The role of Sp140 revealed in IgE and mast cell responses in Collaborative Cross mice

Broadly active intranasal influenza vaccine with a nanocomplex particulate adjuvant targeting mast cells and toll-like receptor 9

Flumist is the only FDA-approved intranasal influenza vaccine. Although it has recently been approved for at-home use, it has significant limitations. These include reduced effectiveness in generating a protective immune response in patients with extensive influenza exposure, safety concerns due to its live attenuated virus formulation, and reduced efficacy due to viral drift/shift. To address this limitation, we have developed a nanocomplex comprised of a mast cell (MC) agonist and toll-like receptor 9 (TLR9) ligand to adjuvant a broadly acting influenza antigen. The newly reported MC agonist was identified by screening mastoparan-7 analogs for MC degranulation activity, which led to a more active peptide analog, MP12W. Positively charged MP12W spontaneously forms nanoparticulate complexes (NPs) with CpG 1826 that were then used to intranasally vaccinate mice with a computationally optimized broadly reactive antigen (COBRA) hemagglutinin (HA) protein. The NPs were further optimized by substituting CpG 1826 with CpG 55.2, a TLR-9 agonist identified by machine learning to be more active in humans. MP12W-CpG 1826 NPs showed an increased pro-inflammatory response and decreased cytotoxicity in vitro compared to M7 complexes, translating into a safer profile in a model of increased hypersensitivity, collaborative cross mice 027 (CC027). Intranasal vaccination with this complex and broadly reactive HA resulted in higher mucosal antibody concentration and increased cytokine production with antigen recall. These responses were enhanced with MP12W-CpG 55.2 NP vaccination. MP12W-CpG NPs provided similar protection in an influenza challenge model. This study demonstrates the potential of this novel intranasal nanocomplex for vaccination.

Mast cell activators as adjuvants for intranasal mucosal vaccines

Mast cells have roles in immune regulation, allergy, and host response to pathogens. Compounds that activate mast cells (MCAs) can serve as vaccine adjuvants, potentially outperforming current FDA-approved options, especially for mucosal vaccines. While most vaccines are administered intramuscularly, intranasal and needle-free formulations offer benefits like improved compliance and accessibility. However, the lack of effective adjuvants limits mucosal vaccine development. This review explores MCAs as promising alternatives to traditional adjuvants, aiming to enhance mucosal vaccine efficacy. We summarize the nascent work of formulating MCAs like compound 48/80 into nanoparticles, with excipients such as chitosan and chitosan/alginate. Other MCAs like the peptide mastoparan 7 complexed with CpG have formed nanoparticle complexes that illustrate protective mucosal immunity in a model of influenza. The small molecule MCA ST101036, when encapsulated in acetalated dextran particles, has demonstrated enhanced immune responses and protection in a West Nile Virus model of infection. This review highlights the potential of MCAs as potent vaccine adjuvants, particularly for mucosal vaccines, and summarizes, recent advancements in formulating these activators into nanoparticles to enhance immune responses and protection.

Mast cells: a novel therapeutic avenue for cardiovascular diseases?

Mast cells are tissue-resident immune cells strategically located in different compartments of the normal human heart (the myocardium, pericardium, aortic valve, and close to nerves) as well as in atherosclerotic plaques. Cardiac mast cells produce a broad spectrum of vasoactive and proinflammatory mediators, which have potential roles in inflammation, angiogenesis, lymphangiogenesis, tissue remodelling, and fibrosis. Mast cells release preformed mediators (e.g. histamine, tryptase, and chymase) and de novo synthesized mediators (e.g. cysteinyl leukotriene C4 and prostaglandin D2), as well as cytokines and chemokines, which can activate different resident immune cells (e.g. macrophages) and structural cells (e.g. fibroblasts and endothelial cells) in the human heart and aorta. The transcriptional profiles of various mast cell populations highlight their potential heterogeneity and distinct gene and proteome expression. Mast cell plasticity and heterogeneity enable these cells the potential for performing different, even opposite, functions in response to changing tissue contexts. Human cardiac mast cells display significant differences compared with mast cells isolated from other organs. These characteristics make cardiac mast cells intriguing, given their dichotomous potential roles of inducing or protecting against cardiovascular diseases. Identification of cardiac mast cell subpopulations represents a prerequisite for understanding their potential multifaceted roles in health and disease. Several new drugs specifically targeting human mast cell activation are under development or in clinical trials. Mast cells and/or their subpopulations can potentially represent novel therapeutic targets for cardiovascular disorders.

