STAT3 is required for IL-21–induced secretion of IgE from human naive B cells

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.

The trajectory of human B-cell function, immune deficiency, and allergy revealed by inborn errors of immunity

The essential role of B cells is to produce protective immunoglobulins (Ig) that recognize, neutralize, and clear invading pathogens. This results from the integration of signals provided by pathogens or vaccines and the stimulatory microenvironment within sites of immune activation, such as secondary lymphoid tissues, that drive mature B cells to differentiate into memory B cells and antibody (Ab)-secreting plasma cells. In this context, B cells undergo several molecular events including Ig class switching and somatic hypermutation that results in the production of high-affinity Ag-specific Abs of different classes, enabling effective pathogen neutralization and long-lived humoral immunity. However, perturbations to these key signaling pathways underpin immune dyscrasias including immune deficiency and autoimmunity or allergy. Inborn errors of immunity that disrupt critical immune pathways have identified non-redundant requirements for eliciting and maintaining humoral immune memory but concomitantly prevent immune dysregulation. Here, we will discuss our studies on human B cells, and how our investigation of cytokine signaling in B cells have identified fundamental requirements for memory B-cell formation, Ab production as well as regulating Ig class switching in the context of protective versus allergic immune responses.

Multifaceted roles for STAT3 in gammaherpesvirus latency revealed through in vivo B cell knockout models

Cancers associated with the oncogenic gammaherpesviruses, Epstein-Barr virus and Kaposi sarcoma herpesvirus, are notable for their constitutive activation of the transcription factor signal transducer and activator of transcription 3 (STAT3). To better understand the role of STAT3 during gammaherpesvirus latency and the B cell response to infection, we used the model pathogen murine gammaherpesvirus 68 (MHV68). Genetic deletion of STAT3 in B cells of CD19cre/+Stat3f/f mice reduced peak MHV68 latency approximately sevenfold. However, infected CD19cre/+Stat3f/f mice exhibited disordered germinal centers and heightened virus-specific CD8 T cell responses compared to wild-type (WT) littermates. To circumvent the systemic immune alterations observed in the B cell-STAT3 knockout mice and more directly evaluate intrinsic roles for STAT3, we generated mixed bone marrow chimeric mice consisting of WT and STAT3 knockout B cells. We discovered a dramatic reduction in latency in STAT3 knockout B cells compared to their WT B cell counterparts in the same lymphoid organ. RNA sequencing of sorted germinal center B cells revealed that MHV68 infection shifts the gene signature toward proliferation and away from type I and type II IFN responses. Loss of STAT3 largely reversed the virus-driven transcriptional shift without impacting the viral gene expression program. STAT3 promoted B cell processes of the germinal center, including IL-21-stimulated downregulation of surface CD23 on B cells infected with MHV68 or EBV. Together, our data provide mechanistic insights into the role of STAT3 as a latency determinant in B cells for oncogenic gammaherpesviruses.IMPORTANCEThere are no directed therapies to the latency program of the human gammaherpesviruses, Epstein-Barr virus and Kaposi sarcoma herpesvirus. Activated host factor signal transducer and activator of transcription 3 (STAT3) is a hallmark of cancers caused by these viruses. We applied the murine gammaherpesvirus pathogen system to explore STAT3 function upon primary B cell infection in the host. Since STAT3 deletion in all CD19+ B cells of infected mice led to altered B and T cell responses, we generated chimeric mice with both normal and STAT3-deleted B cells. B cells lacking STAT3 failed to support virus latency compared to normal B cells from the same infected animal. Loss of STAT3 impaired B cell proliferation and differentiation and led to a striking upregulation of interferon-stimulated genes. These findings expand our understanding of STAT3-dependent processes that are key to its function as a pro-viral latency determinant for oncogenic gammaherpesviruses in B cells and may provide novel therapeutic targets.

IL-17 and IL-21: Their Immunobiology and Therapeutic Potentials

Studies over the last 2 decades have identified IL-17 and IL-21 as key cytokines in the modulation of a wide range of immune responses. IL-17 serves as a critical defender against bacterial and fungal pathogens, while maintaining symbiotic relationships with commensal microbiota. However, alterations in its levels can lead to chronic inflammation and autoimmunity. IL-21, on the other hand, bridges the adaptive and innate immune responses, and its imbalance is implicated in autoimmune diseases and cancer, highlighting its important role in both health and disease. Delving into the intricacies of these cytokines not only opens new avenues for understanding the immune system, but also promises innovative advances in the development of therapeutic strategies for numerous diseases. In this review, we will discuss an updated view of the immunobiology and therapeutic potential of IL-17 and IL-21.

Translatability of findings from cynomolgus monkey to human suggests a mechanistic role for IL-21 in promoting immunogenicity to an anti-PD-1/IL-21 mutein fusion protein

AMG 256 is a bi-specific, heteroimmunoglobulin molecule with an anti-PD-1 antibody domain and a single IL-21 mutein domain on the C-terminus. Nonclinical studies in cynomolgus monkeys revealed that AMG 256 administration led to the development of immunogenicity-mediated responses and indicated that the IL-21 mutein domain of AMG 256 could enhance the anti-drug antibody response directed toward the monoclonal antibody domain. Anti-AMG 256 IgE were also observed in cynomolgus monkeys. A first-in-human (FIH) study in patients with advanced solid tumors was designed with these risks in mind. AMG 256 elicited ADA in 28 of 33 subjects (84.8%). However, ADA responses were only robust and exposure-impacting at the 2 lowest doses. At mid to high doses, ADA responses remained low magnitude and all subjects maintained exposure, despite most subjects developing ADA. Limited drug-specific IgE were also observed during the FIH study. ADA responses were not associated with any type of adverse event. The AMG 256 program represents a unique case where nonclinical studies informed on the risk of immunogenicity in humans, due to the IL-21-driven nature of the response.

Flow Cytometric Identification of Human IgE+ B Lineage Subsets

The use of flow cytometry for immunophenotyping is contingent on the ability to accurately assign biological relevance to the detected signal. This process has historically been challenging when defining IgE expressing B cells or IgE expressing antibody-secreting cells due to widespread expression of receptors for IgE on various leukocyte subsets, including human B cells. Here we describe our implementation of intracellular staining for human IgE following a blocking step to negate the challenge of surface-bound IgE. We also describe our experience with a human B cell culture system that can be used to robustly validate this approach before application to primary human samples. Orthogonal confirmatory techniques remain essential; these are not described in detail, but several possible strategies are suggested.

