Kim L. Good-Jacobson

Memory B cells are essential for long‐lasting immunity induced by both encountered pathogens and vaccines. Functional diversity within the memory B cell pool is established through interactions between memory B cells and the environment in which they develop and reside. This review will discuss novel insights into the role of cytokines encountered in the microenvironment in modulating memory B cell transcriptomic, epigenetic, and phenotypic identity. Specifically, it will focus on how interferons can prime unique memory B cell subpopulations upregulated in chronic viral infection, autoimmunity, and cancer. Understanding how memory B cell identity is established and maintained in interferon‐primed memory B cell subsets, and how memory B cell phenotype relates to function, may help advise novel vaccine design and diagnostic procedures for a wide range of immunopathologies.

Memory B cells underpin the capacity of the immune system to confer durable protective immunity by mounting rapid and enhanced secondary antibody responses. Hence, they are central to vaccine efficacy and to limiting long-term tissue damage after reinfection. Despite their importance, the cellular origins, molecular programs, and tissue-specific specialization of memory B cells remain incompletely understood. Here, we review recent advances in memory B cell development and regulation, with a particular focus on tissue-resident memory B cells. We discuss how memory B cells arise from distinct developmental precursors as well as the extrinsic regulators and molecular programs that govern memory B cell identity and function. We further examine emerging evidence for tissue-resident memory B cell populations in the respiratory airways and their implications for mucosal vaccination strategies against airborne pathogens. Together, these findings provide a framework for leveraging memory B cell biology in clinical applications.

Chemotactic receptors involved in generation of ectopic pulmonary germinal centers (GCs) within inducible bronchus-associated lymphoid tissue (iBALT) are poorly defined. Here, using CIBER Cxcr3 -reporter mice, we demonstrate that the prototypical type 1 inflammatory chemokine receptor CXCR3 is highly induced in influenza A virus (IAV)-reactive B cells in the mediastinal lymph node, spleen, lung, peripheral blood, and airways following intranasal infection. Notably, elevated Cxcr3 was observed in ectopic pulmonary germinal center B (GCB) cells in iBALT relative to their contemporaneous counterparts in secondary lymphoid organs across the timecourse of the response to IAV infection. Mice with a B cell–specific deletion of Cxcr3 displayed a 50 to 60% reduction in the frequency and number of ectopic GCB cells in the lungs at the peak of the response following IAV infection, relative to controls. Furthermore, in cotransfers, Cxcr3 -deficient B cells were substantially outcompeted by their Cxcr3 -sufficient counterparts for ectopic pulmonary GC participation, but were not impacted with respect to GCB cell frequencies in other compartments. Thus, the data elucidate the requirement of B cell–intrinsic CXCR3 expression for efficient generation of ectopic pulmonary GCB cell responses in iBALT following respiratory viral infection with IAV, a finding that broadens understanding of the molecular cues underpinning this key component of local protective humoral immunity to IAV.

STING is an important component in the host innate immune system where its activation by cyclic dinucleotides culminates in the production of interferons and pro-inflammatory cytokines that mediate host defence against infection. While the mechanisms that govern STING-induced interferon production have been comprehensively characterised, how pro-inflammatory cytokines are produced downstream of STING remains less understood. Here we discover that IRF3 is critical for effective STING-mediated inflammatory cytokine production from macrophages as those lacking IRF3 display significant defects. Interestingly, the loss of IRF3 does not impact the activation of the prominent pro-inflammatory transcription factor, NF-κB, but rather affects the AP-1 transcriptional complex. We further discover the role of IRF3 in STING inflammatory responses is independent of its phosphorylation and distinct from its role as a transcription factor for induction of type I interferons. This additional activity of IRF3 is dependent on its recruitment to the previously defined IRF3 binding motif within the C-terminal tail of STING. Hence, our findings reveal an unexpected noncanonical function of IRF3 that is critical for mediating STING-induced pro-inflammatory cytokines from macrophages.

Spatial transcriptomics (ST) has rapidly expanded with the introduction of multiple high-resolution platforms, yet cross-platform benchmarking remains limited and largely focused on technical performance. Here we present SpatialBench , a matched multi-platform resource comprising Visium HD, Xenium and MERSCOPE data together with single-cell and single-nucleus references from a malaria-challenged wild-type and B cell-specific Tbx21 knockout mouse spleen model. In this system, loss of T-bet in B cells disrupts germinal center (GC) polarization and antibody maturation, providing a biologically grounded benchmark for technology comparison. We leveraged this system to systematically evaluate ST platform performance using technical and biological readouts. Across platforms, immune organization and Tbx21 -associated programs were consistently recovered, indicating robustness of major biological signals. Platforms instead differed in the level of biological resolution accessible. Visium HD enabled transcriptome-scale GC characterization and, together with Xenium, resolved dark and light zone organization, whereas GC zonation was not resolved in MERSCOPE, consistent with differences in transcript detection sensitivity. SpatialBench provides a biologically defined reference dataset for evaluation of ST technologies, method development, computational benchmarking, and studies of GC spatial organization in lymphoid tissue.

