Competitive adsorption of plasma proteins at solid-liquid interfaces.

The competitive adsorption of human serum albumin (HSA), human immuno-gamma-globulin (HIgG) and human fibrinogen (HFb) onto polystyrene (PS) at 20 degrees 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 micrograms/cm2.

The adsorption behaviour of two commercial IgG-preparations onto a polystyrene latex surface.

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 microgram cm-2 which was reached at 0.1 g l-1, whereas the other preparation showed no plateau value within the concentration range studied (0.1-7.0 g l-1). Characterization by means of iso-electric focusing and HPLC also showed differences between the two preparations. No differences were observed when immuno-electrophoresis was carried out. These results stress the necessity for proper characterization of proteins used in adsorption studies.