Homeostatic serum IgE is secreted by plasma cells in the thymus and enhances mast cell survival

Antigen presentation for central tolerance induction

The extent of central T cell tolerance is determined by the diversity of self-antigens that developing thymocytes 'see' on thymic antigen-presenting cells (APCs). Here, focusing on insights from the past decade, we review the functional adaptations of medullary thymic epithelial cells, thymic dendritic cells and thymic B cells for the purpose of tolerance induction. Their distinct cellular characteristics range from unconventional phenomena, such as promiscuous gene expression or mimicry of peripheral cell types, to strategic positioning in distinct microenvironments and divergent propensities to preferentially access endogenous or exogenous antigen pools. We also discuss how 'tonic' inflammatory signals in the thymic microenvironment may extend the intrathymically visible 'self' to include autoantigens that are otherwise associated with highly immunogenic peripheral environments.

Mechanisms and risk factors for perinatal allergic disease

Allergies are among the top causes of chronic disease in children. Their pathogenesis classically involves T helper 2 (Th2)-type inflammation driven by IgE-mediated allergen sensing. Triggers influencing allergic disease occur early in life, including before birth. The immature fetal immune system and mucosal barriers undergo periods of plasticity that are open to longitudinal programming by maternal influence. Evidence supports the importance of the maternal immune system in shaping perinatal immunity, as the transfer of cytokines, antibodies, and cells promotes offspring protection from pathogens. However, the same components may lead to allergic predisposition. Maternal-fetal interactions are further modified by epigenetic, metabolic, dietary, and microbiome-mediated effects. Here, we review how diverse maternal exposures and mediators signal across the placenta and through nursing perinatally to promote future tolerance or enhance reactivity against allergens. Improved understanding of the mechanisms predisposing for allergic disease in early life can guide the development of new therapeutics and preventative lifestyle modifications.

Highlight of 2023: Thymic B cells-important players in the establishment of T-cell tolerance

In this article for the Highlights of 2023 Series, we discuss four recent articles that investigated thymic B cells, in both mice and humans. These studies provide important novel insights into the biology of this unique B-cell population, from their activation and differentiation to their role in promoting the negative selection of thymocytes and the generation of regulatory T cells.

Mould allergen Alt a 1 spiked with the micronutrient retinoic acid reduces Th2 response and ameliorates Alternaria allergy in BALB/c mice

BACKGROUND

We investigated the biological function of the mould allergen Alt a 1 as a carrier of micronutrients, such as the vitamin A metabolite retinoic acid (RA) and the influence of RA binding on its allergenicity in vitro and in vivo.

METHODS

Alt a 1-RA complex formation was analyzed in silico and in vitro. PBMCs from Alternaria-allergic donors were stimulated with Alt a 1 complexed with RA (holo-Alt a 1) or empty apo-Alt a 1 and analyzed for cytokine production and CD marker expression. Serum IgE-binding and crosslinking assays to apo- and holo-protein were correlated to B-cell epitope analysis. Female BALB/c mice already sensitized to Alt a 1 were intranasally treated with apo-Alt a 1, holo-Alt a 1 or RA alone before measuring anaphylactic response, serum antibody levels, splenic cytokines and CD marker expression.

RESULTS

In silico docking calculations and in vitro assays showed that the extent of RA binding depended on the higher quaternary state of Alt a 1. Holo-Alt a 1 loaded with RA reduced IL-13 released from PBMCs and CD3+CD4+CRTh2 cells. Complexing Alt a 1 to RA masked its IgE B-cell epitopes and reduced its IgE-binding capacity. In a therapeutic mouse model of Alternaria allergy nasal application of holo-Alt a 1, but not of apo-Alt a 1, significantly impeded the anaphylactic response, impaired splenic antigen-presenting cells and induced IL-10 production.

CONCLUSION

Holo-Alt a 1 binding to RA was able to alleviate Th2 immunity in vitro, modulate an ongoing Th2 response and prevent anaphylactic symptoms in vivo, presenting a novel option for improving allergen-specific immunotherapy in Alternaria allergy.

Longitudinal cytokine and multi-modal health data of an extremely severe ME/CFS patient with HSD reveals insights into immunopathology, and disease severity

Introduction

Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) presents substantial challenges in patient care due to its intricate multisystem nature, comorbidities, and global prevalence. The heterogeneity among patient populations, coupled with the absence of FDA-approved diagnostics and therapeutics, further complicates research into disease etiology and patient managment. Integrating longitudinal multi-omics data with clinical, health,textual, pharmaceutical, and nutraceutical data offers a promising avenue to address these complexities, aiding in the identification of underlying causes and providing insights into effective therapeutics and diagnostic strategies.

