

Hybrid cell lines which secreted antibodies to liver-specific membrane lipoprotein (LSP) were obtained by immunizing SMA and BALB/c mice with human LSP and fusing their splenocytes with the myeloma cell line P3-NSI/1-Ag4-1. The secretion of antibody to LSP (anti-LSP) was monitored by binding to a human hepatocellular carcinoma cell line, SK-Hep-1, which possesses surface membrane LSP, and to 125I-antimouse F(ab')2 antibody in radiobinding assay, and by reacting with 125I-LSP in double-antibody radioimmunoassay. From four separate cell fusions, seven secreting hybrids were cloned by dilutional techniques. Of these, four cell lines produced antibodies reacting with a wide variety of cells. The culture supernatants of the remaining three (6D6, 6G3 and 8F10) demonstrated the strongest binding activities against SK-Hep-1 among the various kinds of cell lines tested. However, binding with other cell lines, including renal cancer cells (SK-RC-6) and myeloid cell (HL-60) also occurred. Absorption test of ascitic fluids derived from 6D6 showed that ascitic fluids lost their capacity to bind to target SK-Hep-1 cells when absorbed with SK-Hep-1. Similarly absorption by SK-RC-6 and HL-60 removed almost all of the binding activity of ascitic fluids. Moreover, the binding activities of the ascitic fluids to SK-RC-6 and HL-60 were eliminated when absorbed with SK-RC-6, HL-60 and SK-Hep-1. The present study indicates that our LSP preparation contains nonspecific organ antigens, and although LSP exists on liver cell membrane, it is also found on the cell membrane of other organs albeit in less quantity.