Secondary influenza challenge triggers resident memory B cell migration and rapid relocation to boost antibody secretion at infected sites

A 14-year influenza reinfection surveillance in Chongqing, China: A retrospective analysis

Influenza poses a significant medical burden and has the potential to cause global pandemics. To better understand the epidemiological characteristics of influenza reinfections and identify factors associated with an increased risk of reinfection, we analyzed influenza data from 2010 to 2023 obtained from the National Notifiable Infectious Disease Reporting Information System in Chongqing, China. The Andersen-Gill model was used to evaluate the association between demographic characteristics and the risk of reinfection. A total of 676,811.47 person-years were observed, with a median time to reinfection of 9.40 months. The log-rank test revealed significant differences in reinfection probability by sex, age, occupation, and residence (p < .001). Independent risk factors for influenza reinfection included male sex (adjusted hazard ratio [aHR]: 1.026, 95% confidence interval [CI]: 1.004-1.049), age ≤ 5 years (aHR: 4.645, 95% CI: 4.292-5.027), 6-18 years (aHR: 3.891, 95% CI: 3.574-4.235), age 46-64 years (aHR: 1.336, 95% CI: 1.158-1.541), and age ≥ 65 years (aHR: 2.946, 95% CI: 2.533-3.426), urban residency (aHR: 1.353, 95% CI: 1.315-1.391), and preschool-aged children (aHR: 2.103, 95% CI: 1.830-2.416). Influenza reinfection in Chongqing is relatively common and significantly associated with several key factors, including male sex, age ≤ 18 or > 45 years, preschool-aged children, and urban residency. These findings underscore the importance of tailored public health strategies, particularly promoting influenza vaccination among at-risk groups, to protect vulnerable populations from reinfection. Future studies are needed to refine influenza prevention measures for at-risk individuals, especially those susceptible to reinfection.

Prospective multicenter study identifying prognostic biomarkers and microbial profiles in severe CAP using BALF, blood mNGS, and PBMC transcriptomics

To identify potential biomarkers associated with the prognosis and severity of severe community-acquired pneumonia (SCAP), we conducted a multi-center prospective study from January 1, 2022, to December 31, 2023, enrolling 14 mild CAP and 75 SCAP patients in Shanghai, China. Patients underwent bronchoalveolar lavage fluid (BALF) and blood metagenomic next-generation sequencing (mNGS) as well as peripheral blood mononuclear cell (PBMC) transcriptomics. Among the 75 SCAP patients, 32 died within 30 days, with older age, a history of allergies, and comorbidities like cerebrovascular disease linked to worse outcomes. BALF mNGS showed greater microbial diversity, revealing a higher prevalence of pathogens, including Acinetobacter baumannii, Klebsiella pneumoniae, and Candida albicans, compared to mild CAP patients. RNA sequencing identified 431 differentially expressed genes in deceased SCAP patients, with significant alterations in immune pathways. Notably, microbial markers such as Pneumocystis jirovecii and viral markers like Human cytomegalovirus were associated with poor outcomes. Transcriptomic biomarkers, including otoferlin (OTOF), MS4A4A, and SIGLEC1, were identified as potential prognostic indicators for SCAP severity. GSEA and traditional GO/KEGG analyses identified key immune and metabolic pathways in SCAP (death) patients, including upregulation of complement activation, oxidative phosphorylation, nitrogen metabolism, while downregulation of adaptive immune response, hematopoietic cell lineage, and antigen processing pathways. These findings underscore the superiority of BALF mNGS over blood mNGS for pathogen detection, revealing microbial differences and transcriptomic alterations between mild and severe cases while identifying prognostic markers for SCAP treatment strategies.

Intranasal vaccination with multi-neuraminidase and M2e virus-like particle vaccine results in greater mucosal immunity and protection against influenza than intramuscular injection

Intramuscular injection of seasonal influenza vaccines provides strain-specific neutralizing antibodies, but not against variants, and no effective mucosal immunity. Here, we report that multi-subtype neuraminidase (NA) and M2 ectodomain repeat (5xM2e) virus-like particle vaccine (NA-M2e) conferred higher efficacy of broad cross-protection after two doses of intranasal delivery than intramuscular injection. The intranasally vaccinated mice displayed high levels of IgA antibodies, IFN-γ+ CD4 and CD8 T cells, germinal center B cells, plasma cells, and early innate immune cells locally in the lungs. In contrast, intramuscular vaccination systemically induced innate and adaptive immune responses in the spleen. Our findings demonstrate that the intranasal delivery of NA-M2e vaccine induces enhanced mucosal immunity and comparable serum IgG antibodies, offering improved efficacy of cross-protection against diverse influenza virus strains compared to the intramuscular injection in a mouse model.

Beyond circulating B cells: Characteristics and role of tissue-infiltrating B cells in systemic sclerosis

B cells play a key role in the pathophysiology of systemic sclerosis (SSc). While they are less characterized than their circulating counterparts, tissue-infiltrating B cells may have a more direct pathological role in tissues. In this review, we decipher the multiple evidence of B cells infiltration in the skin and lungs of SSc patients and animal models of SSc but also of other chronic fibrotic diseases with similar pathological mechanisms such as chronic graft versus host disease, idiopathic pulmonary fibrosis or morphea. We also recapitulate the current knowledge about mechanisms of B cells infiltration and their functions in tissues. Finally, we discuss B cell targeted therapies, and their specific impact on infiltrated B cells. Understanding the local consequences of infiltrating B cells is an important step for a better management of patients and the improvement of therapies in SSc.

Macrophages direct location-dependent recall of B cell memory to vaccination

Vaccines generate long-lived plasma cells and memory B cells (Bmems) that may re-enter secondary germinal centers (GCs) to further mutate their B cell receptor upon boosting and re-exposure to antigen. We show in mouse models that lymph nodes draining the site of primary vaccination harbor a subset of Bmems that reside in the subcapsular niche, generate larger recall responses, and are more likely to re-enter GCs compared with circulating Bmems in non-draining lymph nodes. This location-dependent recall of Bmems into the GC in the draining lymph node was dependent on CD169+ subcapsular sinus macrophages (SSMs) in the subcapsular niche. In human participants, boosting of the BNT162b2 vaccine in the same arm generated more rapid secretion of broadly neutralizing antibodies, GC participation, and clonal expansion of SARS-CoV-2-specific B cells than boosting of the opposite arm. These data reveal an unappreciated role for primed draining lymph node SSMs in Bmem cell fate determination.

Activation and maturation of antigen-specific B cells in nonectopic lung infiltrates are independent of germinal center reactions in the draining lymph node

Pulmonary T and B cells are important for protection of this mucosal barrier site. While viral infections lead to the development of ectopic lymphoid structures highly similar to those in germinal centers in secondary lymphoid organs, little is known about how T/B cooperation occurs in the unstructured, diffuse tissue infiltrates characteristic of autoimmune diseases and nonviral infections. Using a mouse model of interstitial lung inflammation, we found that naive B cells are directly activated in lung tissue. Despite the absence of any germinal center-like structures, the interaction of B cells with peripheral T helper cells results in efficient somatic hypermutation and class switching. As antigen-presenting cells, macrophages are critical for this process. Unique B-cell repertoires indicated that the lung response was autonomous from the lung-draining lymph node. Only lung GC-like B cells were switched to IgA and had a broader repertoire, making them ideal candidates for producing broadly neutralizing immunoglobulins against respiratory pathogens.

