Alick Stephens

Atopic dermatitis increases the effect of exposure to peanut antigen in dust on peanut sensitization and likely peanut allergy.

Background History and severity of atopic dermatitis (AD) are risk factors for peanut allergy. Recent evidence suggests that children can become sensitized to food allergens through an impaired skin barrier. Household peanut consumption, which correlates strongly with peanut protein levels in household dust, is a risk factor for peanut allergy. Objective We sought to assess whether environmental peanut exposure (EPE) is a risk for peanut sensitization and allergy and whether markers of an impaired skin barrier modify this risk. Methods Peanut protein in household dust (in micrograms per gram) was assessed in highly atopic children (age, 3-15 months) recruited to the Consortium of Food Allergy Research Observational Study. History and severity of AD, peanut sensitization, and likely allergy (peanut-specific IgE, ≥5 kUA/mL) were assessed at recruitment into the Consortium of Food Allergy Research study. Results There was an exposure-response relationship between peanut protein levels in household dust and peanut skin prick test (SPT) sensitization and likely allergy. In the final multivariate model an increase in 4 log2 EPE units increased the odds of peanut SPT sensitization (1.71-fold; 95% CI, 1.13- to 2.59-fold; P = .01) and likely peanut allergy (PA; 2.10-fold; 95% CI, 1.20- to 3.67-fold; P < .01). The effect of EPE on peanut SPT sensitization was augmented in children with a history of AD (OR, 1.97; 95% CI, 1.26-3.09; P < .01) and augmented even further in children with a history of severe AD (OR, 2.41; 95% CI, 1.30-4.47; P < .01); the effect of EPE on PA was also augmented in children with a history of AD (OR, 2.34; 95% CI, 1.31-4.18; P < .01). Conclusion Exposure to peanut antigen in dust through an impaired skin barrier in atopically inflamed skin is a plausible route for peanut SPT sensitization and PA.

Peanut allergy: Effect of environmental peanut exposure in children with filaggrin loss-of-function mutations

Background Filaggrin (FLG) loss-of-function mutations lead to an impaired skin barrier associated with peanut allergy. Household peanut consumption is associated with peanut allergy, and peanut allergen in household dust correlates with household peanut consumption. Objective We sought to determine whether environmental peanut exposure increases the odds of peanut allergy and whether FLG mutations modulate these odds. Methods Exposure to peanut antigen in dust within the first year of life was measured in a population-based birth cohort. Peanut sensitization and peanut allergy (defined by using oral food challenges or component-resolved diagnostics [CRD]) were assessed at 8 and 11 years. Genotyping was performed for 6 FLG mutations. Results After adjustment for infantile atopic dermatitis and preceding egg skin prick test (SPT) sensitization, we found a strong and significant interaction between natural log (ln [loge]) peanut dust levels and FLG mutations on peanut sensitization and peanut allergy. Among children with FLG mutations, for each ln unit increase in the house dust peanut protein level, there was a more than 6-fold increased odds of peanut SPT sensitization, CRD sensitization, or both in children at ages 8 years, 11 years, or both and a greater than 3-fold increased odds of peanut allergy compared with odds seen in children with wild-type FLG. There was no significant effect of exposure in children without FLG mutations. In children carrying an FLG mutation, the threshold level for peanut SPT sensitization was 0.92 μg of peanut protein per gram (95% CI, 0.70-1.22 μg/g), that for CRD sensitization was 1.03 μg/g (95% CI, 0.90-1.82 μg/g), and that for peanut allergy was 1.17 μg/g (95% CI, 0.01-163.83 μg/g). Conclusion Early-life environmental peanut exposure is associated with an increased risk of peanut sensitization and allergy in children who carry an FLG mutation. These data support the hypothesis that peanut allergy develops through transcutaneous sensitization in children with an impaired skin barrier.

IgG4 inhibits peanut-induced basophil and mast cell activation in peanut-tolerant children sensitized to peanut major allergens.

Background Most children with detectable peanut-specific IgE (P-sIgE) are not allergic to peanut. We addressed 2 non–mutually exclusive hypotheses for the discrepancy between allergy and sensitization: (1) differences in P-sIgE levels between children with peanut allergy (PA) and peanut-sensitized but tolerant (PS) children and (2) the presence of an IgE inhibitor, such as peanut-specific IgG4 (P-sIgG4), in PS patients. Methods Two hundred twenty-eight children (108 patients with PA, 77 PS patients, and 43 nonsensitized nonallergic subjects) were studied. Levels of specific IgE and IgG4 to peanut and its components were determined. IgE-stripped basophils or a mast cell line were used in passive sensitization activation and inhibition assays. Plasma of PS subjects and patients submitted to peanut oral immunotherapy (POIT) were depleted of IgG4 and retested in inhibition assays. Results Basophils and mast cells sensitized with plasma from patients with PA but not PS patients showed dose-dependent activation in response to peanut. Levels of sIgE to peanut and its components could only partially explain differences in clinical reactivity between patients with PA and PS patients. P-sIgG4 levels (P = .023) and P-sIgG4/P-sIgE (P < .001), Ara h 1–sIgG4/Ara h 1–sIgE (P = .050), Ara h 2–sIgG4/Ara h 2–sIgE (P = .004), and Ara h 3–sIgG4/Ara h 3–sIgE (P = .016) ratios were greater in PS children compared with those in children with PA. Peanut-induced activation was inhibited in the presence of plasma from PS children with detectable P-sIgG4 levels and POIT but not from nonsensitized nonallergic children. Depletion of IgG4 from plasma of children with PS (and POIT) sensitized to Ara h 1 to Ara h 3 partially restored peanut-induced mast cell activation (P = .007). Conclusions Differences in sIgE levels and allergen specificity could not justify the clinical phenotype in all children with PA and PS children. Blocking IgG4 antibodies provide an additional explanation for the absence of clinical reactivity in PS patients sensitized to major peanut allergens.

