Secreted IgD Amplifies Humoral T Helper 2 Cell Responses by Binding Basophils via Galectin-9 and CD44

A novel IgD-FcδR blocker, IgD-Fc-Ig fusion protein, effectively alleviates abnormal activation of T cells the disease progression in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a chronic, multi-organ autoimmune disease with complex pathogenesis and unclear causes. Elevated levels of IgD have been observed in the peripheral blood of SLE patients, suggesting a potential role for IgD through its interaction with the IgD Fc receptor (FcδR). This study aimed to explore the impact of IgD on T cell function in SLE and evaluate the therapeutic potential of targeting the IgD-FcδR pathway using an IgD-Fc-Ig fusion protein. In SLE patients, biomarkers such as BAFF, ESR, anti-dsDNA and SLEDAI-2k, which are used to assess disease activity and clinical presentations, were significantly correlated with sIgD levels. As an IgD-FcδR blocker, IgD-Fc-Ig effectively suppressed the activation and proliferation of CD4+ T cells stimulated by IgD, restored the balance between Th17 and Treg cell subsets, and reduced the expression and interaction of phosphorylated Lck (p-Lck) and JAK2 (p-JAK2). Moreover, in vivo study demonstrated that IgD-Fc-Ig may also ameliorates disease manifestations in MRL/lpr mice with lupus nephritis. IgD-Fc-Ig could reduce serum IgD levels, proteinuria level and the kidney deposition of immune complex C3, ameliorate histopathological changes in kidney and spleen tissue. Additionally, it reversed the state of excessive activation and imbalance of Th17/Treg cell subsets, reduced cytokine levels, and downregulated p-JAK2 and p-STAT3 expression. In conclusion, our study revealed a correlation between abnormally increased sIgD and SLE pathogenesis, IgD-FcδR-Lck-JAK2-STAT3 may act as an important mechanism contributing to T cell activation in SLE. IgD-Fc-Ig fusion protein may represent a promising targeted therapy for SLE.

The Crystal Structure of Human IgD-Fc Reveals Unexpected Differences With Other Antibody Isotypes

Of the five human antibody isotypes, the function of IgD is the least well-understood, although various studies point to a role for IgD in mucosal immunity. IgD is also the least well structurally characterized isotype. Until recently, when crystal structures were reported for the IgD Fab, the only structural information available was a model for intact IgD based on solution scattering data. We now report the crystal structure of human IgD-Fc solved at 3.0 Å resolution. Although similar in overall architecture to other human isotypes, IgD-Fc displays markedly different orientations of the Cδ3 domains in the Cδ3 domain dimer and the lowest interface area of all the human isotypes. The nature of the residues that form the dimer interface also differs from those conserved in the other isotypes. By contrast, the interface between the Cδ2 and Cδ3 domains in each chain is the largest among the human isotypes. This interface is characterized by two binding pockets, not seen in other isotypes, and points to a potential role for the Cδ2/Cδ3 interface in stabilizing the IgD-Fc homodimer. We investigated the thermal stability of IgD-Fc, alone and in the context of an intact IgD antibody, and found that IgD-Fc unfolds in a single transition. Human IgD-Fc clearly has unique structural features not seen in the other human isotypes, and comparison with other mammalian IgD sequences suggests that these unique features might be widely conserved.

Type 2 immunity in allergic diseases

Significant advancements have been made in understanding the cellular and molecular mechanisms of type 2 immunity in allergic diseases such as asthma, allergic rhinitis, chronic rhinosinusitis, eosinophilic esophagitis (EoE), food and drug allergies, and atopic dermatitis (AD). Type 2 immunity has evolved to protect against parasitic diseases and toxins, plays a role in the expulsion of parasites and larvae from inner tissues to the lumen and outside the body, maintains microbe-rich skin and mucosal epithelial barriers and counterbalances the type 1 immune response and its destructive effects. During the development of a type 2 immune response, an innate immune response initiates starting from epithelial cells and innate lymphoid cells (ILCs), including dendritic cells and macrophages, and translates to adaptive T and B-cell immunity, particularly IgE antibody production. Eosinophils, mast cells and basophils have effects on effector functions. Cytokines from ILC2s and CD4+ helper type 2 (Th2) cells, CD8 + T cells, and NK-T cells, along with myeloid cells, including IL-4, IL-5, IL-9, and IL-13, initiate and sustain allergic inflammation via T cell cells, eosinophils, and ILC2s; promote IgE class switching; and open the epithelial barrier. Epithelial cell activation, alarmin release and barrier dysfunction are key in the development of not only allergic diseases but also many other systemic diseases. Recent biologics targeting the pathways and effector functions of IL4/IL13, IL-5, and IgE have shown promising results for almost all ages, although some patients with severe allergic diseases do not respond to these therapies, highlighting the unmet need for a more detailed and personalized approach.

CCR7A defines a subpopulation of IgD+IgM- B cells with higher IgD secreting capacity in the rainbow trout skin

B cells exclusively expressing IgD on the cell surface (IgD+IgM- B cells) have been identified in mammals, where they seem to play a still not well-defined role in peripheral tolerance. These cells have also been reported in catfish (Ictalurus punctatus) peripheral blood and in several mucosal tissues of rainbow trout (Oncorhynchus mykiss), including gut, gills and skin. As in mammals, the precise function of these cells remains obscure, yet, in rainbow trout mucosal surfaces, these cells have been shown to be differentiated to plasma-like cells. Interestingly, in the gills, these IgD+IgM- B cells expressed high levels of the CC chemokine receptor 7 (CCR7), receptor that in mammals controls the migration of B and T cells to secondary lymphoid organs. In this work, we have established that this is also true for the trout skin, where CCR7 defines a specific subset of IgD+IgM- B cells that are further differentiated to a plasma-like profile than those not expressing CCR7. These findings increase the current understanding of this enigmatic B cell population and point to CCR7 as a key differentiation marker for these cells.

Allergen-specific B cell responses in oral immunotherapy-induced desensitization, remission, and natural outgrowth in cow's milk allergy

BACKGROUND

Antigen-specific memory B cells play a key role in the induction of desensitization and remission to food allergens in oral immunotherapy and in the development of natural tolerance (NT). Here, we characterized milk allergen Bos d 9-specific B cells in oral allergen-specific immunotherapy (OIT) and in children spontaneously outgrowing cow's milk allergy (CMA) due to NT.

METHODS

Samples from children with CMA who received oral OIT (before, during, and after), children who naturally outgrew CMA (NT), and healthy individuals were received from Stanford biobank. Bos d 9-specific B cells were isolated by flow cytometry and RNA-sequencing was performed. Protein profile of Bos d 9-specific B cells was analyzed by proximity extension assay.

RESULTS

Increased frequencies of circulating milk allergen Bos d 9-specific B cells were observed after OIT and NT. Milk-desensitized subjects showed the partial acquisition of phenotypic features of remission, suggesting that desensitization is an earlier stage of remission. Within these most significantly expressed genes, IL10RA and TGFB3 were highly expressed in desensitized OIT patients. In both the remission and desensitized groups, B cell activation-, Breg cells-, BCR-signaling-, and differentiation-related genes were upregulated. In NT, pathways associated with innate immunity characteristics, development of marginal zone B cells, and a more established suppressor function of B cells prevail that may play a role in long-term tolerance. The analyses of immunoglobulin heavy chain genes in specific B cells demonstrated that IgG2 in desensitization, IgG1, IgA1, IgA2, IgG4, and IgD in remission, and IgD in NT were predominating. Secreted proteins from allergen-specific B cells revealed higher levels of regulatory cytokines, IL-10, and TGF-β after OIT and NT.