Lung B cells in ectopic germinal centers undergo affinity maturation

The lungs are constantly exposed to the external environment and a myriad of antigenic challenges within the air. Chronic exposure to allergens and other airborne antigens can result in the formation of lymphocyte aggregates in the lung, which can harbor ectopic germinal centers (GCs). After allergen exposure, GCs that form in the lung are much smaller and less densely packed with B cells than lymph node GCs. Despite this, ectopic lung GCs support somatic hypermutation and affinity-based maturation as in lymph node GCs, and export memory B cells (MBCs) directly into the lung tissue. This demonstrates that the lung can locally diversify B cell responses and supports the generation of tissue MBC populations in situ.

The Integrated Pulmonary Immune Response to Pneumonia

Pneumonia is an acute respiratory infection of the lower respiratory tract. The effectiveness of the host immune response determines the severity of infection, or whether pneumonia occurs at all. The lungs house both innate and adaptive immune systems, which integrate their activities to provide host defense that eliminates microbes and prevents lower respiratory infection from becoming severe. Professional immune cells in the lung, like macrophages and lymphocytes, work with lung constituents, like epithelial cells and fibroblasts, to optimize antimicrobial defense. The dynamics of the immune response during infection and the immune components contributing to defense are influenced by prior experiences with respiratory pathogens, remodeling lung immunity in ways that improve responses against subsequent infections. This review covers how innate and adaptive immune activities coordinate inside the lung to provide integrated and effective immune resistance against respiratory pathogens.

EZH2 coordinates memory B-cell programming and recall responses

Antigen-experienced memory B-cells (MBC) are endowed with enhanced functional properties compared to naïve B cells and play an important role in the humoral response. However, the epigenetic enzymes and programs that govern their rapid differentiation are incompletely understood. Here, the role of the histone H3 lysine 27 methyltransferase EZH2 in the formation of MBC in response to an influenza infection was determined in Mus musculus. EZH2 was expressed in all postactivated B-cell subsets, including MBC and antibody-secreting cells (ASC), with maximal expression in germinal center (GC) B cells. Deletion of EZH2 resulted in a skewing of the MBC pool towards a non-GC, IgM+ MBC subset that failed to fully express CCR6 and CD73 at both early and late infection time points. Intriguingly, although EZH2 protein levels were reduced in knockout MBC, deletion was not fully efficient, indicating a strong selective pressure to maintain EZH2 methyltransferase activity. Single-cell RNA-seq of antigen-specific MBC identified a core set of upregulated genes that are likely EZH2 targets across MBC subsets. Finally, defects in the ability to form secondary ASC and GC cells in response to a lethal challenge were observed in EZH2-deficient mice, indicating significant functional impairment in the absence of EZH2. These data show that EZH2 is a critical epigenetic modulator of MBC differentiation and functional potential during reactivation.

Location, Location, Location: Spatial Immune-Stroma Crosstalk Drives Pathogenesis in Asthma

Chronic lung diseases including asthma are characterized by an abnormal immune response and active tissue remodeling. These changes in the architecture of the tissue are a fundamental part of the pathology across the life course of patients suffering from asthma. Current treatments aim at dampening the immune system hyperactivation, but effective drugs targeting stromal or acellular structures are still lacking. This is mainly due to the lack of a detailed understanding of the composition of the large airways and the cellular interactions taking place in this niche. We and others have revealed multiple aspects of the spatial architecture of the airway wall in response to airborne insults. In this review, we discuss four elements that we believe should be the focus of future asthma research across the life course, to increase understanding and improve therapies: (i) specialized lung niches, (ii) the 3D architecture of the epithelium, (iii) the extracellular matrix, and (iv) the vasculature. These components comprise the main stromal structures at the airway wall, each playing a key role in the development of asthma and directing the immune response. We summarize promising future directions that will enhance lung research, ultimately benefiting patients with asthma.

A locally administered single-cycle influenza vaccine expressing a non-fusogenic stabilized hemagglutinin stimulates strong T-cell and neutralizing antibody immunity

Current influenza vaccination approaches protect against specific viral strains, but do not consistently induce broad and long-lasting protection to the diversity of circulating influenza viruses. Single-cycle viruses delivered to the respiratory tract may offer a promising solution as they safely express a diverse array of viral antigens by undergoing just one round of cell infection in their host and stimulate broadly protective resident memory T-cell responses in the lung. We have previously developed a vaccine candidate called S-FLU, which is limited to a single cycle of infection by inactivation of the hemagglutinin signal sequence and induces a broadly cross-reactive T-cell response and antibodies to neuraminidase, but fails to induce neutralizing antibodies to hemagglutinin after intranasal administration. This study describes the development of CLEARFLU, a derivative of S-FLU, which is designed to add a neutralizing antibody response to hemagglutinin. In contrast to S-FLU, which does not express a hemagglutinin molecule at the infected cell surface, CLEARFLU viruses express a stabilized non-fusogenic hemagglutinin. They are equally limited to a single cycle of infection, but induce a neutralizing antibody response to the expressed hemagglutinin in addition to the cytotoxic T-lymphocyte (CTL) responses to internal proteins and antibodies to neuraminidase induced by S-FLU. This represents a notable advantage as CLEARFLU viruses may provide sterile immunity against strain-matched challenge as well as non-sterile protection against a broad range of influenza viruses.

IMPORTANCE

Influenza is a serious public health concern, causing seasonal epidemics as well as pandemics in people. Influenza can also cause severe agricultural losses due to its circulation in farmed poultry and swine. A major challenge in the control of influenza is the diversity of circulating viruses. Developing vaccines that stimulate immunity to a wide array of influenza viruses is therefore important for protecting human and animal populations from disease and death. In this study, we describe an approach for developing influenza vaccines that trigger immune mechanisms shown to induce broad protection against a diversity of viruses, while also conserving the strong protection against specific strains observed in existing vaccines.

Mucosal vaccination against SARS-CoV-2 using recombinant influenza viruses delivering self-assembling nanoparticles

Recombinant influenza viruses are promising vectors that can bolster antibody and resident lymphocyte responses within mucosal sites. This study evaluates recombinant influenza viruses with SARS-CoV-2 RBD genes in eliciting mucosal and systemic responses. Using reverse genetics, we generated replication-competent recombinant influenza viruses carrying heterologous RBD genes in monomeric, trimeric, or ferritin-based nanoparticle forms. Following intranasal immunisation, mice developed potent serological anti-RBD responses, with ferritin nanoparticles superseding monomeric or trimeric RBD responses. While parenteral and mucosal immunisation elicited robust anti-RBD IgG in serum, mucosal immunisation seeded respiratory IgA, RBD-specific lung-resident memory and germinal centre (GC) B cells. In animals with prior intramuscular vaccination, intranasal boosting with recombinant influenza vectors augmented mucosal IgG, IgA, GC and memory B cells, and SARS-CoV-2 lung neutralising titres. Recall of RBD-specific memory B cells via antigen re-exposure in the lung increased antibody-secreting cells in the lung-draining lymph nodes, with maintenance of lung GC B cells. Recombinant influenza-based vaccines effectively deliver highly immunogenic self-assembling nanoparticles, generating antibodies and B cells in the respiratory mucosa. This strategy provides a tractable pathway to augment lung-localised responses against recurrent respiratory viral infections.

