Production and use of antigen tetramers to study antigen-specific B cells

B cells generate antibodies that provide protection from infection, but also cause pathology in autoimmune and allergic conditions. Antigen-specific B cells can be detected by binding their surface antibody receptors with native antigens conjugated to fluorescent probes, a technique that has revealed substantial insight into B cell activation and function. This protocol describes the process of generating fluorescent antigen tetramer probes and delineates a process of enriching large samples based on antigen-specificity for high-resolution analyses of the antigen-specific B cell repertoire. Enrichment of tetramer-binding cells allows for detection of antigen-specific B cells as rare as 1 in 100 million cells, providing sufficient resolution to study naive B cells and IgE-expressing cells by flow cytometry. The generation of antigen tetramers involves antigen biotinylation, assessment of biotin:antigen ratio for optimal tetramer loading and polymerization around a streptavidin-fluorophore backbone. We also describe the construction of a control tetramer to exclude B cells binding to the tetramer backbone. We provide a framework to validate whether tetramer probes are detecting true antigen-specific B cells and discuss considerations for experimental design. This protocol can be performed by researchers trained in basic biomedical/immunological research techniques, using instrumentation commonly found in most laboratories. Constructing the antigen and control tetramers takes 9 h, though their specificity should be assessed before experimentation and may take weeks to months depending on the method of validation. Sample enrichment requires ~2 h but is generally time and cost neutral as fewer cells are run through the flow cytometer.

Type 2-polarized memory B cells hold allergen-specific IgE memory

Allergen-specific immunoglobulin E (IgE) antibodies mediate pathology in diseases such as allergic rhinitis and food allergy. Memory B cells (MBCs) contribute to circulating IgE by regenerating IgE-producing plasma cells upon allergen encounter. Here, we report a population of type 2-polarized MBCs defined as CD23hi, IL-4Rαhi, and CD32low at both the transcriptional and surface protein levels. These MBC2s are enriched in IgG1- and IgG4-expressing cells while constitutively expressing germline transcripts for IgE. Allergen-specific B cells from patients with allergic rhinitis and food allergy were enriched in MBC2s. Furthermore, MBC2s generated allergen-specific IgE during sublingual immunotherapy, thereby identifying these cells as a major reservoir for IgE. The identification of MBC2s provides insights into the maintenance of IgE memory, which is detrimental in allergic diseases but could be beneficial in protection against venoms and helminths.

Heterogeneity, subsets, and plasticity of T follicular helper cells in allergy

Antibody responses are critical for protection against pathogens. However, diseases such as allergic rhinitis or food allergy result from aberrant production of IgE antibodies against otherwise innocuous environmental antigens. The production of allergen-specific IgE requires interaction between B cells and CD4⁺ T cells, and a granular understanding of these interactions is required to develop novel therapies for allergic disease. CD4⁺ T cells are exceptionally heterogeneous in their transcriptional, epigenetic, and proteomic profiles, which poses significant challenges when attempting to define subsets relevant to the study of allergy among a continuum of cells. Defining subsets such as the T follicular helper (T_FH) cell cluster provides a shorthand to understand the functions of CD4⁺ T cells in antibody production and supports mechanistic experimentation for hypothesis-driven discovery. With a focus on allergic disease, this Rostrum article broadly discusses heterogeneity among CD4⁺ T cells and provides a rationale for subdividing T_FH cells into both functional and cytokine-skewed subsets. Further, it highlights the plasticity demonstrated by T_FH cells during the primary response and after recall, and it explores the possibility of harnessing this plasticity to reprogram immunity for therapeutic benefit in allergic disease.

Respiratory mucosal delivery of next-generation COVID-19 vaccine provides robust protection against both ancestral and variant strains of SARS-CoV-2

The emerging SARS-CoV-2 variants of concern (VOCs) threaten the effectiveness of current COVID-19 vaccines administered intramuscularly and designed to only target the spike protein. There is a pressing need to develop next-generation vaccine strategies for broader and long-lasting protection. Using adenoviral vectors (Ad) of human and chimpanzee origin, we evaluated Ad-vectored trivalent COVID-19 vaccines expressing spike-1, nucleocapsid, and RdRp antigens in murine models. We show that single-dose intranasal immunization, particularly with chimpanzee Ad-vectored vaccine, is superior to intramuscular immunization in induction of the tripartite protective immunity consisting of local and systemic antibody responses, mucosal tissue-resident memory T cells and mucosal trained innate immunity. We further show that intranasal immunization provides protection against both the ancestral SARS-CoV-2 and two VOC, B.1.1.7 and B.1.351. Our findings indicate that respiratory mucosal delivery of Ad-vectored multivalent vaccine represents an effective next-generation COVID-19 vaccine strategy to induce all-around mucosal immunity against current and future VOC.

