Dietary assessment in children adhering to a food allergen avoidance diet for allergy prevention.
Objective: The purpose of this investigation was to verify if avoidance of allergenic foods in children adhering to a food allergen avoidance diet from birth was complete and feasible; and whether dietary assessment can be used as a tool in predicting the outcome of double-blind; placebo-controlled food challenges (DBPCFCs). Design: Children adhering to an allergen avoidance diet from birth underwent DBPCFCs. The investigator-dietician verified whether the elimination was complete; using food frequency questionnaires for common allergenic foods. Setting: University Medical Centre Groningen; the Netherlands. Subjects: Thiry-eight children aged 1-13 years; who were consecutively referred to the University Medical Centre Groningen for DBPCFC between January 2002 and February 2004. Results: Among the 38 children undergoing DBPCFCs; there were 15 challenges with egg; 15 with peanut; five with hazelnut and three with soy. Fifteen food challenges (39%) were positive. Small quantities of allergenic foods were inadvertently present in the diets of 13 patients (34%); were possibly present in the diets of 14 patients (37%) and could not be identified in the diets of 11 patients (29%). Seven patients (54%) who had inadvertently ingested small quantities of allergenic foods without sequelae had a positive DBPCFC. Conclusion: Dietary avoidance was incomplete and not feasible in most cases. Tolerance of small amounts of allergenic foods does not preclude positive challenge reactions. Dietary assessment does not seem a useful tool in predicting the outcome of DBPCFC in children adhering to an elimination diet.
Combining skin prick; immediate skin application and specific-IgE testing in the diagnosis of peanut allergy in children
Previous studies have suggested various diagnostic cut-offs of allergy tests for the diagnosis of clinical peanut allergy in children. There are few data relating to the use of combinations of these tests in children. We aimed to determine the validity of previously reported diagnostic cut-off levels of peanut allergen skin tests and peanut specific-immunoglobulin (Ig) E; as well as the usefulness of combinations of these; for predicting clinical peanut allergy in our Allergy Clinic. Children attending the Allergy Clinic with a positive peanut skin prick test (SPT; n = 84) were included in the study. Immediate skin application food tests (I-SAFT) using 1 g of peanut butter (positive if any wheals were detected at 15 min); peanut specific-IgE levels and open-label peanut food challenges were performed. Fifty-two of 85 peanut challenges were positive. Skin prick test specificity was 67% at >/=8 mm and 100% at >/=15 mm. The I-SAFT was 82% specific. A peanut specific-IgE level of 0.37 kU/l was 98% sensitive but 33% specific. A level of 10 kU/l was 100% specific. Combinations of a SPT of >/=8 mm with a positive I-SAFT and a peanut specific-IgE >/=0.37 kU/l were 88% specific with a sensitivity of 38%. Using challenge outcomes as the standard; available in vitro and in vivo diagnostic tests for peanut allergy have poor sensitivity and specificity and combining them does not significantly improve their clinical usefulness. Previously described diagnostic cut-off levels do not have general applicability. Allergy practitioners may need to interpret results of allergy tests in the context of their own practices.
Production of IL-12 by Peyer patch-dendritic cells is critical for the resistance to food allergy
Background: Dendritic cells (DCs) play a pivotal role in antigen presentation and regulation of immune responses; however; their involvement in food allergy remains to be fully understood. Objective: Our aim was to investigate T(H)1-T(H)2 reciprocal regulation of DCs' function in the gut and systemic immune system and its effect on food allergy in mice with different susceptibility to food allergy. Methods: Freshly isolated CD11c(+)B220(-)DCs from peanut-sensitized allergy-susceptible C3H/HeJ and allergy-resistant Balb/c mice were cultured to determine levels of IL-12p70 produced in the presence of cytokines; including IL-4. Systemic levels of IL-12 were assessed in vivo after antigen challenge with or without IL-4. Targeted oral delivery of microencapsulated neutralizing anti-IL-12 antibody to Peyer patches (PPs) was performed in Balb/c before administration of each sensitizing dose. Results: Peyer patch-DCs but not splenic DCs from sensitized C3H/HeJ but not Balb/c mice produced less IL-4-dependent IL-12p70. In vivo data confirmed this was restricted to the gut immune system; and it was not linked to reduced expression of IL-4 receptor or the lack of functional Toll-like receptor 4; instead; IL-4 failed to inhibit IL-10 production by PP-DCs; a pathway critically involved in IL-4-dependent production of IL-12p70. Finally; neutralization of IL-12 within PPs by specific antibody during antigen presentation significantly increased Balb/c susceptibility to food allergy. Conclusion: Reciprocal T(H)1-T(H)2 control of DCs' function within the inductive site of the gut immune system is altered in food allergy. CLINICAL IMPLICATIONS: Production of IL-12p70 by PP-DCs during antigen presentation is critical for the development of food allergy.
