Surface properties of antigen-antibody complexes

In this paper, the authors show that liquid-liquid partition chromatography in an aqueous two-phase system offers unique possibilities of comparing the overall surface properties of intact antibodies in solution before and after binding of antigen. The authors demonstrate that the surface properties of antigen-antibody complexes are dependent on the variable regions of the antibodies, the nature of the antigen and/or possible conformational changes induced by antigen binding. Thus, each antigen-IgG antibody pair formed one type of complex with respect to the exposed dominant surface. The antigen-binding sites of IgG antibodies were exposed and dominant even after binding of hapten or hapten-carrier. In contrast, the antibody-combining sites were concealed upon protein binding and the exposed surfaces of the protein-antibody complexes were related mainly to those of the antigen. IgA1, IgA2, IgE and IgM formed, in comparison to the IgG, hapten-antibody complexes which exhibited surface properties that could be related to both the antigen-binding sites and Fc parts of the antibodies. Moreover, the results indicated that antigen-induced conformational changes occurred in either IgA1, IgA2, IgE, or IgM, but not in IgG1, -2, -3 and -4, making the surfaces of their heavy chain constant regions more similar.