Immunization of low-density lipoprotein receptor deficient (LDL-RD) mice with heat shock protein 65 (HSP-65) promotes early atherosclerosis

Heat shock proteins are a family of approximately 25 highly conserved prote ins upregulated in response to various forms of stress. They play an active role in the development autoimmune diseases in animals, and have been incr iminated in human autoimmune diseases (i.e, rheumatoid arthritis, multiple sclerosis). It has been previously shown, that an induced immune response a gainst Heat shock protein 65 (HSP-65) results in atherosclerotic lesions in normocholesterolemic rabbits. We have supported these findings showing tha t C57BL/6 mice immunized with HSP-65 and fed a high-fat diet develop enhanc ed fatty streaks. To create a model that will eliminate the need for exogen ous supplementation of a high-fat diet, we have immunized:LDL receptor defi cient (LDL-RD) mice with HSP-65 or with heat-killed Mycobacterium tuberculo sis (Mt). Seven groups of LDL-RD mice (n=10), were immunized subcutaneously with different concentrations of HSP-65, Mt or bovine serum albumin (BSA). All mice were fed a normal chow-diet for 3 months. The mice immunized with the higher doses of Mt developed significantly larger fatty streaks when c ompared with their BSA immunized littermates. The size of the lesions in th e aortic sinus were: 31,562+/-5,994 mu m(2) in the 10 mu g Mt and 52,777+/- 5,245 mu m(2) in the 100 mu g Mt vs. 11,500+/-3,750 mu m(2) in the BSA grou p (P<0.05). In the HSP-65-immunized mice, only the group injected with the highest dose (5 mu g, twice) developed significantly larger fatty streaks w hen compared with the BSA-immunized group (28,611+/-4,716 mu m(2) vs. 11,50 0+/-3,750 mu m(2) respectively, (P<0.05). The HSP-65-but not the Mt- or BSA -immunized mice developed high titers of anti HSP-65 antibodies, beginning 10 days after the immunization, which persisted until:they were killed. Imm unohistochemical staining showed CD3-positive lymphocytes in the aortic sin us of mice immunized with Mt or HSP-65, but not in the control group. Thus, we established a mouse model of HSP-65 immune mediated atherosclerosis dev oid of high fat diet supplementation. This model will enable us to further study the role of the immune system in atherosclerosis, via HSP-65 and rais e novel immunomodulatory therapeutic modalities. (C) 2000 Academic Press.