CONCLUSION

Allergen-specific B cells are essential elements in regulating food allergy towards remission in OIT-received and naturally resolved individuals.

Correlation between dietary calcium intake and eczema in American adult population

Eczema is a common chronic skin condition. Previous studies indicated the dietary factors, such as calcium intake, might influence the onset and progression of eczema in the population of gravidas and infants. However, there was no studies on the correlation between dietary calcium and the adult population. In this study, we aim to investigate the correlation between dietary calcium intake and the prevalence of eczema in adults. The characteristics of adults (≥ 18 years) were collected from the National Health and Nutrition Examination Survey (NHANES) 2005-2006 database. Dietary calcium intake was assessed using the 24-hour dietary recall method. The prevalence of eczema was determined through an allergy questionnaire. Logistic regression modeling was applied to analyze the correlation between dietary calcium intake and eczema prevalence. Restricted cubic spline (RCS) was used to investigate the nonlinear relationship between calcium intake and eczema. A two-stage linear regression model was used to calculate the critical effect of calcium intake on the prevalence of eczema by smoothed curve fitting. Subgroup analyses were performed to explore the effect of different demographic characteristics on the relationship between dietary calcium intake and eczema. Results In this cross-sectional study, we collected 4086 adult samples. There were 1930 males (46.9%) and 2156 females (53.1%), at the average age of 46.7 years, and 266 participants (7.6%) were diagnosed with eczema. Logistic regression results showed there was a significant difference between the third quartile group and eczema compared to the 1st quartile group of dietary calcium (OR: 1.913, 95% CI: 1.024-3.576, P = 0.043). The RCS showed an inverted U-shaped correlation between dietary calcium intake and eczema prevalence (non-linear P-value < 0.05). An increase in calcium intake was associated with an increase in eczema prevalence when the logarithmic value of dietary calcium intake was below 7.089 (OR: 1.790, 95% CI: 1.006-3.183, P = 0.048). These data indicated there was an inverted U-shaped correlation between dietary calcium intake and the prevalence of eczema, which suggested moderate reduction of calcium intake might be beneficial in the incidence of eczema. Further prospective studies are needed to explore causal relationships and optimal calcium intake levels to prevent eczema.

Interleukin-33-activated basophils promote asthma by regulating Th2 cell entry into lung tissue

Asthma is characterized by lung eosinophilia, remodeling, and mucus plugging, controlled by adaptive Th2 effector cells secreting IL-4, IL-5, and IL-13. Inhaled house dust mite (HDM) causes the release of barrier epithelial cytokines that activate various innate immune cells like DCs and basophils that can promote Th2 adaptive immunity directly or indirectly. Here, we show that basophils play a crucial role in the development of type 2 immunity and eosinophilic inflammation, mucus production, and bronchial hyperreactivity in response to HDM inhalation in C57Bl/6 mice. Interestingly, conditional depletion of basophils during sensitization did not reduce Th2 priming or asthma inception, whereas depletion during allergen challenge did. During the challenge of sensitized mice, basophil-intrinsic IL-33/ST2 signaling, and not FcεRI engagement, promoted basophil IL-4 production and subsequent Th2 cell recruitment to the lungs via vascular integrin expression. Basophil-intrinsic loss of the ubiquitin modifying molecule Tnfaip3, involved in dampening IL-33 signaling, enhanced key asthma features. Thus, IL-33-activated basophils are gatekeepers that boost allergic airway inflammation by controlling Th2 tissue entry.

MGAT4A/Galectin9-Driven N-Glycosylation Aberration as a Promoting Mechanism for Poor Prognosis of Endometrial Cancer with TP53 Mutation

Emerging evidence recognizes aberrant glycosylation as the malignant characteristics of cancer cells, but little is known about glycogenes' roles in endometrial carcinoma (EC), especially the most aggressive subtype carrying TP53 mutations. Using unsupervised hierarchical clustering, an 11-glycogene cluster is identified to distinguish an EC subtype associated with frequent TP53 mutation and worse prognosis. Among them, MGAT4A (alpha-1,3-mannosyl-glycoprotein 4-β-N-acetylglucosaminyltransferase A) emerges as the most consistently overexpressed glycogene, contributing to EC aggressiveness. In the presence of galectin-9, MGAT4A increases EC cell proliferation and invasion via promoting glucose metabolism. N-glycoproteomics further revealed GLUT1, a glucose transporter, as a glycoprotein modified by MGAT4A. Binding of galectin-9 to the MGAT4A-branched N-glycan on GLUT1 enhances its cell membrane distribution, leading to glucose uptake increase. In addition, oncogenic mutations of TP53 gene in EC cells upregulate MGAT4A expression by disrupting the regulatory oversight exerted by wild-type p53 on tumor-suppressive miRNAs, including miR-34a and miR-449a/b. The findings highlight a new molecular mechanism involving MGAT4A-regulated N-glycosylation on the key regulator of glucose metabolism in p53 mutants-driven EC aggressiveness, which may provide a strategic avenue to combat advanced EC.

Immune cell dynamics and the impact on the efficiency of transvascular antitumor interventional therapies in hepatocellular carcinoma patients

Objective

This study investigates the impact of transvascular antitumor interventional therapies on immune cell dynamics and its correlation with disease control and progression-free survival (PFS) in hepatocellular carcinoma (HCC) patients.

Methods

A single-center observational case-control study was conducted with 119 HCC patients. Transvascular antitumor interventional therapy were administered based on patient-specific evaluations. Peripheral blood samples were collected before and within 28 days after the first treatment to analyze lymphocyte subsets and other immune cells.

Results

Higher counts of total white blood cells (WBCs), lymphocytes, monocytes, and basophils were significantly associated with disease control rate. Subgroup analysis revealed that abnormal BMI, diabetes, infection, and multiple lesions were significantly associated with T cell abnormalities. Age, abnormal BMI, hypertension, and abnormal AFP were linked to total T cell abnormalities. NK cells, B cells, Th cells, Tc/Ts cells, and CD4/CD8 ratios did not show significant differences in PFS probabilities.

Conclusion

Higher counts of WBCs, lymphocytes, monocytes, and basophils, play a crucial role in the effectiveness of HCC interventional therapy.

A Comprehensive Review on Porcine Reproductive and Respiratory Syndrome Virus with Emphasis on Immunity

Porcine reproductive and respiratory syndrome virus (PRRSV) is one of the most important pathogens in pig production worldwide and responsible for enormous production and economic losses. PRRSV infection in gestating gilts and sows induces important reproductive failure. Additionally, respiratory distress is observed in infected piglets and fattening pigs, resulting in growth retardation and increased mortality. Importantly, PRRSV infection interferes with immunity in the respiratory tract, making PRRSV-infected pigs more susceptible to opportunistic secondary pathogens. Despite the availability of commercial PRRSV vaccines for more than three decades, control of the disease remains a frustrating and challenging task. This paper provides a comprehensive overview of PRRSV, covering its history, economic and scientific importance, and description of the viral structure and genetic diversity. It explores the virus's pathogenesis, including cell tropism, viral entry, replication, stages of infection and epidemiology. It reviews the porcine innate and adaptative immune responses to comprehend the modulation mechanisms employed by PRRS for immune evasion.

