Intérêt des allergènes recombinants dans le diagnostic de l’allergie alimentaire

To date, neither in vitro nor in vivo tests can establish with reliability the diagnosis of food allergy. The availability of recombinant allergens (RA) has led to improvement in the standardization of allergenic extracts and enrichment of natural extracts, resulting in more sensitive screening tests. These biotechnological advances facilitate the diagnostic approach which now rests on an individual reaction profile (component resolved diagnosis) with well-characterized allergens classified on a molecular basis. Development of diagnostic tests using RA or peptides expressing some distinctive epitopes of interest may improve the prediction of severe and/or persistent food allergies and guide the choice of the therapeutic measures that follow.     

Éducation de l’allergie alimentaire sévère

Families consisting of children with food allergies have significant deficiencies in their knowledge of how to avoid allergen exposure and how to manage allergic reactions. Although an educational program can considerably improve a family's ability to manage allergic reactions to food and reduce the number of reactions, this approach is used too infrequently, even for children who have severe food allergies. A precise diagnosis is essential before undertaking such a program. It can result in reduction of the number of foods to be avoided and improvement in the child's quality of life. We will propose educational objectives for patients with severe food allergies and means to attain these objectives.     

Épidémiologie de l’allergie alimentaire

The epidemiology of food allergy normally relies on surveys using questionnaire in general populations and studies on cohorts and through professionals in allergy clinics, sometimes completed by prick-tests, specific IgE assays and/or oral challenges. Complementary data are supplied by specialized medical networks. In European countries, the prevalence of food allergy in the pediatric population is about 4.7%, and in adults it is about 3.2%. Striking disparities characterize the response to questionnaires in EU countries. Life-threatening anaphylaxis occurs in 1/10,000 inhabitants, fatal anaphylaxis in 1/1 million inhabitants. A drastic increase of life-threatening and lethal anaphylaxis has been noted in the UK and Australia over the past ten years. In France, there has been an increase of 28% between 2001 and 2006. The Allergy Vigilance Network, which includes 400 allergists, reports that this increase has occurred in the pediatric population. The prevalence of food allergies depends on age and consuming habits. Milk, egg, peanut and tree-nuts are at the top of the list in children. Prunoïdeae, latex-group fruits, Apiaceae, wheat and tree-nuts are the most important food allergens in adults. Peanut and tree nuts are the main offending allergens in severe anaphylactic cases. Since 2002 the Allergy Vigilance Network in France and Belgium has been identifying newly-appearing dangerous allergens. Molluscs, lupine flour and cashew nuts are the most common on this list and labelling these foods is now compulsory. Goat and sheep milk proteins (14 cases), buckwheat (25 cases) and wheat isolates are not yet required to be labelled. The danger of anaphylaxis to goat and sheep proteins (two deaths out of 14 cases) is due to the likelihood of their being masked allergens, for which reason the EU Scientific Agency should be made aware of the necessity of required labelling of foods containing these substances.     

Définitions des termes utilisés en allergologie alimentaire chez l’enfant

In so far as there are no recent medical references that specify terms used in allergy, and particularly terms dealing with food allergy, it seemed to us that it would be of use to compile a glossary that would be helpful in daily practice. The defined terms (plus comments) have been retained according to sequences that correspond to steps in a food allergy work-up. The following terms are entered successively in this review: atopic dermatitis; SCORAD; asthma; pulmonary function tests; medications for children; symptoms and severity of food allergies; immediate skin tests; intradermal tests or “atopy patch-tests”; allergen-specific and total serum IgE levels; oral provocation test; labial provocation test; other tests used in allergy work-ups; allergy, hypersensitivity, atopy; allergens, allergies, sensitizations, allergic cross-reactions; treatment of an allergic reaction.     

