Walnut Allergy Across Europe: Distribution of Allergen Sensitization Patterns and Prediction of Severity.

BACKGROUND: Walnut allergy is common across the globe, but data on the involvement of individual walnut components are scarce. OBJECTIVES: To identify geographical differences in walnut component sensitization across Europe, explore cosensitization and cross-reactivity, and assess associations of clinical and serological determinants with severity of walnut allergy. METHODS: As part of the EuroPrevall outpatient surveys in 12 European cities, standardized clinical evaluation was conducted in 531 individuals reporting symptoms to walnut, with sensitization to all known walnut components assessed in 202 subjects. Multivariable Lasso regression was applied to investigate predictors for walnut allergy severity. RESULTS: Birch-pollen-related walnut sensitization (Jug r 5) dominated in Northern and Central Europe and lipid transfer protein sensitization (Jug r 3) in Southern Europe. Profilin sensitization (Jug r 7) was prominent throughout Europe. Sensitization to storage proteins (Jug r 1, 2, 4, and 6) was detected in up to 10% of subjects. The walnut components that showed strong correlations with pollen and other foods differed between centers. The combination of determinants best predicting walnut allergy severity were symptoms upon skin contact with walnut, atopic dermatitis (ever), family history of atopic disease, mugwort pollen allergy, sensitization to cat or dog, positive skin prick test result to walnut, and IgE to Jug r 1, 5, 7, or carbohydrate determinants (area under the curve = 0.81; 95% CI, 0.73-0.89). CONCLUSIONS: Walnut-allergic subjects across Europe show clear geographical differences in walnut component sensitization and cosensitization patterns. A predictive model combining results from component-based serology testing with results from extract-based testing and information on clinical background allows for good discrimination between mild to moderate and severe walnut allergy.

Clinical and Molecular Characterization of Walnut and Pecan Allergy (NUT CRACKER Study).

BACKGROUND: Diagnostic methods for distinguishing walnut-allergic patients from walnut-sensitized but walnut-tolerant individuals are limited. Furthermore, characteristics of single walnut versus dual walnut-pecan allergy are lacking. OBJECTIVE: To provide clinical and molecular characteristics of walnut- and pecan-allergic patients. METHODS: A prospective cohort study of 76 walnut-sensitized patients was performed. Walnut skin prick test and serum measurements of specific IgE to walnut and its components were performed. Patients were challenged to walnut and pecan unless they regularly consumed walnut and pecan. RESULTS: Of the 76 patients studied, 61 were diagnosed as walnut-allergic and 15 as walnut-tolerant. IgE levels greater than or equal to 0.35 kUA/L to Jug r 1 or 4 provided the best diagnostic method for identifying walnut-allergic patients (accuracy, 0.93). Of the 61 walnut-allergic patients, 49 were pecan-allergic whereas 12 were pecan-tolerant. None of the walnut-tolerant patients was allergic to pecan. Dual allergic patients had significantly lower walnut reaction dose (median, 100 mg vs 1230 mg; P < .001). IgE levels greater than or equal to 0.35 kUA/L to Jug r 4, low-molecular-weight vicilins, or high-molecular-weight vicilins best segregated dual walnut-pecan-allergic patients from single walnut-allergic patients. Inhibition studies demonstrated that walnut pretreatment completely blocked IgE binding to pecan, whereas in some patients, pecan incubation only partially blocked IgE binding to walnut. CONCLUSIONS: Walnut components are helpful in diagnosing walnut allergy and in identifying patients with pecan coallergy. Competitive ELISA indicates that pecan comprises a subset of the allergenic determinants of walnut.

Walnut oral immunotherapy for desensitisation of walnut and additional tree nut allergies (Nut CRACKER): a single-centre, prospective cohort study.

BACKGROUND: The safety and efficacy of oral immunotherapy for tree nut allergy has not been demonstrated to date, and its effectiveness is complicated by the high prevalence of co-allergies to several nuts. This study aimed to investigate the use of walnut oral immunotherapy in the desensitisation of walnut and additional tree nuts in patients who are co-allergic to several nuts. METHODS: In a single-centre, prospective cohort study (the Nut Co-Reactivity ACquiring Knowledge for Elimination Recommendations study) at the Institute of Allergy, Immunology, and Paediatric Pulmonology at the Yitzhak Shamir Medical Centre, we recruited patients aged 4 years or older who were allergic to walnut, with or without co-allergy to pecan, hazelnut, and cashew. The diagnosis of each food allergy was based on a positive skin prick test or specific serum IgE (≥0·35 kUA/L) to the corresponding nut together with a positive oral food challenge, unless an immediate (within 2 h of exposure) reaction in the past year had been documented. Patients with uncontrolled asthma or a medical contraindication to receive adrenaline were excluded. Patients were assigned to walnut oral immunotherapy or the control group (observation and strict dietary exclusion) on the basis of the order of presentation to the clinic. Oral immunotherapy began with a 4-day dose-escalation phase to establish the single highest tolerated dose, which was consumed daily at home for 24 days; subsequent monthly dose escalations were repeated until 4000 mg walnut protein was achieved. Patients who were desensitised to walnut continued to consume 1200 mg walnut protein daily for 6 months as maintenance. The primary outcome was walnut desensitisation (passing an oral food challenge with 4000 mg of walnut protein) at the end of the study, analysed by intention to treat. In patients who were co-allergic to pecan, hazelnut, and cashew, the proportion who achieved cross-desensitisation to these nuts in addition to walnut desensitisation was examined. FINDINGS: 73 patients with a walnut allergy were enrolled between May 15, 2016, and Jan 14, 2018. 49 (89%) of 55 patients in the oral immunotherapy group were desensitised to walnut compared with none of 18 patients in the control group (odds ratio 9·2, 95% CI 4·3-19·5; p<0·0001). Following walnut desensitisation, all patients who were co-allergic to pecan (n=46) were also desensitised to pecan. Additionally, 18 (60%) of 30 patients who were co-allergic to hazelnut or cashew, and 14 (93%) of 15 patients who were co-allergic to hazelnut alone, were either fully desensitised or responded to treatment. 47 (85%) of 55 patients had an adverse reaction (mostly grade 1 or 2) during up-dosing in the clinic; eight patients required intramuscular epinephrine in response to a dose at home. Of 45 patients who had follow-up data for the maintenance phase, all maintained walnut desensitisation and one patient required epinephrine during this period. INTERPRETATION: Walnut oral immunotherapy can induce desensitisation to walnut as well as cross-desensitisation to pecan and hazelnut in patients who have tree nut co-allergies, with a reasonable safety profile. A low daily dose of the allergen maintains desensitisation. FUNDING: None.