Tree nut allergy
Tree nuts are clinically associated with severe immunoglobulin E-mediated systemic allergic reactions independent of pollen allergy and with reactions that are usually confined to the oral mucosa in patients with immunoglobulin E directed toward cross-reacting pollen allergens. The latter reactions can progress to severe and life-threatening episodes in some patients. Many patients with severe tree nut allergy are co-sensitized to peanut. Clinical studies on cross-reactivity between the tree nuts are few in number; but based on reports to date; avoidance of the other tree nuts once sensitivity is diagnosed appears prudent unless specific challenges are performed to ensure clinical tolerance. Even then; great care must be taken to avoid cross-contamination. As with other severe food allergies; a recurrent problem in clinical management is the failure of physicians to prescribe self-injectable epinephrine to patients who are at risk of anaphylaxis.
Prevalence of peanut and tree nut allergy in the United States determined by means of a random digit dial telephone survey: a 5-year follow-up study
BACKGROUND: Allergy to peanuts and tree nuts (TNs) is the leading cause of fatal and near-fatal food allergic reactions. Peanut allergy appears to be increasing in prevalence. OBJECTIVES: We sought to determine the prevalence of self-reported peanut and TN allergy among the general population of the United States in 2002 by sex and age and to compare the results with prevalence estimates obtained 5 years earlier. METHODS: We performed a nationwide; cross-sectional; random telephone survey by using a standardized questionnaire. RESULTS: A total of 4855 households participated (53% participation rate); representing a census of 13;493 individuals. Peanut allergy; TN allergy; or both was self-reported in 166 (1.2%; 95% CI; 1.0%-1.4%) individuals in 155 (3.2%; 95% CI; 2.7%-3.7%) households; overall prevalence rates similar to those reported in 1997. Also similar to the 1997 survey; the severity level was high; with 79% reporting respiratory or multiple organ system reactions and 66% experiencing more than 5 lifetime reactions. Despite the severity and reaction frequency; only 74% of the children and 44% of the adults sought evaluation for the allergy; and fewer than half who did were prescribed self-injectable epinephrine. Applying conservative rules to adjust for persons with unconvincing reactions and a false-positive rate of the survey instrument (7%); a final prevalence estimate of 1.04% (95% CI; 0.9%-1.24%) was obtained. A male predominance of peanut-TN allergy was reported in children younger than 18 years (1.7% vs 0.7%; P =.02); and a female predominance was reported among adults (1.7% vs 0.9%; P =.0008). Although the rate of peanut allergy; TN allergy; or both was not significantly different from 1997 to 2002 among adults; the rate increased from 0.6% to 1.2% among children; primarily as a result of an increase in reported allergy to peanut (0.4% in 1997 to 0.8% in 2002; P =.05). CONCLUSIONS: Self-reported peanut allergy has doubled among children from 1997 to 2002; and peanut allergies; TN allergies; or both continue to be reported by more than 3 million Americans. Considering that reactions are severe and the allergy is persistent; these allergies represent an increasing health concern.
Detection and stability of the major almond allergen in foods.
