Sigbert Schiefer

Secretory group II phospholipase A2 in human atherosclerotic plaques

Atherosclerotic plaques exhibit a series of features that are similar to those of chronic inflammation. Based on the fact that during inflammation several cell types synthesize and secrete a group II phospholipase A2 (PLA2), an immunohistochemical study was undertaken to explore whether this enzyme can be identified in human atherosclerotic lesions. Tissue specimens obtained from 13 patients who had undergone arteriectomy and three specimens with advanced atherosclerotic plaques obtained at autopsy were analyzed and compared to arteries free of atherosclerosis. The results showed that in all areas with atherosclerotic lesions, a staining with monoclonal antibodies raised against group II PLA2 was evident. In normal arteries without thickened intima, this immunostaining was completely negative. With the use of specific monoclonal antibodies against macrophages (anti-KP-1) and smooth muscle cells (anti-alpha-actin), PLA2-positive cells were identified as foam cells mainly derived from macrophages. In addition to these cells, other regions of the thickened intima gave a partially positive reaction with anti-PLA2 antibodies, but could not be stained with either anti-KP-1 or anti-alpha-actin. Some of these regions were localized on edges of calcification and cell necrosis. Other PLA2-positive regions seem to be associated with extracellular matrix structures. In summary, the findings of this study may be regarded as further evidence to support the link between atherosclerosis and chronic inflammatory processes. In view of the fact that the in vitro modification of lipoproteins by PLA2-treatment induces lipid deposition in macrophages, the results of this study suggest that group II PLA2 may actively be involved in the formation of foam cells in vivo.

Precipitation methods for the determination of LDL-cholesterol.

The selective precipitation of low-density lipoproteins (LDL) with polyvinyl sulfate (PVS), and the immunoprecipitation of high-density lipoproteins (HDL) and very-low-density lipoproteins (VLDL) with an anti-HDL antibody, can both be used to establish simple methods for the determination of LDL cholesterol. Whereas the PVS method requires the calculation of LDL cholesterol as the difference of total and supernatant cholesterol, the immunoprecipitation method allows the direct measurement of LDL cholesterol in the supernatant. As a first step, both methods were optimized to yield accurate values for normolipemic and slightly hyperlipemic serum samples. Moreover, the determination of LDL-cholesterol in lipemic sera can be achieved by a combination of immunoprecipitation and polyanion precipitation.