Tingible body macrophages arise from lymph node-resident precursors and uptake B cells by dendrites

The unusual metabolism of germinal center B cells

In the germinal center (GC), B cells undergo rounds of somatic hypermutation (SHM), proliferation, and positive selection to develop into high-affinity, long-lived plasma cells and memory B cells. It is well established that, upon activation, B cells significantly alter their metabolism, but until recently little was understood about their metabolism within the GC. In this review we discuss novel in vivo models in which GC B cell (GCBC) metabolism is disrupted; these have greatly increased our understanding of B cell metabolic phenotype. GCBCs are unusual in that, unlike almost all other rapidly proliferating immune cells, they use little glycolysis but prefer fatty acid oxidation (FAO) to fuel ATP synthesis, whilst preferentially utilizing glucose and amino acids as carbon and nitrogen sources for biosynthetic pathways.

The cellular factors that impair the germinal center in advanced age

Long-lasting immunological memory is a core feature of the adaptive immune system that allows an organism to have a potent recall response to foreign agents that have been previously encountered. Persistent humoral immunity is afforded by long-lived memory B cells and plasma cells, which can mature in germinal centers (GCs) in secondary lymphoid organs. The development of new GC-derived immunity diminishes with age, thereby impairing our immune system's response to both natural infections and vaccinations. This review will describe the current knowledge of how aging affects the cells and microenvironment of the GC. A greater understanding of how the GC changes with age, and how to circumvent these changes, will be critical for tailoring vaccines for older people. This area of research is critical given the twenty-first century will witness a doubling of the aging population and an increased frequency of pandemics.

Durable lymphocyte subset elimination upon a single dose of AAV-delivered depletion antibody dissects immune control of chronic viral infection

To interrogate the role of specific immune cells in infection, cancer, and autoimmunity, immunologists commonly use monoclonal depletion antibodies (depletion-mAbs) or genetically engineered mouse models (GEMMs). To generate a tool that combines specific advantages and avoids select drawbacks of the two methods, we engineered adeno-associated viral vectors expressing depletion mAbs (depletion-AAVs). Single-dose depletion-AAV administration durably eliminated lymphocyte subsets in mice and avoided accessory deficiencies of GEMMs, such as marginal zone defects in B cell-deficient animals. Depletion-AAVs can be used in animals of different genetic backgrounds, and multiple depletion-AAVs can readily be combined. Exploiting depletion-AAV technology, we showed that B cells were required for unimpaired CD4+ and CD8+ T cell responses to chronic lymphocytic choriomeningitis virus (LCMV) infection. Upon B cell depletion, CD8+ T cells failed to suppress viremia, and they only helped resolve chronic infection when antibodies dampened viral loads. Our study positions depletion-AAVs as a versatile tool for immunological research.

The cross-talk between B cells and macrophages

B cells and macrophages are significant immune cells that maintain the immune balance of the body. B cells are involved in humoral immunity, producing immune effects mainly by secreting antibodies. Macrophages participate in non-specific and specific immune responses. To gain a further understanding of macrophages and B cells, researchers have not only paid attention to the unidirectional influence between B cells and macrophages, but also have focused on the cross-talk between them, and the effect of this cross talk on diseases. Therefore, this review summarizes the influence of macrophages on B cells, the ways and mechanisms by which B cells affect macrophages, and their cross-talk, leading to a more comprehensive understanding of the mechanism of the interaction between macrophages and B cells.

Cellular and Molecular Immunity to Influenza Viruses and Vaccines

Immune responses to influenza (flu) antigens reflect memory of prior infections or vaccinations, which might influence immunity to new flu antigens. Memory of past antigens has been termed "original antigenic sin" or, more recently, "immune imprinting" and "seniority". We have researched a comparison between the immune response to live flu infections and inactivated flu vaccinations. A brief history of antibody generation theories is presented, culminating in new findings about the immune-network theory and suggesting that a network of clones exists between anti-idiotypic antibodies and T cell receptors. Findings regarding the 2009 pandemic flu strain and immune responses to it are presented, including memory B cells and conserved regions within the hemagglutinin protein. The importance of CD4+ memory T cells and cytotoxic CD8+ T cells responding to both infections and vaccinations are discussed and compared. Innate immune cells, like natural killer (NK) cells and macrophages, are discussed regarding their roles in adaptive immune responses. Antigen presentation via macroautophagy processes is described. New vaccines in development are mentioned along with the results of some clinical trials. The manuscript concludes with how repeated vaccinations are impacting the immune system and a sketch of what might be behind the imprinting phenomenon, including future research directions.

