Affinity of Polyclonal IgG and F(ab')2 Fragments for Different Polymeric Surfaces

In this paper we show experimental data of antibody adsorption isotherms onto polystyrene surfaces. These values corroborate the important role played by both the electrostatic and the hydrophobic interactions in protein adsorption processes. To do that, we have worked with a well-known protein (IgG) and its F(ab')₂ fragment. Both macromolecules differ in isoelectric points and molecular weights. The first factor allows us to study the influence of the electrostatic forces that come into play if the adsorption isotherms are carried out at different pHs in low ionic strength media. In addition, we have used four different colloidal polymer particles (latex) in order to analyze the importance of the hydrophobic driving force for protein adsorption. Our results clearly indicate that: (i) the most hydrophobic latex adsorbs the maximum amounts of both antibody molecules, and (ii) the highest affinity shown by antibodies for sorbent surfaces is found when both have opposite sign of charge, that is, under favourable electrostatic interaction conditions. On the other hand, when adsorbing IgG and F(ab')₂ as a function of pH at low ionic strength media, a maximum amount of adsorbed antibodies is observed near the isoelectric point of the protein-latex complex. Finally, we have also quantified the adsorption affinity using a thermodynamic equation that allows us to calculate the standard free energy for the transfer of one mole of protein from bulk water to the surface.