Human B Cell Receptor Repertoire Sequencing

Next-generation sequencing has the potential to uncover the complex nature of B cell immunity by revealing the full complexity of B cell receptor (BCR) repertoires in health and disease. However, there are drawbacks which can compromise the validity of the repertoire analysis caused by quantitative bias and accumulation of sequencing errors during the library preparation and sequencing. Here, we provide an optimized protocol designed to minimize bias for reproducible and accurate preparation of human BCR repertoire libraries for high-throughput sequencing.

Quantifying Human Naïve B Cell Proliferation Kinetics and Differentiation in Controlled In Vitro Cell Culture

Division tracking dyes like Cell Trace Violet (CTV) enable the quantification of cell proliferation, division, and survival kinetics of human naïve B cell responses in vitro. Human naïve B cells exhibit distinct responses to different stimuli, with CpG and anti-Ig inducing a T cell-independent (TI) response, while CD40L and IL-21 promote a T cell-dependent (TD) response that induces isotype switching and differentiation into antibody-secreting cells (ASCs). Both stimulation methods yield valuable insights into the intrinsic programming of B cell health within individuals, making them useful for clinical investigations. For instance, quantitative analysis from these B cell populations could reveal biologically meaningful measurements such as the average number of division rounds and the time to cells' fate. Here, we describe a novel in vitro culture setup for CTV-labelled human naïve B cells and a method for obtaining precise time-based data on proliferation, division-linked isotype switching, and differentiation.

The origins and longevity of IgE responses as indicated by serological and cellular studies in mice and humans

The existence of long-lived IgE antibody-secreting cells (ASC) is contentious, with the maintenance of sensitization by the continuous differentiation of short-lived IgE+ ASC a possibility. Here, we review the epidemiological profile of IgE production, and give an overview of recent discoveries made on the mechanisms regulating IgE production from mouse models. Together, these data suggest that for most individuals, in most IgE-associated diseases, IgE+ ASC are largely short-lived cells. A subpopulation of IgE+ ASC in humans is likely to survive for tens of months, although due to autonomous IgE B cell receptor (BCR) signaling and antigen-driven IgE+ ASC apoptosis, in general IgE+ ASC probably do not persist for the decades that other ASC are inferred to do. We also report on recently identified memory B cell transcriptional subtypes that are the likely source of IgE in ongoing responses, highlighting the probable importance of IL-4Rα in their regulation. We suggest the field should look at dupilumab and other drugs that prohibit IgE+ ASC production as being effective treatments for IgE-mediated aspects of disease in most individuals.

Requirements of IL-4 during the Generation of B Cell Memory

IL-4 has long been established as a key regulator of Th cells and for promoting effective B cell survival and isotype class switching. Yet, despite having been extensively studied, the specific role of IL-4 in generating humoral memory in vivo is unclear. In this review, we explore the recent studies that unravel the cellular sources and spatiotemporal production of IL-4, the relationship between IL-4 and IL-21 during germinal center responses and the formation of Ab-secreting cells, and the current understanding of whether IL-4 promotes or suppresses memory B cell generation in vitro and in vivo.

Long term longitudinal follow-up of an AD-HIES cohort: the impact of early diagnosis and enrollment to IPINet centers on the natural history of Job's syndrome

Job's syndrome, or autosomal dominant hyperimmunoglobulin E syndrome (AD-HIES, STAT3-Dominant Negative), is a rare inborn error of immunity (IEI) with multi-organ involvement and long-life post-infective damage. Longitudinal registries are of primary importance in improving our knowledge of the natural history and management of these rare disorders. This study aimed to describe the natural history of 30 Italian patients with AD-HIES recorded in the Italian network for primary immunodeficiency (IPINet) registry. This study shows the incidence of manifestations present at the time of diagnosis versus those that arose during follow up at a referral center for IEI. The mean time of diagnostic delay was 13.7 years, while the age of disease onset was < 12 months in 66.7% of patients. Respiratory complications, namely bronchiectasis and pneumatoceles, were present at diagnosis in 46.7% and 43.3% of patients, respectively. Antimicrobial prophylaxis resulted in a decrease in the incidence of pneumonia from 76.7% to 46.7%. At the time of diagnosis, skin involvement was present in 93.3% of the patients, including eczema (80.8%) and abscesses (66.7%). At the time of follow-up, under therapy, the prevalence of complications decreased: eczema and skin abscesses reduced to 63.3% and 56.7%, respectively. Antifungal prophylaxis decreased the incidence of mucocutaneous candidiasis from 70% to 56.7%. During the SARS-CoV-2 pandemic, seven patients developed COVID-19. Survival analyses showed that 27 out of 30 patients survived, while three patients died at ages of 28, 39, and 46 years as a consequence of lung bleeding, lymphoma, and sepsis, respectively. Analysis of a cumulative follow-up period of 278.7 patient-years showed that early diagnosis, adequate management at expertise centers for IEI, prophylactic antibiotics, and antifungal therapy improve outcomes and can positively influence the life expectancy of patients.

Human Monoclonal IgE Antibodies-a Major Milestone in Allergy

PURPOSE OF REVIEW

Bound to its high affinity receptor on mast cells and basophils, the IgE antibody molecule plays an integral role in the allergic reaction. Through interactions with the allergen, it provides the sensitivity and specificity parameters for cell activation and mediator release that produce allergic symptoms. Advancements in human hybridoma technologies allow for the generation and molecular definition of naturally occurring allergen-specific human IgE monoclonal antibodies.

RECENT FINDINGS

A high-resolution structure of dust mite allergen Der p 2 in complex with Fab of the human IgE mAb 2F10 was recently determined using X-ray crystallography. The structure reveals the fine molecular details of IgE 2F10 binding its 750 Å2 conformational epitope on Der p 2. This review provides an overview of this major milestone in allergy, the first atomic resolution structure of an authentic human IgE epitope. The molecular insights that IgE epitopes provide will allow for structure-based design approaches to the development of novel diagnostics, antibody therapeutics, and immunotherapies.

