Simultaneous binding of the anti-cancer IgM monoclonal antibody PAT-SM6 to low density lipoproteins and GRP78

Atherogenesis in human - clinical aspects of circulating immune complexes

It has been suggested that circulating immune complexes containing low density lipoproteins (LDL-CIC) play a role in atherogenesis and are involved in the formation of early atherosclerotic lesions. The complexes, as well as anti-LDL antibody were found in the blood of patients with atherosclerotic process in various cardiovascular diseases, well as in the blood of animals with experimentally modulated atherosclerosis. One can assume that the presence anti-LDL antibodies in blood is a result of an immune response that is induced by modification of lipoproteins. LDL-CIC differ from native LDL in many aspects. They have much lower levels of sialic acid, a smaller diameter and a higher density electronegativity than native LDL. The fraction of the LDL-CIC in serum is an important manifestation of the atherosclerotic process. LDL-CIC, unlike the native LDL is able to induce intracellular accumulation of neutral lipids, especially esterified cholesterol in cell cultures obtained from healthy human aortic intima and macrophages in culture. After removal of the LDL-CIC, the serum of CHD-patients loses its atherogenic properties. The titer of the LDL-CIC in the blood serum significantly correlate with the progression of atherosclerosis and in vivo has the highest diagnostic yield of measured among other lipid parameters. Increasing CIC- cholesterol could also increase the risk of coronary artery atherosclerosis.

Circulating IgM Requires Plasma Membrane Disruption to Bind Apoptotic and Non-Apoptotic Nucleated Cells and Erythrocytes

Autoimmunity is associated with defective phagocytic clearance of apoptotic cells. IgM deficient mice exhibit an autoimmune phenotype consistent with a role for circulating IgM antibodies in apoptotic cell clearance. We have extensively characterised IgM binding to non-apoptotic and apoptotic mouse thymocytes and human Jurkat cells using flow cytometry, confocal imaging and electron microscopy. We demonstrate strong specific IgM binding to a subset of Annexin-V (AnnV)+PI (Propidium Iodide)+ apoptotic cells with disrupted cell membranes. Electron microscopy studies indicated that IgM+AnnV+PI+ apoptotic cells exhibited morphologically advanced apoptosis with marked plasma membrane disruption compared to IgM-AnnV+PI+ apoptotic cells, suggesting that access to intracellular epitopes is required for IgM to bind. Strong and comparable binding of IgM to permeabilised non-apoptotic and apoptotic cells suggests that IgM bound epitopes are 'apoptosis independent' such that IgM may bind any cell with profound disruption of cell plasma membrane integrity. In addition, permeabilised erythrocytes exhibited significant IgM binding thus supporting the importance of cell membrane epitopes. These data suggest that IgM may recognize and tag damaged nucleated cells or erythrocytes that exhibit significant cell membrane disruption. The role of IgM in vivo in conditions characterized by severe cell damage such as ischemic injury, sepsis and thrombotic microangiopathies merits further exploration.