Lymphosarcoma, cold urticaria, IgG1 monoclonal cryoglobulin and complement abnormalities.

A patient with lymphosarcoma and cold urticaria showed evidence of complement activation by the classical pathway with low levels of the early complement components, normal levels of late acting components, normal functioning of the alternate pathway and reduction of the C1-inhibitor level. The serum contained an IgG1 monoclonal cryoglobulin responsible for the complement activation. In vitro tests demonstrated a high capacity of the serum to activate C1.