Immunology of allergen immunotherapy

Allergen immunotherapy (AIT) is the only disease-modifying therapy for allergic disease. Through repeated inoculations of low doses of allergen-either as whole proteins or peptides-patients can achieve a homeostatic balance between inflammatory effectors induced and/or associated with allergen contact, and mediators of immunologic non-responsiveness, potentially leading to sustained clinical improvements. AIT for airborne/respiratory tract allergens and insect venoms have traditionally been supplied subcutaneously, but other routes and modalities of administration can also be effective. Despite differences of allergen administration, there are some similarities of immunologic responses across platforms, with a general theme involving the restructuring and polarization of adaptive and innate immune effector cells. Here we review the immunology of AIT across various delivery platforms, including subcutaneous, sublingual, epicutaneous, intradermal, and intralymphatic approaches, emphasizing shared mechanisms associated with achieving immunologic non-responsiveness to allergen.

Termination of CD40L co-stimulation promotes human B cell differentiation into antibody-secreting cells

Human naïve B cells are notoriously difficult to differentiate into antibody-secreting cells (ASCs) in vitro while maintaining sufficient cell numbers to evaluate the differentiation process. B cells require T follicular helper (T_FH ) cell-derived signals like CD40L and IL-21 during germinal center (GC) responses to undergo differentiation into ASCs. Cognate interactions between B and T_FH cells are transient; after T_FH contact, B cells cycle between GC light and dark zones where T_FH contact is present and absent, respectively. Here, we elucidated that the efficacy of naïve B cells in ACS differentiation is dramatically enhanced by the release of CD40L stimulation. Multiparameter phospho-flow and transcription factor (TF)-flow cytometry revealed that termination of CD40L stimulation downmodulates NF-κB and STAT3 signaling. Furthermore, the termination of CD40 signaling downmodulates C-MYC, while promoting ASC TFs BLIMP1 and XBP-1s. Reduced levels of C-MYC in the differentiating B cells are later associated with crucial downmodulation of the B cell signature TF PAX5 specifically upon the termination of CD40 signaling, resulting in the differentiation of BLIMP1 high expressing cells into ASCs. The data presented here are the first steps to provide further insights how the transient nature of CD40 signaling is in fact needed for efficient human naïve B cell differentiation to ASCs.

Human T-bet governs the generation of a distinct subset of CD11chighCD21low B cells

High-level expression of the transcription factor T-bet characterizes a phenotypically distinct murine B cell population known as "age-associated B cells" (ABCs). T-bet-deficient mice have reduced ABCs and impaired humoral immunity. We describe a patient with inherited T-bet deficiency and largely normal humoral immunity including intact somatic hypermutation, affinity maturation and memory B cell formation in vivo, and B cell differentiation into Ig-producing plasmablasts in vitro. Nevertheless, the patient exhibited skewed class switching to IgG1, IgG4, and IgE, along with reduced IgG2, both in vivo and in vitro. Moreover, T-bet was required for the in vivo and in vitro development of a distinct subset of human B cells characterized by reduced expression of CD21 and the concomitantly high expression of CD19, CD20, CD11c, FCRL5, and T-bet, a phenotype that shares many features with murine ABCs. Mechanistically, human T-bet governed CD21^loCD11c^hi B cell differentiation by controlling the chromatin accessibility of lineage-defining genes in these cells: FAS, IL21R, SEC61B, DUSP4, DAPP1, SOX5, CD79B, and CXCR4. Thus, human T-bet is largely redundant for long-lived protective humoral immunity but is essential for the development of a distinct subset of human CD11c^hiCD21^lo B cells.

Immune and barrier characterization of atopic dermatitis skin phenotype in Tanzanian patients

BACKGROUND

Atopic dermatitis (AD) is a common disease, with particularly high prevalence found in Africa. It is increasingly recognized that patients with AD of different ethnic backgrounds have unique molecular signatures in the skin, potentially accounting for treatment response variations. Nevertheless, the skin profile of patients with AD from Africa is unknown, hindering development of new treatments targeted to this patient population.

OBJECTIVE

To characterize the skin profile of patients with AD from Africa.

METHODS

Gene expression studies, including RNA sequencing (using threshold of fold change of >2 and false discovery rate of <0.05) and real-time polymerase chain reaction, were performed on skin biopsies of Tanzanian patients with moderate-to-severe AD and controls.

RESULTS

Tanzanian AD skin presented robust up-regulations of multiple key mediators of both T helper 2 (TH2) (interleukin 13 [IL-13], IL-10, IL-4R, CCL13,CCL17,CCL18,CCL26) and TH22 (IL22, S100As) pathways. Markers related to TH17 and IL-23 (IL-17A, IL-23A, IL-12, PI3, DEFB4B) and TH1 (interferon gamma, CXCL9,CXCL10,CXCL11) were also significantly overexpressed in AD tissues (FDR<.05), albeit to a lesser extent. IL-36 isoforms revealed substantial up-regulations in African skin. The barrier fingerprint of Tanzanian AD revealed no suppression of hallmark epidermal barrier differentiation genes, such as filaggrin, loricrin, and periplakin, with robust attenuation of lipid metabolism genes (ie, AWAT1).

CONCLUSION

The skin phenotype of Tanzanian patients with AD is consistent with that of African Americans, exhibiting dominant TH2 and TH22 skewing, minimal dysregulation of terminal differentiation, and even broader attenuation of lipid metabolism-related products. These data highlight the unique characteristic of AD in Black individuals and the need to develop unique treatments targeting patients with AD from these underrepresented populations.

Rare clinical presentations of hyper-IgE syndrome in a patient with dental abnormalities: A case report

Asthma and anaphylaxis are two atypical presentations of hyper-IgE syndrome (HIES). Early diagnosis and management of HIES can improve quality of life of patients through minimizing orthodontic problems and other complications related to this disorder.

TLR2 deficiency promotes IgE and inhibits IgG1 class-switching following ovalbumin sensitization

BACKGROUND

To explore the roles of Toll-like receptor (TLR)2 in Th2 cytokine production and immunoglobulin (Ig) class switching following ovalbumin (OVA) sensitization.

METHODS

TLR2-/- and wild-type C57BL/6 mice were sensitized by intraperitoneal injection with OVA. Lung pathology was assessed by hematoxylin and eosin staining. Abundance of interleukin (IL)4, IL5, IL13, and IL21 transcripts in the lungs was quantified by RT-PCR. OVA-specific IgG1, IgG2a, IgG2b, IgE and IgM were quantified by enzyme-linked immunosorbent assay. Phosphorylated signal transducer and activator of transcription (STAT)3 in lung tissue was detected by immunohistochemistry staining and nuclear factor (NF) κB activation was measured by immunofluorescence staining. STAT3 activation was inhibited using cryptotanshinone (CPT) treatment. Germline transcripts (Iμ-Cμ, Iγ-Cγ, Iα-Cα or Iε-Cε), post-recombination transcripts (Iμ-Cγ, Iμ-Cα or Iμ- Cε) and mature transcripts (VHDJH-Cγ, VHDJH-Cα or VHDJH-Cε) were analyzed from splenic B cells of OVA-sensitized wild-type mice (with or without CPT treatment) and TLR2-/- mice (with or without IL21 treatment).