Implications of PD-L1 expression on the immune microenvironment in HER2-positive gastric cancer

In the KEYNOTE-811 study, anti-HER2 and immunotherapy treatments resulted in longer survival in HER2-positive gastric cancer patients with CPS ≥ 1, whereas CPS < 1 patients lacked notable benefits. We studied this in a real-world cohort of 106 HER2-positive, CPS < 1 patients and found no survival differences between those treated with anti-HER2 therapy alone or with added immunotherapy. Thus, we investigate the tumor microenvironment variations in 160 HER2-positive patients, CPS ≥ 1 cases exhibited elevated spatial effective scores of immune cells, including CD4, CD8 subtypes, and NK cells, compared to CPS < 1. Furthermore, through single-cell sequencing in eight HER2-positive individuals, gene expressions revealed regulation of T-cell co-stimulation in CPS ≥ 1 and IL-1 binding in CPS < 1 cases. Notably, we discovered a CPS < 1 subtype marked by CXCR4+M2 macrophages, associated with poor prognosis, whose proportion and expression were reduced when benefiting from anti-HER2 therapy. These findings suggest CPS ≥ 1 patients, due to their immune microenvironment composition, may respond better to anti-PD-1/PD-L1 therapy.

Immunoglobulin class-switch recombination: Mechanism, regulation, and related diseases

Maturation of the secondary antibody repertoire requires class-switch recombination (CSR), which switches IgM to other immunoglobulins (Igs), and somatic hypermutation, which promotes the production of high-affinity antibodies. Following immune response or infection within the body, activation of T cell-dependent and T cell-independent antigens triggers the activation of activation-induced cytidine deaminase, initiating the CSR process. CSR has the capacity to modify the functional properties of antibodies, thereby contributing to the adaptive immune response in the organism. Ig CSR defects, characterized by an abnormal relative frequency of Ig isotypes, represent a rare form of primary immunodeficiency. Elucidating the molecular basis of Ig diversification is essential for a better understanding of diseases related to Ig CSR defects and could provide clues for clinical diagnosis and therapeutic approaches. Here, we review the most recent insights on the diversification of five Ig isotypes and choose several classic diseases, including hyper-IgM syndrome, Waldenström macroglobulinemia, hyper-IgD syndrome, selective IgA deficiency, hyper-IgE syndrome, multiple myeloma, and Burkitt lymphoma, to illustrate the mechanism of Ig CSR deficiency. The investigation into the underlying mechanism of Ig CSR holds significant potential for the advancement of increasingly precise diagnostic and therapeutic approaches.

A Galectin-9-Driven CD11chigh Decidual Macrophage Subset Suppresses Uterine Vascular Remodeling in Preeclampsia

BACKGROUND

Preeclampsia is a serious disease of pregnancy that lacks early diagnosis methods or effective treatment, except delivery. Dysregulated uterine immune cells and spiral arteries are implicated in preeclampsia, but the mechanistic link remains unclear.

METHODS

Single-cell RNA sequencing and spatial transcriptomics were used to identify immune cell subsets associated with preeclampsia. Cell-based studies and animal models including conditional knockout mice and a new preeclampsia mouse model induced by recombinant mouse galectin-9 were applied to validate the pathogenic role of a CD11chigh subpopulation of decidual macrophages (dMφ) and to determine its underlying regulatory mechanisms in preeclampsia. A retrospective preeclampsia cohort study was performed to determine the value of circulating galectin-9 in predicting preeclampsia.

RESULTS

We discovered a distinct CD11chigh dMφ subset that inhibits spiral artery remodeling in preeclampsia. The proinflammatory CD11chigh dMφ exhibits perivascular enrichment in the decidua from patients with preeclampsia. We also showed that trophoblast-derived galectin-9 activates CD11chigh dMφ by means of CD44 binding to suppress spiral artery remodeling. In 3 independent preeclampsia mouse models, placental and plasma galectin-9 levels were elevated. Galectin-9 administration in mice induces preeclampsia-like phenotypes with increased CD11chigh dMφ and defective spiral arteries, whereas galectin-9 blockade or macrophage-specific CD44 deletion prevents such phenotypes. In pregnant women, increased circulating galectin-9 levels in the first trimester and at 16 to 20 gestational weeks can predict subsequent preeclampsia onset.

CONCLUSIONS

These findings highlight a key role of a distinct perivascular inflammatory CD11chigh dMφ subpopulation in the pathogenesis of preeclampsia. CD11chigh dMφ activated by increased galectin-9 from trophoblasts suppresses uterine spiral artery remodeling, contributing to preeclampsia. Increased circulating galectin-9 may be a biomarker for preeclampsia prediction and intervention.

Research advancements and perspectives of inflammatory bowel disease: A comprehensive review

Inflammatory bowel disease (IBD) is a chronic inflammatory disease with increasing incidence, such as Crohn's disease and ulcerative colitis. The accurate etiology and pathogenesis of IBD remain unclear, and it is generally believed that it is related to genetic susceptibility, gut microbiota, environmental factors, immunological abnormalities, and potentially other factors. Currently, the mainstream therapeutic drugs are amino salicylic acid agents, corticosteroids, immunomodulators, and biological agents, but the remission rates do not surpass 30-60% of patients in a real-life setting. As a consequence, there are many studies focusing on emerging drugs and bioactive ingredients that have higher efficacy and long-term safety for achieving complete deep healing. This article begins with a review of the latest, systematic, and credible summaries of the pathogenesis of IBD. In addition, we provide a summary of the current treatments and drugs for IBD. Finally, we focus on the therapeutic effects of emerging drugs such as microRNAs and lncRNAs, nanoparticles-mediated drugs and natural products on IBD and their mechanisms of action.

Integrating spatial and single-cell transcriptomics to characterize the molecular and cellular architecture of the ischemic mouse brain

Neuroinflammation is acknowledged as a pivotal pathological event after cerebral ischemia. However, there is limited knowledge of the molecular and spatial characteristics of nonneuronal cells, as well as of the interactions between cell types in the ischemic brain. Here, we used spatial transcriptomics to study the ischemic hemisphere in mice after stroke and sequenced the transcriptomes of 19,777 spots, allowing us to both visualize the transcriptional landscape within the tissue and identify gene expression profiles linked to specific histologic entities. Cell types identified by single-cell RNA sequencing confirmed and enriched the spatial annotation of ischemia-associated gene expression in the peri-infarct area of the ischemic hemisphere. Analysis of ligand-receptor interactions in cell communication revealed galectin-9 to cell-surface glycoprotein CD44 (LGALS9-CD44) as a critical signaling pathway after ischemic injury and identified microglia and macrophages as the main source of galectins after stroke. Extracellular vesicle-mediated Lgals9 delivery improved the long-term functional recovery in photothrombotic stroke mice. Knockdown of Cd44 partially reversed these therapeutic effects, inhibiting oligodendrocyte differentiation and remyelination. In summary, our study provides a detailed molecular and cellular characterization of the peri-infact area in a murine stroke model and revealed Lgals9 as potential treatment target that warrants further investigation.