B cells in non-lymphoid tissues

B cells have long been understood to be drivers of both humoral and cellular immunity. Recent advances underscore this importance but also indicate that in infection, inflammatory disease and cancer, B cells function directly at sites of inflammation and form tissue-resident memory populations. The spatial organization and cellular niches of tissue B cells have profound effects on their function and on disease outcome, as well as on patient response to therapy. Here we review the role of B cells in peripheral tissues in homeostasis and disease, and discuss the newly identified cellular and molecular signals that are involved in regulating their activity. We integrate emerging data from multi-omic human studies with experimental models to propose a framework for B cell function in tissue inflammation and homeostasis.

Inverted HA-EV immunization elicits stalk-specific influenza immunity and cross-protection in mice

Enhancing protective immunity in the respiratory tract is crucial to combat influenza infection and transmission. Developing mucosal universal influenza vaccines requires effective delivery platforms to overcome the respiratory mucosal barrier and stimulate appropriate innate immune reactions, thereby bridging adaptive immune responses with minimal necessary inflammation. Meanwhile, the vaccine platforms must be biocompatible. This study employed cell-derived extracellular vesicles (EVs) as a mucosal universal influenza vaccine platform. By conjugating influenza hemagglutinin (HA) onto EV surfaces through HA-receptor interaction, we achieved an upside-down (inverted) influenza HA configuration that exposed the conserved HA stalk region while partially hiding the globular head domain. Intranasal immunization with the resulting EVs induced robust HA stalk- and virus-specific serum antibody and mucosal immune responses in mice, protecting against heterologous virus infection. Notably, EVs derived from the lung epithelial cell line A549 induced superior cross-reactive antibodies and enhanced protection upon intranasal immunization. EVs conjugating multivalent HA elicited broadly cross-reactive antibody and cellular responses against different influenza strains. Our results demonstrated that EVs conjugating multiple inverted HAs represented an effective strategy for developing a mucosal universal influenza vaccine.

Affinity maturation of antibody responses is mediated by differential plasma cell proliferation

Increased antibody affinity over time after vaccination, known as affinity maturation, is a prototypical feature of immune responses. Recent studies have shown that a diverse collection of B cells, producing antibodies with a wide spectrum of different affinities, is selected into the plasma cell (PC) pathway. How affinity-permissive selection enables PC affinity maturation remains unknown. We found that PC precursors (prePCs) expressing high-affinity antibodies received higher levels of T follicular helper cell (TFH cell)-derived help and divided at higher rates compared with their lower-affinity counterparts once they left the germinal center. Our findings indicate that differential cell division by selected prePCs accounts for how diverse precursors develop into a PC compartment that mediates serological affinity maturation.

Tissue-resident immune cells: from defining characteristics to roles in diseases

Tissue-resident immune cells (TRICs) are a highly heterogeneous and plastic subpopulation of immune cells that reside in lymphoid or peripheral tissues without recirculation. These cells are endowed with notably distinct capabilities, setting them apart from their circulating leukocyte counterparts. Many studies demonstrate their complex roles in both health and disease, involving the regulation of homeostasis, protection, and destruction. The advancement of tissue-resolution technologies, such as single-cell sequencing and spatiotemporal omics, provides deeper insights into the cell morphology, characteristic markers, and dynamic transcriptional profiles of TRICs. Currently, the reported TRIC population includes tissue-resident T cells, tissue-resident memory B (BRM) cells, tissue-resident innate lymphocytes, tissue-resident macrophages, tissue-resident neutrophils (TRNs), and tissue-resident mast cells, but unignorably the existence of TRNs is controversial. Previous studies focus on one of them in specific tissues or diseases, however, the origins, developmental trajectories, and intercellular cross-talks of every TRIC type are not fully summarized. In addition, a systemic overview of TRICs in disease progression and the development of parallel therapeutic strategies is lacking. Here, we describe the development and function characteristics of all TRIC types and their major roles in health and diseases. We shed light on how to harness TRICs to offer new therapeutic targets and present burning questions in this field.

Alveolar Macrophages in Viral Respiratory Infections: Sentinels and Saboteurs of Lung Defense

Respiratory viral infections continue to cause pandemic and epidemic outbreaks in humans and animals. Under steady-state conditions, alveolar macrophages (AlvMϕ) fulfill a multitude of tasks in order to maintain tissue homeostasis. Due to their anatomic localization within the deep lung, AlvMϕ are prone to detect and react to inhaled viruses and thus play a role in the early pathogenesis of several respiratory viral infections. Here, detection of viral pathogens causes diverse antiviral and proinflammatory reactions. This fact not only makes them promising research targets, but also suggests them as potential targets for therapeutic and prophylactic approaches. This review aims to give a comprehensive overview of the current knowledge about the role of AlvMϕ in respiratory viral infections of humans and animals.

Immune crosstalk between respiratory and intestinal mucosal tissues in respiratory infections

Mucosal tissues, including those in the respiratory and gastrointestinal tracts, are critical barrier surfaces for pathogen invasion. Infections at these sites not only trigger local immune response, but also recruit immune cells from other tissues. Emerging evidence in the mouse models and human samples indicates that the immune crosstalk between the lung and gut critically impacts and determines the course of respiratory disease. Here we summarize the current knowledge of the immune crosstalk between the respiratory and gastrointestinal tracts, and discuss how immune cells are recruited and migrate between these tissues during respiratory infections. We also discuss how commensal bacteria contribute to these processes.

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.

Dissecting immunological mechanisms underlying influenza viral nucleoprotein-induced mucosal immunity against diverse viral strains

The nucleoprotein (NP) of type A influenza virus (IAV) is highly conserved across all virus strains, making it an attractive candidate antigen for universal vaccines. While various studies have explored NP-induced mucosal immunity, here we interrogated the mechanistic differences between intramuscular (IM) and intranasal (IN) delivery of a recombinant adenovirus carrying NP fused with a bifunctional CD40 ligand. Despite being less effective than IM delivery in inducing systemic cellular immune responses and antibody-dependent cellular cytotoxicity (ADCC), IN immunization elicited superior antigen-specific recall humoral and cellular response in the nasal associated lymphoid tissue (NALT) of the upper respiratory tract, the initial site of immune recognition and elimination of inhaled pathogens. IN vaccination also induced significantly stronger pulmonary T cell responses in the lower respiratory tract than IM vaccination, in particular the CD8 T cells. Moreover, blocking lymphocyte circulation abrogated IM but not IN immunization induced protection, illustrating the critical role of local memory immune response upon viral infection. Notably, the CD40-targeted nasal delivery not only improved the magnitude but also the breadth of protection, including against lethal challenge with a newly isolated highly pathogenic avian H5N1 strain. These findings are informative for the design of universal mucosal vaccines, where the predominant mode of protection is independent of neutralizing antibodies.