RESULTS

The lungs of TLR2-/- mice showed a lesser degree of inflammation than wild-type mice after OVA sensitization. Following OVA sensitization, levels of IL4, IL13, and IL21, but not IL5, were significantly lower in TLR2-/- compared with wild-type mice. Moreover, OVA-specific IgG1 and IgE titers were markedly lower and higher, respectively, in TLR2-/- mice. TLR2 deficiency inhibited STAT3 activation but not NF-κB p65 activation. CPT treatment reduced IgG1 titers via inhibition of Stat3 phosphorylation. Both TLR2 knockout and CPT treatment reduced the frequencies of Iγ1-Cγ1, Iγ3-Cγ3 and Iα-Cα transcripts, but IL21 treatment compensated for the effects of TLR2 deficiency.

CONCLUSION

These results suggest a role of TLR2 in restricting OVA-sensitized lung inflammation via promotion of IgG1 and inhibition of IgE class switching regulated by IL21 and STAT3.

CD40L-Stimulated B Lymphocytes Are Polarized toward APC Functions after Exposure to IL-4 and IL-21

B lymphocytes have multiple functions central to humoral immunity, including Ag presentation to T cells, cytokine secretion, and differentiation into Ab-secreting plasma cells. In vitro expansion of human B cells by continuous IL-4 stimulation and engagement of their CD40 receptor by CD40L has allowed the use of these IL-4-CD40-B cells in research for the induction of Ag-specific T cell immune responses. However, in vivo, follicular helper T cells also influence B cell activity through the secretion of IL-21. The impact of both cytokines on multiple B cell functions is not clearly defined. To further understand these cytokines in CD40-B cell biology, we stimulated CD40-B cells with IL-4 or IL-21 or both (Combo) and characterized the proliferation, subsets, and functions of these cells. We demonstrate that IL-21- and Combo-CD40-B cells are highly proliferative cells that can be rapidly expanded to high numbers. We show that IL-21-CD40-B cells polarize to Ab-secreting plasma cells, whereas IL-4- and Combo-CD40-B cells are mostly activated mature B cells that express molecules associated with favorable APC functions. We further demonstrate that both IL-4- and Combo-CD40-B cells are efficient in promoting T cell activation and proliferation compared with IL-21-CD40-B cells. Thus, our study provides a better appreciation of CD40-B cell plasticity and biology. In addition, the stimulation of B cells with CD40L, IL-4, and IL-21 allows for the fast generation of high numbers of efficient APC, therefore providing a prospective tool for research and clinical applications such as cancer immunotherapy.

WSB1 and IL21R Genetic Variants Are Involved in Th2 Immune Responses to Ascaris lumbricoides

Genetic and epigenetic factors are considered to be critical for host-parasite interactions. There are limited data on the role of such factors during human infections with Ascaris lumbricoides. Here, we describe the potential role of genetic factors as determinants of the Th2 immune response to A. lumbricoides in Brazilian children. Stool samples were collected from the children to detect A. lumbricoides by microscopy and peripheral blood leukocytes (PBLs) were cultured in whole blood cultures for detection of cytokines (IL-5, IL-10, and IL-13) in vitro. Levels of anti-A. lumbricoides IgE and IgG4 were measured in plasma. DNA was extracted from PBLs and genotyped using Illumina 2.5 Human Omni Beadchip. Candidate genes associated with A. lumbricoides responses were identified and SNVs in these selected genes associated with the Th2 immune response to A. lumbricoides. Haplotype, gene expression, and epigenetic analyses were done to identify potential associations with Th2 immune responses. GWAS on samples from 1,189 children identified WSB1 as a candidate gene, and IL-21R was selected as a biologically relevant linked gene for further analysis. Variants in WSB1 and IL21R were associated with markers of Th2 immune responses: increased A. lumbricoides-specific IgE and IL-5/IL-13 by PBLs from infected compared to uninfected individuals. In infected children, WSB1 but not IL21R gene expression was suppressed and increased methylation was observed in the WSB1 promoter region. This is the first study to show an association between genetic variants in WSB1 and IL21R and Th2 immune responses during A. lumbricoides infections in children. WSB1/IL21R pathways could provide a potential target for the treatment of Th2-mediated diseases.

Pseurotin D Inhibits the Activation of Human Lymphocytes

Background: Pseurotins, a family of secondary metabolites of different fungi characterized by an unusual spirocyclic furanone-lactam core, are suggested to have different biological activities including the modulation of immune response. Purpose: Complex characterization of the effects of pseurotin D on human lymphocyte activation in order to understand the potential of pseurotin to modulate immune response in humans. Methods: CD4+ and CD8+ T cells and CD19+ B cells isolated from human blood were activated by various activators simultaneously with pseurotin D treatment. The effects of pseurotin were tested on the basis of changes in cell viability, apoptosis, activation of signal transducers and activators of transcription (STAT) signaling pathways, production of tumor necrosis factor (TNF)-α by T cells, expression of activation markers CD69 and CD25 on T cells and Human Leukocyte Antigen–DR isotype (HLA-DR) on B cells, and the differentiation markers CD20, CD27, CD38, and immunoglobulin (Ig) D on B cells. Results: Pseurotin D significantly inhibited the activation of both CD4+ and CD8+ human T cells complemented by the inhibition of TNF-α production without significant acute toxic effects. The Pseurotin D-mediated inhibition of T-cell activation was accompanied by the induction of the apoptosis of T cells. This corresponded with the inhibited phosphorylation of STAT3 and STAT5. In human B cells, pseurotin D did not significantly inhibit their activation; however, it affected their differentiation. Conclusions: Our results advance the current mechanistic understanding of the pseurotin-induced inhibition of lymphocytes and suggest pseurotins as new attractive chemotypes for future research in the context of immune-modulatory drugs.

