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.