Studies of human IgM anti-IgG cryoglobulins: II. Isoelectric focusing characteristics of the reactive antigen and residual serum IgG pools

The co-isoelectric focusing characteristics of the antigen-IgG and residual IgG pools in the serum of patients with mixed IgM:IgG cryoglobulinemia have been determined. The antigen IgG purified from five IgM cryoglobulins and the residual IgG purified from serum depleted of cryoglobulin were radiolabelled and co-isoelectric focused in polyacrylamide gels in order to determine if the IgM anti-globulin reacted in order to determine if the IgM anti-globulin reacted with IgGs having unique physicochemical properties. Electrofocusing profiles of the IgG from four sera showed only minor differences when the antigen-IgG was compared to residual serum IgG. In one instance, the IEF profile of the antigen-IgG pool was markedly restricted and of a different charge dispersion than the residual serum IgG. This correlated with the limited antigenic specificity previously shown for the autologous IgM antiglobulin.