IL-21 is a broad negative regulator of IgE class switch recombination in mouse and human B cells

IgE antibodies may elicit potent allergic reactions, and their production is tightly controlled. The tendency to generate IgE has been thought to reflect the balance between type 1 and type 2 cytokines, with the latter promoting IgE. Here, we reevaluated this paradigm by a direct cellular analysis, demonstrating that IgE production was not limited to type 2 immune responses yet was generally constrained in vivo. IL-21 was a critical negative regulator of IgE responses, whereas IFN-γ, IL-6, and IL-10 were dispensable. Follicular helper T cells were the primary source of IL-21 that inhibited IgE responses by directly engaging the IL-21 receptor on B cells and triggering STAT3-dependent signaling. We reconciled previous discordant results between mouse and human B cells and revealed that the inhibition of IgE class switch recombination by IL-21 was attenuated by CD40 signaling, whereas IgG1 class switch recombination was potentiated by IL-21 in the context of limited IL-4. These findings establish key features of the extrinsic regulation of IgE production by cytokines.

On Two Cases with Autosomal Dominant Hyper IgE Syndrome: Importance of Immunological Parameters for Clinical Course and Follow-Up

Autosomal dominant hyper-IgE syndrome (AD-HIES) is a rare disease described in 1966. It is characterized by severe dermatitis, a peculiar face, frequent infections, extremely high levels of serum IgE and eosinophilia, all resulting from a defect in the STAT3 gene. A variety of mutations in the SH2 and DNA-binding domain have been described, and several studies have searched for associations between the severity of the clinical symptoms, laboratory findings, and the type of genetic alteration. We present two children with AD-HIES–a girl with the most common STAT3 mutation (R382W) and a boy with a rare variant (G617E) in the same gene, previously reported in only one other patient. Herein, we discuss the clinical and immunological findings in our patients, focusing on their importance on disease course and management.

Flow Cytometric Methods for the Detection of Intracellular Signaling Proteins and Transcription Factors Reveal Heterogeneity in Differentiating Human B Cell Subsets

The flow cytometric detection of intracellular (IC) signaling proteins and transcription factors (TFs) will help to elucidate the regulation of B cell survival, proliferation and differentiation. However, the simultaneous detection of signaling proteins or TFs with membrane markers (MMs) can be challenging, as the required fixation and permeabilization procedures can affect the functionality of conjugated antibodies. Here, a phosphoflow method is presented for the detection of activated NF-κB p65 and phosphorylated STAT1, STAT3, STAT5 and STAT6, together with the B cell differentiation MMs CD19, CD27 and CD38. Additionally, a TF-flow method is presented that allows the detection of the B cell TFs PAX5, c-MYC, BCL6 and AID and antibody-secreting cell (ASC) TFs BLIMP1 and XBP-1s, together with MMs. Applying these methods on in vitro-induced human B cell differentiation cultures showed significantly different steady-state levels, and responses to stimulation, of phosphorylated signaling proteins in CD27-expressing B cell and ASC populations. The TF-flow protocol and Uniform Manifold Approximation and Projection (UMAP) analysis revealed heterogeneity in TF expression within stimulated CD27- or CD38-expressing B cell subsets. The methods presented here allow for the sensitive analysis of STAT, NF-κB p65 signaling and TFs, together with B cell differentiation MMs, at single-cell resolution. This will aid the further investigation of B cell responses in both health and disease.

Protein kinase 2 (CK2): a potential regulator of immune cell development and function in cancer

Protein kinase CK2, formally known as casein kinase II, is ubiquitously expressed and highly conserved serine/threonine or tyrosine kinase enzyme that regulates diverse signaling pathways responsible for cellular processes (i.e., cell proliferation and apoptosis) via interactions with over 500 known substrates. The enzyme's physiological interactions and cellular functions have been widely studied, most notably in the blood and solid malignancies. CK2 has intrinsic role in carcinogenesis as overexpression of CK2 subunits (α, α`, and β) and deregulation of its activity have been linked to various forms of cancers. CK2 also has extrinsic role in cancer stroma or in the tumor microenvironment (TME) including the immune cells. However, very few research studies have focused on extrinsic role of CK2 in regulating immune responses as a therapeutic alternative for cancer. The following review discusses CK2's regulation of key signaling events [Nuclear factor kappa B (NF-κB), Janus kinase/signal transducer and activators of transcription (JAK/STAT), Hypoxia inducible factor-1alpha (HIF-1α), Cyclooygenase-2 (COX-2), Extracellular signal-regulated kinase/mitogen-activated protein kinase (ERK/MAPK), Notch, Protein kinase B/AKT, Ikaros and Wnt] that can influence the development and function of immune cells in cancer. Potential clinical trials using potent CK2 inhibitors will facilitate and improve the treatment of human malignancies.

Altered chromatin landscape in circulating T follicular helper and regulatory cells following grass pollen subcutaneous and sublingual immunotherapy

BACKGROUND

Allergen-specific immunotherapy is a disease-modifying treatment that induces long-term T-cell tolerance.

OBJECTIVE

We sought to evaluate the role of circulating CXCR5⁺PD-1⁺ T follicular helper (cT_FH) and T follicular regulatory (T_FR) cells following grass pollen subcutaneous immunotherapy (SCIT) and sublingual immunotherapy (SLIT) and the accompanying changes in their chromatin landscape.

METHODS

Phenotype and function of cT_FH cells were initially evaluated in the grass pollen-allergic (GPA) group (n = 28) and nonatopic healthy controls (NAC, n = 13) by mathematical algorithms developed to manage high-dimensional data and cell culture, respectively. cT_FH and T_FR cells were further enumerated in NAC (n = 12), GPA (n = 14), SCIT- (n = 10), and SLIT- (n = 8) treated groups. Chromatin accessibility in cT_FH and T_FR cells was assessed by assay for transposase-accessible chromatin sequencing (ATAC-seq) to investigate epigenetic mechanisms underlying the differences between NAC, GPA, SCIT, and SLIT groups.

RESULTS

cT_FH cells were shown to be distinct from T_H2- and T_H2A-cell subsets, capable of secreting IL-4 and IL-21. Both cytokines synergistically promoted B-cell class switching to IgE and plasma cell differentiation. Grass pollen allergen induced cT_FH-cell proliferation in the GPA group but not in the NAC group (P < .05). cT_FH cells were higher in the GPA group compared with the NAC group and were lower in the SCIT and SLIT groups (P < .01). Time-dependent induction of IL-4, IL-21, and IL-6 was observed in nasal mucosa following intranasal allergen challenge in the GPA group but not in SCIT and SLIT groups. T_FR and IL-10⁺ cT_FH cells were induced in SCIT and SLIT groups (all, P < .01). ATAC-seq analyses revealed differentially accessible chromatin regions in all groups.

