A mutation in Themis contributes to anaphylaxis severity following oral peanut challenge in CC027 mice

BACKGROUND

The development of peanut allergy is due to a combination of genetic and environmental factors, although specific genes have proven difficult to identify. Previously, we reported that peanut-sensitized CC027/GeniUnc (CC027) mice develop anaphylaxis upon oral challenge to peanut, unlike C3H/HeJ (C3H) mice.

OBJECTIVE

To determine the genetic basis of orally-induced anaphylaxis to peanut in CC027 mice.

METHODS

A genetic mapping population between CC027 and C3H mice was designed to identify the genetic factors that drive oral anaphylaxis. A total of 356 CC027xC3H backcrossed mice were generated, sensitized to peanut, then challenged to peanut by oral gavage. Anaphylaxis and peanut-specific IgE were quantified for all mice. T-cell phenotyping was conducted on CC027 and five additional CC strains.

RESULTS

Anaphylaxis to peanut was absent in 77% of backcrossed mice, with 19% showing moderate anaphylaxis, and 4% having severe anaphylaxis. A total of eight genetic loci were associated with variation in response to peanut challenge, six associated with anaphylaxis (temperature decrease) and two associated with peanut-specific IgE levels. There were two major loci that impacted multiple aspects of the severity of acute anaphylaxis, at which the CC027 allele was associated with worse outcome. At one of these loci, CC027 has a private genetic variant in the Themis (thymocyte-expressed molecule involved in selection) gene. Consistent with Themis' described functions, we found that CC027 have more immature T cells with fewer CD8+, CD4+, and CD4+CD25+CD127- regulatory T cells.

CONCLUSION

Our results demonstrate a key role for Themis in the orally-reactive CC027 mouse model of peanut allergy.

Different airborne particulates trigger distinct immune pathways leading to peanut allergy in a mouse model

BACKGROUND

Environmental exposure to peanut through non-oral routes is a risk factor for peanut allergy. Early-life exposure to air pollutants, including particulate matter (PM), is associated with sensitization to foods through unknown mechanisms. We investigated whether PM promotes sensitization to environmental peanut and the development of peanut allergy in a mouse model.

METHODS

C57BL/6J mice were co-exposed to peanut and either urban particulate matter (UPM) or diesel exhaust particles (DEP) via the airways and assessed for peanut sensitization and development of anaphylaxis following peanut challenge. Peanut-specific CD4+ T helper (Th) cell responses were characterized by flow cytometry and Th cytokine production. Mice lacking select innate immune signaling genes were used to study mechanisms of PM-induced peanut allergy.

RESULTS

Airway co-exposure to peanut and either UPM- or DEP-induced systemic sensitization to peanut and anaphylaxis following peanut challenge. Exposure to UPM or DEP triggered activation and migration of lung dendritic cells to draining lymph nodes and induction of peanut-specific CD4+ Th cells. UPM- and DEP-induced distinct Th responses, but both stimulated expansion of T follicular helper (Tfh) cells essential for peanut allergy development. MyD88 signaling was critical for UPM- and DEP-induced peanut allergy, whereas TLR4 signaling was dispensable. DEP-induced peanut allergy and Tfh-cell differentiation depended on IL-1 but not IL-33 signaling, whereas neither cytokine alone was necessary for UPM-mediated sensitization.

CONCLUSION

Environmental co-exposure to peanut and PM induces peanut-specific Tfh cells and peanut allergy in mice.

A Mouse Model of Shrimp Allergy with Cross-Reactivity to Crab and Lobster

Food allergies are a growing public health problem with recent estimates of 10% of the US population affected by this immunologic disease. The quality of life is greatly impaired in food allergic individuals and their caregivers due to constant vigilance and fear of accidental exposure. Shellfish allergies are of particular concern because their prevalence has increased over the past 15 years, now affecting an estimated 3% of the adult population and 1.3% of children in the USA. Additionally, they are rarely outgrown, can result in fatal reactions, and there are no FDA-approved therapies for shellfish allergies. Reactions to one type of shellfish, crustaceans (shrimp, lobster, and crab), can be especially severe. The major crustacean allergens are highly conserved across species, resulting in high cross-reactivity of IgE between shrimp, lobster, and crab in allergic individuals. To develop novel therapies for shellfish allergies, preclinical mouse models are required. In this chapter, we present detailed methodology to induce shrimp allergy in CC027 mice. Once sensitized, mice produce shrimp-specific IgE, that is cross-reactive with lobster and crab, and experience anaphylaxis upon shrimp challenge. This model can be used to further investigate mechanisms of sensitization and preclinical testing of therapies.

Desensitization and remission after peanut sublingual immunotherapy in 1- to 4-year-old peanut-allergic children: A randomized, placebo-controlled trial

BACKGROUND

Prior studies of peanut sublingual immunotherapy (SLIT) have suggested a potential advantage with younger age at treatment initiation.

OBJECTIVE

We studied the safety and efficacy of SLIT for peanut allergy in 1- to 4-year-old children.

METHODS

Peanut-allergic 1- to 4-year-old children were randomized to receive 4 mg peanut SLIT versus placebo. Desensitization was assessed by double-blind, placebo-controlled food challenge (DBPCFC) after 36 months of treatment. Participants desensitized to at least 443 mg peanut protein discontinued therapy for 3 months and then underwent DBPCFC to assess for remission. Biomarkers were measured at baseline and longitudinally during treatment.

