A TLR9-dependent checkpoint governs B cell responses to DNA-containing antigens

J Clin Invest. 2017 May 1;127(5):1651-1663. doi: 10.1172/JCI89931. Epub 2017 Mar 27.


Mature B cell pools retain a substantial proportion of polyreactive and self-reactive clonotypes, suggesting that activation checkpoints exist to reduce the initiation of autoreactive B cell responses. Here, we have described a relationship among the B cell receptor (BCR), TLR9, and cytokine signals that regulate B cell responses to DNA-containing antigens. In both mouse and human B cells, BCR ligands that deliver a TLR9 agonist induce an initial proliferative burst that is followed by apoptotic death. The latter mechanism involves p38-dependent G1 cell-cycle arrest and subsequent intrinsic mitochondrial apoptosis and is shared by all preimmune murine B cell subsets and CD27- human B cells. Survival or costimulatory signals rescue B cells from this fate, but the outcome varies depending on the signals involved. B lymphocyte stimulator (BLyS) engenders survival and antibody secretion, whereas CD40 costimulation with IL-21 or IFN-γ promotes a T-bet+ B cell phenotype. Finally, in vivo immunization studies revealed that when protein antigens are conjugated with DNA, the humoral immune response is blunted and acquires features associated with T-bet+ B cell differentiation. We propose that this mechanism integrating BCR, TLR9, and cytokine signals provides a peripheral checkpoint for DNA-containing antigens that, if circumvented by survival and differentiative cues, yields B cells with the autoimmune-associated T-bet+ phenotype.

MeSH terms

  • Animals
  • Antigens / immunology*
  • B-Cell Activating Factor / genetics
  • B-Cell Activating Factor / immunology
  • B-Lymphocytes / immunology*
  • CD40 Antigens / genetics
  • CD40 Antigens / immunology
  • Cell Differentiation / genetics
  • Cell Differentiation / immunology
  • Cell Line
  • DNA / immunology*
  • Female
  • G1 Phase Cell Cycle Checkpoints / genetics
  • G1 Phase Cell Cycle Checkpoints / immunology*
  • Interferon-gamma / genetics
  • Interferon-gamma / immunology
  • Interleukins / genetics
  • Interleukins / immunology
  • MAP Kinase Signaling System / genetics
  • MAP Kinase Signaling System / immunology
  • Male
  • Mice
  • Mice, Knockout
  • Receptors, Antigen, B-Cell / genetics
  • Receptors, Antigen, B-Cell / immunology
  • T-Box Domain Proteins / genetics
  • T-Box Domain Proteins / immunology
  • Toll-Like Receptor 9 / genetics
  • Toll-Like Receptor 9 / immunology*
  • p38 Mitogen-Activated Protein Kinases / genetics
  • p38 Mitogen-Activated Protein Kinases / immunology


  • Antigens
  • B-Cell Activating Factor
  • CD40 Antigens
  • IFNG protein, human
  • IFNG protein, mouse
  • Interleukins
  • Receptors, Antigen, B-Cell
  • T-Box Domain Proteins
  • T-box transcription factor TBX21
  • TLR9 protein, human
  • TNFSF13B protein, human
  • Tlr9 protein, mouse
  • Toll-Like Receptor 9
  • Interferon-gamma
  • DNA
  • p38 Mitogen-Activated Protein Kinases
  • interleukin-21