Methods

This study focused on an exceptionally severe ME/CFS patient with hypermobility spectrum disorder (HSD) during a period of marginal symptom improvements. Longitudinal cytokine profiling was conducted alongside the collection of extensive multi-modal health data to explore the dynamic nature of symptoms, severity, triggers, and modifying factors. Additionally, an updated severity assessment platform and two applications, ME-CFSTrackerApp and LexiTime, were introduced to facilitate real-time symptom tracking and enhance patient-physician/researcher communication, and evaluate response to medical intervention.

Results

Longitudinal cytokine profiling revealed the significance of Th2-type cytokines and highlighted synergistic activities between mast cells and eosinophils, skewing Th1 toward Th2 immune responses in ME/CFS pathogenesis, particularly in cognitive impairment and sensorial intolerance. This suggests a potentially shared underlying mechanism with major ME/CFS comorbidities such as HSD, Mast cell activation syndrome, postural orthostatic tachycardia syndrome (POTS), and small fiber neuropathy. Additionally, the data identified potential roles of BCL6 and TP53 pathways in ME/CFS etiology and emphasized the importance of investigating adverse reactions to medication and supplements and drug interactions in ME/CFS severity and progression.

Discussion

Our study advocates for the integration of longitudinal multi-omics with multi-modal health data and artificial intelligence (AI) techniques to better understand ME/CFS and its major comorbidities. These findings highlight the significance of dysregulated Th2-type cytokines in patient stratification and precision medicine strategies. Additionally, our results suggest exploring the use of low-dose drugs with partial agonist activity as a potential avenue for ME/CFS treatment. This comprehensive approach emphasizes the importance of adopting a patient-centered care approach to improve ME/CFS healthcare management, disease severity assessment, and personalized medicine. Overall, these findings contribute to our understanding of ME/CFS and offer avenues for future research and clinical practice.

Disturbances in the IgG Antibody Profile in HIV-Exposed Uninfected Infants Associated with Maternal Factors

Over the last 20 years, the incidence of vertical HIV transmission has decreased from 25%-42% to less than 1%. Although there are no signs of infection, the health of HIV-exposed uninfected (HEU) infants is notoriously affected during the first months of life, with opportunistic infections being the most common disease. Some studies have reported effects on the vertical transfer of antibodies, but little is known about the subclass distribution of these antibodies. We proposed to evaluate the total IgG concentration and its subclasses in HIV+ mothers and HEU pairs and to determine which maternal factors condition their levels. In this study, plasma from 69 HEU newborns, their mothers, and 71 control pairs was quantified via immunoassays for each IgG isotype. Furthermore, we followed the antibody profile of HEUs throughout the first year of life. We showed that mothers present an antibody profile characterized by high concentrations of IgG1 and IgG3 but reduced IgG2, and HEU infants are born with an IgG subclass profile similar to that of their maternal pair. Interestingly, this passively transferred profile could remain influenced even during their own antibody production in HEU infants, depending on maternal conditions such as CD4+ T-cell counts and maternal antiretroviral treatment. Our findings indicate that HEU infants exhibit an altered IgG subclass profile influenced by maternal factors, potentially contributing to their increased susceptibility to infections.

Making sense of plasma cell heterogeneity

Plasma cells (PCs) are essential for the quality and longevity of protective immunity. The canonical humoral response to vaccination involves induction of germinal centers in lymph nodes followed by maintenance by bone marrow-resident PCs, although there are many variations of this theme. Recent studies have highlighted the importance of PCs in nonlymphoid organs, including the gut, central nervous system, and skin. These sites harbor PCs with distinct isotypes and possible immunoglobulin-independent functions. Indeed, bone marrow now appears unique in housing PCs derived from multiple other organs. The mechanisms through which the bone marrow maintains PC survival long-term and the impact of their diverse origins on this process remain very active areas of research.

Thymus antibody-secreting cells possess an interferon gene signature and are preferentially expanded in young female mice

Antibody-secreting cells (ASCs) are key contributors to humoral immunity through immunoglobulin production and the potential to be long-lived. ASC persistence has been recognized in the autoimmune thymus (THY); however, only recently has this population been appreciated in healthy THY tissue. We showed that the young female THY was skewed toward higher production of ASCs relative to males. However, these differences disappeared with age. In both sexes, THY ASCs included Ki-67+ plasmablasts which required CD154(CD40L) signals for their propagation. Single cell RNA-sequencing revealed that THY ASCs were enriched for an interferon responsive transcriptional signature relative to those from bone marrow and spleen. Flow cytometry confirmed that THY ASCs had increased levels of Toll-like receptor 7 as well as CD69 and major histocompatibility complex class II. Overall, we identified fundamental aspects of THY ASC biology which may be leveraged for future in depth studies of this population in both health and disease.

