Regulatory CD4+ T Cells Recognize Major Histocompatibility Complex Class II Molecule-Restricted Peptide Epitopes of Apolipoprotein B.

BACKGROUND: CD4+ T cells play an important role in atherosclerosis, but their antigen specificity is poorly understood. Immunization with apolipoprotein B (ApoB, core protein of low density lipoprotein) is known to be atheroprotective in animal models. Here, we report on a human APOB peptide, p18, that is sequence-identical in mouse ApoB and binds to both mouse and human major histocompatibility complex class II molecules. METHODS: We constructed p18 tetramers to detect human and mouse APOB-specific T cells and assayed their phenotype by flow cytometry including CD4 lineage transcription factors, intracellular cytokines, and T cell receptor activation. Apolipoprotein E-deficient ( Apoe-/-) mice were vaccinated with p18 peptide or adjuvants alone, and atherosclerotic burden in the aorta was determined. RESULTS: In human peripheral blood mononuclear cells from donors without cardiovascular disease, p18 specific CD4+ T cells detected by a new human leukocyte antigen-antigen D related-p18 tetramers were mostly Foxp3+ regulatory T cells (Tregs). Donors with subclinical cardiovascular disease as detected by carotid artery ultrasound had Tregs coexpressing retinoic acid-related orphan receptor gamma t or T-bet, which were both almost absent in donors without cardiovascular disease. In Apoe-/- mice, immunization with p18 induced Tregs and reduced atherosclerotic lesions. After peptide restimulation, responding CD4+ T cells identified by Nur77-GFP (green fluorescent protein) were highly enriched in Tregs. A new mouse I-Ab-p18 tetramer identified the expansion of p18-specific CD4+ T cells on vaccination, which were enriched for interleukin-10-producing Tregs. CONCLUSIONS: These findings show that APOB p18-specific CD4+ T cells are mainly Tregs in healthy donors, but coexpress other CD4 lineage transcription factors in donors with subclinical cardiovascular disease. This study identifies ApoB peptide 18 as the first Treg epitope in human and mouse atherosclerosis.

Vaccination for atherosclerosis: a novel therapeutic paradigm.

Numerous studies have identified a role for the innate and adaptive immune response in atherosclerosis; both pro- and antiatherogenic roles for the immune responses have been demonstrated. Common autoantigens against which an immune response has been identified in experimental and human models of atherosclerosis include oxidized low-density lipopoteins, beta2 glycoprotein 1 and heat shock protein 60. Activation of atheroprotective adaptive immune responses have been demonstrated for oxidized low-density lipoprotein-related antigens. Conversely, atheroprotection has been demonstrated with the induction of immune tolerance through activation of mucosal immunity to heat shock protein 65/60 and beta2 glycoprotein 1. Recent identification of specific immunoreactive antigenic epitopes in the apolipoprotein B-100 component of low density lipoproetin and early experimental observations have provided proof of concept that active vaccination using specific apolipoprotein B-100-related antigens may emerge as a novel immunomodulating atheroprotective strategy.

Recombinant human antibodies against aldehyde-modified apolipoprotein B-100 peptide sequences inhibit atherosclerosis.

BACKGROUND: Accumulation and oxidation of LDL are believed to be important initiating factors in atherosclerosis. Oxidized LDL is recognized by the immune system, and animal studies have suggested that these immune responses have a protective effect against atherosclerosis. Aldehyde-modified peptide sequences in apolipoprotein B-100 (apoB-100) are major targets for these immune responses. METHODS AND RESULTS: Human IgG1 antibodies against 2 malondialdehyde (MDA)-modified apoB-100 peptide sequences were produced through screening of a single-chain antibody-fragment library and subsequent cloning into a pcDNA3 vector. Three weekly doses of these antibodies were injected into male apoE-/- mice. Phosphate-buffered saline and human IgG1 antibodies against fluorescein isothiocyanate were used as controls. One of the IgG1 antibodies significantly and dose-dependently reduced the extent of atherosclerosis as well as the plaque content of oxidized LDL epitopes and macrophages. In cell culture studies, human monocytes were incubated with native LDL or oxidized LDL, in the presence of antibodies. The same antibody induced an increase in monocyte binding and uptake of oxidized LDL. CONCLUSIONS: These findings suggest that antibodies are important mediators of atheroprotective immune responses directed to oxidized LDL. Thus, passive immunization against MDA-modified apoB-100 peptide sequences may represent a novel therapeutic approach for prevention and treatment of cardiovascular disease.