The Road Toward Transformative Treatments for Food Allergy

A series of landmark studies have provided conclusive evidence that the early administration of food allergens dramatically prevents the emergence of food allergy. One of the greatest remaining challenges is whether patients with established food allergy can return to health. This challenge is particularly pressing in the case of allergies against peanut, tree nuts, fish, and shellfish which are lifelong in most patients and may elicit severe reactions. The standard of care for food allergy is allergen avoidance and the timely administration of epinephrine upon accidental exposure. Epinephrine, and other therapeutic options like antihistamines provide acute symptom relief but do not target the underlying pathology of the disease. In principle, any transformative treatment for established food allergy would require the restoration of a homeostatic immunological state. This may be attained through either an active, non-harmful immune response (immunological tolerance) or a lack of a harmful immune response (e.g., anergy), such that subsequent exposures to the allergen do not elicit a clinical reaction. Importantly, such a state must persist beyond the course of the treatment and exert its protective effects permanently. In this review, we will discuss the immunological mechanisms that maintain lifelong food allergies and are, consequently, those which must be dismantled or reprogrammed to instate a clinically non-reactive state. Arguably, the restoration of such a state in the context of an established food allergy would require a reprogramming of the immune response against a given food allergen. We will discuss existing and experimental therapeutic strategies to eliminate IgE reactivity and, lastly, will propose outstanding questions to pave the road to the development of novel, transformative therapeutics in food allergy.

Cigarette smoke exposure attenuates the induction of antigen-specific IgA in the murine upper respiratory tract

The upper respiratory tract is highly exposed to airborne pathogens and serves as an important inductive site for protective antibody responses, including mucosal IgA and systemic IgG. However, it is currently unknown to what extent inhaled environmental toxins, such as a cigarette smoke, affect the ability to induce antibody-mediated immunity at this site. Using a murine model of intranasal lipopolysaccharide and ovalbumin (LPS/OVA) immunization, we show that cigarette smoke exposure compromises the induction of antigen-specific IgA in the upper airways and systemic circulation. Deficits in OVA-IgA were observed in conjunction with a reduced accumulation of OVA-specific IgA antibody-secreting cells (ASCs) in the nasal mucosa, inductive tissues (NALT, cervical lymph nodes, spleen) and the blood. Nasal OVA-IgA from smoke-exposed mice also demonstrated reduced avidity during the acute post-immunization period in association with an enhanced mutational burden in the cognate nasal Igha repertoire. Mechanistically, smoke exposure attenuated the ability of the nasal mucosa to upregulate VCAM-1 and pIgR, suggesting that cigarette smoke may inhibit both nasal ASC homing and IgA transepithelial transport. Overall, these findings demonstrate the immunosuppressive nature of tobacco smoke and illustrate the diversity of mechanisms through which this noxious stimulus can interfere with IgA-mediated immunity in the upper airways.

Memory Generation and Re-Activation in Food Allergy

Recent evidence has highlighted the critical role of memory cells in maintaining lifelong food allergies, thereby identifying these cells as therapeutic targets. IgG⁺ memory B cells replenish pools of IgE-secreting cells upon allergen exposure, which contract thereafter due to the short lifespan of tightly regulated IgE-expressing cells. Advances in the detection and highly dimensional analysis of allergen-specific B and T cells from allergic patients have provided insight on their phenotype and function. The newly identified Th2A and Tfh13 populations represent a leap in our understanding of allergen-specific T cell phenotypes, although how these populations contribute to IgE memory responses remains poorly understood. Within, we discuss the mechanisms by which memory B and T cells are activated, integrating knowledge from human systems and fundamental research. We then focus on memory reactivation, specifically, on the pathways of secondary IgE responses. Throughout, we identify areas of future research which will help identify immunotargets for a transformative therapy for food allergy.

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.

Perturbations to Homeostasis in Experimental Models Revealed Innate Pathways Driving Food Allergy

While type 2 immunity has been conventionally viewed as beneficial against helminths, venoms, and poisons, and harmful in allergy, contemporary research has uncovered its critical role in the maintenance of homeostasis. The initiation of a type 2 immune response involves an intricate crosstalk between structural and immune cells. Structural cells react to physical and chemical tissue perturbations by secreting alarmins, which signal the innate immune system to restore homeostasis. This pathway acts autonomously in the context of sterile injury and in the presence of foreign antigen initiates an adaptive Th2 response that is beneficial in the context of venoms, toxins, and helminths, but not food allergens. The investigation of the triggers and mechanisms underlying food allergic sensitization in humans is elusive because sensitization is a silent process. Therefore, the central construct driving food allergy modeling is based on introducing perturbations of tissue homeostasis along with an allergen which will result in an immunological and clinical phenotype that is consistent with that observed in humans. The collective evidence from multiple models has revealed the pre-eminent role of innate cells and molecules in the elicitation of allergic sensitization. We posit that, with the expanding use of technologies capable of producing formidable datasets, models of food allergy will continue to have an indispensable role to delineate mechanisms and establish causal relationships.