RESULTS

Fifty participants (25 peanut SLIT, 25 placebo) with a median age of 2.4 years were enrolled across 2 sites. The primary end point of desensitization was met with actively treated versus placebo participants having a significantly greater median cumulative tolerated dose (4443 mg vs 143 mg), higher likelihood of passing the month 36 DBPCFC (60% vs 0), and higher likelihood of demonstrating remission (48% vs 0). The highest rate of desensitization and remission was seen in 1- to 2-year-olds, followed by 2- to 3-year-olds and 3- to 4-year-olds. Longitudinal changes in peanut skin prick testing, peanut-specific IgG4, and peanut-specific IgG4/IgE ratio were seen in peanut SLIT but not placebo participants. Oropharyngeal itching was more commonly reported by peanut SLIT than placebo participants. Skin, gastrointestinal, upper respiratory, lower respiratory, and multisystem adverse events were similar between treatment groups.

CONCLUSION

Peanut SLIT safely induces desensitization and remission in 1- to 4-year-old children, with improved outcomes seen with younger age at initiation.

A mutation in Themis contributes to peanut-induced oral anaphylaxis in CC027 mice

Background

The development of peanut allergy is due to a combination of genetic and environmental factors, although specific genes have proven difficult to identify. Previously, we reported that peanut-sensitized CC027/GeniUnc (CC027) mice develop anaphylaxis upon oral challenge to peanut, unlike C3H/HeJ (C3H) mice.

Objective

To determine the genetic basis of orally-induced anaphylaxis to peanut in CC027 mice.

Methods

A genetic mapping population between CC027 and C3H mice was designed to identify the genetic factors that drive oral anaphylaxis. A total of 356 CC027xC3H backcrossed mice were generated, sensitized to peanut, then challenged to peanut by oral gavage. Anaphylaxis and peanut-specific IgE were quantified for all mice. T-cell phenotyping was conducted on CC027 and five additional CC strains.

Results

Anaphylaxis to peanut was absent in 77% of backcrossed mice, with 19% showing moderate anaphylaxis, and 4% having severe anaphylaxis. A total of eight genetic loci were associated with variation in response to peanut challenge, six associated with anaphylaxis (temperature decrease) and two associated with peanut-specific IgE levels. There were two major loci that impacted multiple aspects of the severity of acute anaphylaxis, at which the CC027 allele was associated with worse outcome. At one of these loci, CC027 has a private genetic variant in the Themis (thymocyte-expressed molecule involved in selection) gene. Consistent with Themis' described functions, we found that CC027 have more immature T cells with fewer CD8+, CD4+, and CD4+CD25+CD127- regulatory T cells.

Conclusion

Our results demonstrate a key role for Themis in the orally-reactive CC027 mouse model of peanut allergy.

Food-specific IgA levels in esophageal biopsies are not sufficiently high to predict food triggers in eosinophilic esophagitis

BACKGROUND

Eosinophilic esophagitis (EoE) is an immune-mediated disease, characterized by Th2-type inflammation linked to specific foods. No currently available allergy tests reliably identify food triggers in EoE, leading to empiric dietary elimination strategies. Recently, milk- and wheat-specific IgA in esophageal brushings were linked to clinical food triggers. In this study, we aimed to determine whether food-specific IgA from esophageal biopsies is associated with known food triggers.

METHODS

A prior cohort of 21 patients (median age 39 years) with confirmed EoE underwent empirical elimination diets and subsequent reintroduction of foods to determine triggers. Archived baseline biopsies were used to quantify levels of peanut-, milk-, soy-, egg-, wheat-specific and total IgA by enzyme-linked immunosorbent assay.

RESULTS

Overall, 13 patients (62%) responded to the dietary elimination as determined by histology (<15 eos/hpf), with milk and egg being the most common triggers. Biopsies had varying amounts of total IgA, while food-specific IgA was only detectable in 48 of 105 (46%) samples. Food-specific IgA was normalized to total IgA for each sample and stratified by whether a food was a known trigger. For all foods tested, there were no significant differences in IgA between positive and negative triggers.

CONCLUSIONS

Food-specific IgA in esophageal biopsies was not associated with previously identified food triggers in this cohort. Future studies comparing food-specific IgA in esophageal brushings, mucous scrapings, and biopsies from patients with known triggers will be critical to determining whether food-specific IgA may serve as a biomarker for identification of EoE triggers.

A single priming event prevents oral tolerance to peanut

BACKGROUND

Indoor dust (ID) is a source of peanut proteins and immunostimulatory adjuvants (e.g. LPS) that can promote airway sensitization to peanut. We aimed to determine whether a single airway exposure to peanut plus adjuvant is sufficient to prevent oral tolerance.

METHODS

To determine the effect of a single priming event, C57BL/6J mice were exposed once to peanut plus adjuvant through the airway, followed by either airway or low-dose oral exposure to peanut, and assessed for peanut allergy. Oral tolerance was investigated by feeding high-dose peanut followed by airway sensitization. To determine whether a single priming could prevent oral tolerance, the high-dose peanut regimen was applied after a single airway exposure to peanut plus adjuvant. Peanut-specific IgE and IgG1 were quantified, and mice were challenged to peanut to assess allergy. Peanut-specific CD4+ memory T cells (CD4+ TCRβ+ CD44hi CD154+ ) were quantified in mediastinal lymph nodes following airway priming.

RESULTS

Mice co-exposed to peanut with LPS or ID through the airway were primed to develop peanut allergy after subsequent low-dose oral or airway exposures to peanut. Oral tolerance was induced in mice fed high-dose peanut prior to airway sensitization. In contrast, mice fed high-dose peanut following a single airway exposure to peanut plus adjuvant led to allergy. Peanut-specific CD4+ memory T cells were detected as early as 7 days after the single airway priming with peanut plus adjuvant, however, delaying peanut feeding even 1 day following priming led to allergy, whereas peanut feeding the same day as priming led to tolerance.