The ontogenesis and heterogeneity of basophils

Basophils are the rarest leukocytes, but they have essential roles in protection against helminths, allergic disorders, autoimmune diseases, and some cancers. For years, the clinical significance of basophils has been neglected because of the lack of proper experimental tools to study them. The development of basophil-specific antibodies and animal models, along with genomic advances like single-cell transcriptomics, has greatly enhanced our understanding of basophil biology. Recent discoveries regarding basophils prompted us to write this review, emphasizing the basophil developmental pathway. In it, we chronologically examine the steps of basophil development in various species, which reveals the apparent advent of basophils predating IgE and basophil's IgE-independent regulatory role in primitive vertebrates. Then, we cover studies of basophil development in adult bone marrow, and compare those of murine and human basophils, introducing newly identified basophil progenitors and mature basophil subsets, as well as the transcription factors that regulate the transitions between them. Last, we discuss the heterogeneity of tissue-resident basophils, which may develop through extramedullary hematopoiesis. We expect that this review will contribute to a deeper understanding of basophil biology from the intricate aspects of basophil development and differentiation, offering valuable insights for both researchers and clinicians.

IgD+IgM- B Cells in Common Variable Immunodeficiency

Common variable immunodeficiency (CVID) is the most frequent form of primary hypogammaglobulinemia in adults. In addition to recurrent infections and respiratory manifestations, CVID patients may present several non-infection complications such as autoimmune diseases. The mechanisms that lead to immune dysregulation in CVID are not completely understood. Given the role of IgD on naïve B cells in the maintenance of tolerance and secreted IgD in the respiratory mucosa, we evaluated the frequency of IgD+ naïve and IgD+ memory B cells in CVID patients. Here, no differences were observed in the percentages and proliferative responses of anergic IgD+IgM-CD27- B cells between CVID patients, with or without autoimmune disease, and the control group. Interestingly, in the compartment of memory B cells, the percentage of IgD+IgM- cells was higher only in CVID patients with allergic rhinitis/allergic asthma. Our results may indicate that anergic IgD+IgM-CD27- B cells may not be compromised in our CVID cohort. However, IgD+IgM- memory B cells may play a role in the immunopathogenesis of allergic rhinitis/allergic asthma in CVID patients. Further studies are needed to better understand the participation of IgD+IgM- memory B cells in the immunopathogenesis of allergic rhinitis/allergic asthma in CVID patients.

Teleost IgD+IgM- B cells in gills and skin have a plasmablast profile, but functionally and phenotypically differ from IgM+IgD- B cells in these sites

Although most B cells in teleost systemic compartments co-express IgM and IgD on the surface, cells exclusively expressing either of the two Igs are common in fish mucosal tissues, providing us with a unique opportunity to further characterize IgD+IgM- B cells, an intriguing B cell subset. Hence, we compared the phenotype of IgD+IgM- cells to that of IgM+IgD- B cells in rainbow trout gills and skin, also establishing the response of these subsets to immune stimulation. The transcriptional profile and secreting capacity of IgD+IgM- B cells corresponded to that of cells that have started a differentiation program toward plasmablasts, similarly to IgM+IgD- B cells. Yet, IgM+IgD- B cells retained high levels of surface MHC II and antigen-processing abilities, while these were much lower in IgD+IgM- cells, suggesting important differences in their antigen-presenting capacities. Our findings contribute to a deeper understanding of the enigmatic role of IgD in mucosal surfaces.

Antibody-mediated regulation of basophils: emerging views and clinical implications

An increasing number of human diseases, including allergies, infections, inflammation, and cancer, involve roles for basophils. Traditionally viewed as the rarest leukocytes that are present only in the circulation, basophils have recently emerged as important players in systemic as well as tissue-specific immune responses. Their functions are regulated by immunoglobulins (Igs), and this enables basophils to integrate diverse adaptive and innate immunity signals. IgE is well known to regulate basophil responses in the context of type 2 immunity and allergic inflammation; however, growing evidence shows that IgG, IgA, and IgD also shape specific aspects of basophil functions relevant to many human diseases. We discuss recent mechanistic advances underpinning antibody-mediated basophil responses and propose strategies for the treatment of basophil-associated disorders.

Galectin-9 Facilitates Epstein-Barr Virus Latent Infection and Lymphomagenesis in Human B Cells

The immune regulator galectin-9 (Gal-9) is commonly involved in the regulation of cell proliferation, but with various impacts depending on the cell type. Here, we revealed that Gal-9 expression was persistently increased in Epstein-Barr virus (EBV)-infected primary B cells from the stage of early infection to the stage of mature lymphoblastoid cell lines (LCLs). This sustained upregulation paralleled that of gene sets related to cell proliferation, such as oxidative phosphorylation, cell cycle activation, and DNA replication. Knocking down or blocking Gal-9 expression obstructed the establishment of latent infection and outgrowth of EBV-infected B cells, while exogenous Gal-9 protein promoted EBV acute and latent infection and outgrowth of EBV-infected B cells at the early infection stage. Mechanically, stimulator of interferon gene (STING) activation or signal transducer and activator of transcription 3 (STAT3) inhibition impeded the outgrowth of EBV-infected B cells and promotion of Gal-9-induced lymphoblastoid cell line (LCL) transformation. Accordingly, Gal-9 expression was upregulated by forced EBV nuclear antigen 1 (EBNA1) expression in 293T cells in vitro. Clinical data showed that Gal-9 expression in B-cell lymphomas (BCLs) correlated positively with EBNA1 and disease stage. Targeting Gal-9 slowed LCL tumor growth and metastasis in xenografted immunodeficient mice. These findings highlight an oncogenic role of Gal-9 in EBV-associated BCLs, indicating that Gal-9 boosts the transformation of EBV-infected B cells. IMPORTANCE The cross talk between Epstein-Barr virus (EBV) and the host cell transcriptome assumes important roles in the oncogenesis of EBV-associated malignancies. Here, we first observed that endogenous Gal-9 expression was persistently increased along with an overturned V-type change in antivirus signaling during the immortalization of EBV-transformed B cells. Upregulation of Gal-9 promoted the outgrowth and latent infection of EBV-infected B cells, which was linked to B-cell-origin tumors by suppressing STING signaling and subsequently promoting STAT3 phosphorylation. EBV nuclear antigen EBNA1 induced Gal-9 expression and formed a positive feedback loop with Gal-9 in EBV-infected B cells. Tumor Gal-9 levels were positively correlated with disease stage and EBNA1 expression in patients with B-cell lymphomas (BCLs). Targeting Gal-9 slowed the growth and metastases of LCL tumors in immunodeficient mice. Altogether, our findings indicate that Gal-9 is involved in the lymphomagenesis of EBV-positive BCLs through cross talk with EBNA1 and STING signals.

B cells defined by immunoglobulin isotypes

The ability of B cells to generate antibodies and provide long-lived protective immunity is the cornerstone of vaccination and has contributed to the success of modern medicine. The nine different antibody subclasses produced by humans have effector functions that differ according to antigen type and route of exposure. Expression of the appropriate isotype is critical for effective humoral immunity, and it is becoming clear that subclass specificity is to some extent reflected at the cellular level. Understanding the mechanisms that govern the induction, expansion, and maintenance of B cells expressing different antibody subclasses informs the strategic manipulation of responses to benefit human health. This article provides an overview of the mechanisms by which the different human antibody subclasses regulate immunity, presents an update on how antibody subclass expression is regulated at the cellular level and highlights key areas for future research.

Mechanisms in AIT: Insights 2021

BACKGROUND

Allergen-specific immunotherapy (AIT) is currently the only treatment with potential long-term disease-modifying effects for patients suffering from allergic diseases such as allergic rhinitis, allergic asthma, venom allergy, or IgE-mediated food allergy. A better understanding of the molecular mechanisms underlying immune responses during successful AIT is of utmost importance and it may help to develop more effective and safer treatments.