Spatially-resolved transcriptomics reveal macrophage heterogeneity and prognostic significance in diffuse large B-cell lymphoma

Macrophages are abundant immune cells in the microenvironment of diffuse large B-cell lymphoma (DLBCL). Macrophage estimation by immunohistochemistry shows varying prognostic significance across studies in DLBCL, and does not provide a comprehensive analysis of macrophage subtypes. Here, using digital spatial profiling with whole transcriptome analysis of CD68+ cells, we characterize macrophages in distinct spatial niches of reactive lymphoid tissues (RLTs) and DLBCL. We reveal transcriptomic differences between macrophages within RLTs (light zone /dark zone, germinal center/ interfollicular), and between disease states (RLTs/ DLBCL), which we then use to generate six spatially-derived macrophage signatures (MacroSigs). We proceed to interrogate these MacroSigs in macrophage and DLBCL single-cell RNA-sequencing datasets, and in gene-expression data from multiple DLBCL cohorts. We show that specific MacroSigs are associated with cell-of-origin subtypes and overall survival in DLBCL. This study provides a spatially-resolved whole-transcriptome atlas of macrophages in reactive and malignant lymphoid tissues, showing biological and clinical significance.

The multivalency game ruling the biology of immunity

Macrophages play a crucial role in our immune system, preserving tissue health and defending against harmful pathogens. This article examines the diversity of macrophages influenced by tissue-specific functions and developmental origins, both in normal and disease conditions. Understanding the spectrum of macrophage activation states, especially in pathological situations where they contribute significantly to disease progression, is essential to develop targeted therapies effectively. These states are characterized by unique receptor compositions and phenotypes, but they share commonalities. Traditional drugs that target individual entities are often insufficient. A promising approach involves using multivalent systems adorned with multiple ligands to selectively target specific macrophage populations based on their phenotype. Achieving this requires constructing supramolecular structures, typically at the nanoscale. This review explores the theoretical foundation of engineered multivalent nanosystems, dissecting the key parameters governing specific interactions. The goal is to design targeting systems based on distinct cell phenotypes, providing a pragmatic approach to navigating macrophage heterogeneity's complexities for more effective therapeutic interventions.

IL-21 shapes germinal center polarization via light zone B cell selection and cyclin D3 upregulation

Germinal center (GC) dysregulation has been widely reported in the context of autoimmunity. Here, we show that interleukin 21 (IL-21), the archetypal follicular helper T cell (Tfh) cytokine, shapes the scale and polarization of spontaneous chronic autoimmune as well as transient immunization-induced GC. We find that IL-21 receptor deficiency results in smaller GC that are profoundly skewed toward a light zone GC B cell phenotype and that IL-21 plays a key role in selection of light zone GC B cells for entry to the dark zone. Light zone skewing has been previously reported in mice lacking the cell cycle regulator cyclin D3. We demonstrate that IL-21 triggers cyclin D3 upregulation in GC B cells, thereby tuning dark zone inertial cell cycling. Lastly, we identify Foxo1 regulation as a link between IL-21 signaling and GC dark zone formation. These findings reveal new biological roles for IL-21 within GC and have implications for autoimmune settings where IL-21 is overproduced.

Hijacking homeostasis: Regulation of the tumor microenvironment by apoptosis

Cancers are genetically driven, rogue tissues which generate dysfunctional, obdurate organs by hijacking normal, homeostatic programs. Apoptosis is an evolutionarily conserved regulated cell death program and a profoundly important homeostatic mechanism that is common (alongside tumor cell proliferation) in actively growing cancers, as well as in tumors responding to cytotoxic anti-cancer therapies. Although well known for its cell-autonomous tumor-suppressive qualities, apoptosis harbors pro-oncogenic properties which are deployed through non-cell-autonomous mechanisms and which generally remain poorly defined. Here, the roles of apoptosis in tumor biology are reviewed, with particular focus on the secreted and fragmentation products of apoptotic tumor cells and their effects on tumor-associated macrophages, key supportive cells in the aberrant homeostasis of the tumor microenvironment. Historical aspects of cell loss in tumor growth kinetics are considered and the impact (and potential impact) on tumor growth of apoptotic-cell clearance (efferocytosis) as well as released soluble and extracellular vesicle-associated factors are discussed from the perspectives of inflammation, tissue repair, and regeneration programs. An "apoptosis-centric" view is proposed in which dying tumor cells provide an important platform for intricate intercellular communication networks in growing cancers. The perspective has implications for future research and for improving cancer diagnosis and therapy.

Molecular mechanisms insulating proliferation from genotoxic stress in B lymphocytes

In mammals, B cells strictly segregate proliferation from somatic mutation as they develop within the bone marrow and then mature through germinal centers (GCs) in the periphery. Failure to do so risks autoimmunity and neoplastic transformation. Recent work has described how B cell progenitors transition between proliferation and mutation via cytokine signaling pathways, epigenetic chromatin regulation, and remodeling of 3D chromatin conformation. We propose a three-zone model of the GC that describes how proliferation and mutation are regulated. Using this model, we consider how recent mechanistic discoveries in B cell progenitors inform models of GC B cell function and reveal fundamental mechanisms underpinning humoral immunity, autoimmunity, and lymphomagenesis.

Tingible body macrophages: Gargantuan chameleons of the germinal center

Tingible body macrophages in lymph node are involved in cleaning up debris from apoptotic B cells. Gurwisz et al. (2023. J. Exp. Med.https://doi.org/10.1084/jem.20222173) and Grootveld et al. (2023. Cell.https://doi.org/10.1016/j.cell.2023.02.004) report how tingible body macrophages, originating from tissue-resident macrophages, clear apoptotic B cells in the germinal center using a "stand-hunting" strategy.