Lung-resident lymphocytes and their roles in respiratory infections and chronic respiratory diseases

Recent scientific breakthroughs have blurred traditional boundaries between innate and adaptive immunity, revealing a sophisticated network of tissue-resident cells that deliver immediate, localized immune responses. These lymphocytes not only provide rapid frontline defense but also present a paradoxical role in the pathogenesis of respiratory diseases such as asthma, chronic obstructive pulmonary disease, pulmonary fibrosis, and the long-term tissue consequences of viral infections including severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2). This review traverses the intricate landscape of lung-resident lymphocytes, delving into their origins, diverse functions, and their dualistic impact on pulmonary health. We dissect their interactions with the microenvironment and the regulatory mechanisms guiding their activity, with an emphasis on their contribution to both immune protection and immunopathology. This review aims to elucidate the complex narrative of these cells, enhancing our understanding of the development of precise therapeutic strategies to combat acute and chronic pulmonary diseases. Through this exploration, the review aspires to shed light on the potential of harnessing lung-resident lymphocytes for the treatment of respiratory conditions.

Affinity maturation of antibody responses is mediated by differential plasma cell proliferation

Increased antibody affinity over time after vaccination, known as affinity maturation, is a prototypical feature of immune responses. Recent studies have shown that a diverse collection of B cells, producing antibodies with a wide spectrum of different affinities, are selected into the plasma cell (PC) pathway. How affinity-permissive selection enables PC affinity maturation remains unknown. Here we report that PC precursors (prePC) expressing high affinity antibodies receive higher levels of T follicular helper (Tfh)-derived help and divide at higher rates than their lower affinity counterparts once they leave the GC. Thus, differential cell division by selected prePCs accounts for how diverse precursors develop into a PC compartment that mediates serological affinity maturation.

Antibody-mediated control mechanisms of viral infections

Antibodies generated after vaccination or natural pathogen exposure are essential mediators of protection against many infections. Most studies with viruses have focused on antibody neutralization, in which protection is conferred by the fragment antigen binding region (Fab) through targeting of different steps in the viral lifecycle including attachment, internalization, fusion, and egress. Beyond neutralization, the fragment crystallizable (Fc) region of antibodies can integrate innate and adaptive immune responses by engaging complement components and distinct Fc gamma receptors (FcγR) on different host immune cells. In this review, we discuss recent advances in our understanding of antibody neutralization and Fc effector functions, and the assays used to measure them. Additionally, we describe the contexts in which these mechanisms are associated with protection against viruses and highlight how Fc-FcγR interactions can improve the potency of antibody-based therapies.

Regional specialization within the mammalian respiratory immune system

The respiratory tract is exposed to infection from inhaled pathogens, including viruses, bacteria, and fungi. So far, a comprehensive assessment that integrates common and distinct aspects of the immune response along different areas of the respiratory tract has been lacking. Here, we discuss key recent findings regarding anatomical, functional, and microbial factors driving regional immune adaptation in the mammalian respiratory system, how they differ between mice and humans, and the similarities and differences with the gastrointestinal tract. We demonstrate that, under evolutionary pressure, mammals evolved spatially organized immune defenses that vary between the upper and lower respiratory tract. Overall, we propose that the functional specialization of the immune response along the respiratory tract has fundamental implications for the management of infectious or inflammatory diseases.

Phenotypic, transcriptomic, and spatial characterization of CD45RB+ naïve mature B cells: Implications in Sjögren's disease

The conventional classification of mature B cells overlooks the diversity within IgD+ CD27- naïve B cells. Here, to identify distinct mature naïve B cells, we categorized CD45RBMEM55- B cells (NA RB-) and CD45RBMEM55+ B cells (NA RB+) and explore their function and localization in circulation and tissues under physiological and pathological conditions. NA RB+ B cells, found in secondary lymphoid organs, differentiate into plasmablasts and secrete IgM. In Sjögren's disease, their numbers decrease, and they show over-activation and abnormal migration, suggesting an adaptive disease response. NA RB+ B cells also appear in inflamed salivary glands, indicating involvement in local immune responses. These findings highlight the distinct roles of NA RB+ B cells in health and Sjögren's disease.

A guide to adaptive immune memory

Immune memory - comprising T cells, B cells and plasma cells and their secreted antibodies - is crucial for human survival. It enables the rapid and effective clearance of a pathogen after re-exposure, to minimize damage to the host. When antigen-experienced, memory T cells become activated, they proliferate and produce effector molecules at faster rates and in greater magnitudes than antigen-inexperienced, naive cells. Similarly, memory B cells become activated and differentiate into antibody-secreting cells more rapidly than naive B cells, and they undergo processes that increase their affinity for antigen. The ability of T cells and B cells to form memory cells after antigen exposure is the rationale behind vaccination. Understanding immune memory not only is crucial for the design of more-efficacious vaccines but also has important implications for immunotherapies in infectious disease and cancer. This 'guide to' article provides an overview of the current understanding of the phenotype, function, location, and pathways for the generation, maintenance and protective capacity of memory T cells and memory B cells.

A Prime-Boost Vaccination Approach Induces Lung Resident Memory CD8+ T Cells Derived from Central Memory T Cells That Prevent Tumor Lung Metastasis

Memory T cells play a key role in immune protection against cancer. Vaccine-induced tissue-resident memory T (TRM) cells in the lung have been shown to protect against lung metastasis. Identifying the source of lung TRM cells can help to improve strategies, preventing tumor metastasis. Here, we found that a prime-boost vaccination approach using intramuscular DNA vaccine priming, followed by intranasal live-attenuated influenza-vectored vaccine (LAIV) boosting induced higher frequencies of lung CD8+ TRM cells compared with other vaccination regimens. Vaccine-induced lung CD8+ TRM cells, but not circulating memory T cells, conferred significant protection against metastatic melanoma and mesothelioma. Central memory T (TCM) cells induced by the DNA vaccination were major precursors of lung TRM cells established after the intranasal LAIV boost. Single-cell RNA sequencing analysis indicated that transcriptional reprogramming of TCM cells for differentiation into TRM cells in the lungs started as early as day 2 post the LAIV boost. Intranasal LAIV altered the mucosal microenvironment to recruit TCM cells via CXCR3-dependent chemotaxis and induced CD8+ TRM-associated transcriptional programs. These results identified TCM cells as the source of vaccine-induced CD8+ TRM cells that protect against lung metastasis. Significance: Prime-boost vaccination shapes the mucosal microenvironment and reprograms central memory T cells to generate lung resident memory T cells that protect against lung metastasis, providing insights for the optimization of vaccine strategies.