Type III interferon drives thymic B cell activation and regulatory T cell generation

The activation of thymic B cells is critical for their licensing as antigen presenting cells and resulting ability to mediate T cell central tolerance. The processes leading to licensing are still not fully understood. By comparing thymic B cells to activated Peyer's patch B cells at steady state, we found that thymic B cell activation starts during the neonatal period and is characterized by TCR/CD40-dependent activation, followed by immunoglobulin class switch recombination (CSR) without forming germinal centers. Transcriptional analysis also demonstrated a strong interferon signature, which was not apparent in the periphery. Thymic B cell activation and CSR were primarily dependent on type III IFN signaling, and loss of type III IFN receptor in thymic B cells resulted in reduced thymocyte regulatory T cell (Treg) development. Finally, from TCR deep sequencing, we estimate that licensed B cells induce development of a substantial fraction of the Treg cell repertoire. Together, these findings reveal the importance of steady-state type III IFN in generating licensed thymic B cells that induce T cell tolerance to activated B cells.

Thymus antibody-secreting cells: once forgotten but not lost

Antibody-secreting cells are essential contributors to the humoral response. This is due to multiple factors which include: 1) the ability to secrete thousands of antibodies per second, 2) the ability to regulate the immune response and 3) the potential to be long-lived. Not surprisingly, these cells can be found in numerous sites within the body which include organs that directly interface with potential pathogens (e.g., gut) and others that provide long-term survival niches (e.g., bone marrow). Even though antibody-secreting cells were first identified in the thymus of both humans and rodents in the 1960s, if not earlier, only recently has this population begun to be extensively investigated. In this article, we provide an update regarding the current breath of knowledge pertaining to thymus antibody-secreting cells and discuss the potential roles of these cells and their impact on health.

Activation-induced cytidine deaminase expression by thymic B cells promotes T-cell tolerance and limits autoimmunity

Elimination of self-reactive T cells in the thymus is critical to establish T-cell tolerance. A growing body of evidence suggests a role for thymic B cells in the elimination of self-reactive thymocytes. To specifically address the role of thymic B cells in central tolerance, we investigated the phenotype of thymic B cells in various mouse strains, including non-obese diabetic (NOD) mice, a model of autoimmune diabetes. We noted that isotype switching of NOD thymic B cells is reduced as compared to other, autoimmune-resistant, mouse strains. To determine the impact of B cell isotype switching on thymocyte selection and tolerance, we generated NOD.AID^-/- mice. Diabetes incidence was enhanced in these mice. Moreover, we observed reduced clonal deletion and a resulting increase in self-reactive CD4⁺ T cells in NOD.AID^-/- mice relative to NOD controls. Together, this study reveals that AID expression in thymic B cells contributes to T-cell tolerance.

Molecular links between allergy and cancer

Epidemiologic studies show both positive and negative associations between allergies and cancer. Allergic diseases may protect against tumorigenesis by promoting the immune surveillance, while carcinogenesis may be promoted through inflammatory responses from allergies. Histamine receptor antagonists are the focus of recent cancer studies because of their promising beneficial effect on tumor development. Also, cytokines, particularly IL-4 or IL-33, IgE as well as allergy-related immune cells such as eosinophils can contribute to tumor growth suppression. Depending on cancer types, cancer therapy may be more beneficial when considering combinatorial immunotherapy. In this review, we give an overview on molecular links between allergies and cancer.

Induction of natural IgE by glucocorticoids

IgE mediates allergic responses by coating mast cell or basophil surfaces and inducing degranulation upon binding a specific allergen. IgE can also be spontaneously produced in the absence of foreign allergens; yet the origin, regulation, and functions of such "natural" IgE still remain largely unknown. Here, we find that glucocorticoids enhance the production of IgE in B cells both in vivo and ex vivo without antigenic challenge. Such IgE production is promoted by B cell-intrinsic glucocorticoid receptor signaling that reinforces CD40 signaling and synergizes with the IL-4/STAT6 pathway. In addition, we found that rare B cells in the mesenteric lymph nodes are responsible for the production of glucocorticoid-inducible IgE. Furthermore, locally produced glucocorticoids in the gut may induce natural IgE during perturbations of gut homeostasis, such as dysbiosis. Notably, mice preemptively treated with glucocorticoids were protected from subsequent pathogenic anaphylaxis. Together, our results suggest that glucocorticoids, classically considered to be broadly immunosuppressive, have a selective immunostimulatory role in B cells.

IgE-expressing long-lived plasma cells in persistent sensitization

Persistent allergies affect the quality of life of patients and increase economic burdens. Many clinical observations indicate the presence of IgE⁺ long-lived plasma cells (LLPCs), which account for the persistent secretion of specific IgE; however, the characteristics of the IgE⁺ LLPCs have yet to be identified clearly. In this review, we summarized the generation of IgE⁺ PCs, discussed the prosurvival factors in the microenvironment, and reviewed the unique IgE-BCR signaling, which may bring insights into understanding the survival mechanisms of IgE⁺ LLPCs.