CONCLUSIONS

A single airway exposure to peanut plus adjuvant is sufficient to prime the immune system to develop allergy following subsequent high-dose oral exposure. These results highlight the importance of introducing peanut as early as possible to prevent sensitization through a non-oral priming event.

Environmental Exposure to Foods as a Risk Factor for Food Allergy

PURPOSE OF REVIEW

Many factors have been reported to contribute to the development of food allergy. Here, we summarize the role of environmental exposure to foods as a major risk factor for developing food allergy.

RECENT FINDINGS

Peanut proteins are detectable and biologically active in household environments, where infants spend a majority of their time, providing an environmental source of allergen exposure. Recent evidence from clinical studies and mouse models suggests both the airway and skin are routes of exposure that lead to peanut sensitization. Environmental exposure to peanut has been clearly associated with the development of peanut allergy, although other factors such as genetic predisposition, microbial exposures, and timing of oral feeding of allergens also likely contribute. Future studies should more comprehensively assess the contributions of each of these factors for a variety of food allergens to provide more clear targets for prevention of food allergy.

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.

Peanut-Specific IgG4 and IgA in Saliva Are Modulated by Peanut Oral Immunotherapy

BACKGROUND

Antigen-specific immunoglobulin responses have yet to be studied at the oral mucosal surface during peanut oral immunotherapy (PnOIT).

OBJECTIVE

We aimed to quantify salivary peanut-specific IgG4 (PNsIgG4) and IgA (PNsIgA) and total IgG4 and IgA in participants from the Immune Tolerance Network's IMPACT study, a phase 2 PnOIT trial.

METHODS

Peanut-allergic children, aged 12 months to younger than 48 months at screening, were enrolled and randomized to PnOIT or placebo oral immunotherapy (OIT) for 134 weeks. Per-protocol analysis included 69 PnOIT and 23 placebo participants. Double-blind, placebo-controlled food challenges were conducted at weeks 134 and 160 to assess desensitization and remission, respectively. Saliva samples were collected at baseline and 30, 82, 134, and 160 weeks to quantify PNsIgG4, PNsIgA, and total IgG4 and IgA.

RESULTS

Participants who received PnOIT experienced significant increases in PNsIgG4 in saliva, whereas participants on placebo did not (P < .01 at all time points). The PNsIgA/total IgA ratio was also significantly increased in participants treated with PnOIT when compared with those receiving placebo at 30 and 82 weeks (P < .05). During PnOIT, desensitized participants had increased PNsIgA that plateaued, whereas the not desensitized/no remission group did not change over time. Interestingly, when the PnOIT group was evaluated by clinical outcome, PNsIgA was higher at baseline in the not desensitized/no remission group than in the desensitized/remission group (P < .05).

CONCLUSIONS

PnOIT induces substantial increases in allergen-specific IgG4 and IgA in saliva. These data provide insight into OIT-induced mucosal responses and suggest the utility of these easily obtained samples for biomarker development.

Kinetics of basophil hyporesponsiveness during short-course peanut oral immunotherapy

BACKGROUND

Oral immunotherapy (OIT) leads to suppression of mast cell and basophil degranulation along with changes in the adaptive immune response.

OBJECTIVES

This study aimed to determine how rapidly these effects occur during OIT and more broadly, the kinetics of basophil and mast cell suppression throughout the course of therapy.

METHODS

Twenty participants, age 4 to 12 years, were enrolled in a peanut OIT trial and assessed for desensitization and sustained unresponsiveness after 9 months of therapy. Blood was collected 5 times in the first month and then intermittently throughout to quantify immunoglobulins and assess basophil activation by CD63, CD203c, and phosphorylated SYK (pSYK).

RESULTS

Twelve of 16 participants that completed the trial were desensitized after OIT, with 9 achieving sustained unresponsiveness after discontinuing OIT for 4 weeks. Basophil hyporesponsiveness, defined by lower CD63 expression, was detected as early as day 90. pSYK was correlated with CD63 expression, and there was a significant decrease in pSYK by day 250. CD203c expression remained unchanged throughout therapy. Interestingly, although basophil activation was decreased across the cohort during OIT, basophil activation did not correlate with individual clinical outcomes. Serum peanut-specific IgG4 and IgA increased throughout therapy, whereas IgE remained unchanged.

CONCLUSIONS

Suppression of basophil activation occurs within the first 90 days of peanut OIT, ultimately leading to suppression of signaling through pSYK.

Induction of food-specific IgG by Gene Gun-delivered DNA vaccines

Background

Shellfish and tree nut allergies are among the most prevalent food allergies, now affecting 2%–3% and 1% of the US population, respectively. Currently, there are no approved therapies for shellfish or tree nut allergies, with strict avoidance being the standard of care. However, oral immunotherapy for peanut allergy and subcutaneous immunotherapy for environmental allergens are efficacious and lead to the production of allergen-specific IgG, which causes suppression of allergen effector cell degranulation. Since allergen-specific IgG is a desired response to alleviate IgE-mediated allergies, we tested transcutaneously-delivered DNA vaccines targeting shellfish and tree nut allergens for their ability to induce antigen-specific IgG, which would have therapeutic potential for food allergies.

Methods

We assessed Gene Gun-delivered DNA vaccines targeting either crustacean shellfish or walnut/pecan allergens, with or without IL-12, in naïve mice. Three strains of mice, BALB/cJ, C3H/HeJ and CC027/GeniUnc, were evaluated for IgG production following vaccination. Vaccines were administered twice via Gene Gun, three weeks apart and then blood was collected three weeks following the final vaccination.

