Monoclonal anti-galactan IgA J 539 binds intercatenarily to its polysaccharide antigen. Observations on the binding of antibody to a macromolecular antigen.

Highly purified P. Zopfii galactan of mol. wt 2 X 10(5) binds monoclonal IgA J 539 with a Ka of 5.80 X 10(5) M-1 if the polysaccharide concn is expressed in blocks of 30 galactosyl residues. This is the same Ka as found for the antibody and methyl beta (1,6)-beta-D-galactopyranosyltetraoside, the ligand capable of filling the entire combining area of the immunoglobulin. This same polysaccharide precipitates monomeric IgA J 539 on agar-double diffusion. It is concluded that the antibody binds to intercatenary galactosyl residues of the antigen.