CONCLUSIONS

For the first time, we showed dysregulation of cT_FH cells in the GPA group compared to NAC, SCIT, and SLIT groups and induction of T_FR and IL-10⁺ cT_FH cells following SCIT and SLIT. Changes in the chromatin landscape were observed following allergen-specific immunotherapy in cT_FH and T_FR cells.

Primary Atopic Disorders

Primary atopic disorders describes a series of monogenic diseases that have allergy- or atopic effector–related symptoms as a substantial feature. The underlying pathogenic genetic lesions help illustrate fundamental pathways in atopy, opening up diagnostic and therapeutic options for further study in those patients, but ultimately for common allergic diseases as well. Key pathways affected in these disorders include T cell receptor and B cell receptor signaling, cytokine signaling, skin barrier function, and mast cell function, as well as pathways that have not yet been elucidated. While comorbidities such as classically syndromic presentation or immune deficiency are often present, in some cases allergy alone is the presenting symptom, suggesting that commonly encountered allergic diseases exist on a spectrum of monogenic and complex genetic etiologies that are impacted by environmental risk factors.

Natural pseurotins and analogs thereof inhibit activation of B-cells and differentiation into the plasma cells

BACKGROUND

The frequency of allergic diseases is constantly rising. Dysregulated production of isotype E immunoglobulins is one of the key factors behind allergic reactions and its modulation is therefore an important target for pharmacological intervention. Natural products of the pseurotin family were reported to be inhibitors of IgE production in B-cells. Mechanistic details underlying these effects are however not well understood.

PURPOSE

In the present study, we synthesized new analogs of natural pseurotins and extensively investigated their inhibitory effects on activation, proliferation and differentiation of B-cells, as well as on the production of IgE.

STUDY DESIGN

Effects of two natural pseurotins (pseurotins A and D) and a collection of fully synthetic pseurotin analogs were studied on mouse B-cells stimulated by the combination of IL-4 and E. coli lipopolysaccharide. The IgE production was determined along with cell viability and cell proliferation. The phosphorylation of selected members of the STAT transcription factor family was subsequently investigated. Finally, the in vivo effect of pseurotin D on the ovalbumin-induced delayed type hypersensitivity response was tested in mice.

RESULTS

We discovered that several fully synthetic pseurotin analogs were able to decrease the production of IgE in stimulated B-cells with potency comparable to that of pseurotins A and D. We found that the two natural pseurotins and the active synthetic analogs inhibited the phosphorylation of STAT3, STAT5 and STAT6 proteins in stimulated B-cells, resulting in the inhibition of B-cell proliferation and differentiation into the plasma cells. In vivo, pseurotin D decreased ovalbumin-induced foot pad edema.

CONCLUSION

Our results advance the current mechanistic understanding of the pseurotin-induced inhibition of IgE production in B-cells by linking the effect to STAT signaling, and associated modulation of B-cell proliferation and differentiation. Together with our finding that structurally simpler pseurotin analogs were able to reproduce the effects of natural pseurotins, the presented work has implications for the future research on these secondary metabolites in the context of allergic diseases.

IL-21 in Conjunction with Anti-CD40 and IL-4 Constitutes a Potent Polyclonal B Cell Stimulator for Monitoring Antigen-Specific Memory B Cells

Detection of antigen-specific memory B cells for immune monitoring requires their activation, and is commonly accomplished through stimulation with the TLR7/8 agonist R848 and IL-2. To this end, we evaluated whether addition of IL-21 would further enhance this TLR-driven stimulation approach; which it did not. More importantly, as most antigen-specific B cell responses are T cell-driven, we sought to devise a polyclonal B cell stimulation protocol that closely mimics T cell help. Herein, we report that the combination of agonistic anti-CD40, IL-4 and IL-21 affords polyclonal B cell stimulation that was comparable to R848 and IL-2 for detection of influenza-specific memory B cells. An additional advantage of anti-CD40, IL-4 and IL-21 stimulation is the selective activation of IgM⁺ memory B cells, as well as the elicitation of IgE⁺ ASC, which the former fails to do. Thereby, we introduce a protocol that mimics physiological B cell activation through helper T cells, including induction of all Ig classes, for immune monitoring of antigen-specific B cell memory.

Orthognathic Surgical Treatment in a Patient With Hyperimmunoglobulin E Syndrome

Autosomal-dominant hyperimmunoglobulin E syndrome (HIES), or Job syndrome, is a rare, multisystem, primary immunodeficiency disorder. Additionally, patients may also suffer from connective tissue, dental, and bone malformations. While current management of HIES is directed at prophylactic antibiotics to prevent infections, there is limited work describing surgical considerations for these patients, particularly with respect to hardware placement. Here we report a case of a patient with HIES who underwent orthognathic surgery for maxillary advancement and mandibular setback to address his severe class III malocclusion. The patient's postoperative course was complicated by significant infection, requiring multiple operations and ultimately, hardware removal after bone healing. Although this patient ultimately had a good outcome, the role of orthognathic surgery with implant placement in patients with HIES should be approached with caution and careful consideration.

Interleukin (IL)-21 in Inflammation and Immunity During Parasitic Diseases

Parasitic diseases cause significant morbidity and mortality in the developing and underdeveloped countries. No efficacious vaccines are available against most parasitic diseases and there is a critical need for developing novel vaccine strategies for care. IL-21 is a pleiotropic cytokine whose functions in protection and immunopathology during parasitic diseases have been explored in limited ways. IL-21 and its cognate receptor, IL-21R, are highly expressed in parasitized organs of infected humans as well in murine models of the human parasitic diseases. Prior studies have indicated the ability of the IL-21/IL-21R signaling axis to regulate the effector functions (e.g., cytokine production) of T cell subsets by enhancing the expression of T-bet and STAT4 in human T cells, resulting in an augmented production of IFN-γ. Mice deficient for either IL-21 (Il21^−/−) or IL-21R (Il21r^−/−) showed significantly reduced inflammatory responses following parasitic infections as compared with their WT counterparts. Targeting the IL-21/IL-21R signaling axis may provide a novel approach for the development of new therapeutic agents for the prevention of parasite-induced immunopathology and tissue destruction.

