Coimmunoprecipitation of apo(a) and β-2 glycoprotein I in HepG2 supernatants. HepG2 cells, endogenously expressing β-2 glycoprotein I, were transiently transfected with different apo(a) isoforms (r-apo(a)K10 and K26) or empty vector control. Supernatants were harvested 60 hours postransfection and coimmunoprecipitated using polyclonal antibody against β-2 glycoprotein I (pAB1). Immunoprecipitation of apo(a) with the apo(a)-specific MoAb, 1A2, served as positive control. Immunoprecipitates were resolved by 4% to 12% Tris-Glycin gel electrophoresis and immunodetected by immunoblot analysis using anti-apo(a) MoAb 1A2.