The nasopharyngeal tissues provide a frontline defense against airborne exposure to viruses, bacteria, and allergens. In this issue of JEM, Tachó-Piñot et al. (https://doi.org/10.1084/jem.20251752) show that mutated IgD+ B cell subsets populate epithelial areas of nasopharyngeal mucosa, ready to tackle a multitude of antigenic targets.

Soil-transmitted helminths are one of the most common infections globally, yet how to promote effective gut-associated humoral responses is not well understood. We identify the histone methyltransferase MLL1 as a key target to promote IgA-driven responses. Mll1 was increased in germinal center B cells in gut-associated lymphoid tissues, and Mll1-deficiency led to changes in the histone modification H3K4me3 on key B cell and immune-regulatory genes. Correspondingly, MLL1-deficient B cells had defective germinal centers and IgG1 in response to the helminth Trichuris muris. Yet Mll1^f/fCd23^cre/+ mice expelled worms more rapidly compared to control mice. Accelerated worm clearance correlated with elevated immunoglobulin A (IgA)⁺ plasma cells, as well as both serum and fecal IgA. RNA-sequencing identified CCR9 as a key MLL1-regulated molecule. As such, Mll1^f/fCd23^cre/+ mice infected with T. muris had increased IgA⁺CCR9⁺ PC localized in the large intestine. Regulation of IgA by MLL1 was confirmed beyond T. muris infection. In vitro cultures confirmed Mll1-deficiency increased IgA⁺ plasma cells in a B cell-intrinsic manner, and IgA production was also increased in Mll1^f/fCd23^cre/+ mice infected with the bacterium Citrobacter rodentium. This study reveals MLL1 as a key target to promote IgA responses to gut-associated infections.

Disruptor of telomeric silencing 1-like (DOT1L) is an epigenetic regulator that promotes gene expression by methylating lysine 79 on histone H3 and recruits transcription factors to gene targets. DOT1L is also an oncogenic driver in cancers that affect developing lymphocytes, yet how DOT1L activity regulates B-cell maturation remains poorly defined. Here, we use deep-sequencing and conditional knockout models to elucidate gene targets of H3K79me2, and the mechanistic contribution of DOT1L, during key stages of murine B-cell development. In the bone marrow, Dot1l was upregulated in pro B cells. Deep sequencing revealed that H3K79me2 accumulated during maturation. The genomic distribution of H3K79me2 peaks indicated that DOT1L regulates transcription and the cell cycle across different stages of B-cell development. As such, DOT1L was found to be essential for pre B-cell expansion, leading to a significant decrease in pre B cells in the absence of DOT1L and a skewing of the B-cell receptor repertoire to favor proximal VH usage. In addition to the effective generation of a diverse B-cell pool, DOT1L was also required to establish the marginal zone (MZ) B-cell gene expression program. Attenuation of MZ B cells and a bottlenecking at the pre-MZ B-cell stage in Dot1L-deficient mice correlated to H3K79me2 peaks at key MZ-regulatory genes such as Lfng and Dock10 in developing B cells. In contrast, Dot1l was reexpressed in germinal center (GC) B cells postimmunization to deposit H3K79me2 at key GC B-cell gene loci during GC differentiation. Together, these data demonstrate a vital role for DOT1L during B-cell lymphopoiesis, MZ B-cell generation, and GC B-cell biology.

CD4⁺ T follicular helper (T_FH) cells support tailored B cell responses against multiple classes of pathogens. To reveal how diverse T_FH phenotypes are established, we profiled mouse T_FH cells in response to viral, helminth and bacterial infection. We identified a core T_FH signature that is distinct from CD4⁺ T follicular regulatory and effector cells and identified pathogen-specific transcriptional modules that shape T_FH function. Cytokine-transcriptional T_FH programming demonstrated that type I interferon and TGFβ signaling direct individual T_FH phenotypes to instruct B cell output. Cytokine-directed T_FH transcriptional phenotypes are shared within human germinal centers, but distinct T_FH phenotypes dominate between donors and following immune challenge or in antibody-mediated disease. Finally, we identified new cell surface markers that align with distinct T_FH phenotypes. Thus, we provide a comprehensive resource of T_FH diversity in humans and mice to enable immune monitoring during infection and disease and to inform the development of context-specific vaccines.