Impaired memory B-cell development and antibody maturation with a skewing toward IgE in patients with STAT3 hyper-IgE syndrome

BACKGROUND

Signal transducer and activator of transcription 3 hyper-IgE syndrome (STAT3-HIES) is caused by heterozygous mutations in the STAT3 gene and is associated with eczema, elevated serum IgE, and recurrent infections resembling severe atopic dermatitis, while clinically relevant specific IgE is almost absent.

METHODS

To investigate the impact of STAT3 signaling on B-cell responses, we assessed lymph node and bone marrow, blood B and plasma cell subsets, somatic hypermutations in Ig genes, and in vitro proliferation and antibody production in STAT3-HIES patients and healthy controls.

RESULTS

Lymph nodes of STAT3-HIES patients showed normal germinal center architecture and CD138⁺ plasma cells residing in the paracortex, which expressed IgE, IgG, and IgM but not IgA. IgE⁺ plasma cells were abundantly present in STAT3-HIES bone marrow. Proliferation of naive B cells upon stimulation with CD40L and IL-4 was similar in patients and controls, while patient cells showed reduced responses to IL-21. IgE, IgG1, IgG3 and IgA1 transcripts showed reduced somatic hypermutations. Peripheral blood IgE⁺ memory B-cell frequencies were increased in STAT3-HIES, while other memory B-cell frequencies except for IgG4⁺ cells were decreased.

CONCLUSIONS

Despite impaired STAT3 signaling, STAT3-HIES patients can mount in vivo T-cell-dependent B-cell responses, while circulating memory B cells, except for those expressing IgG4 and IgE, were reduced. Reduced molecular maturation demonstrated the critical need of STAT3 signaling for optimal affinity maturation and B-cell differentiation, supporting the need for immunoglobulin substitution therapy and explaining the high IgE serum level in the majority with absent allergic symptoms.

Activation-induced cytidine deaminase plays crucial role in ovalbumin-induced food allergy and promoted by IL-21

The prevalence of IgE-mediated food allergy is increasing in the whole wide world which often causes skin and gastrointestinal tract symptoms, or even fatal anaphylactic shock. However, the evaluation of food allergens remains difficult, and the mechanism of food allergy is still not fully clear. To study the gene expression profile in food allergy animal models and identify the regulatory mechanism of the crucial genes, two administration routes were used to build animal models in our study. OVA-specific IgE and IL-4 levels were tested by ELISA, transcriptome profiling was carried out by microarray, and the regulatory mechanism of the highest expressed gene was studied in the primary spleen cells. We found that activation-induced cytidine deaminase (Aicda) is the highest expressed gene in the allergic mice, IL-21 can dramatically enhance the expression of Aicda in the lymph node microenvironment, and IL-17A can promote this effect significantly though it has only limited influence by itself. At last, we illuminated that the promotion of IL-21 on Aicda is partially through STAT3. In summary, our results suggest that IL-21 and IL-17A may play important role in the expression of Aicda as well as food allergy.

Immunologic mechanisms of a short-course of Lolium perenne peptide immunotherapy: A randomized, double-blind, placebo-controlled trial

BACKGROUND

A 3-week short-course of adjuvant-free hydrolysates of Lolium perenne peptide (LPP) immunotherapy for rhinoconjunctivitis with or without asthma over 4 physician visits is safe, well tolerated, and effective.

OBJECTIVE

We sought to investigate immunologic mechanisms of LPP immunotherapy in a subset of patients who participated in a phase III, multicenter, randomized, double-blind, placebo-controlled trial (clinical.govNCT02560948).

METHODS

Participants were randomized to receive LPP (n = 21) or placebo (n = 11) for 3 weeks over 4 visits. Grass pollen-induced basophil, T-cell, and B-cell responses were evaluated before treatment (visit [V] 2), at the end of treatment (V6), and after the pollen season (V8).

RESULTS

Combined symptom and rescue medication scores (CSMS) were lower during the peak pollen season (-35.1%, P = .03) and throughout the pollen season (-53.7%, P = .03) in the LPP-treated group compared with those in the placebo-treated group. Proportions of CD63⁺ and CD203c^brightCRTH2⁺ basophils were decreased following LPP treatment at V6 (10 ng/mL, P < .0001) and V8 (10 ng/mL, P < .001) compared to V2. No change in the placebo-treated group was observed. Blunting of seasonal increases in levels of grass pollen-specific IgE was observed in LPP-treated but not placebo-treated group. LPP immunotherapy, but not placebo, was associated with a reduction in proportions of IL-4⁺ T_H2 (V6, P = .02), IL-4⁺ (V6, P = .003; V8, P = .004), and IL-21⁺ (V6, P = .003; V8, P = .002) follicular helper T cells. Induction of FoxP3⁺, follicular regulatory T, and IL-10⁺ regulatory B cells were observed at V6 (all P < .05) and V8 (all P < .05) in LPP-treated group. Induction of regulatory B cells was associated with allergen-neutralizing IgG₄-blocking antibodies.

CONCLUSION

For the first time, we demonstrate that the immunologic mechanisms of LPP immunotherapy are underscored by immune modulation in the T- and B-cell compartments, which is necessary for its effect.

Hyper IgE syndromes: clinical and molecular characteristics

Hyper IgE syndromes comprise a group of rare primary immunodeficiency disorders characterized by a triad of atopic dermatitis, recurrent skin and lung infections along with elevated IgE levels. Job syndrome or autosomal dominant hyper IgE syndrome because of heterozygous loss-of-function mutations with dominant negative effect in signal transducer and activator of transcription-3 is the prototype of these disorders. However, several other genetically characterized immunodeficiency disorders have been identified over the past decade and joined the umbrella of hyper IgE syndromes including autosomal recessive mutations in the DOCK8, ZNF431 and PGM3 genes and heterozygous mutations with dominant negative effect in the CARD11 gene. Moreover, a number of phenotypically distinct immunodeficiency disorders can mimic hyper IgE syndromes, adding to the diagnostic challenge. Herein, we will concisely review these disorders, their molecular bases, highlighting key distinguishing clinical and laboratory findings and therapeutic options.

