Abstract-The immune system represents a promising novel target for prevention of atherosclerosis. Several pilot vaccines that reduce atherosclerosis in experimental animals have been developed. The aluminum hydroxide adjuvant Alum has been shown to have antiatherogenic properties in itself, suggesting that it may be a suitable adjuvant in possible future atherosclerosis vaccines. Key Words: atherosclerosis Ⅲ lipids Ⅲ regulatory T cells Ⅲ vaccine T he possibility of treating autoimmune diseases by immune modulation with autoantigens has been gaining increasing attention. Ongoing clinical trials in this area include vaccines for type 1 diabetes, rheumatoid arthritis, multiple sclerosis, and Alzheimer's disease. 1 A vaccine against atherosclerosis based on modulation of autoimmune responses against antigens in oxidized LDL is also in late preclinical development. 2 Adjuvants enhancing the immunogenicity of vaccine antigens are critical components of almost all vaccines and play an important role in modulating the characteristics of the subsequent immune response. Aluminumcontaining adjuvants are the most widely used adjuvants in clinical vaccines, and their safety is well documented. 3 Interestingly, it has recently been demonstrated that the aluminum hydroxide adjuvant Alum has atheroprotective properties in itself, suggesting that it could be a particularly suitable adjuvant in a potential future atherosclerosis vaccine. 4 Aluminum-containing adjuvants primarily induce humoral immunity but are less effective in activating T cellmediated delayed-type hypersensitivity immune responses. 5 Their mechanism of action is generally considered to involve delayed clearance of the antigen from the injection site, 6 induction of a local inflammatory response stimulating the recruitment and activation of antigen-presenting cells (APCs), 7-10 and conversion of soluble antigens into a particulate form facilitating their uptake by phagocytosis in APCs. 11,12 However, it is unclear how these mechanisms can contribute to a protection against atherosclerosis when Alum is administered in absence of an antigen. In the present study, we investigated the possibility that Alum, when injected into a hypercholesterolemic environment, could adsorb self antigens and activate immune responses against these in a manner that contributes to protection against atherosclerosis.
Materials and Methods
Mice, Immunization, and Tissue PreparationMale apolipoprotein (apo)E-deficient and wild-type C57BL/6 mice were from Taconic Laboratory. Food and tap water were administered ad libitum. Mice were given subcutaneous injections (100 L) with Alum (aluminum hydroxide; Pierce) in PBS (1:1) at 6, 9, and 11 weeks of age. Injections of only PBS served as controls. Mice were euthanized at 12 or 25 weeks of age by intraperitoneal injection of ketamine and xylazine. Spleens were harvested and stored in PBS on Original