Identification of cytoskeletal intermediate filaments of vascular endothelial cells as targets for autoantibodies in patient sera

Abstract

Autoantibodies present in sera of patients suffering from various inflammatory conditions react with fibrillar structures, “microfibrils” (MF), which are abundant in developing fetal connective tissue. The purpose of this study was to further characterize the target antigens and to look for potential antigenic target structures in the adult organism using the indirect immunofluorescence (IFL) technique. Bright vascular endothelial staining was regularly observed in various tissues, e.g., kidneys, skin, and vessels accompanying nerves using anti-MF-positive patient area. A weak staining of the media was seen in arteries. Placental vessels were convenient in vitro targets in a screening assay for anti-MF antibodies. The cytoplasmic structures responsible for the endothelial cell fluorescence were identified using cultured umbilical vein endothelial cells as the IFL substrate. In these cells the fluorescence had the typical perinuclear distribution and fibrillar appearance of cytoskeletal intermediate filaments (IMF). We could further show that anti-IMF and anti-MF autoantibodies gave indistinguishable staining patterns. Some anti- MF IMF -positive sera could be neutralized by “insoluble” placental preparations obtained by procedures for preparation of IMF polypeptides. Immunization with a 50,000-dalton “insoluble” polypeptide produced antibodies with a reactivity similar to that of the autoantibodies. The IFL staining and absorption results were consistent with the ultrastructurally demonstrated large amounts of intermediate filaments in vascular endothelial cells. The results suggest that circulating anti-IMF autoantibodies might be involved in inflammatory reactions in cases of vascular endothelial injury.