B1a B Lymphocytes Are Atheroprotective by Secreting Natural IgM That Increases IgM Deposits and Reduces Necrotic Cores in Atherosclerotic Lesions

Abstract

Rationale: Aggravated atherosclerosis in B lymphocyte-deficient chimeric mice and reduced atherosclerosis after transfer of unfractionated spleen B lymphocytes into splenectomized mice have led to the widely held notion that B lymphocytes are atheroprotective. However, B lymphocytes can be pathogenic, because their depletion by anti-CD20 antibody ameliorated atherosclerosis, and transfer of B2 lymphocytes aggravated atherosclerosis. These observations raise the question of the identity of the atheroprotective B-lymphocyte population.Objective: The purpose of the study was to identify an atheroprotective B-lymphocyte subset and mechanisms by which they confer atheroprotection. Methods and Results:

High Levels of (Un)Switched Memory B Cells Are Associated With Better Outcome in Patients With Advanced Atherosclerotic Disease

“…To date, it is generally accepted that (auto)antibody‐producing B1 B cells are atheroprotective26, 27 and this protective effect depends on IgM secretion,28 whereas conventional B2 B cells are generally considered proatherogenic 29. This proatherogenic phenotype in mice has mainly been attributed to the production of pathogenic IgG antibodies against oxidized low‐density lipoprotein (oxLDL) and the immune effector function of these B cells 27, 28, 30, 31, 32, 33. In human atherosclerosis, however, there is conflicting evidence about the role of autoantibodies directed against oxLDL.…”

Anti‐TIM‐1 Monoclonal Antibody (RMT1‐10) Attenuates Atherosclerosis By Expanding IgM‐producing B1a Cells

“…In splenectomy experiments, spleens of 6‐ to 8‐week‐old ApoE‐KO mice were removed surgically under aseptic conditions to remove peritoneal B1a cells as described previously 1, 18, 19. In sham operation, spleen was treated as the way in splenectomy procedure without removing the spleen 1…”

“…B lymphocytes and non‐B‐lymphocyte populations in spleen and peritoneal cavity were analyzed with fluorochrome conjugated antibodies (BD Pharmingen, San Diego, CA) on FACS‐Canto II (BD Biosciences) as described 1, 20, 21. Phycoerythrin (PE)‐conjugated anti‐CD19, Allophycocyanin (APC)‐conjugated anti‐CD5, APC‐Cy7–conjugated anti‐CD11b, Pacific Blue‐conjugated anti‐CD4, PerCP‐conjugated anti‐CD8α, Fluorescein isothiocyanate (FITC)‐ conjugated anti‐TCR‐b and PE‐Cy7–conjugated anti‐NK1.1 antibodies were used in lymphocyte analysis.…”

“…To assess atherosclerosis, Oil Red O‐stained atherosclerotic lesions at aortic sinus (6 sequential sections at 80‐μm intervals) were used to measure both total intimal lesion areas and Oil Red O‐stained lipid deposition areas as described before 20. For necrotic core assessment in atherosclerotic lesions, aortic root atherosclerotic lesions were stained with hematoxylin and eosin (H&E) to identify acellular areas as necrotic cores and measured as described previously 1, 26, 27. To determine lesion efferocytosis, macrophages in atherosclerotic lesions were double‐labeled with CD68 and terminal dUTP nick end‐labeling (TUNEL) using immunofluorescence.…”

“…We have previously reported that peritoneal B1a cells are atheroprotective1 and proposed that therapeutic expansion of atheroprotective B1a cells might be an approach to reduce atherosclerosis 2. Their atheroprotective effect is associated with B1a‐derived polyclonal natural immunoglobulin M (IgM) which accumulates in atherosclerotic lesions to reduce apoptotic cell numbers and necrotic core size, thereby reducing the severity of inflammation in lesions; IgM plays a key role in recognizing phosphatidylserine on apoptotic cells, facilitating apoptotic cell removal by phagocytosis 3.…”