Haemagglutination-enhancing factor protein in chicken serum. I. Purification of an active protein and production of a monospecific antiserum against it.

The haemagglutinating activity of the IgG fraction of chicken alloantibodies is greatly enhanced by the addition of normal chicken serum. The effect is due to a macromolecular beta-globulin, which has been purified by salt precipitation, gel filtration, and ion-exchange chromatography. Immunization of rabbits with the purified product gave a monospecific antiserum against the haemagglutination-enhancing factor (HEF) protein. By means of this rabbit antiserum it is shown that HEF is co-precipitated with antigen-antibody complexes. This indicates that HEF exerts its effect by binding to chicken IgG antibody after the latter has reacted with antigen.