HDL apoprotein immunization induces T cell-mediated venulitis and inflammation in aorta

Abstract

The hypothesis that atherosclerotic processes are mostly caused by immune (autoimmune) mechanisms has recently been gaining attraction. At the same time, the autoimmune hypothesis of atherogenesis has not become generally accepted and requires additional evidence. Previously, we were able to induce changes in the aortic wall similar to those observed in the early stages of human atherosclerosis, and also to produce visceral obesity in normocholesterolaemic Wistar rats by a single immunization with human native high- or low-density lipoproteins. We also found that the immune response to native human HDL causes atherosclerosis-like lesions in the rabbit aorta, such as adipocyte and chondrocyte metaplasia, proteoglycan deposits, and leukocyte infiltration. Atherosclerosis-like lesions developed in the aorta of hnHDL-immunized rabbits against a background of normal blood LDL-cholesterol level. Thus, an immune response against HDL or LDL may be an independent cause of atherogenesis. The aim of this study was to test whether immunization with human HDL apoproteins (apoA1 and apoE proteins) would induce atherosclerosis-like lesions in the aorta of normocholesterolemic Wistar rats. HDL apoproteins were isolated from human or rat plasma. Wistar rats (n = 5) aged 2 months were used for immunization with human HDL apoproteins. HDL apoproteins were administered as a single intradermal injection of 100 mg per rat in incomplete Freund’s adjuvant. Control rats were injected subcutaneously with incomplete Freund’s adjuvant (n = 5). Rats were dissected 25 weeks after immunization. Rat aorta sections were stained with hematoxylin and eosin for light microscopy. T lymphocytes infiltration was determined by immunohistochemical staining with FITC-labeled antibodies specific to rat CD3. CD3+T lymphocytes were detected using an Olympus BX53 fluorescent microscope. The level of antibodies to human and rat HDL apoproteins was determined by indirect enzyme-linked immunosorbent assay. Immunization with HDL apoproteins induced a T cell mediated immune response without production of autoantibodies to HDL apoproteins. The aortic intima and adventitia were infiltrated with T lymphocytes in rats immunized with HDL apoproteins. Pronounced T lymphocytic infiltration was found in all layers of the vein wall in rats immunized with human HDL apoproteins. Thus, immunization with HDL apoproteins causes T cell mediated inflammation of the aorta and venulitis.