MATERIALS AND METHODS

PubMed literature review was performed using keywords such as allergen-specific immunotherapy; regulatory T cells; regulatory B cells; regulatory innate lymphoid cells; and allergen-specific antibody from years 2018 to 2021.

RESULTS

The proposed mechanism of long-term tolerance induction in AIT, even upon treatment discontinuation, involves basophils, mast cells, innate lymphoid cells, dendritic cells, allergen-specific regulatory T and B cells, downregulation of effector type 2 responses, decrease in the production of IgE and increase in production of allergen-specific blocking antibodies, such as IgG2 and IgG4.

CONCLUSION

We summarize the most recent advances related to mechanisms involved in the restoration of healthy immune responses to allergens during AIT. Our knowledge in this regard has significantly improved over the last years, which might well contribute to design novel and improved therapeutic approaches.

The dual aspects of IgD in the development of tolerance and the pathogenesis of allergic diseases

The cell-surface form of IgD is co-expressed with IgM on mature, naïve B cells as B-cell receptors. The secreted IgD antibody (Ab) is found in relatively modest concentrations in the blood and other body fluids as it has a relatively short serum half-life. IgD Abs produced in the upper-respiratory mucosa presumably participate in host defense against pathogens. The allergen-mediated cross-linkage of basophil-bound IgD Ab enhances type 2 cytokine secretion; IgD Ab may also interfere with IgE-mediated basophil degranulation, suggesting dual and opposing roles of IgD Ab in allergen sensitization and the development of allergen immune tolerance. We recently demonstrated that children with egg allergies who avoided all forms of egg have lower ovomucoid-specific IgD and IgG₄ Ab levels than those who only partially avoided egg products and that different mechanisms may regulate allergen-specific IgD Ab production compared to allergen-specific IgG₄ Ab production. The relationship between antigen-specific IgD Ab levels and the clinical improvement of asthma and food allergies suggests that antigen-specific IgD Ab affects the process of outgrowing allergies. We discuss the possibility that allergen-specific IgD Ab production reflects low-affinity, allergen-specific IgE production as children outgrow a food allergy.

Mechanisms and biomarkers of successful allergen-specific immunotherapy

Allergen-specific immunotherapy (AIT) is considered the only curative treatment for allergic diseases mediated by immunoglobulin E (IgE). Currently, the route of administration depends both on the different types of causal allergens and on its effectiveness and safety profile. Several studies have reported the mechanisms and changes in humoral and cellular response underlying AIT; however, the full picture remains unknown. Knowledge of who can benefit from this type of treatment is urgently needed due to the patient safety risks and costs of AIT. In vivo or in vitro biomarkers have become a strategy to predict clinical outcomes in precision medicine. There are currently no standardized biomarkers that allow determining successful responses to AIT, however, some studies have found differences between responders and nonresponders. In addition, different candidates have been postulated that may have the potential to become biomarkers. In this review, we aim to summarize the findings to date related to biomarkers in different IgE-mediated allergic diseases (respiratory, food, and venom allergy) with the potential to define who will benefit from AIT.

Impact of the mucosal milieu on antibody responses to allergens

Respiratory and digestive mucosal surfaces are continually exposed to common environmental antigens, which include potential allergens. Although innocuous in healthy individuals, allergens cause allergy in predisposed subjects and do so by triggering a pathologic T_H2 cell response that induces IgE class switching and somatic hypermutation in allergen-specific B cells. The ensuing affinity maturation and plasma cell differentiation lead to the abnormal release of high-affinity IgE that binds to powerful FcεRI receptors on basophils and mast cells. When cross-linked by allergen, FcεRI-bound IgE instigates the release of prestored and de novo-induced proinflammatory mediators. Aside from causing type I hypersensitivity reactions underlying allergy, IgE affords protection against nematodes or venoms from insects and snakes, which raises questions as to the fundamental differences between protective and pathogenic IgE responses. In this review, we discuss the impact of the mucosal environment, including the epithelial and mucus barriers, on the induction of protective IgE responses against environmental antigens. We further discuss how perturbations of these barriers may contribute to the induction of pathogenic IgE production.

AllergoOncology: Danger signals in allergology and oncology: A European Academy of Allergy and Clinical Immunology (EAACI) Position Paper

The immune system interacts with many nominal 'danger' signals, endogenous danger-associated (DAMP), exogenous pathogen (PAMP) and allergen (AAMP)-associated molecular patterns. The immune context under which these are received can promote or prevent immune activating or inflammatory mechanisms and may orchestrate diverse immune responses in allergy and cancer. Each can act either by favouring a respective pathology or by supporting the immune response to confer protective effects, depending on acuity or chronicity. In this Position Paper under the collective term danger signals or DAMPs, PAMPs and AAMPs, we consider their diverse roles in allergy and cancer and the connection between these in AllergoOncology. We focus on their interactions with different immune cells of the innate and adaptive immune system and how these promote immune responses with juxtaposing clinical outcomes in allergy and cancer. While danger signals present potential targets to overcome inflammatory responses in allergy, these may be reconsidered in relation to a history of allergy, chronic inflammation and autoimmunity linked to the risk of developing cancer, and with regard to clinical responses to anti-cancer immune and targeted therapies. Cross-disciplinary insights in AllergoOncology derived from dissecting clinical phenotypes of common danger signal pathways may improve allergy and cancer clinical outcomes.

Mechanisms of allergen immunotherapy supporting its disease-modifying effect

Allergen immunotherapy (AIT) is considered the only disease-modifying treatment available at present for allergic disorders. Its main benefits include improvement of symptoms, decreased need for pharmacotherapy, prevention of new sensitizations and sustained effect after AIT completion. The key pillars of AIT-induced tolerance include a shift from Th2 to Th1 response, an increase of regulatory T and B cells, pro-inflammatory effector cell downregulation and IgE suppression, in addition to IgG4, IgA and IgD induction. AIT may also induce trained immunity, characterized by a durable decrease in group 2 of innate lymphoid cells (ILCs) and increased ILC1 and ILC3s. Understanding the immune mechanisms of AIT is essential for validating biomarkers for the prediction of AIT response and for achieving AIT success.

Rad52 mediates class-switch DNA recombination to IgD

In B cells, IgD is expressed together with IgM through alternative splicing of primary VHDJH-Cμ-s-m-Cδ-s-m RNAs, and also through IgD class switch DNA recombination (CSR) via double-strand DNA breaks (DSB) and synapse of Sμ with σδ. How such DSBs are resolved is still unknown, despite our previous report showing that Rad52 effects the ‘short-range’ microhomology-mediated synapsis of intra-Sμ region DSBs. Here we find that induction of IgD CSR downregulates Zfp318, and promotes Rad52 phosphorylation and recruitment to Sμ and σδ, thereby leading to alternative end-joining (A-EJ)-mediated Sμ-σδ recombination with extensive microhomologies, VHDJH-Cδs transcription and sustained IgD secretion. Rad52 ablation in mouse Rad52−/− B cells aborts IgD CSR in vitro and in vivo and dampens the specific IgD antibody response to OVA. Rad52 knockdown in human B cells also abrogates IgD CSR. Finally, Rad52 phosphorylation is associated with high levels of IgD CSR and anti-nuclear IgD autoantibodies in patients with systemic lupus erythematosus and in lupus-prone mice. Our findings thus show that Rad52 mediates IgD CSR through microhomology-mediated A-EJ in concert with Zfp318 downregulation.

