Immune complex-like activity associated with abnormal serum lipoproteins in systemic erythematosus.

Sera from four patients with systemic lupus erythematosus (SLE) were shown to contain abnormal lipoproteins which behaved as immune complexes (IC). One IC lipoprotein (IC VLDL) had the density in ultracentrifugation of very low density lipoprotein, but a markedly altered electrophoretic mobility. A second IC lipoprotein (IC LDL) had the electrophoretic mobility of very low density lipoprotein but was slightly denser than low density lipoprotein on ultracentrifugation. Both the IC VLDL and IC LDL contained IgG and behaved as IC in the Clq deviation test, platelet aggregation and rheumatoid factor inhibition assays, but not in the conglutinin and Clq binding assays and the Clq solid phase assay. These differences could be due to the low densities of the IC VLDL and IC LDL. The abnormal lipoprotein IC disappeared with clinical remission in two patients and were not present in the sera of other patients with inactive or mild SLE, Type IV hyperlipidaemia, or during prednisone therapy or plasma exchange for other conditions. These IC appeared to be markers of severe and active SLE.