Clinical & immunological features of peanut allergy

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Monitoring of IgE-mediated food allergy in childhood

Background: The prevalence of IgE-mediated food allergy (FA) in childhood varies from 6% to 8% in the first year of life compared to 1% to 2% in adults. In contrast to adults, FA in childhood, often part of the “allergic march”, resolves in more than 85% of children, especially those with hypersensitivity to cow's milk and egg. Aim: This paper explains the rationale for continuing care for childhood FA and describes how children should be monitored for resolution/persistence of FA. Methods: A clinical, multidisciplinary approach and management algorithm based on relevant, peer-reviewed original research articles and reviews using the keywords anaphylaxis, atopic eczema, children, milk allergy, double-blind placebo-controlled food challenge, egg allergy, epinephrine, failure to thrive, food allergy, food challenge, food hypersensitivity, immunoglobulin E, nutrition, natural history, paediatrics, peanut allergy, prevalence, psychosocial factors, quality of life, radioallergosorbent test, and tolerance from years 1966 to 2003 in MEDLINE. Additional studies were identified from article reference lists. Results: A combination of outcome measures, a multidisciplinary approach involving a dietitian and allergy nurse specialist, and a management algorithm are useful tools in clinical management. Conclusions: Prospective studies of non-selected children, optimally from birth cohorts, are needed to evaluate the effects of such management programmes regarding FA in childhood

Peanut allergic subjects' peripheral blood mononuclear cell proliferative responses to crude peanut protein

Background Peanut allergy is characterized by a high frequency of severe and occasionally fatal reactions. Objective To determine if there are features of the in vitro cellular response that may account for the observed severity of peanut allergy. Methods Skin-prick testing (SPT), RAST assay of serum peanut-specific and total IgE and mixed peripheral blood mononuclear cells (PBMC) proliferative responses to crude peanut protein were measured in 44 peanut allergics with varying severity of clinical reactions. PBMC responses of 13 non-peanut allergic controls (six atopic) were also studied. Results Subjects' PBMCs proliferated more than controls', even without stimulation. Subjects' PBMC proliferative responses did not correlate with clinical severity, SPT weal size or peanut-specific IgE levels. Controls’ PBMCs did not respond to peanut. There was no correlation between PBMC response and time since last reaction to peanut. Subjects' PBMCs responded more than controls, to mitogen as well as allergen. Proliferation increased with increasing concentration of peanut protein (P < 0.0001). Conclusion PBMCs of peanut allergics demonstrate a dose-dependent response to peanut which does not correlate with clinical severity, SPT reaction or levels of peanut specific IgE. The response is antigen-specific. Peanut protein is not mitogenic and is not acting as a superantigen. While there are non-specific differences in the PBMC responses of peanut allergic individuals compared with atopic and non-atopic controls, these differences do not explain the unique severity of peanut allergy

Peanut allergy: an overview

Allergic reactions to peanuts killed at least six people in the UK in 1993. Since then peanut allergy has generated a huge amount of interest among the general public, the medical profession and government agencies. The first case of peanut allergy was reported in 1920. However, no systematic studies of the subject were undertaken until the early 1980s. Before the recent increase in interest in peanut allergy, only two UK papers had reported six cases of peanut allergy - two of these patients died

Clinical characteristics of peanut allergy

Background Current clinical advice regarding peanut allergy is based on small series of patients. Objective To determine, in a large group of peanut allergic subjects, the patterns of clinical severity, symptom progression and availability and use of rescue medications. Methods Questionnaire study of 622 self-reported allergic subjects Results A total of 406 patients (66%) reported symptoms on contact with peanut. Only 121 (19%) had been knowingly exposed to peanut before the first documented reaction, implying a high frequency of occult sensitization. Severe symptoms were more common in adults. Abdominal symptoms were significantly associated with collapse. Fifty per cent reported reactions in the previous year. Only 82 (13%) had been admitted to hospital because of a reaction. Adrenaline was carried in some form by 65% though only 78 subjects (12.5%) had ever received injected adrenaline. Only 18/43 subjects (41%) who collapsed were given adrenaline. Skin-prick test weal size correlated weakly with severity but there were large overlaps between the groups. Peanut-specific IgE peaked in the teenage group, but did not correlate with severity. Conclusions Peanut allergy is characterized by more severe symptoms than other food allergies and by high rates of symptoms on minimal contact. Skin-prick testing and peanut-specific IgE levels do not predict clinical severity. Avoidance of peanut is difficult. Many people suffering severe relations are inadequately treated. Sufferers need education and training in the use of rescue medication

Resolution of peanut allergy following bone marrow transplantation for primary immunodeficiency