Multiple-Cytokine Profiling: A Novel Method for Early Prediction of the Efficacy of Sublingual Immunotherapy in Allergic Rhinitis Patients

Background

Methods

Results

Conclusion

CD44 v5 domain inhibition represses the polarization of Th2 cells by interfering with the IL-4/IL-4R signaling pathway

The balance between T helper type 1 (Th1) and T helper type 2 (Th2) cells is critical for both innate and acquired immune reactions. However, the precise mechanisms of T helper-cell differentiation remain unclear. As an important T-cell activation molecule, CD44 participates in the differentiation of Th1 and Th2 cells. We demonstrated that CD44 variant exon v5 (CD44 v5) is highly expressed by induced human Th2 cells. To investigate the role of the CD44 v5 domain in Th2 cell differentiation, we treated human CD4+ T cells with anti-CD44v5 antibody and observed that the levels of phosphorylated STAT6 and GATA3 and the secretion of interleukin-4 (IL-4) were significantly decreased after the treatment. We also further found that the inhibition of Th2 differentiation was caused by the degradation of the alpha chain of IL-4 receptor (IL-4Rα), the CD44 v5 domain colocalized with IL-4Rα on cell surface and the degradation of IL-4Rα increased after CD44 v5 domain blocking or ablating. Our results indicated that CD44v5 antibody treatment interrupted the interaction between CD44 v5 domain and IL-4Rα, but the CD44 v5 domain blockage would not spoil the colocalization between IL-4R expression and T-cell receptor and the immunological synapse formation; similar results were also found in CD44v5-deficient CD4+ T cells. In conclusion, we revealed the function of the CD44 v5 domain in Th2 cell differentiation; blocking or ablating the CD44 v5 domain could accelerate IL-4Rα degradation and then induce the Th2 cell inhibition.

Basophils as a potential therapeutic target in cancer

Basophils, which are considered as redundant relatives of mast cells and the rarest granulocytes in peripheral circulation, have been neglected by researchers in the past decades. Previous studies have revealed their vital roles in allergic diseases and parasitic infections. Intriguingly, recent studies even reported that basophils might be associated with cancer development, as activated basophils synthesize and release a variety of cytokines and chemokines in response to cancers. However, it is still subject to debate whether basophils function as tumor-protecting or tumor-promoting components; the answer may depend on the tumor biology and the microenvironment. Herein, we reviewed the role of basophils in cancers, and highlighted some potential and promising therapeutic strategies.

Guidelines for the use of flow cytometry and cell sorting in immunological studies (third edition)

The third edition of Flow Cytometry Guidelines provides the key aspects to consider when performing flow cytometry experiments and includes comprehensive sections describing phenotypes and functional assays of all major human and murine immune cell subsets. Notably, the Guidelines contain helpful tables highlighting phenotypes and key differences between human and murine cells. Another useful feature of this edition is the flow cytometry analysis of clinical samples with examples of flow cytometry applications in the context of autoimmune diseases, cancers as well as acute and chronic infectious diseases. Furthermore, there are sections detailing tips, tricks and pitfalls to avoid. All sections are written and peer-reviewed by leading flow cytometry experts and immunologists, making this edition an essential and state-of-the-art handbook for basic and clinical researchers.

Immunoglobulin D and its encoding genes: An updated review

Since the identification of a functional Cδ gene in ostriches, immunoglobulin (Ig) D has been considered to be an extremely evolutionarily conserved Ig isotype besides the IgM found in all classes of jawed vertebrates. However, in contrast to IgM (which remains stable over evolutionary time), IgD shows considerable structural plasticity among vertebrate species and, moreover, its functions are far from elucidated even in humans and mice. Recently, several studies have shown that high expression of the IgD-B-cell receptor (IgD-BCR) may help physiologically autoreactive B cells survive in peripheral lymphoid tissues thanks to unresponsiveness to self-antigens and help their entry into germinal centers to "redeem" autoreactivity via somatic hypermutation. Other studies have demonstrated that secreted IgD may enhance mucosal homeostasis and immunity by linking B cells with basophils to optimize T-helper-2 cell-mediated responses and to constrain IgE-mediated basophil degranulation. Herein, we review the new discoveries on IgD-encoding genes in jawed vertebrates in the past decade. We also highlight advances in the functions of the IgD-BCR and secreted IgD in humans and mice.

Allergic Rhinitis: What Do We Know About Allergen-Specific Immunotherapy?

Allergic rhinitis (AR) is an IgE-mediated disease that is characterized by Th2 joint inflammation. Allergen-specific immunotherapy (AIT) is indicated for AR when symptoms remain uncontrolled despite medication and allergen avoidance. AIT is considered to have been effective if it alleviated allergic symptoms, decreased medication use, improved the quality of life even after treatment cessation, and prevented the progression of AR to asthma and the onset of new sensitization. AIT can be administered subcutaneously or sublingually, and novel routes are still being developed, such as intra-lymphatically and epicutaneously. AIT aims at inducing allergen tolerance through modification of innate and adaptive immunologic responses. The main mechanism of AIT is control of type 2 inflammatory cells through induction of various functional regulatory cells such as regulatory T cells (Tregs), follicular T cells (Tfr), B cells (Bregs), dendritic cells (DCregs), innate lymphoid cells (IL-10⁺ ILCs), and natural killer cells (NKregs). However, AIT has a number of disadvantages: the long treatment period required to achieve greater efficacy, high cost, systemic allergic reactions, and the absence of a biomarker for predicting treatment responders. Currently, adjunctive therapies, vaccine adjuvants, and novel vaccine technologies are being studied to overcome the problems associated with AIT. This review presents an updated overview of AIT, with a special focus on AR.

Extrafollicular IgD+ B cells generate IgE antibody secreting cells in the nasal mucosa

Increased IgE is a typical feature of allergic rhinitis. Local class-switch recombination has been intimated but B cell precursors and mechanisms remain elusive. Here we describe the dynamics underlying the generation of IgE-antibody secreting cells (ASC) in human nasal polyps (NP), mucosal tissues rich in ASC without germinal centers (GC). Using VH next generation sequencing, we identified an extrafollicular (EF) mucosal IgD+ naïve-like intermediate B cell population with high connectivity to the mucosal IgE ASC. Mucosal IgD+ B cells, express germline epsilon transcripts and predominantly co-express IgM. However, a small but significant fraction co-express IgG or IgA instead which also show connectivity to ASC IgE. Phenotypically, NP IgD+ B cells display an activated profile and molecular evidence of BCR engagement. Transcriptionally, mucosal IgD+ B cells reveal an intermediate profile between naïve B cells and ASC. Single cell IgE ASC analysis demonstrates lower mutational frequencies relative to IgG, IgA, and IgD ASC consistent with IgE ASC derivation from mucosal IgD+ B cell with low mutational load. In conclusion, we describe a novel mechanism of GC-independent, extrafollicular IgE ASC formation at the nasal mucosa whereby activated IgD+ naïve B cells locally undergo direct and indirect (through IgG and IgA), IgE class switch.