Results

Vaccination with shellfish allergen DNA led to increased shrimp-specific IgG in all three strains, with the highest production in C3H/HeJ from the vaccine alone, whereas the vaccine with IL-12 led to the highest IgG production in BALB/cJ and CC027/GeniUnc mice. Similar IgG production was also induced against lobster and crab allergens. For walnut/pecan vaccines, BALB/cJ and C3H/HeJ mice produced significantly higher walnut- and pecan-specific IgG with the vaccine alone compared to the vaccine with IL-12, while the CC027 mice made significantly higher IgG with the addition of IL-12. Notably, intramuscular administration of the vaccines did not lead to increased antigen-specific IgG production, indicating that Gene Gun administration is a superior delivery modality.

Conclusions

Overall, these data demonstrate the utility of DNA vaccines against two lifelong food allergies, shellfish and tree nuts, suggesting their potential as a food allergy therapy in the future.

Mouse Models of Food Allergy in the Pursuit of Novel Treatment Modalities

The prevalence of IgE-mediated food allergies has increased dramatically in the past three decades, now affecting up to 10% of the US population. IgE-mediated food allergy is an immunologic disease, involving a variety of cells, including B and T cells, mast cells, basophils, ILC2s, and epithelial cells. Mouse models of food allergy mimic the overall immunologic processes known to exist in humans. Due to the limitations of invasive sampling of human tissue and the similarities of the human and mouse immune systems, comprehensive pathogenesis studies of food allergy have been performed in mouse models. Mouse models have been effective in elucidating the roles of non-oral routes of sensitization and identifying key cells and molecules involved in allergic sensitization. Furthermore, the development of novel therapeutic approaches for food allergy has been accelerated through the use of pre-clinical mouse models. Despite the groundbreaking findings stemming from research in mice, there are continued efforts to improve the translational utility of these models. Here, we highlight the achievements in understanding food allergy development and efforts to bring novel treatment approaches into clinical trials.

The airway as a route of sensitization to peanut: An update to the dual allergen exposure hypothesis

Food allergies have increased at an alarming rate over the past 2 decades, indicating that environmental factors are driving disease progression. It has been postulated that sensitization to foods, in particular, peanut, occurs through impaired skin. Peanut allergens have been quantified in household dust and may be the culprit source. Indeed, T_H2 cell-skewing innate cytokines can be driven by application of food antigens on both intact and impaired skin of mice, resulting in antigen-specific IgE production and anaphylaxis following allergen exposure. However, allergy induction through the skin can be prevented by induction of oral tolerance before skin exposure. These observations led to the dual allergen exposure hypothesis, according to which oral exposure to food antigens leads to tolerance and antigen exposure on impaired skin leads to allergy. Here, we propose the airway as an alternative route of sensitization in the dual allergen exposure hypothesis that leads to food allergy. Specifically, we will provide evidence from mouse models and human cell-based studies that together implicate the airway as a plausible route of sensitization.

Fecal IgA, Antigen Absorption, and Gut Microbiome Composition Are Associated With Food Antigen Sensitization in Genetically Susceptible Mice

Food allergy is a potentially fatal disease affecting 8% of children and has become increasingly common in the past two decades. Despite the prevalence and severe nature of the disease, the mechanisms underlying sensitization remain to be further elucidated. The Collaborative Cross is a genetically diverse panel of inbred mice that were specifically developed to study the influence of genetics on complex diseases. Using this panel of mouse strains, we previously demonstrated CC027/GeniUnc mice, but not C3H/HeJ mice, develop peanut allergy after oral exposure to peanut in the absence of a Th2-skewing adjuvant. Here, we investigated factors associated with sensitization in CC027/GeniUnc mice following oral exposure to peanut, walnut, milk, or egg. CC027/GeniUnc mice mounted antigen-specific IgE responses to peanut, walnut and egg, but not milk, while C3H/HeJ mice were not sensitized to any antigen. Naïve CC027/GeniUnc mice had markedly lower total fecal IgA compared to C3H/HeJ, which was accompanied by stark differences in gut microbiome composition. Sensitized CC027/GeniUnc mice had significantly fewer CD3+ T cells but higher numbers of CXCR5+ B cells and T follicular helper cells in the mesenteric lymph nodes compared to C3H/HeJ mice, which is consistent with their relative immunoglobulin production. After oral challenge to the corresponding food, peanut- and walnut-sensitized CC027/GeniUnc mice experienced anaphylaxis, whereas mice exposed to milk and egg did not. Ara h 2 was detected in serum collected post-challenge from peanut-sensitized mice, indicating increased absorption of this allergen, while Bos d 5 and Gal d 2 were not detected in mice exposed to milk and egg, respectively. Machine learning on the change in gut microbiome composition as a result of food protein exposure identified a unique signature in CC027/GeniUnc mice that experienced anaphylaxis, including the depletion of Akkermansia. Overall, these results demonstrate several factors associated with enteral sensitization in CC027/GeniUnc mice, including diminished total fecal IgA, increased allergen absorption and altered gut microbiome composition. Furthermore, peanuts and tree nuts may have inherent properties distinct from milk and eggs that contribute to allergy.

Model of Walnut Allergy in CC027/GeniUnc Mice Recapitulates Key Features of Human Disease

Tree nut allergies affect 1% of the United States population, are often severe in nature and rarely outgrown. Despite the severity and prevalence, there are no FDA-approved treatments for tree nut allergy. Development of a therapeutic would be expedited by having a mouse model that mimics the human disease. We utilized the CC027/GeniUnc mouse strain, which was previously identified as an orally reactive model of peanut allergy, to develop a model of walnut allergy. Mice were sensitized with walnut and cholera toxin for 4 weeks and subsequently challenged by oral gavage. Blood samples were collected to measure serum IgE. Walnut-sensitized mice produced high levels of walnut-IgE and were cross-sensitized to pecan. Oral challenges with walnut resulted in severe anaphylaxis and accompanying allergic symptoms. Importantly, pecan challenges also led to severe allergic reactions, indicating cross-reactivity to pecan. Overall, this novel mouse model reproduces key characteristics of human walnut allergy, which provides a platform to develop novel therapies and better understand sensitization mechanisms.

