STUDIES OF HUMAN-IGM ANTI-IGG CRYOGLOBULINS .1. PATTERNS OF REACTIVITY WITH AUTOLOGOUS AND ISOLOGOUS HUMAN-IGG AND ITS SUBUNITS

Abstract

Monoclonal human anti-Ig[immunoglobulin]G preparations purified from mixed IgM-IgG cryoglobulins were tested for their antigenic specificity by hemagglutination-inhibition assay. A panel of the 14 IgG preparations of the 4 .gamma.-chain subclasses were prepared from myeloma sera and used as inhibitors of hemagglutination. Each of 6 IgM anti-globulins demonstrated different reactivity profiles with these IgG preparations. The fraction of the serum IgG which had bound to and cryoprecipitated with the IgM preparations, termed antigen-IgG, was purified and assayed for subclass content. The .gamma. chain subclasses found in the antigen-IgG fractions showed that each IgM cryoprecipitated an IgG from serum which had different quantities of the subclasses present. These autologous reactivity patterns were in instances different from the specificities expected from the results obtained with the myeloma proteins. When all antigen-IgG pools were tested with each IgM, some antiglobulins showed stronger reactivity with isologous than with their own, antigen-IgG pools. The IgM anti-IgG preparations were compared in reactivity with IgG and its subunits to localize the antigenic determinant(s) with which these autoantibodies react. H chains showed far greater reactivity than Fc fragment for 5/6 IgM preparations. L chains, F(ab'')2, pFc'' and Fab were non-reactive. A relationship between the length of papain digestion and Fc reactivity was demonstrated. Based on the data, possible locations for the antigenic determinant(s) were considered.