Neutrophils promote T-cell activation through the regulated release of CD44-bound Galectin-9 from the cell surface during HIV infection

The interaction of neutrophils with T cells has been the subject of debate and controversies. Previous studies have suggested that neutrophils may suppress or activate T cells. Despite these studies, the interaction between neutrophils and T cells has remained a largely unexplored field. Here, based on our RNA sequencing (RNA-seq) analysis, we found that neutrophils have differential transcriptional and functional profiling depending on the CD4 T-cell count of the HIV-infected individual. In particular, we identified that neutrophils in healthy individuals express surface Galectin-9 (Gal-9), which is down-regulated upon activation, and is consistently down-regulated in HIV-infected individuals. However, down-regulation of Gal-9 was associated with CD4 T-cell count of patients. Unstimulated neutrophils express high levels of surface Gal-9 that is bound to CD44, and, upon stimulation, neutrophils depalmitoylate CD44 and induce its movement out of the lipid raft. This process causes the release of Gal-9 from the surface of neutrophils. In addition, we found that neutrophil-derived exogenous Gal-9 binds to cell surface CD44 on T cells, which promotes LCK activation and subsequently enhances T-cell activation. Furthermore, this process was regulated by glycolysis and can be inhibited by interleukin (IL)-10. Together, our data reveal a novel mechanism of Gal-9 shedding from the surface of neutrophils. This could explain elevated plasma Gal-9 levels in HIV-infected individuals as an underlying mechanism of the well-characterized chronic immune activation in HIV infection. This study provides a novel role for the Gal-9 shedding from neutrophils. We anticipate that our results will spark renewed investigation into the role of neutrophils in T-cell activation in other acute and chronic conditions, as well as improved strategies for modulating Gal-9 shedding.

This study shows that HIV-infected individuals have different neutrophil profiles depending on their CD4 T cell count. In particular, neutrophils express high levels of surface Gal-9 but this is shed upon stimulation; this exogenous Gal-9 binds to CD44 on T cells, which promotes LCK activation and subsequently enhances T cell activation.

Primary Immune Responses and Affinity Maturation Are Controlled by IgD

Mature B cells co-express IgM and IgD B cell antigen receptors (BCR) on their surface. While IgM BCR expression is already essential at early stages of development, the role of the IgD-class BCR remains unclear as most B cell functions appeared unchanged in IgD-deficient mice. Here, we show that IgD-deficient mice have an accelerated rate of B cell responsiveness as they activate antibody production within 24h after immunization, whereas wildtype (WT) animals required 3 days to activate primary antibody responses. Strikingly, soluble monovalent antigen suppresses IgG antibody production induced by multivalent antigen in WT mice. In contrast, IgD-deficient mice were not able to modulate IgG responses suggesting that IgD controls the activation rate of B cells and subsequent antibody production by sensing and distinguishing antigen-valences. Using an insulin-derived peptide we tested the role of IgD in autoimmunity. We show that primary autoreactive antibody responses are generated in WT and in IgD-deficient mice. However, insulin-specific autoantibodies were detected earlier and caused more severe symptoms of autoimmune diabetes in IgD-deficient mice as compared to WT mice. The rapid control of autoimmune diabetes in WT animals was associated with the generation of high-affinity IgM that protects insulin from autoimmune degradation. In IgD-deficient mice, however, the generation of high-affinity protective IgM is delayed resulting in prolonged autoimmune diabetes. Our data suggest that IgD is required for the transition from primary, highly autoreactive, to secondary antigen-specific antibody responses generated by affinity maturation.

NIgPred: Class-Specific Antibody Prediction for Linear B-Cell Epitopes Based on Heterogeneous Features and Machine-Learning Approaches

Upon invasion by foreign pathogens, specific antibodies can identify specific foreign antigens and disable them. As a result of this ability, antibodies can help with vaccine production and food allergen detection in patients. Many studies have focused on predicting linear B-cell epitopes, but only two prediction tools are currently available to predict the sub-type of an epitope. NIgPred was developed as a prediction tool for IgA, IgE, and IgG. NIgPred integrates various heterologous features with machine-learning approaches. Differently from previous studies, our study considered peptide-characteristic correlation and autocorrelation features. Sixty kinds of classifier were applied to construct the best prediction model. Furthermore, the genetic algorithm and hill-climbing algorithm were used to select the most suitable features for improving the accuracy and reducing the time complexity of the training model. NIgPred was found to be superior to the currently available tools for predicting IgE epitopes and IgG epitopes on independent test sets. Moreover, NIgPred achieved a prediction accuracy of 100% for the IgG epitopes of a coronavirus data set. NIgPred is publicly available at our website.

Development of Multidrug Resistance in Acute Myeloid Leukemia Is Associated with Alterations of the LPHN1/GAL-9/TIM-3 Signaling Pathway

P-glycoprotein (known as ABCB1 transporter) expression in myeloid blasts of acute myeloid leukemia (AML) or myelodysplastic syndrome (MDS) leads to the commonly observed multidrug resistance. Overexpression of latrophilin-1 was detected in leukemic cells from AML patients. In a previous study, we showed that ABCB1 overexpression is associated with decreased latrophilin-1 expression in MOLM-13/VCR and SKM-1/VCR AML cell variants derived from MOLM-13 and SKM-1 cells by vincristine selection/adaptation. In the present study, we found that if ABCB1 overexpression occurs in myeloid blasts of newly diagnosed MDS patients, latrophilin-1 expression is attenuated. Latrophilin-1 may initiate TIM-3- and galectin-9-mediated immune escape. We demonstrated changes in the expression of both proteins by comparing ABCB1-positive cell variants (MOLM-13/VCR, SKM-1/VCR) with their ABCB1-negative counterparts. Galectin-9 was present in our cell lines in eight protein isoforms for which we identified the respective transcription variants resulting from alternative splicing, and we verified their structure by sequencing. The isoform profile of galectin-9 was different between ABCB1-positive and ABCB1-negative cell variants. The interaction partner of galectin-9 is CD44, and its expression was altered in the ABCB1-positive variants MOLM-13/VCR and SKM-1/VCR compared to their ABCB1-negative counterparts.

Basophils and their effector molecules in allergic disorders

Basophils are the rarest granulocytes which represent <1% of peripheral blood leukocytes. Basophils bear several phenotypic similarities to tissue-resident mast cells and therefore had been erroneously considered as blood-circulating mast cells. However, recent researches have revealed that basophils play nonredundant roles in allergic inflammation, protective immunity against parasitic infections and regulation of innate and acquired immunity. Basophils are recruited to inflamed tissues and activated in an IgE-dependent or IgE-independent manner to release a variety of effector molecules. Such molecules, including IL-4, act on various types of cells and play versatile roles, including the induction and termination of allergic inflammation and the regulation of immune responses. Recent development of novel therapeutic agents has enabled us to gain further insights into basophil biology in human disorders. In this review, we highlight the recent advances in the field of basophil biology with a particular focus on the role of basophils in allergic inflammation. Further studies on basophils and their effector molecules will help us identify novel therapeutic targets for treating allergic disorders.

Biology and dynamics of B cells in the context of IgE-mediated food allergy

An increasing number of people suffer from IgE-mediated food allergies. The immunological mechanisms that cause IgE-mediated food allergy have been extensively studied. B cells play a key role in the development of IgE-mediated food allergies through the production of allergen-specific antibodies. While this particular function of B cells has been known for many years, we still do not fully understand the mechanisms that regulate the induction and maintenance of allergen-specific IgE production. It is still not fully understood where in the body IgE class switch recombination of food allergen-specific B cells occurs, and what processes are involved in the immunological memory of allergen-specific IgE responses. B cells can also contribute to the regulation of allergen-specific immune responses through other mechanisms such as antigen presentation and cytokine production. Recent technological advances have enabled highly detailed analysis of small subsets of B cells down to the single-cell level. In this review, we provide an overview of the current knowledge on the biology of B cells in relation to IgE-mediated food allergies.