Peanut applied to the skin of nonhuman primates induces antigen-specific IgG but not IgE

Introduction

Previous studies in humans support the dual‐allergen exposure hypothesis, and several studies in mouse models have demonstrated that cutaneous exposure to disrupted or intact skin can lead to sensitization to peanut. However, the field lacks definitive evidence that cutaneous exposure leads to peanut allergy in humans or other primates.

Methods

Peanut extract was applied to the shaved back of the neck of four male and four female African green monkeys three times per week for 4 weeks. An oral food challenge (OFC) was performed the following week by gavage of 200 mg of peanut protein, and vital signs were monitored for 30 minutes post‐OFC. Blood was collected at baseline, day 11, day 32, and 30 minutes post‐OFC. Total IgE, and peanut‐specific immunoglobulin E (IgE) and immunoglobulin G (IgG) were quantified in serum collected throughout the 4 weeks. Histamine was measured in serum collected 30 minutes post‐OFC.

Results

Peanut‐specific IgE was undetectable at any time points in any of the monkeys, and there was no consistent increase in total IgE. During the oral challenge, none of the monkeys experienced allergic symptoms and histamine levels did not change. However, seven of the eight monkeys produced increasing peanut‐specific IgG by day 32, indicating that repeated skin exposure to peanut is immunogenic.

Conclusions

Skin exposure to peanut did not lead to sensitization in this study, and monkeys did not experience anaphylaxis upon peanut challenge. However, monkeys produced increased peanut‐specific IgG throughout peanut exposure, indicating that repeated skin exposure to peanut is immunogenic.

Systematic quantification of the dynamics of newly synthesized proteins unveiling their degradation pathways in human cells

Proteins are continuously synthesized during cell growth and proliferation. At the same time, excessive and misfolded proteins have to be degraded, otherwise they are a burden to cells. Protein degradation is essential to maintain proteostasis in cells, and dysfunction of protein degradation systems results in numerous diseases such as cancer and neurodegenerative diseases. Despite the importance of protein degradation, the degradation pathways of many proteins remain to be explored. Here, we comprehensively investigated the degradation of newly synthesized proteins in human cells by integrating metabolic labeling, click chemistry, and multiplexed proteomics, and systematic and quantitative analysis of newly synthesized proteins first revealed the degradation pathways of many proteins. Bioinformatic analysis demonstrates that proteins degraded through two major pathways have distinct properties and functions. Proteins degraded through the ubiquitin-proteasome pathway contain more disordered structures, whereas those through the autophagy-lysosome pathway have significantly higher hydrophobicity. Systematic and quantitative investigation of the dynamics of newly synthesized proteins provides unprecedented and valuable information about protein degradation, which leads to a better understanding of protein properties and cellular activities.

Biomarkers in Food Allergy Immunotherapy

PURPOSE OF REVIEW

Investigational allergen immunotherapies (AITs) including oral immunotherapy (OIT), sublingual immunotherapy (SLIT), and epicutaneous immunotherapy (EPIT) have proven to increase allergen thresholds required to elicit an allergic reaction in a majority of subjects. However, these studies lack consistent biomarkers to predict therapy outcomes. Here, we will review biomarkers that are currently being investigated for AIT.

RECENT FINDINGS

The mechanisms underlying the therapeutic benefit of AIT involve various cell types, including mast cells, basophils, T cells, and B cells. Skin prick and basophil activation tests assess effector cell sensitivity to allergen and are decreased in subjects on AIT. Allergen-specific IgE increases initially and decreases with continued therapy, while allergen-specific IgG and IgA increase throughout therapy. Allergen-induced regulatory T cells (Tregs) increase throughout therapy and were found to be associated with sustained unresponsiveness after OIT. Subjects on OIT and SLIT have decreased Th2 cytokine production during therapy. Although trends have been reported, a common limitation of these biomarkers is that none are able to reproducibly predict prognosis during AIT. Further studies are needed to expand the currently available biomarker repertoire to provide personalized approaches to AIT.

Evolution of Immune Responses in Food Immunotherapy

Food allergies are a growing public health concern affecting approximately 8% of children and 10% of adults in the United States. Several immunotherapy approaches are under active investigation, including oral immunotherapy, epicutaneous immunotherapy, and sublingual immunotherapy. Each of these approaches uses a similar strategy of administering small, increasing amounts of allergen to the allergic subject. Immunologic studies have described changes in the T-cell compartment, serum and salivary immunoglobulin profile, and mast cell and basophil degranulation status in response to allergens. This review highlights the immunologic changes induced by food allergen-specific immunotherapy and discusses future directions in this field.

Indoor dust acts as an adjuvant to promote sensitization to peanut through the airway

BACKGROUND

There is growing evidence that environmental peanut exposure through non-oral routes, including the skin and respiratory tract, can result in peanut sensitization. Environmental adjuvants in indoor dust can promote sensitization to inhaled antigens, but whether they contribute to peanut allergy development is unclear.

OBJECTIVE

We investigated whether indoor dust promotes airway sensitization to peanut and peanut allergy development in mice.

METHODS

Female and male C57BL/6J mice were exposed via the airways to peanut, indoor dust extract, or both for 2 weeks. Mice were then challenged with peanut and assessed for anaphylaxis. Peanut-specific immunoglobulins, peanut uptake by lung conventional dendritic cells (cDCs), lung innate cytokines, and T cell differentiation in lung-draining lymph nodes were quantified. Innate cytokine production by primary human bronchial epithelial cells exposed to indoor dust was also determined.

