Abstract
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.
Authors
Vishal J. Sindhava, Michael A. Oropallo, Krishna Moody, Martin Naradikian, Lauren E. Higdon, Lin Zhou, Arpita Myles, Nathaniel Green, Kerstin Nündel, William Stohl, Amanda M. Schmidt, Wei Cao, Stephanie Dorta-Estremera, Taku Kambayashi, Ann Marshak-Rothstein, Michael P. Cancro
Figure 1
Addition of BLyS prevents AM14 and WT B cells from undergoing proliferation-associated cell death following stimulation with BCR-delivered TLR9 ligands.
Copyright © 2021 American Society for Clinical Investigation
ISSN: 0021-9738 (print), 1558-8238 (online)