Determination of cryoglobulins as lipoprotein-autoantibody immune complexes and antigenic determinants against antilipoprotein autoantibody.

Serum IgG-antilipoprotein-autoantibody activity (at 4 degrees C) of a plane xanthoma patient was shown by double-immunodiffusion method. Cryoglobulins in the serum were dissociated to polyclonal IgG and alpha- and beta-lipoproteins by acidification and were reconstructed by neutralization. IgG fraction of the cryoglobulins precipitated with lipoproteins. The cryoglobulins were thus demonstrated to be immune complexes of polyclonal IgG-antilipoprotein-autoantibody and both alpha- and beta-lipoproteins. A part of the lipoprotein-autoantibody immune complexes was not cryoprecipitable. Antigenic determinants for the autoantibody existed in the lipid moieties of lipoproteins, in contrast to the apoproteins which determined the specificity to heteroimmune antilipoprotein antibody. The presence of more than nine different antigenic determinants against the autoantibody indicated that lipoproteins were immunologically heterogeneous depending upon the lipid moieties. Lipoproteins reactive with the autoantibody varied quantitatively in normal individuals and were not detected in a primary hyper-beta-lipoproteinaemia patient and in a primary biliary liver cirrhosis patient with much lipoprotein-X. The absence of antigenicity in the two patients' sera is most likely caused by abnormal lipid moieties of lipoproteins.