Phosphatase and tensin homolog (PTEN) is vital for B cell development, acting as a key negative regulator in the PI3K signaling pathway. We used CD23-cre to generate PTEN-conditional knockout mice (CD23-cKO) to examine the impact of PTEN mutation on peripheral B cells. Unlike mb1-cre-mediated PTEN deletion in early B cells, CD23-cKO mutants exhibited systemic inflammation with increased IL-6 production in mature B cells upon CpG stimulation. Inflammatory B cells in CD23-cKO mice showed elevated phosphatidylinositol 3-phosphate [PI(3)P] levels and increased TLR9 endosomal localization. Pharmacological inhibition of PI(3)P synthesis markedly reduced TLR9-mediated IL-6. Single-cell RNA-sequencing (RNA-seq) revealed altered endocytosis, BANK1, and NF-κB1 expression in PTEN-deficient B cells. Ectopic B cell receptor (BCR) expression on non-inflammatory mb1-cKO B cells restored BANK1 and NF-κB1 expression, enhancing TLR9-mediated IL-6 production. Our study highlights PTEN as a crucial inflammatory checkpoint, regulating TLR9/IL-6 axis by fine-tuning PI(3)P homeostasis. Additionally, BCR downregulation prevents the differentiation of inflammatory B cells in PTEN deficiency.
© 2024 The Author(s).

HIV-1 envelope (Env) proteins designed to induce neutralizing antibody responses allow study of the role of affinities (equilibrium dissociation constant [KD]) and kinetic rates (association/dissociation rates) on B cell antigen recognition. It is unclear whether affinity discrimination during B cell activation is based solely on Env protein binding KD and whether B cells discriminate among proteins of similar affinities that bind with different kinetic rates. Here, we use a panel of Env proteins and Ramos B cell lines expressing immunoglobulin M (IgM) B cell receptors (BCRs) with specificity for CD4-binding-site broadly neutralizing antibodies to study the role of antigen binding kinetic rates on both early (proximal/distal signaling) and late events (BCR/antigen internalization) in B cell activation. Our results support a kinetic model for B cell activation in which Env protein affinity discrimination is based not on overall KD but on sensing of association rate and a threshold antigen-BCR half-life.
Copyright © 2022 The Authors. Published by Elsevier Inc. All rights reserved.

h4>SUMMARY/h4> HIV-1 Envelope (Env) proteins designed to induce neutralizing antibody responses allow study of the role of affinities (equilibrium dissociation constant, K D ) and kinetic rates (association/dissociation rates) on B cell antigen recognition. It is unclear whether affinity discrimination during B cell activation is based solely on Env protein binding K D , and whether B cells discriminate between proteins of similar affinities but that bind with different kinetic rates. Here we used a panel of Env proteins and Ramos B cell lines expressing IgM BCRs with specificity for CD4 binding-site broadly neutralizing (bnAb) or a precursor antibody to study the role of antigen binding kinetic rates on both early (proximal/distal signaling) and late events (BCR/antigen internalization) in B cell activation. Our results support a kinetic model for B cell activation in which Env protein affinity discrimination is based not on overall K D , but on sensing of association rate and a threshold antigen-BCR half-life.

The immune microenvironment of pancreatic ductal adenocarcinoma (PDA) is comprised of a heterogeneous population of cells that are critical for disease evolution. Prominent among these are the specialized CD1dhiCD5+ regulatory B (Breg) cells that exert a pro-tumorigenic role by promoting tumor cell proliferation. Dissecting the molecular pathways regulating this immune sub-population can thus be valuable for uncovering potential therapeutic targets. Here, we investigate Bruton's tyrosine kinase (BTK), a key B-cell kinase, as a potential regulator of CD1dhiCD5+ Breg differentiation in the pancreatic tumor microenvironment. Treatment of cytokine-induced B cells in vitro with the high specificity BTK inhibitor Tirabrutinib inhibited CD1dhiCD5+ Breg differentiation and production of IL-10 and IL-35, essential mediators of Breg immunosuppressive functions. The BTK signaling pathway was also found to be active in vivo in PanIN-associated regulatory B cells. Tirabrutinib treatment of mice bearing orthotopic KrasG12D-pancreatic lesions severely compromised stromal accumulation of the CD1dhiCD5+ Breg population. This was accompanied by an increase in stromal CD8+IFNγ+ cytotoxic T cells and significant attenuation of tumor cell proliferation and PanIN growth. Our results uncover a novel role for BTK in regulating CD1dhiCD5+ Breg differentiation and emphasize its potential as a therapeutic target for pancreatic cancer.

Complete activation of B cells relies on their capacity to extract tethered antigens from immune synapses by either exerting mechanical forces or promoting their proteolytic degradation through lysosome secretion. Whether antigen extraction can also be tuned by local cues originating from the lymphoid microenvironment has not been investigated. We here show that the expression of Galectin-8-a glycan-binding protein found in the extracellular milieu, which regulates interactions between cells and matrix proteins-is increased within lymph nodes under inflammatory conditions where it enhances B cell arrest phases upon antigen recognition in vivo and promotes synapse formation during BCR recognition of immobilized antigens. Galectin-8 triggers a faster recruitment and secretion of lysosomes toward the B cell-antigen contact site, resulting in efficient extraction of immobilized antigens through a proteolytic mechanism. Thus, extracellular cues can determine how B cells sense and extract tethered antigens and thereby tune B cell responses in vivo.
Copyright © 2018 The Authors. Published by Elsevier Inc. All rights reserved.