Binding of secretory piece to polymeric IgA and IgM paraproteins in vitro.

By means of immunoelectrophoresis and the immunoselection technique the binding of free secretory piece to serum paraproteins of different classes was studied . Only the polymeric IgA and not the monomeric forms, nor paraproteins of IgG or IgD classes, were found to bind free secretory piece . This property was not dependent on the subclass or the light chain type of the tested paraproteins. In addition higher polymers of IgM with sedimentation coefficients of 25S to 30S also bound the secretory piece, whereas 19S forms did not.