RESULTS

Inhalational exposure to low levels of peanut in combination with indoor dust, but neither alone, resulted in production of peanut-specific IgE and development of anaphylaxis upon peanut challenge. Indoor dust triggered production of innate cytokines in murine lungs and in primary human bronchial epithelial cells. Additionally, inhaled indoor dust stimulated maturation and migration of peanut-laden lung type 1 cDCs to draining lymph nodes. Inhalational exposure to peanut and indoor dust induced peanut-specific T helper 2 cell differentiation and accumulation of T follicular helper cells in draining lymph nodes, which were associated with increased B cell numbers and peanut-specific immunoglobulin production.

CONCLUSIONS & CLINICAL RELEVANCE

Indoor dust promotes airway sensitization to peanut and development of peanut allergy in mice. Our findings suggest that environmental adjuvants in indoor dust may be determinants of peanut allergy development in children.

Genetic diversity between mouse strains allows identification of the CC027/GeniUnc strain as an orally reactive model of peanut allergy

BACKGROUND

Improved animal models are needed to understand the genetic and environmental factors that contribute to food allergy.

OBJECTIVE

We sought to assess food allergy phenotypes in a genetically diverse collection of mice.

METHODS

We selected 16 Collaborative Cross (CC) mouse strains, as well as the classic inbred C57BL/6J, C3H/HeJ, and BALB/cJ strains, for screening. Female mice were sensitized to peanut intragastrically with or without cholera toxin and then challenged with peanut by means of oral gavage or intraperitoneal injection and assessed for anaphylaxis. Peanut-specific immunoglobulins, T-cell cytokines, regulatory T cells, mast cells, and basophils were quantified.

RESULTS

Eleven of the 16 CC strains had allergic reactions to intraperitoneal peanut challenge, whereas only CC027/GeniUnc mice reproducibly experienced severe symptoms after oral food challenge (OFC). CC027/GeniUnc, C3H/HeJ, and C57BL/6J mice all mounted a T_H2 response against peanut, leading to production of IL-4 and IgE, but only the CC027/GeniUnc mice reacted to OFC. Orally induced anaphylaxis in CC027/GeniUnc mice was correlated with serum levels of Ara h 2 in circulation but not with allergen-specific IgE or mucosal mast cell protease 1 levels, indicating systemic allergen absorption is important for anaphylaxis through the gastrointestinal tract. Furthermore, CC027/GeniUnc, but not C3H/HeJ or BALB/cJ, mice can be sensitized in the absence of cholera toxin and react on OFC to peanut.

CONCLUSIONS

We have identified and characterized CC027/GeniUnc mice as a strain that is genetically susceptible to peanut allergy and prone to severe reactions after OFC. More broadly, these findings demonstrate the untapped potential of the CC population in developing novel models for allergy research.

Tree nut allergies: Allergen homology, cross-reactivity, and implications for therapy

Tree nut allergy is a potentially life-threatening disease that is increasing in prevalence, now affecting 1% of the general population in the United States. While other food allergies often resolve spontaneously, tree nut allergies are outgrown in less than 10% of cases. Due to the likelihood of cross-sensitization to multiple tree nut allergens, the current treatment guideline is strict avoidance of all nuts once one tree nut allergy has been diagnosed. For example, walnut and pecan are highly cross-reactive, along with cashew and pistachio, but the extent of clinical, IgE-mediated cross-reactivity among other tree nuts remains unclear, therefore making avoidance of all tree nuts a safe approach. There have been recent advances in immunotherapy for food allergies. For instance, there are investigational immunotherapies for milk, egg and peanut allergies, specifically oral immunotherapy, sublingual immunotherapy and epicutaneous immunotherapy. However, there are no large randomized controlled clinical trials for tree nut allergies. Even though there has been less research into tree nut allergy immunotherapies, the evidence of T-cell cross-reactivity among tree nuts exists in animal models and in T cells from allergic patients indicates that immunotherapeutic interventions may be possible. Here, we review the literature regarding epidemiology, allergen homology and cross-reactivity among tree nuts, and explore how current findings can be employed for effective therapy.

An enrichment method based on synergistic and reversible covalent interactions for large-scale analysis of glycoproteins

Protein glycosylation is ubiquitous in biological systems and essential for cell survival. However, the heterogeneity of glycans and the low abundance of many glycoproteins complicate their global analysis. Chemical methods based on reversible covalent interactions between boronic acid and glycans have great potential to enrich glycopeptides, but the binding affinity is typically not strong enough to capture low-abundance species. Here, we develop a strategy using dendrimer-conjugated benzoboroxole to enhance the glycopeptide enrichment. We test the performance of several boronic acid derivatives, showing that benzoboroxole markedly increases glycopeptide coverage from human cell lysates. The enrichment is further improved by conjugating benzoboroxole to a dendrimer, which enables synergistic benzoboroxole–glycan interactions. This robust and simple method is highly effective for sensitive glycoproteomics analysis, especially capturing low-abundance glycopeptides. Importantly, the enriched glycopeptides remain intact, making the current method compatible with mass-spectrometry-based approaches to identify glycosylation sites and glycan structures.

Understanding the functions of protein glycosylation critically depends on methods to efficiently enrich glycoproteins from complex samples. Here, the authors develop a strategy using dendrimer-conjugated benzoboroxole to enhance glycopeptide enrichment, providing the basis for more comprehensive glycoprotein analyses.