Lung influenza virus-specific memory CD4 T cell location and optimal cytokine production are dependent on interactions with lung antigen-presenting cells

Influenza A virus (IAV) infection leads to the formation of mucosal memory CD4 T cells that can protect the host. An in-depth understanding of the signals that shape memory cell development is required for more effective vaccine design. We have examined the formation of memory CD4 T cells in the lung following IAV infection of mice, characterizing changes to the lung landscape and immune cell composition. IAV-specific CD4 T cells were found throughout the lung at both primary and memory time points. These cells were found near lung airways and in close contact with a range of immune cells including macrophages, dendritic cells, and B cells. Interactions between lung IAV-specific CD4 T cells and major histocompatibility complex (MHC)II+ cells during the primary immune response were important in shaping the subsequent memory pool. Treatment with an anti-MHCII blocking antibody increased the proportion of memory CD4 T cells found in lung airways but reduced interferon-γ expression by IAV-specific immunodominant memory CD4 T cells. The immunodominant CD4 T cells expressed higher levels of programmed death ligand 1 (PD1) than other IAV-specific CD4 T cells and PD1+ memory CD4 T cells were located further away from MHCII+ cells than their PD1-low counterparts. This distinction in location was lost in mice treated with anti-MHCII antibodies. These data suggest that sustained antigen presentation in the lung impacts the formation of memory CD4 T cells by regulating their cytokine production and location.

Emerging Biochemical and Immunologic Mechanisms in the Pathogenesis of IgA Nephropathy

IgA nephropathy is a mesangioproliferative glomerular disease with significant morbidity and mortality. Most patients with IgA nephropathy develop kidney failure in their lifetime, reducing their life expectancy by a decade. Since its first description in 1968, it has been established that kidneys of IgA nephropathy patients are injured as "innocent bystanders" by nephritogenic IgA1-containing immune complexes. Results from clinical, biochemical, immunologic, and genetic studies suggest a multistep pathogenetic mechanism. In genetically predisposed individuals, this process results in formation of circulating immune complexes due to the binding of IgG/IgA autoantibodies to the polymeric IgA1 molecules with incomplete O-glycosylation. This event is followed by the addition of other proteins, such as complement C3, resulting in the formation of nephritogenic immune complexes. These complexes are not effectively removed from the circulation, and some of them pass through the fenestration of glomerular endothelial cells to enter the mesangial space and activate mesangial cells. It is thought that the process is initiated by soluble immune complexes and that their accumulation results in the formation of immunodeposits that further amplify glomerular injury. Here we summarize current understanding of the pathogenesis of IgA nephropathy and discuss experimental model systems that can inform development of new therapeutic strategies and targets.

Inflammatory response to SARS-CoV 2 and other respiratory viruses

INTRODUCTION

Lower respiratory tract infections (LRTI) remain a significant global cause of mortality and disability. Viruses constitute a substantial proportion of LRTI cases, with their pandemic potential posing a latent threat. After the SARS-CoV-2 pandemic, the resurgence of other respiratory viruses, including Influenza and Respiratory Syncytial Virus responsible for LRTI has been observed especially in susceptible populations.

AREAS COVERED

This review details the inflammatory mechanisms associated with three primary respiratory viruses: SARS-CoV-2, Influenza, and Respiratory Syncytial Virus (RSV). The focus will be on elucidating the activation of inflammatory pathways, understanding cellular contributions to inflammation, exploring the role of interferon and induced cell death in the response to these pathogens and detailing viral evasion mechanisms. Furthermore, the distinctive characteristics of each virus will be explained.

EXPERT OPINION

The study of viral pneumonia, notably concerning SARS-CoV-2, Influenza, and RSV, offers critical insights into infectious and inflammatory mechanisms with wide-ranging implications. Addressing current limitations, such as diagnostic accuracy and understanding host-virus interactions, requires collaborative efforts and investment in technology. Future research holds promise for uncovering novel therapeutic targets, exploring host microbiome roles, and addressing long-term sequelae. Integrating advances in molecular biology and technology will shape the evolving landscape of viral pneumonia research, potentially enhancing global public health outcomes.

Primary nasal influenza infection rewires tissue-scale memory response dynamics

The nasal mucosa is often the initial site of respiratory viral infection, replication, and transmission. Understanding how infection shapes tissue-scale primary and memory responses is critical for designing mucosal therapeutics and vaccines. We generated a single-cell RNA-sequencing atlas of the murine nasal mucosa, sampling three regions during primary influenza infection and rechallenge. Compositional analysis revealed restricted infection to the respiratory mucosa with stepwise changes in immune and epithelial cell subsets and states. We identified and characterized a rare subset of Krt13+ nasal immune-interacting floor epithelial (KNIIFE) cells, which concurrently increased with tissue-resident memory T (TRM)-like cells. Proportionality analysis, cell-cell communication inference, and microscopy underscored the CXCL16-CXCR6 axis between KNIIFE and TRM cells. Secondary influenza challenge induced accelerated and coordinated myeloid and lymphoid responses without epithelial proliferation. Together, this atlas serves as a reference for viral infection in the upper respiratory tract and highlights the efficacy of local coordinated memory responses.

Vaccine and antiviral drug promise for preventing post-acute sequelae of COVID-19, and their combination for its treatment

Introduction

Most healthy individuals recover from acute SARS-CoV-2 infection, whereas a remarkable number continues to suffer from unexplained symptoms, known as Long COVID or post-acute COVID-19 syndrome (PACS). It is therefore imperative that methods for preventing and treating the onset of PASC be investigated with the utmost urgency.

Methods

A mathematical model of the immune response to vaccination and viral infection with SARS-CoV-2, incorporating immune memory cells, was developed.

Results and discussion

Similar to our previous model, persistent infection was observed by the residual virus in the host, implying the possibility of chronic inflammation and delayed recovery from tissue injury. Pre-infectious vaccination and antiviral medication administered during onset can reduce the acute viral load; however, they show no beneficial effects in preventing persistent infection. Therefore, the impact of these treatments on the PASC, which has been clinically observed, is mainly attributed to their role in preventing severe tissue damage caused by acute viral infections. For PASC patients with persistent infection, vaccination was observed to cause an immediate rapid increase in viral load, followed by a temporary decrease over approximately one year. The former was effectively suppressed by the coadministration of antiviral medications, indicating that this combination is a promising treatment for PASC.

Regulation of B-cell function and expression of CD11c, T-bet, and FcRL5 in response to different activation signals

CD11c, FcRL5, or T-bet are commonly expressed by B cells expanding during inflammation, where they can make up >30% of mature B cells. However, the association between the proteins and differentiation and function in the host response remains largely unclear. We have assessed the co-expression of CD11c, T-bet, and FcRL5 in an in vitro B-cell culture system to determine how stimulation via the BCR, toll-like receptor 9 (TLR9), and different cytokines influence CD11c, T-bet, and FcRL5 expression. We observed different expression dynamics for all markers, but a largely overlapping regulation of CD11c and FcRL5 in response to BCR and TLR9 activation, while T-bet was strongly dependent on IFN-γ signaling. Investigating plasma cell differentiation and APC functions, there was no association between marker expression and antibody secretion or T-cell help. Rather the functions were associated with TLR9-signalling and B-cell-derived IL-6 production, respectively. These results suggest that the expression of CD11c, FcRL5, and T-bet and plasma cell differentiation and improved APC functions occur in parallel and are regulated by similar activation signals, but they are not interdependent.

