Complement activation and phagocytosis of cryoglobulin particles in a patient with plasma cell proliferative disease

The serum of a patient with a non-aggressive plasma cell proliferative disorder contained two monoclonal immunoglobulins: IgG3 lambda in moderate concentration and having cryoglobulin features, and IgA kappa in low concentration and without cryoprecipitability. The patient's serum had low complement concentration and C3 was partly converted into split products in vivo. Complement (C3) together with cryoglobulin and fibrinogen was found by immunofluorescence in sections from skin showing vasculitis. The cryoglobulin particles which formed at room temp. were vividly phagocytized in vitro by neutrophile granulocytes from the patient and from normal individuals as demonstrated in light microscopy and ultramicroscopy.