Adsorption of complement proteins on surfaces with a hydrophobicity gradient

Abstract

Activation of the complement system is recognized as one of the major problems with respect to biocompatibility of biomaterials. The binding of C3 (central component of complement) and B (factor B, an activator of C3) and H (factor H, an inhibitor of C3 activation) plays a crucial role in the activation of the alternative pathway of complement on the surfaces of biomaterials during extracorporeal procedures. Here we report on the adsorption of C3, B or H on to the silica surface with a hydrophobicity gradient. The amount of native 125I-C3 bound to both hydrophilic and hydrophobic surfaces was very similar (0.8 and 0.9 μg/cm 2; 4 × 10 −12 mol/cm 2). Neither factor H nor factor B was able to displace already adsorbed 125I-C3 from either of the surfaces. The extent of binding of factors B and H to preadsorbed C3 was a function of the surface hydrophobicity: more 125I-B or 125I-H was bound to C3 adsorbed at the hydrophilic end than at the hydrophobic end of the gradient surface. The binding of 125I-B or 125I-H to preadsorbed C3 appeared to be influenced by the availability of their binding sites on adsorbed C3 molecules rather than by the amount of surface-bound C3. At the hydrophobic end of the gradient surface the molar binding ratio of B C3 was considerably smaller than the molar binding ratio of H C3 . It can be speculated that the hydrophobicity of the surface determines orientation and/or conformation of adsorbed C3 molecule; when adsorbed at the hydrophobic end of the gradient, C3 molecule predominantly exposes the binding site to which only factor H can bind. A substantial decrease in binding of C3, B or H on to the hydrophobicity gradient surface was observed in the presence of other serum or plasma proteins, particularly at the hydrophobic end of the gradient surface.