Allergen Recognition Patterns in Walnut Allergy Are Age Dependent and Correlate with the Severity of Allergic Reactions.

BACKGROUND: Walnut is an important elicitor of food allergy in children and adults with a high rate of severe reactions. Multicenter studies using a common clinical protocol and a comprehensive allergen are lacking. OBJECTIVE: To investigate potential correlations between molecular sensitization patterns and clinical characteristics of walnut-allergic patients. METHODS: A total of 91 walnut-allergic subjects and 24 tolerant controls from Switzerland, Germany, and Spain were included. Walnut allergy was established by food challenge in all but anaphylactic subjects. Specific IgE (sIgE) to walnut extract, rJug r 1 (2S albumin), rJug r 3 (nonspecific lipid transfer protein 1), nJug r 4 (11S globulin), rJug r 5 (PR-10 protein), 2 vicilin fractions, profiling, and cross-reactive carbohydrate determinant was determined by ImmunoCAP. A threshold of 0.10 kUA/L was used for positivity. RESULTS: Sensitivity of sIgE to walnut extract was 87% and increased to 96% for the sum of all walnut components. sIgE to walnut extract and all walnut components, except rJug r 5, was significantly higher in patients younger than 14 years at inclusion. Stratification by age at onset of walnut allergy led to similar results. All patients younger than 14 years had severe reactions, whereas 38% of patients 14 years or older were mild reactors. Severe reactors (n = 70) had higher sIgE levels than did mild reactors (n = 21) to walnut extract (P < .0001), rJug r 1 (P < .0001), nJug r 4 (P = .0003), and both vicilin fractions (P < .0001), but not to Jug r 3 and Jug r 5. CONCLUSIONS: Sensitization to walnut storage proteins is acquired in childhood and correlates with severe reactions. sIgE levels to storage proteins Jug r 1 and Jug r 4 and vicilin fractions, but not to nonspecific lipid transfer protein and PR-10 proteins, correlate with systemic reactions to walnut.

Complex formation of myrosinase isoenzymes in oilseed rape seeds are dependent on the presence of myrosinase-binding proteins.

The enzyme myrosinase (EC 3.2.3.1) degrades the secondary compounds glucosinolates upon wounding and serves as a defense to generalist pests in Capparales. Certain myrosinases are present in complexes together with other proteins such as myrosinase-binding proteins (MBP) in extracts of oilseed rape (Brassica napus) seeds. Immunhistochemical analysis of wild-type seeds showed that MBPs were present in most cells but not in the myrosin cells, indicating that the complex formation observed in extracts is initiated upon tissue disruption. To study the role of MBP in complex formation and defense, oilseed rape antisense plants lacking the seed MBPs were produced. Western blotting and immunohistochemical staining confirmed depletion of MBP in the transgenic seeds. The exclusive expression of myrosinase in idioblasts (myrosin cells) of the seed was not affected by the down-regulation of MBP. Using size-exclusion chromatography, we have shown that myrosinases with subunit molecular masses of 62 to 70 kD were present as free dimers from the antisense seed extract, whereas in the wild type, they formed complexes. In accordance with this, MBPs are necessary for myrosinase complex formation of the 62- to 70-kD myrosinases. The product formed from sinalbin hydrolysis by myrosinase was the same whether MBP was present or not. The performance of a common beetle generalist (Tenebrio molitor) fed with seeds, herbivory by flea beetles (Phyllotreta undulata) on cotyledons, or growth rate of the Brassica fungal pathogens Alternaria brassicae or Lepthosphaeria maculans in the presence of seed extracts were not affected by the down-regulation of MBP, leaving the physiological function of this protein family open.

The third myrosinase gene TGG3 in Arabidopsis thaliana is a pseudogene specifically expressed in stamen and petal.

Genomic clones and full-length cDNA for the myrosinase gene TGG3 from Arabidopsis thaliana ecotype Columbia were sequenced. The TGG3 gene was similar with the earlier described myrosinase genes and shared the conserved intron/exon splice sites but had an insertion of one nucleotide in exon 5, a deletion of two nucleotides in exon 6 and a deletion of approximately 210 nucleotides in exon 12. These mutations shifted the open reading frame in exon 5 and resulted in a truncated protein. Analysis of the TGG3 DNA sequence from five other Arabidopsis ecotypes showed polymorphisms, but in no case did a functional TGG3 gene appear to be present. Although TGG3 apparently is a pseudogene, it was expressed specifically in stamen and petal according to RT-PCR analysis, while TGG1 and TGG2 transcripts were present in most of the tested tissues. Western blot analysis showed only one myrosinase band of 68 kDa corresponding to TGG1 and TGG2 in flower samples, while no band corresponding to TGG3 was encountered. Apparently only two functional myrosinases are present in this gene family in Arabidopsis.