[The basophil: From control of immunity to control of leukemias]

The basophils, first described by Paul Ehlrich in 1879, are rare circulating cells, representing approximately 0.01 to 0.3% of the blood leukocytes. Until recently, these cells have been neglected because of their minority status among immune cells and because they show some similarities to mast cells residing in tissues. However, basophils and mast cells are now recognized as distinct cell lines and it appears that basophils have important and non-redundant functions, distinct from those of mast cells. On the one hand, basophils have beneficial contribution to protective immunity, in particular against parasitic infections. On the other hand, basophils are involved in the development of various benign and malignant pathologies, ranging from allergy to certain leukemias. Basophils interact with other immune cells or neoplastic cells through direct contacts or soluble mediators, such as cytokines and proteases, thus contributing to the regulation of the immune system but also to allergic responses, and probably to the process of neoplastic transformation. In this review, we will develop recent knowledge on the involvement of basophils in the modulation of innate and adaptive immunity. We will then describe the benign or malignant circumstances in which an elevation of circulating basophils can be observed. Finally, we will discuss the role played by these cells in the pathophysiology of certain leukemias, particularly during chronic myeloid leukemia.

Physiological and Pathological Inflammation Induced by Antibodies and Pentraxins

Macrophages play a key role in induction of inflammatory responses. These inflammatory responses are mostly considered to be instigated by activation of pattern recognition receptors (PRRs) or cytokine receptors. However, recently it has become clear that also antibodies and pentraxins, which can both activate Fc receptors (FcRs), induce very powerful inflammatory responses by macrophages that can even be an order of magnitude greater than PRRs. While the physiological function of this antibody-dependent inflammation (ADI) is to counteract infections, undesired activation or over-activation of this mechanism will lead to pathology, as observed in a variety of disorders, including viral infections such as COVID-19, chronic inflammatory disorders such as Crohn's disease, and autoimmune diseases such as rheumatoid arthritis. In this review we discuss how physiological ADI provides host defense by inducing pathogen-specific immunity, and how erroneous activation of this mechanism leads to pathology. Moreover, we will provide an overview of the currently known signaling and metabolic pathways that underlie ADI, and how these can be targeted to counteract pathological inflammation.

Interrupting reactivation of immunologic memory diverts the allergic response and prevents anaphylaxis

BACKGROUND

IgE production against innocuous food antigens can result in anaphylaxis, a severe life-threatening consequence of allergic reactions. The maintenance of IgE immunity is primarily facilitated by IgG+ memory B cells, as IgE+ memory B cells and IgE+ plasma cells are extremely scarce and short-lived, respectively.

OBJECTIVE

Our aim was to investigate the critical requirements for an IgE recall response in peanut allergy.

METHODS

We used a novel human PBMC culture platform, a mouse model of peanut allergy, and various experimental readouts to assess the IgE recall response in the presence and absence of IL-4Rα blockade.

RESULTS

In human PBMCs, we have demonstrated that blockade of IL-4/IL-13 signaling aborted IgE production after activation of a recall response and skewed the cytokine response away from a dominant type 2 signature. TH2A cells, identified by single-cell RNA sequencing, expanded with peanut stimulation and maintained their pathogenic phenotype in spite of IL-4Rα blockade. In mice with allergy, anti-IL-4Rα provided long-lasting suppression of the IgE recall response beyond antibody treatment and fully protected against anaphylaxis.

CONCLUSION

The findings reported here advance our understanding of events mediating the regeneration of IgE in food allergy.

A Longitudinal Analysis Reveals Early Activation and Late Alterations in B Cells During Primary HIV Infection in Mozambican Adults

Primary HIV infection (PHI) and subsequent chronic infection alter B-cell compartment. However, longitudinal analysis defining the dynamics of B-cell alterations are still limited. We longitudinally studied B-cell subsets in individuals followed for 1 year after PHI (n = 40). Treated and untreated chronic HIV infected (n = 56) and HIV-uninfected individuals (n = 58) were recruited as reference groups at the Manhiça District in Mozambique. B cells were analyzed by multicolor flow-cytometry. Anti-HIV humoral response and plasma cytokines were assessed by ELISA or Luminex-based technology. A generalized activation of B cells induced by HIV occurs early after infection and is characterized by increases in Activated and Tissue-like memory cells, decreases in IgM-IgD- (switched) and IgM-only B cells. These alterations remain mostly stable until chronic infection and are reverted in part by ART. In contrast, other parameters followed particular dynamics: PD-1 expression in memory cells decreases progressively during the first year of infection, Transitional B cells expand at month 3-4 after infection, and Marginal zone-like B cells show a late depletion. Plasmablasts expand 2 months after infection linked to plasma viral load and anti-p24 IgG3 responses. Most of well-defined changes induced by HIV in B-cell activation and memory subsets are readily observed after PHI, lasting until ART initiation. However, subsequent changes occur after sustained viral infection. These data indicate that HIV infection impacts B cells in several waves over time, and highlight that early treatment would result in beneficial effects on the B-cell compartment.

The therapeutic implications of activated immune responses via the enigmatic immunoglobulin D

Immunoglobulin D (IgD) is an enigmatic antibody and the least appreciated member of the immunoglobulin (Ig) family. Since its discovery over half a century ago, the essence of its function in the immune system has been somewhat enigmatic and less well-defined than other antibody classes. Membrane-bound IgD (mIgD) is mostly recognized as B-cell receptor (BCR) while secreted IgD (sIgD) has been recently implicated in 'arming' basophils and mast cells in mucosal innate immunity. Activations of immune responses via mIgD-BCR or sIgD by specific antigens or anti-IgD antibody thereby produce a broad and complex mix of cellular, antibody and cytokine responses from both the innate and adaptive immune systems. Such broadly activated immune responses via IgD were initially deemed to potentiate and exacerbate the onset of autoimmune and allergic conditions. Paradoxically, treatments with anti-IgD antibody suppressed and ameliorated autoimmune conditions and allergic inflammations in mouse models without compromising the host's general immune defence, demonstrating a unique and novel therapeutic application for anti-IgD antibody treatment. Herein, this review endeavored to collate and summarize the evidence of the unique characteristics and features of activated immune responses via mIgD-BCR and sIgD that revealed an unappreciated immune-regulatory function of IgD in the immune system via an amplifying loop of anti-inflammatory Th2 and tolerogenic responses, and highlighted a novel therapeutic paradigm in harnessing these immune responses to treat human autoimmune and allergic conditions.

Basophils and Eosinophils in Nematode Infections

Helminths remain one of the most prolific pathogens in the world. Following infection helminths interact with various epithelial cell surfaces, including skin, lung, and gut. Recent works have shown that epithelial cells produce a series of cytokines such as TSLP, IL-33, and IL-25 that lead to the induction of innate and acquired type 2 immune responses, which we named Type 2 epithelial cytokines. Although basophils and eosinophils are relatively rare granulocytes under normal conditions (0.5% and 5% in peripheral blood, respectively), both are found with increased frequency in type 2 immunity, including allergy and helminth infections. Recent reports showed that basophils and eosinophils not only express effector functions in type 2 immune reactions, but also manipulate the response toward helminths. Furthermore, basophils and eosinophils play non-redundant roles in distinct responses against various nematodes, providing the potential to intervene at different stages of nematode infection. These findings would be helpful to establish vaccination or therapeutic drugs against nematode infections.