Distinct parameters of the basophil activation test reflect the severity and threshold of allergic reactions to peanut

Background The management of peanut allergy relies on allergen avoidance and epinephrine autoinjector for rescue treatment in patients at risk of anaphylaxis. Biomarkers of severity and threshold of allergic reactions to peanut could significantly improve the care for patients with peanut allergy. Objective We sought to assess the utility of the basophil activation test (BAT) to predict the severity and threshold of reactivity to peanut during oral food challenges (OFCs). Methods The severity of the allergic reaction and the threshold dose during OFCs to peanut were determined. Skin prick tests, measurements of specific IgE to peanut and its components, and BATs to peanut were performed on the day of the challenge. Results Of the 124 children submitted to OFCs to peanut, 52 (median age, 5 years) reacted with clinical symptoms that ranged from mild oral symptoms to anaphylaxis. Severe reactions occurred in 41% of cases, and 57% reacted to 0.1 g or less of peanut protein. The ratio of the percentage of CD63+ basophils after stimulation with peanut and after stimulation with anti-IgE (CD63 peanut/anti-IgE) was independently associated with severity (P = .001), whereas the basophil allergen threshold sensitivity CD-sens (1/EC50 × 100, where EC50 is half maximal effective concentration) value was independently associated with the threshold (P = .020) of allergic reactions to peanut during OFCs. Patients with CD63 peanut/anti-IgE levels of 1.3 or greater had an increased risk of severe reactions (relative risk, 3.4; 95% CI, 1.8-6.2). Patients with a CD-sens value of 84 or greater had an increased risk of reacting to 0.1 g or less of peanut protein (relative risk, 1.9; 95% CI, 1.3-2.8). Conclusions Basophil reactivity is associated with severity and basophil sensitivity is associated with the threshold of allergic reactions to peanut. CD63 peanut/anti-IgE and CD-sens values can be used to estimate the severity and threshold of allergic reactions during OFCs.

Peanut protein in household dust is related to household peanut consumption and is biologically active

BACKGROUND Peanut allergy is an important public health concern. To understand the pathogenesis of peanut allergy, we need to determine the route by which children become sensitized. A dose-response between household peanut consumption (HPC; used as an indirect marker of environmental peanut exposure) and the development of peanut allergy has been observed; however, environmental peanut exposure was not directly quantified. OBJECTIVE We sought to explore the relationship between reported HPC and peanut protein levels in an infants home environment and to determine the biological activity of environmental peanut. METHODS Peanut protein was quantified in wipe and dust samples collected from 45 homes with infants by using a polyclonal peanut ELISA. Environmental peanut protein levels were compared with peanut consumption assessed by using a validated peanut food frequency questionnaire and other clinical and household factors. Biological activity of peanut protein in dust was assessed with a basophil activation assay. RESULTS There was a positive correlation between peanut protein levels in the infants bed, crib rail, and play area and reported HPC over 1 and 6 months. On multivariate regression analysis, HPC was the most important variable associated with peanut protein levels in the infants bed sheet and play area. Dust samples containing high peanut protein levels induced dose-dependent activation of basophils in children with peanut allergy. CONCLUSIONS We have shown that an infants environmental exposure to peanut is most likely to be due to HPC. Peanut protein in dust is biologically active and should be assessed as a route of possible early peanut sensitization in infants.