Peanut allergy is a severe and life-threatening form of food allergy. Treatments are being developed but the mainstays of current management remain avoidance of peanut and appropriate use of rescue medication. We report the case of a boy with peanut allergy who required a bone marrow transplant (BMT) for combined immunodeficiency. A food challenge, 2 years after transplant, showed that his peanut allergy had resolved. Allergic disorders constitute a form of immune deviation and while we do not advocate BMT as a treatment for peanut allergy, we believe this case provides an insight into the basic mechanisms involved in food allergy

HLA class II DRB1, DQB1 and DPB1 genotypic associations with peanut allergy: evidence from a family-based and case-control study

Background Peanut is one of the most common foods provoking allergic reactions and is the most frequent cause of fatal and near-fatal food-induced anaphylaxis. However, as yet, little is known of the genetic and immunological mechanisms which underly peanut allergy. Objective Based on findings in other allergic diseases, we have investigated whether particular human leucocyte antigen (HLA) class II genetic polymorphisms contribute to the development of peanut allergy. Methods All individuals from 37 families each containing one or more peanut allergic individuals, plus nine unrelated patients (161 individuals in total, defined as the study group) were typed for the HLA class II DRB1, DQB1 and DPB1 loci, by PCR-based techniques. Genotype frequencies were compared with those found in 293 unrelated controls. Results Four class II genotypes (DRB1*08 (13.7% vs 4.8%; Pc = 0.026), DRB1*08/12 tyr 16 (22.4% vs 8.2%; Pc = 0.021), DQB1*04 (12.2% vs 2.7%; Pc = 0.0026) and DPB1*0301 (49.1 vs 22.5%; Pc = 0.00062)) were present at a significantly higher frequency in the study group compared with controls. Three of these genotypes (DRB1*08 (18.0%; Pc = 0.027), DRB1*08/12 tyr16 (24.0%; Pc = 0.029) and DQB1*04 (16.7%; Pc = 0.0029)) were also significantly increased in peanut allergic individuals compared with controls. In addition, two genotypes (DPB1*0101 and 0201) were significantly decreased in frequency in the overall study group, but not specifically in peanut allergic individuals. Conclusion While other genetic factors may be important, results from this study indicate that HLA class II genetic polymorphism may play a role in determining susceptibility to peanut allergy

Application of an electrophoretic methodology for the identification of low molecular weight proteins in foods

Identification and characterisation of food proteins are core features of food allergy research. Current methods used to identify allergenic proteins in food have insufficient resolution and are unable to delect low molecular weight proteins. In this study we report the use of a simple SDS-PAGE method which allows resolution of small proteins. We have subsequently applied this method and reported presence of low molecular weight proteins in a range of hydrolysed milk formulae (Nutramigen, Pregistimil, Alfare, Pepti-Junior and Pregomin), and crude peanut protein extract. The molecular weight distribution for the peanut extract and the hydrolysates ranged between 5-200kDa and 2-17kDa respectively

Does severity of low-dose, double-blind, placebo-controlled food challenges reflect severity of allergic reactions to peanut in the community

Background: The severity of allergic reactions to food appears to be affected by many interacting factors. It is uncertain whether challenge-based reactions reflect the severity of past reactions or can predict future risk.Objective: To explore the relationship of a subject's clinical history of past reactions to the severity of reaction elicited by a low-dose, double-blind, placebo-controlled food challenge (DBPCFC) with peanut.Method: Cross-sectional questionnaire assessment of community-based allergic reactions and low-dose DBPCFC in self-selected peanut-allergic subjects. Reaction severity was assessed using a novel scoring system, taking account of the dose of allergen ingested.Results: Forty subjects (15 males, 23 children, 23 asthmatics by history) were studied. Only the most recent community reaction predicted the severity of reaction in the DBPCFC, but even this association was weak (r=0.37, P=0.03). Peanut-specific IgE (PsIgE) and skin prick test (SPT) weal size were not associated with community score but PsIgE level correlated well with the challenge score (r=0.6, P=0.001). Asthma did not affect the eliciting dose or challenge score directly but the association of PsIgE and challenge score was stronger in those without asthma (r=0.72, P=0.001) than in those with asthma (r=0.48, P=0.02).Conclusions: The scoring system developed appears to improve the sensitivity of assessment of reactions induced by DBPCFC. This is the first prospective study showing an association between PsIgE levels and clinical reactivity in DBPCFC, an effect that is more pronounced in non-asthmatics. This finding has important implications for the clinical care of subjects with food allergy. There is a poor correlation between the severity of reported reactions in the community and the severity of reaction elicited during low-dose DBPCFC with peanut