Differential response of IgM and IgG memory B cell populations to CD40L: insights of T cell - memory B cell interactions

Memory B cells (mBCs) are characterized by their long-term stability, fast reactivation, and capability to rapidly differentiate into antibody-secreting cells (ASCs). However, the role of T cells in the differentiation of mBCs, in contrast to naive B cells, remains to be delineated. We study the role of T cells in mBC responses, using CD40L stimulation and autologous T-B co-cultures. Our results showed that increased CD40L levels led to a selective increased proliferation of IgM+ mBC, which did not class-switched, resulting in higher frequencies of IgM+ ASCs and a lower frequency of IgG+ ASCs. The IgG+/IgA+ mBCs were unaffected. We further compared the transcription of immune-related genes in IgM+ and IgG+ pre-plasmablasts cultured at high (500 ng/mL) and low (50 ng/mL) CD40L levels. In response to increased CD40L levels, both populations exhibited a core response to genes related to activation (TRAF1, AKT3, CD69, and CD80). However, they differed in genes related to cytokine/chemokine/homing interactions (CCL3/4/17, LTA, NKX2-3, BCL2 and IL21R) and cell-cell interactions (HLADR, CD40, and ICOSL), which were largely confined to IgG+ cells. Our findings revealed that in co-cultures with a high T-ratio, the response was similar to that found in cultures with high CD40L levels. These results suggest that IgG+ mBCs have a greater capacity for proliferation and T cell interaction, and weaker migration capabilities, leading to a preference for an IgG response over IgM in the short term. This adaptable response could fine-tune the memory repertoire with different functions of IgG versus IgM mBCs.

Regulation of pulmonary plasma cell responses during secondary infection with influenza virus

During secondary infection with influenza virus, plasma cells (PCs) develop within the lung, providing a local source of antibodies. However, the site and mechanisms that regulate this process are poorly defined. Here, we show that while circulating memory B cells entered the lung during rechallenge and were activated within inducible bronchus-associated lymphoid tissues (iBALTs), resident memory B (BRM) cells responded earlier, and their activation occurred in a different niche: directly near infected alveoli. This process required NK cells but was largely independent of CD4 and CD8 T cells. Innate stimuli induced by virus-like particles containing ssRNA triggered BRM cell differentiation in the absence of cognate antigen, suggesting a low threshold of activation. In contrast, expansion of PCs in iBALTs took longer to develop and was critically dependent on CD4 T cells. Our work demonstrates that spatially distinct mechanisms evolved to support pulmonary secondary PC responses, and it reveals a specialized function for BRM cells as guardians of the alveoli.

Xiaoer niuhuang qingxin powder alleviates influenza a virus infection by inhibiting the activation of the TLR4/MyD88/NF-κB signaling pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Xiaoer Niuhuang Qingxin Powder (XNQP) is a classic traditional Chinese medicine formula with significant clinical efficacy for treating febrile convulsions and influenza.

AIM OF THE STUDY

This study aims to explore the potential mechanisms of XNQP in combating combating the influenza A virus, providing a theoretical basis for its clinical application.

MATERIALS AND METHODS

The present investigation employed network pharmacology and bioinformatics analysis to determine the TLR4/MyD88/NF-κB signaling pathway as a viable target for XNQP intervention in IAV infection.Subsequently, a mouse model of influenza A virus infection was established, and different doses of XNQP were used for intervention. The protein expression levels of TLR4/MyD88/NF-κB were detected using HE staining, Elisa, immunohistochemistry, immunofluorescence, and western blot.

RESULTS

The results showed that treatment with XNQP after IAV infection reduced the mortality and prolonged the survival time of infected mice. It reduced the release of TNF-α and IFN-γ in the serum and alleviated pathological damage in the lung tissue following infection. Additionally, the levels of TLR4, MyD88, NF-κB, and p-NF-κB P65 proteins were significantly reduced in lung tissue by XNQP. The inhibitory effect of XNQP on the expression of MyD88 and NF-κB was antagonized when TLR4 signaling was overexpressed. Consequently, the expression levels of MyD88, NF-κB, and p-NF-κB P65 were increased in lung tissue. Conversely, the expression levels of the proteins MyD88, NF-κB, and p-NF-κB P65 were downregulated when TLR4 signaling was inhibited.

CONCLUSIONS

XNQP alleviated lung pathological changes, reduced serum levels of inflammatory factors, reduced mortality, and prolonged survival time in mice by inhibiting the overexpression of the TLR4/MyD88/NF-κB signaling pathway in lung tissues after IAV infection.

Inhaled aerosol viral-vectored vaccines against tuberculosis

Bacille Calmette-Guérin (BCG) remains the sole licensed vaccine against tuberculosis (TB), despite its variable efficacy in protecting against pulmonary TB. The development of effective TB vaccines faces significant challenges, marked by the absence of validated correlates of protection and predictive animal models. Strategic approaches to enhance TB vaccines and augment BCG efficacy include utilising prime-boost strategies with viral-vectored vaccines and exploring innovative delivery techniques, such as mucosal vaccine administration. Viral vectors offer numerous advantages, including the capacity to accommodate genes encoding extensive antigenic fragments and the induction of robust immune responses. Aerosol delivery aligns with the route of Mycobacterium tuberculosis infection and holds the potential to enhance protective mucosal immunity. Aerosolised viral-vectored vaccines overcome anti-vector immunity, facilitating repeated aerosol deliveries.

Polyanhydride nanovaccine against H3N2 influenza A virus generates mucosal resident and systemic immunity promoting protection

Influenza A virus (IAV) causes significant morbidity and mortality worldwide due to seasonal epidemics and periodic pandemics. The antigenic drift/shift of IAV continually gives rise to new strains and subtypes, aiding IAV in circumventing previously established immunity. As a result, there has been substantial interest in developing a broadly protective IAV vaccine that induces, durable immunity against multiple IAVs. Previously, a polyanhydride nanoparticle-based vaccine or nanovaccine (IAV-nanovax) encapsulating H1N1 IAV antigens was reported, which induced pulmonary B and T cell immunity and resulted in cross-strain protection against IAV. A key feature of IAV-nanovax is its ability to easily incorporate diverse proteins/payloads, potentially increasing its ability to provide broad protection against IAV and/or other pathogens. Due to human susceptibility to both H1N1 and H3N2 IAV, several H3N2 nanovaccines were formulated herein with multiple IAV antigens to examine the "plug-and-play" nature of the polyanhydride nanovaccine platform and determine their ability to induce humoral and cellular immunity and broad-based protection similar to IAV-nanovax. The H3N2-based IAV nanovaccine formulations induced systemic and mucosal B cell responses which were associated with antigen-specific antibodies. Additionally, systemic and lung-tissue resident CD4 and CD8 T cell responses were enhanced post-vaccination. These immune responses corresponded with protection against both homologous and heterosubtypic IAV infection. Overall, these results demonstrate the plug-and-play nature of the polyanhydride nanovaccine platform and its ability to generate immunity and protection against IAV utilizing diverse antigenic payloads.

B cell heterogeneity in human tuberculosis highlights compartment-specific phenotype and functional roles

B cells are important in tuberculosis (TB) immunity, but their role in the human lung is understudied. Here, we characterize B cells from lung tissue and matched blood of patients with TB and found they are decreased in the blood and increased in the lungs, consistent with recruitment to infected tissue, where they are located in granuloma associated lymphoid tissue. Flow cytometry and transcriptomics identify multiple B cell populations in the lung, including those associated with tissue resident memory, germinal centers, antibody secretion, proinflammatory atypical B cells, and regulatory B cells, some of which are expanded in TB disease. Additionally, TB lungs contain high levels of Mtb-reactive antibodies, specifically IgM, which promotes Mtb phagocytosis. Overall, these data reveal the presence of functionally diverse B cell subsets in the lungs of patients with TB and suggest several potential localized roles that may represent a target for interventions to promote immunity or mitigate immunopathology.

