Isotherms of human serum albumin (HSA), human immunoglobulin G (HIgG), and human fibrinogen (HFb) onto a polystyrene (PS)-latex were determined by depletion of protein in the solution, which was either followed by radioactivity measurements or by UV spectroscopy. Different adsorption isotherms for the same protein were obtained when either radioactivity measurements or UV spectroscopy was used as a detection technique. In order to obtain reliable results from competitive protein adsorption experiments, a method based on the use of high-performance liquid chromatography was developed. A strong preferential adsorption of HFb was observed when adsorption studies were carried out with mixtures of HSA, HFb, and HIgG. When adsorption studies were carried out with solutions containing HSA monomer and dimer, a strong preferential adsorption of HSA dimer was also observed.

SUMMARYThe competitive adsorption of human serum albumin (HSA), human immuno-7-globulin (HIgG) and human fibrinogen (HFb) onto polystyrene (PS) at 20°C and a pH of 7.35 (phosphate-buffered saline) was studied. Protein adsorption was studied using enzyme immunoassay. The results obtained with the immunoassay were compared with those obtained using radiolabelled proteins. Recent studies revealed that the adsorption behaviour of radiolabelled proteins onto surfaces differs from that of the non-labelled proteins, which may lead to misinterpretation of adsorption data. Differences in the adsorption behaviour of the labelled proteins as compared to non-labelled proteins can possibly be explained by the formation of modified proteins during the labelling procedure as shown by ion-exchange high-performance liquid chromatography (HPLC). The competitive adsorption of HSA, HIgG and HFb onto a PS latex was studied by measuring the depletion of proteins in solution. The decrease in protein concentration in solution was determined by HPLC techniques. A strong preferential adsorption of HFb was observed with maximum adsorption values of 0.6 ug/cm 2.

The adsorption behaviour of two commercial preparations of human IgG onto a polystyrene latex surface was studied The adsorption isotherms obtained differed markedly. one preparation showed a plateau value of 0.4 ,ug cm-' which was reached at 0.1 g I-', whereas the other preparation showed no plateau value within the concentration range studied (0.1-7.0 g I-'). Characterization by means of is&electric focusing and HPLC also showed differences between the two preparations. No differences were observed when immune-electrophoresis was carried out. These results stress the necessity for proper characterization of proteins used in adsorption studies. MATERIALS AND METHOOSHuman IgG obtained from Kabi AB, Stockholm, Sweden (KIgG; batch no. 78185) was prepared from Cohn fraction II $ Ill. After precipitation with alcohol in the cold, chromatography on DEAE Sephadex was carried out, followed by freeze-drying. The total protein content was 95%. of which 98% was lgG15.Human IgG, obtained from the Centraal Laboratorium van de Bloedtransfusiedienst, Amsterdam, The Netherlands (CIgG) was prepared from Cohn fraction II -/-III. It was precipitated with alcohol in the cold and then freeze-dried15. The total protein content was 74% (as determined in our laboratory). Figure 7 shows HPLC-chromatograms for both IgG-0 1984 Butterworth Et Co (Publishers) Ltd. RESULTS Characterization