Immune sensing of food allergens promotes avoidance behaviour

In addition to its canonical function of protection from pathogens, the immune system can also alter behaviour1,2. The scope and mechanisms of behavioural modifications by the immune system are not yet well understood. Here, using mouse models of food allergy, we show that allergic sensitization drives antigen-specific avoidance behaviour. Allergen ingestion activates brain areas involved in the response to aversive stimuli, including the nucleus of tractus solitarius, parabrachial nucleus and central amygdala. Allergen avoidance requires immunoglobulin E (IgE) antibodies and mast cells but precedes the development of gut allergic inflammation. The ability of allergen-specific IgE and mast cells to promote avoidance requires cysteinyl leukotrienes and growth and differentiation factor 15. Finally, a comparison of C57BL/6 and BALB/c mouse strains revealed a strong effect of the genetic background on the avoidance behaviour. These findings thus point to antigen-specific behavioural modifications that probably evolved to promote niche selection to avoid unfavourable environments.

Peanut butter feeding induces oral tolerance in genetically diverse collaborative cross mice

Background

Early dietary introduction of peanut has shown efficacy in clinical trials and driven pediatric recommendations for early introduction of peanut to children with heightened allergy risk worldwide. Unfortunately, tolerance is not induced in every case, and a subset of patients are allergic prior to introduction. Here we assess peanut allergic sensitization and oral tolerance in genetically diverse mouse strains.

Objective

We aimed to determine whether environmental adjuvant-driven airway sensitization and oral tolerance to peanut could be induced in various genetically diverse mouse strains.

Methods

C57BL/6J and 12 Collaborative Cross (CC) mouse strains were fed regular chow or ad libitum peanut butter to induce tolerance. Tolerance was tested by attempting to sensitize mice via intratracheal exposure to peanut and lipopolysaccharide (LPS), followed by intraperitoneal peanut challenge. Peanut-specific immunoglobulins and peanut-induced anaphylaxis were assessed.

Results

Without oral peanut feeding, most CC strains (11/12) and C57BL/6J induced peanut-specific IgE and IgG1 following airway exposure to peanut and LPS. With oral peanut feeding none of the CC strains nor C57BL/6J mice became sensitized to peanut or experienced anaphylaxis following peanut challenge.

Conclusion

Allergic sensitization and oral tolerance to peanut can be achieved across a range of genetically diverse mice. Notably, the same strains that became allergic via airway sensitization were tolerized by feeding high doses of peanut butter before sensitization, suggesting that the order and route of peanut exposure are critical for determining the allergic fate.

IL-4 receptor alpha signaling alters oral food challenge and immunotherapy outcomes in mice

BACKGROUND

Food allergy diagnosis and management causes a number of social and emotional challenges for individuals with food allergies and their caregivers. This has led to increased interest in developing approaches to accurately predict food allergy diagnosis, severity of food allergic reactions, and treatment outcomes. However, the utility of these approaches is somewhat conflicting.

OBJECTIVE

We sought to develop and utilize a murine model that mimics the disease course of food allergy diagnosis and treatment in humans and to identify biomarkers that predict reactivity during food challenge (FC) and responsiveness during oral immunotherapy (OIT) and how these outcomes are modified by genetics.

METHODS

Skin-sensitized intestinal IL-9 transgenic (IL9Tg) and IL9Tg mice backcrossed onto the IL-4RαY709F background received a single intragastric exposure of egg antigen (ovalbumin), underwent oral FC and OIT; food allergy severity, mast cell activation, and ovalbumin-specific IgE levels were examined to determine the predictability of these outcomes in determining reactivity and treatment outcomes.