Competitive Protein Binding Influences Heparin-Based Modulation of Spatial Growth Factor Delivery for Bone Regeneration

Tissue engineering strategies involving the in vivo delivery of recombinant growth factors are often limited by the inability of biomaterials to spatially control diffusion of the delivered protein within the site of interest. The poor spatiotemporal control provided by porous collagen sponges, which are used for the clinical delivery of bone morphogenetic protein-2 (BMP-2) for bone regeneration, has necessitated the use of supraphysiological protein doses, leading to inflammation and heterotopic ossification. This study describes a novel tissue engineering strategy to spatially control rapid BMP-2 diffusion from collagen sponges in vivo by creating a high-affinity BMP-2 sink around the collagen sponge. We designed an electrospun poly-ɛ-caprolactone nanofiber mesh containing physically entrapped heparin microparticles, which have been previously demonstrated to bind and retain large amounts of BMP-2. Nanofiber meshes containing 0.05 and 0.10 mg of microparticles/cm2 demonstrated increased BMP-2 binding and decreased BMP-2 release in vitro compared with meshes without microparticles. However, when microparticle-containing meshes were used in vivo to limit the diffusion of BMP-2 delivered by using collagen sponges in a rat femoral defect, no differences in heterotopic ossification or biomechanical properties were observed. Further investigation revealed that, although BMP-2 binding to heparin microparticles was rapid, the presence of serum components attenuated microparticle-BMP-2 binding and increased BMP-2 release in vitro. These observations provide a plausible explanation for the results observed in vivo and suggest that competitive protein binding in vivo may hinder the ability of affinity-based biomaterials to modulate growth factor delivery.

Global Analysis of Secreted Proteins and Glycoproteins in Saccharomyces cerevisiae

Protein secretion is essential for numerous cellular activities, and secreted proteins in bodily fluids are a promising and noninvasive source of biomarkers for disease detection. Systematic analysis of secreted proteins and glycoproteins will provide insight into protein function and cellular activities. Yeast (Saccharomyces cerevisiae) is an excellent model system for eukaryotic cells, but global analysis of secreted proteins and glycoproteins in yeast is challenging due to the low abundances of secreted proteins and contamination from high-abundance intracellular proteins. Here, by using mild separation of secreted proteins from cells, we comprehensively identified and quantified secreted proteins and glycoproteins through inhibition of glycosylation and mass spectrometry-based proteomics. In biological triplicate experiments, 245 secreted proteins were identified, and comparison with previous experimental and computational results demonstrated that many identified proteins were located in the extracellular space. Most quantified secreted proteins were down-regulated from cells treated with an N-glycosylation inhibitor (tunicamycin). The quantitative results strongly suggest that the secretion of these down-regulated proteins was regulated by glycosylation, while the secretion of proteins with minimal abundance changes was contrarily irrelevant to protein glycosylation, likely being secreted through nonclassical pathways. Glycoproteins in the yeast secretome were globally analyzed for the first time. A total of 27 proteins were quantified in at least two protein and glycosylation triplicate experiments, and all except one were down-regulated under N-glycosylation inhibition, which is solid experimental evidence to further demonstrate that the secretion of these proteins is regulated by their glycosylation. These results provide valuable insight into protein secretion, which will further advance protein secretion and disease studies.

Yeast rRNA Expansion Segments: Folding and Function

Divergence between prokaryotic and eukaryotic ribosomal RNA (rRNA) and among eukaryotic ribosomal RNAs is focused in expansion segments (ESs). Eukaryotic ribosomes are significantly larger than prokaryotic ribosomes partly because of their ESs. We hypothesize that larger rRNAs of complex organisms could confer increased functionality to the ribosome. Here, we characterize the binding partners of Saccharomyces cerevisiae expansion segment 7 (ES7), which is the largest and most variable ES of the eukaryotic large ribosomal subunit and is located at the surface of the ribosome. In vitro RNA-protein pull-down experiments using ES7 as a bait indicate that ES7 is a binding hub for a variety of non-ribosomal proteins essential to ribosomal function in eukaryotes. ES7-associated proteins observed here cluster into four groups based on biological process, (i) response to abiotic stimulus (e.g., response to external changes in temperature, pH, oxygen level, etc.), (ii) ribosomal large subunit biogenesis, (iii) protein transport and localization, and (iv) transcription elongation. Seven synthetases, Ala-, Arg-, Asp-, Asn-, Leu-, Lys- and TyrRS, appear to associate with ES7. Affinities of AspRS, TyrRS and LysRS for ES7 were confirmed by in vitro binding assays. The results suggest that ES7 in S. cerevisiae could play a role analogous to the multi-synthetase complex present in higher order organisms and could be important for the appropriate function of the ribosome. Thermal denaturation studies and footprinting experiments confirm that isolated ES7 is stable and maintains a near-native secondary and tertiary structure.

Quantification of tunicamycin-induced protein expression and N-glycosylation changes in yeast

Tunicamycin is a potent protein N-glycosylation inhibitor that has frequently been used to manipulate protein glycosylation in cells. However, protein expression and glycosylation changes as a result of tunicamycin treatment are still unclear. Using yeast as a model system, we systematically investigated the cellular response to tunicamycin at the proteome and N-glycoproteome levels. By utilizing modern mass spectrometry-based proteomics, we quantified 4259 proteins, which nearly covers the entire yeast proteome. After the three-hour tunicamycin treatment, more than 5% of proteins were down-regulated by at least 2 fold, among which proteins related to several glycan metabolism and glycolysis-related pathways were highly enriched. Furthermore, several proteins in the canonical unfolded protein response pathway were up-regulated because the inhibition of protein N-glycosylation impacts protein folding and trafficking. We also comprehensively quantified protein glycosylation changes in tunicamycin-treated cells, and more than one third of quantified unique glycopeptides (168 of 465 peptides) were down-regulated. Proteins containing down-regulated glycopeptides were related to glycosylation, glycoprotein metabolic processes, carbohydrate processes, and cell wall organization according to gene ontology clustering. The current results provide the first global view of the cellular response to tunicamycin at the proteome and glycoproteome levels.

