Toll-Like Receptor (TLR)4 and MyD88 are Essential for Atheroprotection by Peritoneal B1a B Cells

J Am Heart Assoc. 2016 Nov 14;5(11):e002947. doi: 10.1161/JAHA.115.002947.

Abstract

Background: We previously identified peritoneal B1a cells that secrete natural IgM as a key atheroprotective B cell subset. However, the molecules that activate atheroprotective B1a cells are unknown. Here, we investigated whether Toll-like receptors (TLRs) TLR2, TLR4, and TLR9 expressed by B1a cells are required for IgM-mediated atheroprotection.

Methods and results: We adoptively transferred B1a cells from wild-type mice or from mice deficient in TLR2, TLR4, TLR9, or myeloid differentiation primary response 88 (MyD88) into ApoE-/- mice depleted of peritoneal B1a cells by splenectomy and fed a high-fat diet for 8 weeks. Elevations in plasma total, anti-oxLDL (oxidized low-density lipoprotein), anti-leukocyte, anti-CD3, anti-CD8, and anti-CD4 IgMs in atherosclerotic mice required B1a cells expressing TLR4 and MyD88, indicating a critical role for TLR4-MyD88 signaling for IgM secretion. Suppression of atherosclerosis was also critically dependent on B1a cells expressing TLR4-MyD88. Atherosclerosis suppression was associated not only with reductions in lesion apoptotic cells, necrotic cores, and oxLDL, but also with reduced lesion CD4+ and CD8+ T cells. Transforming growth factor beta 1 (TGF-β1) expression, including macrophages expressing TGF-β1, was increased, consistent with increased IgM-mediated phagocytosis of apoptotic cells by macrophages. Reductions in lesion inflammatory cytokines tumor necrosis factor alpha (TNF-α), interleukin (IL) 1β, and IL-18 were consistent with augmented TGF-β1 expression.

Conclusions: TLR4-MyD88 expression on B1a cells is critical for their IgM-dependent atheroprotection that not only reduced lesion apoptotic cells and necrotic cores, but also decreased CD4 and CD8 T-cell infiltrates and augmented TGF-β1 expression accompanied by reduced lesion inflammatory cytokines TNF-α, IL-1β, and IL-18.

Keywords: B1a cells; IgM; Toll‐like receptor 4/MyD88; atherosclerosis; cytokine; inflammation.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Atherosclerosis / genetics
  • Atherosclerosis / immunology*
  • B-Lymphocyte Subsets / immunology*
  • B-Lymphocytes / immunology
  • Diet, High-Fat
  • Immunoglobulin M / immunology*
  • Interleukin-18 / immunology
  • Interleukin-1beta / immunology
  • Male
  • Mice
  • Mice, Knockout
  • Mice, Knockout, ApoE
  • Myeloid Differentiation Factor 88 / genetics
  • Myeloid Differentiation Factor 88 / immunology*
  • Peritoneum / cytology
  • Peritoneum / immunology
  • Phagocytosis / immunology
  • Real-Time Polymerase Chain Reaction
  • Toll-Like Receptor 2 / genetics
  • Toll-Like Receptor 2 / immunology
  • Toll-Like Receptor 4 / genetics
  • Toll-Like Receptor 4 / immunology*
  • Toll-Like Receptor 9 / genetics
  • Toll-Like Receptor 9 / immunology
  • Transforming Growth Factor beta1 / immunology
  • Tumor Necrosis Factor-alpha / immunology

Substances

  • IL1B protein, mouse
  • Immunoglobulin M
  • Interleukin-18
  • Interleukin-1beta
  • Myd88 protein, mouse
  • Myeloid Differentiation Factor 88
  • Tgfb1 protein, mouse
  • Tlr2 protein, mouse
  • Tlr4 protein, mouse
  • Tlr9 protein, mouse
  • Toll-Like Receptor 2
  • Toll-Like Receptor 4
  • Toll-Like Receptor 9
  • Transforming Growth Factor beta1
  • Tumor Necrosis Factor-alpha