Distribution of peanut protein in the home environment

BACKGROUND To halt the increase in peanut allergy, we must determine how children become sensitized to peanut. High household peanut consumption used as an indirect marker of environmental peanut exposure is associated with the development of peanut allergy. OBJECTIVE We sought to validate a method to quantify environmental peanut exposure, to determine how peanut is transferred into the environment after peanut consumption, and to determine whether environmental peanut persists despite cleaning. METHODS After initial comparative studies among 3 ELISA kits, we validated and used the Veratox polyclonal peanut ELISA to assess peanut protein concentrations in dust and air and on household surfaces, bedding, furnishings, hand wipes, and saliva. RESULTS The Veratox polyclonal peanut ELISA had the best rate of recovery of an independent peanut standard. We demonstrated 100% sensitivity and specificity and a less than 15% coefficient of variation for intra-assay, interassay, and interoperator variability. There was high within-home correlation for peanut protein levels in dust and household surface wipes. Airborne peanut levels were lower than the limit of quantitation for the Veratox polyclonal peanut ELISA in a number of simulated scenarios, except for a brief period directly above peanuts being deshelled. Peanut protein persisted on hands and in saliva 3 hours after peanut consumption. Peanut protein was completely removed from granite tables after cleaning with detergent, and levels were reduced but still present after detergent cleaning of laminate and wooden table surfaces, pillows, and sofa covers. CONCLUSIONS Peanut spread easily around the home and might be resistant to usual cleaning methods. Peanut protein can be transferred into the environment by means of hand transfer and saliva but is unlikely to be aerosolized.

Enquiring About Tolerance (EAT) study: Feasibility of an early allergenic food introduction regimen

Background The influence of early exposure to allergenic foods on the subsequent development of food allergy remains uncertain. Objective We sought to determine the feasibility of the early introduction of multiple allergenic foods to exclusively breast-fed infants from 3 months of age and the effect on breastfeeding performance. Methods We performed a randomized controlled trial. The early introduction group (EIG) continued breastfeeding with sequential introduction of 6 allergenic foods: cows milk, peanut, hard-boiled hens egg, sesame, whitefish (cod), and wheat; the standard introduction group followed the UK infant feeding recommendations of exclusive breastfeeding for around 6 months with no introduction of allergenic foods before 6 months of age. Results One thousand three hundred three infants were enrolled. By 5 months of age, the median frequency of consumption of all 6 foods was 2 to 3 times per week for every food in the EIG and no consumption for every food in the standard introduction group (P < .001 for every comparison). By 6 months of age, nonintroduction of the allergenic foods in the EIG was less than 5% for each of the 6 foods. Achievement of the stringent per-protocol consumption target for the EIG proved more difficult (42% of evaluable EIG participants). Breastfeeding rates in both groups significantly exceeded UK government data for equivalent mothers (P < .001 at 6 and at 9 months of age). Conclusion Early introduction, before 6 months of age, of at least some amount of multiple allergenic foods appears achievable and did not affect breastfeeding. This has important implications for the evaluation of food allergy prevention strategies.

Cutaneous lymphocyte antigen and α4β7 T-lymphocyte responses are associated with peanut allergy and tolerance in children.

It is unclear whether the initial route of allergen exposure in early life could influence the subsequent development of allergy, with cutaneous sensitization leading to peanut allergy (PA), and tolerance induced by oral exposure. The skin‐ and gastrointestinal (GI)‐homing markers, cutaneous lymphocyte antigen (CLA) and α4β7 integrin, are used to determine whether the state of PA correlates with peanut‐specific CLA responses, with tolerance associated with predominant α4β7 responses.

IgE‐mediated facilitated antigen presentation underlies higher immune responses in peanut allergy

To cite this article: Turcanu V, Stephens AC, Chan SMH, Rancé F, Lack G. IgE‐mediated facilitated antigen presentation underlies higher immune responses in peanut allergy. Allergy 2010; 65: 1274–1281.

Allergen specificity of early peanut consumption and effect on development of allergic disease in the Learning Early About Peanut Allergy study cohort

Background: Early introduction of dietary peanut in high‐risk infants with severe eczema, egg allergy, or both prevented peanut allergy at 5 years of age in the Learning Early About Peanut Allergy (LEAP) study. The protective effect persisted after 12 months of avoiding peanuts in the 12‐month extension of the LEAP study (LEAP‐On). It is unclear whether this benefit is allergen and allergic disease specific. Objective: We sought to assess the effect of early introduction of peanut on the development of allergic disease, food sensitization, and aeroallergen sensitization. Methods: Asthma, eczema, and rhinoconjunctivitis were diagnosed based on clinical assessment. Reported allergic reactions and consumption of tree nuts and sesame were recorded by questionnaire. Sensitization to food allergens and aeroallergens was determined by means of skin prick testing and specific IgE measurement. Results: A high and increasing burden of food allergen and aeroallergen sensitization and allergic disease was noted across study time points; 76% of LEAP participants had at least 1 allergic disease at 60 months of age. There were no differences in allergic disease between LEAP groups. There were small differences in sensitization and reported allergic reactions for select tree nuts, with levels being higher in the LEAP consumption group. Significant resolution of eczema and sensitization to egg and milk occurred in LEAP participants and was not affected by peanut consumption. Conclusion: Early consumption of peanut in infants at high risk of peanut allergy is allergen specific and does not prevent the development of other allergic disease, sensitization to other food allergens and aeroallergens, or reported allergic reactions to tree nuts and sesame. Furthermore, peanut consumption does not hasten the resolution of eczema or egg allergy. GRAPHICAL ABSTRACT Figure. No caption available.