Systematic study of the dynamics and half-lives of newly synthesized proteins in human cells

Protein dynamics are essential in regulating nearly every cellular event, and aberrant proteostasis is the source of many diseases. It is extraordinarily difficult to globally study protein dynamics and accurately measure their half-lives. Here we have developed a chemical proteomics method integrating protein labeling, click chemistry and multiplexed proteomics, which overcomes current challenges with existing methods. Labeling with both azidohomoalanine (AHA) and heavy lysine allows us to selectively enrich newly synthesized proteins, clearly distinguish them from existing proteins, and reduce the impact of heavy amino acid recycling. Moreover, multiplexed proteomics enables us to quantify proteins at multiple time points simultaneously, thus increasing the accuracy of measuring protein abundance changes and their half-lives. Systematic investigation of newly synthesized protein dynamics will provide insight into proteostasis and the molecular mechanisms of disease.

Systematic and site-specific analysis of N-sialoglycosylated proteins on the cell surface by integrating click chemistry and MS-based proteomics

Glycoproteins on the cell surface are ubiquitous and essential for cells to interact with the extracellular matrix, communicate with other cells, and respond to environmental cues. Although surface sialoglycoproteins can dramatically impact cell properties and represent different cellular statuses, global and site-specific analysis of sialoglycoproteins only on the cell surface is extraordinarily challenging. An effective method integrating metabolic labeling, copper-free click chemistry and mass spectrometry-based proteomics was developed to globally and site-specifically analyze surface N-sialoglycoproteins. Surface sialoglycoproteins metabolically labeled with a functional group were specifically tagged through copper-free click chemistry, which is ideal because it is quick, specific and occurs under physiological conditions. Sequentially tagged sialoglycoproteins were enriched for site-specific identification by mass spectrometry. Systematic and quantitative analysis of the surface N-sialoglycoproteome in cancer cells with distinctive invasiveness demonstrated many N-sialoglycoproteins up-regulated in invasive cells, the majority of which contained cell adhesion-related domains. This method is very effective to globally and site-specifically analyze N-sialoglycoproteins on the cell surface, and will have extensive applications in the biological and biomedical research communities. Site-specific information regarding surface sialoglycoproteins can serve as biomarkers for disease detection, targets for vaccine development and drug treatment.

Mass spectrometric analysis of the cell surface N-glycoproteome by combining metabolic labeling and click chemistry

Cell surface N-glycoproteins play extraordinarily important roles in cell-cell communication, cell-matrix interactions, and cellular response to environmental cues. Global analysis is exceptionally challenging because many N-glycoproteins are present at low abundances and effective separation is difficult to achieve. Here, we have developed a novel strategy integrating metabolic labeling, copper-free click chemistry, and mass spectrometry (MS)-based proteomics methods to analyze cell surface N-glycoproteins comprehensively and site-specifically. A sugar analog containing an azido group, N-azidoacetylgalactosamine, was fed to cells to label glycoproteins. Glycoproteins with the functional group on the cell surface were then bound to dibenzocyclooctyne-sulfo-biotin via copper-free click chemistry under physiological conditions. After protein extraction and digestion, glycopeptides with the biotin tag were enriched by NeutrAvidin conjugated beads. Enriched glycopeptides were deglycosylated with peptide-N-glycosidase F in heavy-oxygen water, and in the process of glycan removal, asparagine was converted to aspartic acid and tagged with 18O for MS analysis. With this strategy, 144 unique N-glycopeptides containing 152 N-glycosylation sites were identified in 110 proteins in HEK293T cells. As expected, 95% of identified glycoproteins were membrane proteins, which were highly enriched. Many sites were located on important receptors, transporters, and cluster of differentiation proteins. The experimental results demonstrated that the current method is very effective for the comprehensive and site-specific identification of the cell surface N-glycoproteome and can be extensively applied to other cell surface protein studies.

A universal chemical enrichment method for mapping the yeast N-glycoproteome by mass spectrometry (MS)

Glycosylation is one of the most common and important protein modifications in biological systems. Many glycoproteins naturally occur at low abundances, which makes comprehensive analysis extremely difficult. Additionally, glycans are highly heterogeneous, which further complicates analysis in complex samples. Lectin enrichment has been commonly used, but each lectin is inherently specific to one or several carbohydrates, and thus no single or collection of lectin(s) can bind to all glycans. Here we have employed a boronic acid-based chemical method to universally enrich glycopeptides. The reaction between boronic acids and sugars has been extensively investigated, and it is well known that the interaction between boronic acid and diols is one of the strongest reversible covalent bond interactions in an aqueous environment. This strong covalent interaction provides a great opportunity to catch glycopeptides and glycoproteins by boronic acid, whereas the reversible property allows their release without side effects. More importantly, the boronic acid-diol recognition is universal, which provides great capability and potential for comprehensively mapping glycosylation sites in complex biological samples. By combining boronic acid enrichment with PNGase F treatment in heavy-oxygen water and MS, we have identified 816 N-glycosylation sites in 332 yeast proteins, among which 675 sites were well-localized with greater than 99% confidence. The results demonstrated that the boronic acid-based chemical method can effectively enrich glycopeptides for comprehensive analysis of protein glycosylation. A general trend seen within the large data set was that there were fewer glycosylation sites toward the C termini of proteins. Of the 332 glycoproteins identified in yeast, 194 were membrane proteins. Many proteins get glycosylated in the high-mannose N-glycan biosynthetic and GPI anchor biosynthetic pathways. Compared with lectin enrichment, the current method is more cost-efficient, generic, and effective. This method can be extensively applied to different complex samples for the comprehensive analysis of protein glycosylation.