Principles and therapeutic applications of adaptive immunity

Adaptive immunity provides protection against infectious and malignant diseases. These effects are mediated by lymphocytes that sense and respond with targeted precision to perturbations induced by pathogens and tissue damage. Here, we review key principles underlying adaptive immunity orchestrated by distinct T cell and B cell populations and their extensions to disease therapies. We discuss the intracellular and intercellular processes shaping antigen specificity and recognition in immune activation and lymphocyte functions in mediating effector and memory responses. We also describe how lymphocytes balance protective immunity against autoimmunity and immunopathology, including during immune tolerance, response to chronic antigen stimulation, and adaptation to non-lymphoid tissues in coordinating tissue immunity and homeostasis. Finally, we discuss extracellular signals and cell-intrinsic programs underpinning adaptive immunity and conclude by summarizing key advances in vaccination and engineering adaptive immune responses for therapeutic interventions. A deeper understanding of these principles holds promise for uncovering new means to improve human health.

B cells in the pneumococcus-infected lung are heterogeneous and require CD4+ T cell help including CD40L to become resident memory B cells

Recovery from respiratory pneumococcal infections generates lung-localized protection against heterotypic bacteria, mediated by resident memory lymphocytes. Optimal protection in mice requires re-exposure to pneumococcus within days of initial infection. Serial surface marker phenotyping of B cell populations in a model of pneumococcal heterotypic immunity revealed that bacterial re-exposure stimulates the immediate accumulation of dynamic and heterogeneous populations of B cells in the lung, and is essential for the establishment of lung resident memory B (BRM) cells. The B cells in the early wave were activated, proliferating locally, and associated with both CD4+ T cells and CXCL13. Antagonist- and antibody-mediated interventions were implemented during this early timeframe to demonstrate that lymphocyte recirculation, CD4+ cells, and CD40 ligand (CD40L) signaling were all needed for lung BRM cell establishment, whereas CXCL13 signaling was not. While most prominent as aggregates in the loose connective tissue of bronchovascular bundles, morphometry and live lung imaging analyses showed that lung BRM cells were equally numerous as single cells dispersed throughout the alveolar septae. We propose that CD40L signaling from antigen-stimulated CD4+ T cells in the infected lung is critical to establishment of local BRM cells, which subsequently protect the airways and parenchyma against future potential infections.

Role of germinal center and CD39highCD73+ B cells in the age-related tonsillar involution

BACKGROUND

The tonsils operate as a protection ring of mucosa at the gates of the upper aero-digestive tract. They show similarities with lymph nodes and participate as inductive organs of systemic and mucosal immunity. Based on the reduction of their size since puberty, they are thought to experience involution in adulthood. In this context, we have used tonsillar mononuclear cells (TMC) isolated from patients at different stages of life, to study the effect of ageing and the concomitant persistent inflammation on these immune cells.

RESULTS

We found an age-dependent reduction in the proportion of germinal center B cell population (BGC) and its T cell counterpart (T follicular helper germinal center cells, TfhGC). Also, we demonstrated an increment in the percentage of local memory B cells and mantle zone T follicular helper cells (mTfh). Furthermore, younger tonsils rendered higher proportion of proliferative immune cells within the freshly isolated TMC fraction than those from older ones. We demonstrated the accumulation of a B cell subset (CD20+CD39highCD73+ cells) metabolically adapted to catabolize adenosine triphosphate (ATP) as patients get older. To finish, tonsillar B cells from patients at different ages did not show differences in their proliferative response to stimulation ex vivo, in bulk TMC cultures.

CONCLUSIONS

This paper sheds light on the changing aspects of the immune cellular landscape, over the course of time and constant exposure, at the entrance of the respiratory and digestive systems. Our findings support the notion that there is a re-modelling of the immune functionality of the excised tonsils over time. They are indicative of a transition from an effector type of immune response, typically oriented to reduce pathogen burden early in life, to the development of an immunosuppressive microenvironment at later stages, when tissue damage control gets critical provided the time passed under immune attack. Noteworthy, when isolated from such histologic microenvironment, older tonsillar B cells seem to level their proliferation capacity with the younger ones. Understanding these features will not only contribute to comprehend the differences in susceptibility to pathogens among children and adults but would also impact on vaccine developments intended to target these relevant mucosal sites.

Primary nasal viral infection rewires the tissue-scale memory response

The nasal mucosa is frequently the initial site of respiratory viral infection, replication, and transmission. Recent work has started to clarify the independent responses of epithelial, myeloid, and lymphoid cells to viral infection in the nasal mucosa, but their spatiotemporal coordination and relative contributions remain unclear. Furthermore, understanding whether and how primary infection shapes tissue-scale memory responses to secondary challenge is critical for the rational design of nasal-targeting therapeutics and vaccines. Here, we generated a single-cell RNA-sequencing (scRNA-seq) atlas of the murine nasal mucosa sampling three distinct regions before and during primary and secondary influenza infection. Primary infection was largely restricted to respiratory mucosa and induced stepwise changes in cell type, subset, and state composition over time. Type I Interferon (IFN)-responsive neutrophils appeared 2 days post infection (dpi) and preceded transient IFN-responsive/cycling epithelial cell responses 5 dpi, which coincided with broader antiviral monocyte and NK cell accumulation. By 8 dpi, monocyte-derived macrophages (MDMs) expressing Cxcl9 and Cxcl16 arose alongside effector cytotoxic CD8 and Ifng-expressing CD4 T cells. Following viral clearance (14 dpi), rare, previously undescribed Krt13+ nasal immune-interacting floor epithelial (KNIIFE) cells expressing multiple genes with immune communication potential increased concurrently with tissue-resident memory T (TRM)-like cells and early IgG+/IgA+ plasmablasts. Proportionality analysis coupled with cell-cell communication inference, alongside validation by in situ microscopy, underscored the CXCL16-CXCR6 signaling axis between MDMs and effector CD8 T cells 8dpi and KNIIFE cells and TRM cells 14 dpi. Secondary influenza challenge with a homologous or heterologous strain administered 60 dpi induced an accelerated and coordinated myeloid and lymphoid response without epithelial proliferation, illustrating how tissue-scale memory to natural infection engages both myeloid and lymphoid cells to reduce epithelial regenerative burden. Together, this atlas serves as a reference for viral infection in the upper respiratory tract and highlights the efficacy of local coordinated memory responses upon rechallenge.