RESULTS

Subcutaneous sensitization and a single intragastric allergen challenge of egg antigen to BALB/c IL9Tg mice and Il4raY709F IL9Tg induced a food allergic reaction. Enhanced IL-4Rα signaling altered the symptoms induced by the first oral exposure, decreased the cumulative antigen dose, increased the severity of reaction during oral FC, and altered the frequency of adverse events and OIT outcomes. Biomarkers after first oral exposure indicated that only the severity of the initial reaction significantly correlated with cumulative dose of oral FC.

CONCLUSION

Collectively, these data indicate that single nucleotide polymorphisms in IL-4Rα can alter clinical symptoms of food allergic reactions, severity, and reactive dose during FC and OIT, and that severity of first reaction can predict the likelihood of reaction during FC in mice with IL-4Rα gain of function.

New perspectives on the origins and heterogeneity of mast cells

Mast cells are immune cells of the haematopoietic lineage that are now thought to have multifaceted functions during homeostasis and in various disease states. Furthermore, while mast cells have been known for a long time to contribute to allergic disease in adults, recent studies, mainly in mice, have highlighted their early origins during fetal development and potential for immune functions, including allergic responses, in early life. Our understanding of the imprinting of mast cells by particular tissues of residence and their potential for regulatory interactions with organ systems such as the peripheral immune, nervous and vascular systems is also rapidly evolving. Here, we discuss the origins of mast cells and their diverse and plastic phenotypes that are influenced by tissue residence. We explore how divergent phenotypes and functions might result from both their hard-wired 'nature' defined by their ontogeny and the 'nurture' they receive within specialized tissue microenvironments.

Immune chromatin reader SP140 regulates microbiota and risk for inflammatory bowel disease

Inflammatory bowel disease (IBD) is driven by host genetics and environmental factors, including commensal microorganisms. Speckled Protein 140 (SP140) is an immune-restricted chromatin "reader" that is associated with Crohn's disease (CD), multiple sclerosis (MS), and chronic lymphocytic leukemia (CLL). However, the disease-causing mechanisms of SP140 remain undefined. Here, we identify an immune-intrinsic role for SP140 in regulating phagocytic defense responses to prevent the expansion of inflammatory bacteria. Mice harboring altered microbiota due to hematopoietic Sp140 deficiency exhibited severe colitis that was transmissible upon cohousing and ameliorated with antibiotics. Loss of SP140 results in blooms of Proteobacteria, including Helicobacter in Sp140-/- mice and Enterobacteriaceae in humans bearing the CD-associated SP140 loss-of-function variant. Phagocytes from patients with the SP140 loss-of-function variant and Sp140-/- mice exhibited altered antimicrobial defense programs required for control of pathobionts. Thus, mutations within this epigenetic reader may constitute a predisposing event in human diseases provoked by microbiota.

Using the Collaborative Cross and Diversity Outbred Mice in Immunology

The Collaborative Cross (CC) and the Diversity Outbred (DO) stock mouse panels are the most powerful murine genetics tools available to the genetics community. Together, they combine the strength of inbred animal models with the diversity of outbred populations. Using the 63 CC strains or a panel of DO mice, each derived from the same 8 parental mouse strains, researchers can map genetic contributions to exceptionally complex immunological and infectious disease traits that would require far greater powering if performed by genome-wide association studies (GWAS) in human populations. These tools allow genes to be studied in heterozygous and homozygous states and provide a platform to study epistasis between interacting loci. Most importantly, once a quantitative phenotype is investigated and quantitative trait loci are identified, confirmatory genetic studies can be performed, which is often problematic using the GWAS approach. In addition, novel stable mouse models for immune phenotypes are often derived from studies utilizing the DO and CC mice that can serve as stronger model systems than existing ones in the field. The CC/DO systems have contributed to the fields of cancer immunology, autoimmunity, vaccinology, infectious disease, allergy, tissue rejection, and tolerance but have thus far been greatly underutilized. In this article, we present a recent review of the field and point out key areas of immunology that are ripe for further investigation and awaiting new CC/DO research projects. We also highlight some of the strong computational tools that have been developed for analyzing CC/DO genetic and phenotypic data. Additionally, we have formed a centralized community on the CyVerse infrastructure where immunogeneticists can utilize those software tools, collaborate with groups across the world, and expand the use of the CC and DO systems for investigating immunogenetic phenomena. © 2022 Wiley Periodicals LLC.