Autoantibodies against low-density lipoprotein and atherogenic potential of blood

Blood serum of ischaemic heart disease patients possesses an atherogenic potential which manifests itself in the accumulation of cholesterol in cultured smooth muscle cells of human aorta and in mouse peritoneal macrophages. Recently it was found that serum atherogenicity is associated with the presence in the blood of modified (desialylated) low-density lipoprotein (LDL) and of autoantibodies against LDL (anti-LDL). In the blood, anti-LDL and LDL form circulating immune complexes (CIC). Blood serum atherogenic potential is directly related to the content of LDL cholesterol or apolipoprotein B in CIC. The present study elucidates the effect of LDL and anti-LDL concentrations on the atherogenic properties of blood serum. After the addition of exogenic LDL, in certain atherogenic sera a significant increase in CIC cholesterol as well as the increase of serum atherogenic potential revealed in cell culture were registered. In these sera free anti-LDL capable of binding to exogenous LDL were detected. In other atherogenic sera and in all non-atherogenic sera, the LDL increase failed to be accompanied by any changes in the CIC cholesterol. In these sera no free anti-LDL were detected. The addition of exogenous anti-LDL into non-atherogenic sera was accompanied by 2.5-fold increase in CIC cholesterol and by the appearance of atherogenic properties in these sera. Affinity chromatography was used to remove anti-LDL from atherogenic sera. This removal was accompanied by 2.5- to 3-fold decrease in the CIC cholesterol up to the level characteristic of non-atherogenic serum of healthy donors. The removal of anti-LDL led to disappearance of serum atherogenic properties. From these data we assume that the CIC LDL level and, consequently, serum atherogenic potential is to a considerable degree determined by anti-LDL concentration in the serum.