B cell memory: from generation to reactivation: a multipronged defense wall against pathogens

Development of B cell memory is a conundrum that scientists are still exploring. Studies have been conducted in vitro and using advanced animal models to elucidate the mechanism underlying the generation of memory B cells (MBCs), the precise roles of MBCs against pathogens, and their protective functions against repeated infections throughout life. Lifelong immunity against invading diseases is mainly the result of overcoming a single infection. This protection is largely mediated by the two main components of B cell memory-MBCs and long-lived plasma cells (PCs). The chemical and cellular mechanisms that encourage fat selection for MBCs or long-lived PCs are an area of active research. Despite the fact that nearly all available vaccinations rely on the capacity to elicit B-cell memory, we have yet to develop successful vaccines that can induce broad-scale protective MBCs against some of the deadliest diseases, including malaria and AIDS. A deeper understanding of the specific cellular and molecular pathways that govern the generation, function, and reactivation of MBCs is critical for overcoming the challenges associated with vaccine development. Here, we reviewed literature on the development of MBCs and their reactivation, interaction with other cell types, strategies against invading pathogens, and function throughout life and discussed the recent advances regarding the key signals and transcription factors which regulate B cell memory and their relevance to the quest for vaccine development.

Mucosal Immunity against SARS-CoV-2 in the Respiratory Tract

The respiratory tract, the first-line defense, is constantly exposed to inhaled allergens, pollutants, and pathogens such as respiratory viruses. Emerging evidence has demonstrated that the coordination of innate and adaptive immune responses in the respiratory tract plays a crucial role in the protection against invading respiratory pathogens. Therefore, a better understanding of mucosal immunity in the airways is critical for the development of novel therapeutics and next-generation vaccines against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and other respiratory viruses. Since the coronavirus disease 2019 pandemic, our knowledge of mucosal immune responses in the airways has expanded. In this review, we describe the latest knowledge regarding the key components of the mucosal immune system in the respiratory tract. In addition, we summarize the host immune responses in the upper and lower airways following SARS-CoV-2 infection and vaccination, and discuss the impact of allergic airway inflammation on mucosal immune responses against SARS-CoV-2.

Distinct fibroblast functions associated with fibrotic and immune-mediated inflammatory diseases and their implications for therapeutic development

Fibroblasts are ubiquitous cells that can adopt many functional states. As tissue-resident sentinels, they respond to acute damage signals and shape the earliest events in fibrotic and immune-mediated inflammatory diseases. Upon sensing an insult, fibroblasts produce chemokines and growth factors to organize and support the response. Depending on the size and composition of the resulting infiltrate, these activated fibroblasts may also begin to contract or relax thus changing local stiffness within the tissue. These early events likely contribute to the divergent clinical manifestations of fibrotic and immune-mediated inflammatory diseases. Further, distinct changes to the cellular composition and signaling dialogue in these diseases drive progressive fibroblasts specialization. In fibrotic diseases, fibroblasts support the survival, activation and differentiation of myeloid cells, granulocytes and innate lymphocytes, and produce most of the pathogenic extracellular matrix proteins. Whereas, in immune-mediated inflammatory diseases, sequential accumulation of dendritic cells, T cells and B cells programs fibroblasts to support local, destructive adaptive immune responses. Fibroblast specialization has clear implications for the development of effective induction and maintenance therapies for patients with these clinically distinct diseases.

Memory B cells

Recent advances in studies of immune memory in mice and humans have reinforced the concept that memory B cells play a critical role in protection against repeated infections, particularly from variant viruses. Hence, insights into the development of high-quality memory B cells that can generate broadly neutralizing antibodies that bind such variants are key for successful vaccine development. Here, we review the cellular and molecular mechanisms by which memory B cells are generated and how these processes shape the antibody diversity and breadth of memory B cells. Then, we discuss the mechanisms of memory B cell reactivation in the context of established immune memory; the contribution of antibody feedback to this process has now begun to be reappreciated.

mRNA COVID-19 vaccine elicits potent adaptive immune response without the acute inflammation of SARS-CoV-2 infection

SARS-CoV-2 infection and vaccination elicit potent immune responses. Our study presents a comprehensive multimodal single-cell analysis of blood from COVID-19 patients and healthy volunteers receiving the SARS-CoV-2 vaccine and booster. We profiled immune responses via transcriptional analysis and lymphocyte repertoire reconstruction. COVID-19 patients displayed an enhanced interferon signature and cytotoxic gene upregulation, absent in vaccine recipients. B and T cell repertoire analysis revealed clonal expansion among effector cells in COVID-19 patients and memory cells in vaccine recipients. Furthermore, while clonal αβ T cell responses were observed in both COVID-19 patients and vaccine recipients, expansion of clonal γδ T cells was found only in infected individuals. Our dataset enables side-by-side comparison of immune responses to infection versus vaccination, including clonal B and T cell responses. Our comparative analysis shows that vaccination induces a robust, durable clonal B and T cell responses, without the severe inflammation associated with infection.

Germinal centers output clonally diverse plasma cell populations expressing high- and low-affinity antibodies

Germinal centers (GCs) form in lymph nodes after immunization or infection to facilitate antibody affinity maturation and memory and plasma cell (PC) development. PC differentiation is thought to involve stringent selection for GC B cells expressing the highest-affinity antigen receptors, but how this plays out during complex polyclonal responses is unclear. We combine temporal lineage tracing with antibody characterization to gain a snapshot of PCs developing during influenza infection. GCs co-mature B cell clones with antibody affinities spanning multiple orders of magnitude; however, each generates PCs with similar efficiencies, including weak binders. Within lineages, PC selection is not restricted to variants with the highest-affinity antibodies. Differentiation is commonly associated with proliferative expansion to produce "nodes" of identical PCs. Immunization-induced GCs generate fewer PCs but still of low- and high-antibody affinities. We propose that generating low-affinity antibody PCs reflects an evolutionary compromise to facilitate diverse serum antibody responses.

Rheumatoid Arthritis-Specific Autoimmunity in the Lung Before and at the Onset of Disease

OBJECTIVE

The lung is implicated as a site for breach of tolerance prior to onset of seropositive rheumatoid arthritis (RA). To substantiate this, we investigated lung-resident B cells in bronchoalveolar lavage (BAL) samples from untreated early RA patients and anti-citrullinated protein antibody (ACPA)-positive individuals at risk for developing RA.

METHODS

Single B cells (n = 7,680) were phenotyped and isolated from BAL samples from individuals at risk of RA (n = 3) and at RA diagnosis (n = 9). The immunoglobulin variable region transcripts were sequenced and selected for expression as monoclonal antibodies (n = 141). Monoclonal ACPAs were tested for reactivity patterns and binding to neutrophils.

RESULTS

Using our single-cell approach, we found significantly increased proportions of B lymphocytes in ACPA+ compared to ACPA- individuals. Memory and double-negative B cells were prominent in all subgroups. Upon antibody re-expression, 7 highly mutated citrulline-autoreactive clones originating from different memory B cell subsets were identified, both in individuals at risk of RA and early RA patients. Lung IgG variable gene transcripts from ACPA+ individuals carried frequent mutation-induced N-linked Fab glycosylation sites (P < 0.001), often in the framework 3 of the variable region. Two of the lung ACPAs bound to activated neutrophils, 1 from an individual at risk of RA and 1 from an early RA patient.

CONCLUSION

T cell-driven B cell differentiation resulting in local class switching and somatic hypermutation are evident in lungs before as well as in early stages of ACPA+ RA. Our findings add to the notion of lung mucosa being a site for initiation of citrulline autoimmunity preceding seropositive RA.