Characterization and demonstration of human liver-specific protein (LSP) and apo-LSP

Liver-specific protein (LSP) prepared by standard methods from five normal human livers showed significant variations in terms of quantitative yield, lipid/protein ratio and migration characteristics of different components on SDS-polyacrylamide gel electrophoresis. This heterogeneity is probably related to varying amounts of different molecular species in the LSP preparations. Delipidation and re-chromatography of the LSP preparation appeared to result in relative enrichment of apo-LSP which showed immunological identity with LSP. Rabbit antiserum to LSP gave a precipitin line of identity with standard antisera to human LSP (anti-LSP) from two other laboratories. After extensive absorption, anti-LSP showed selective reactivity with a surface membrane antigen on a human hepatocellular carcinoma cell line (PLC/PRF/5) that exhibits functional and morphological characteristics of differentiated hepatocytes. The antiserum did not react with cell lines derived from other organs as determined by the indirect fluorescent antibody technique. The surface staining of viable PLC/PRF/5 cells was eliminated by absorption with LSP and apo-LSP, but not with the equivalent kidney fractions. These findings support the concept of a liver-specific antigen and suggest that the PLC/PRF/5 cell line may serve as a source of homogeneous LSP.