Almond major protein (AMP or amandin); the primary storage protein in almonds; is the major allergen recognized by almond-allergic patients. A rabbit antibody-based inhibition ELISA assay for detecting and quantifying AMP in commercial foods has been developed; and this assay; in conjunction with Western blotting analyses; has been applied to the investigation of the antigenic stability of AMP to harsh food-processing conditions. The ELISA assay detects purified AMP at levels as low as 87 +/-16 ng/mL and can detect almond at between 5 and 37 ppm in the tested foods. The assay was used to quantify AMP in aqueous extracts of various foods that were defatted and spiked with known amounts of purified AMP or almond flour. In addition; AMP was quantified in commercially prepared and processed almond-containing foods. Neither blanching; roasting; nor autoclaving of almonds markedly decreased the detectability of AMP in subsequent aqueous extracts of almonds. Western blots using both rabbit antisera and sera from human almond-allergic patients confirm a general stability of the various peptides that comprise this complex molecule and show that the rabbit antibody-based assay recognizes substantially the same set of peptides as does the IgE in sera from almond-allergic patients.
Cashew allergy: observations of 42 children without associated peanut allergy
BACKGROUND: Cashew allergy seems to be increasingly frequent. The goal of the present study was to analyse the clinical features and results of investigations of 42 children with cashew allergy. METHODS: The clinical features and results of skin prick tests; specific IgE assays; and food challenges were analysed. RESULTS: The mean age at first allergic reaction was 2 years and the mean age at diagnosis of cashew allergy was 2.7 years. One in five children (12%) had a prior history of exposure to cashew nuts. Fifty-six per cent had skin symptoms; 25% had respiratory signs and 17% had digestive signs. Eighteen children had proven; associated food allergies (pistachio; seven; egg; five; mustard; three; shrimp; two; cow milk; one). The mean wheal diameter of the skin prick tests was 7 mm (3-16 mm) and the mean specific IgE level was 3.1 kUA/L (<0.35->100 kUA/L). Eight children had positive food challenges. CONCLUSION: The increase in cashew allergy is worrying because it affects young children who may have a reaction without ever having been exposed to cashews. Almost one-third of children are allergic to pistachios; which belong to the same botanical family as cashews. Clinical history is generally and sufficiently suggestive to diagnose cashew allergy without recourse to food challenges.
Food allergy to peanuts in France - evaluation of 142 observations
BACKGROUND: The increase in frequency of peanut allergy and fatal cases have been reported. OBJECTIVES: The objective of this study is to document the severity of food allergy to peanuts by evaluating the reactive dose of peanuts and to search for the role of peanut oil. METHODS: This study is carried out on the basis of 142 observations collected according to the same diagnostic methodology in two allergy centres in France. Skin-prick-tests were performed with peanut powder; peanut oil and peanut oil proteinic extract. Labial provocation tests were performed on 121 patients. The reactive dose of peanuts and the role of peanut oil were determined by standardized oral provocation tests in 50 and 62 patients respectively. The data are computerized and the data bank includes 509 food allergic patients. RESULTS: Allergy to peanuts represents 28% of food allergies and occurs under 1 year of age in 46% of cases; under 15 years of age in 93%. The clinical features were atopic dermatitis (40%); angioedema (37%); asthma (14%); anaphylactic shock (6%) and digestive symptoms (1.4%). The specific IgE were class 3 or higher in 80% of cases. The total reactive dose was less than 100 mg in 25% of cases; from 100 mg to 1 g in 62.5%. All patients reacted to a dose of less than 7.1 g. The threshold of peanut reactivity was lower than the threshold of egg reactivity. An allergy to peanut oil was demonstrated in 14 patients. CONCLUSION: The severity of peanut allergy and the early onset of the occurrence of this allergy is documented. The role of residual allergenic proteins in peanut oil is established by positive skin-prick tests to proteic extracts from peanut oil and by double-blind placebo-controlled challenges to peanut oil. The increased consumption of allergens in the form of peanut oil and fats can contribute to the occurrence or persistence of symptoms and may be suspected to increase the risk of sensitisation.