Genetic engineering in primary human B cells with CRISPR-Cas9 ribonucleoproteins

Genome editing in human cells with targeted nucleases now enables diverse experimental and therapeutic genome engineering applications, but extension to primary human B cells remains limited. Here we report a method for targeted genetic engineering in primary human B cells, utilizing electroporation of CRISPR-Cas9 ribonucleoproteins (RNPs) to introduce gene knockout mutations at protein-coding loci with high efficiencies that in some cases exceeded 80%. Further, we demonstrate knock-in editing of targeted nucleotides with efficiency exceeding 10% through co-delivery of oligonucleotide templates for homology directed repair. We delivered Cas9 RNPs in two distinct in vitro culture systems to achieve editing in both undifferentiated B cells and activated B cells undergoing differentiation, reflecting utility in diverse experimental conditions. In summary, we demonstrate a powerful and scalable research tool for functional genetic studies of human B cell biology that may have further applications in engineered B cell therapeutics.

Circulating CXCR5+CD4+ T cells participate in the IgE accumulation in allergic asthma

The pathogenesis of allergic asthma is primarily characterized by abnormality in immunoglobin(Ig)E pathway, suggesting a possible role for follicular helper T cells (Tfh) in the genesis of excessive IgE accumulation. The blood chemokine (C-X-C motif) receptor 5 (CXCR)5⁺CD4⁺ T cells, known as "circulating" Tfh, share common functional characteristics with Tfh cells from germinal centers. The aim of this study was to determine the phenotypes and functions of circulating CXCR5⁺CD4⁺ T cells in allergic asthmatics. Here we found the frequency of the circulating CXCR5⁺CD4⁺ T cells was raised in allergic asthma compared with healthy control (HC). Phenotypic assays showed that activated circulating CXCR5⁺CD4⁺ T cells display the key features of Tfh cells, including invariably coexpressed programmed cell death (PD)-1 and inducible costimulator (ICOS). The frequency of interleukin IL-4⁺-, IL-21⁺-producing CXCR5⁺CD4⁺ T cells was increased in allergic asthma patients compared with HC. Furthermore, sorted circulating CXCR5⁺CD4⁺ T cells from allergic asthma patients boosted IgE production in coculture assay which could be inhibited by IL-4 or IL-21 blockage. Interestingly, IL-4⁺-, IL-21⁺-CXCR5⁺CD4⁺ T cells positively correlated with total IgE in the blood. Our data indicated that circulating CXCR5⁺CD4⁺ T cells may have a significant role in facilitating IgE production in allergic asthma patients.

A proteomics analysis reveals that A2M might be regulated by STAT3 in persistent allergic rhinitis

BACKGROUND

Proteomics tools can be used to identify the differentially expressed proteins related to allergic rhinitis (AR). However, the large numbers of proteins related to AR have not yet been explored using an advanced quantitative proteomics approach, known as isobaric tags for relative and absolute quantitation (iTRAQ).

OBJECTIVES

To identify differentially expressed proteins in persistent AR patients and to explore the regulatory signalling pathways involving the identified proteins.

METHODS

Forty-five persistent AR patients and 20 healthy controls were recruited for this study. iTRAQ was used to identify the proteins that were differentially expressed between these two groups, and a bioinformatics analysis was then conducted to identify the signalling pathways associated with the identified proteins. Immunofluorescence labelling was performed to detect alpha-2-macroglobulin (A2M), STAT3, p-STAT3 and IL17 in the nasal mucosa.

RESULTS

A total of 133 differentially expressed proteins were identified. We then determined the top 10 regulatory pathways associated with these proteins and found that the blood coagulation pathway had the most significant association. A2M, a protein involved in the blood coagulation pathway, was found to be differentially expressed in the serum of AR patients. The bioinformatics analysis indicated that STAT3 is an upstream transcription factor that might regulate A2M expression. An immunofluorescence study further confirmed that STAT3 and A2M are co-localized in nasal mucosa cells. Additionally, A2M, STAT3, p-STAT3, and IL17 are elevated in AR patients. The expressional level of A2M is positively related to IL17 and the symptom of the congestion in AR subjects.

CONCLUSIONS

The blood coagulation pathway may be a key regulatory network pathway contributing to the allergic inflammatory response in AR patients. A2M, which is regulated by STAT3, may be an important protein in the pathogenesis of allergic rhinitis in AR patients.

Pathogenic mechanisms of IgE-mediated inflammation in self-destructive autoimmune responses

Autoantibodies of the IgG subclass are pathogenic in a number of autoimmune disorders such as systemic lupus erythomatosus. The presence of circulating IgE autoantibodies in autoimmune patients has also been known for almost 40 years. Despite their role in allergies, IgE autoantibodies are not associated with a higher rate of atopy in these patients. However, recently they have been recognized as active drivers of autoimmunity through mechanisms involving the secretion of Type I interferons by plasmacytoid dendritic cells (pDC), the recruitment of basophils to lymph nodes, and the activation of adaptive immune responses through B and T cells. Here, we will review the formation, prevalence, affinity, and roles of the IgE autoantibodies that have been described in autoimmunity. We also present novel evidence supporting that triggering of IgE receptors in pDC induces LC3-associated phagocytosis, a cellular process also known as LAP that is associated with interferon responses. The activation of pDC with immune complexes formed by DNA-specific IgE antibodies also induce potent B-cell differentiation and plasma cell formation, which further define IgE's role in autoimmune humoral responses.

Mechanism involved in interleukin-21-induced phagocytosis in human monocytes and macrophages

The interleukin (IL)-21/IL-21 receptor (R) is a promising system to be exploited for the development of therapeutic strategies. Although the biological activities of IL-21 and its cell signalling events have been largely studied in immunocytes, its interaction with human monocytes and macrophages have been neglected. Previously, we reported that IL-21 enhances Fc gamma receptor (FcRγ)-mediated phagocytosis in human monocytes and in human monocyte-derived macrophages (HMDM) and identified Syk as a novel molecular target of IL-21. Here, we elucidate further how IL-21 promotes phagocytosis in these cells. Unlike its ability to enhance phagocytosis of opsonized sheep red blood cells (SRBCs), IL-21 did not promote phagocytosis of Escherichia coli and zymosan by monocytes and did not alter the cell surface expression of CD16, CD32 and CD64. In HMDM, IL-21 was found to enhance phagocytosis of zymosan. In addition, we found that IL-21 activates p38, protein kinase B (Akt), signal transducer and activator of transcription (STAT)-1 and STAT-3 in monocytes and HMDM. Using a pharmacological approach, we demonstrate that IL-21 enhances phagocytosis by activating some mitogen-activated protein kinases (MAPKs) and phosphoinositide 3-kinase (PI3K)-Akt and Janus kinase (JAK)-STAT pathways. These results obtained in human monocytes and macrophages have to be considered for a better exploitation of the IL-21/IL-21R system for therapeutic purposes.