Serological heterogeneity of the IgM components of mixed (monoclonal IgM–polyclonal IgG) cryoglobulins

Mixed IgG–IgM cryoglobulins were isolated from the sera of seven patients with macroglobulinaemia or cryoglobulinaemia. The IgM components of all seven cryoproteins were monoclonal, containing κ light chains only, whereas the IgG components were polyclonal, containing both κ and λ light chains. Despite their apparent immunological homogeneity, the IgM components showed a wide range of antiglobulin activity. The data indicate that serological specificity may vary from one mixed cryoglobulin to another and that the monoclonal IgM components of different mixed cryoglobulins represent a heterologous group of antiglobulins.