Histoire de l'allergie alimentaire : des précurseurs à l'histoire contemporaine

Food allergies are an important public health problem. Relatively unheard of during the 1970–1980 s, they had almost always been associated with the same allergens (cow milk, chicken eggs, and fish). Since then, they have become more frequent and more varied, involving about 4% of the general population of all ages; the prevalence may even be 5–6% or more among children. They are also becoming more and more severe, and interfering more in daily living. Beginning in the 1980 s, the story of food allergy has been marked by the explosion of the occurrence of peanut allergy, the prevalence of which has at least doubled over the past five years. Another important tendency has been an increase in the frequency of allergy to shelled fruits (e.g. exotic nuts) and to certain plant allergens (e.g. sesame, buckwheat and wheat). There has also been an increase in the number of near-fatal and fatal cases of food-related anaphylaxis, justifying the establishment of a monitoring network. The workup of food allergies has become more standardized, allowing a definitive diagnosis to be more easily established, thus justifying avoidance of the responsible substance. Indeed, until recently, in the absence of effective preventive measures and a good risk-benefit ratio, the prevention of food allergies depended on avoidance of the responsible food(s), which recommendation is nevertheless often not followed as prescribed. Other preventive measures (antihistamines, corticosteroids, adrenalin auto-injectors) are then adopted to avoid recurrences, which can be considered as evidence of treatment failure. Recent years have been marked by standardization of preventive measures based on the Project of Individual Care and by the establishment of educational protocols. The future may see the development of specific immunotherapy (until now, difficult and dangerous), modification of food allergens, and treatments that block IgE-dependant allergic reactions. For example, the preliminary results of a clinical trial of sublingual immunotherapy with hazelnut appear to be promising. Considering the difficulty of diagnosis and prevention, the social and psychological repercussions of food allergies are considerable for both children and their families.     

Quel est le profil d’un asthme sévère chez l’enfant ?

Severe asthma is estimated to occur in 9.6% of asthmatics. Even though severe asthma does not occur frequently in asthmatic children, still it accounts for 80% of health expenditures in this group of patients. International guidelines grade the severity of asthma in four stages (intermittent, mild persistent, moderate, severe) according to daytime and night time symptoms, the frequency of exacerbations that affect the patient's activities, and the forced expiratory volume in the first second (FEV₁) before starting treatment. This classification appears insufficient for an evaluation of the severity of asthma in children because it does not take into account their current treatment, namely, inhaled corticoids, as well as previous acute severe exacerbations, the condition of the lower airways, the existence of an atopic terrain, and the importance of the patient's age and sex on the severity of the asthma. Finally, it must be remembered that in the clinical workup of a child with severe asthma, it is first of all necessary to rule out “false asthma” (by systematic etiologic investigation), to distinguish between severe asthma and poorly controlled asthma related to co-existing conditions not otherwise considered, an inadequate environment, and poor adherence to prescribed therapy.     

Immunopathologie de l'asthme sévère

Severe asthma represents a heterogeneous entity for which the immunopathology is poorly understood, in part because of the difficulty of obtaining material in situ material from patients. There are two types of severe asthma, depending on the presence or absence of eosinophils. The pathophysiology of severe asthma of early onset with eosinophilia is similar to that of less severe asthma, with infiltration of Th2 lymphocytes; such cases are more likely to have exacerbations. When the onset occurs later, asthma is much more like the hypereosinophilic syndromes. Severe asthma without eosinophilia is more often accompanied by neutrophil infiltration; this type of asthma responds poorly to corticoids. Induced sputum can be used for non-invasive longitudinal follow-up of bronchial inflammation in severe asthma, allowing evaluation of cellular activation during and between exacerbations. The ISEA study (Induced Sputum in Exacerbations of Asthma) revealed that simultaneous activation of Th1 and Th2 lymphocytes and a greater deficiency of T regulatory lymphocytes occur during the course of exacerbations. This type of approach is indispensable for the identification of relevant therapeutic targets, and ultimately for the identification of early markers that are predictive of exacerbations.     

Otite séreuse et allergie

Respiratory and/or food allergy is common in children. Serous otitis media is also very frequent in children, especially those between three and six years of age. On the other hand, in spite of promising animal studies, a cause-and-effect relation between these two conditions in man has not been established. Concerning the treatment, avoidance of food allergens may be as efficacious for an active serous otitis media as for avoidance of a new episode. Conversely, antihistamines do not appear to be efficacious, at least with respect to being curative.     

Immunothérapie et allergie alimentaire

Immunotherapy trials on food allergy were published some years ago and few of them were randomized. The protocols used varied and IgE-mediated food allergies were the first studied. Immunotherapy is mainly indicated for persistent food allergy after the usual age of recovery. Other factors, such as the dose of the allergen and the nature of the symptoms due to food allergy, are less well-defined with regard to indications for immunotherapy. Different techniques are available: the subcutaneous route, with well-known adverse effects when currently available extracts are used; the oral route, with efficacy in a third of the cases and the sublingual route, which seems to be promising. The real effect of immunotherapy, whether persistent, transitory or merely an increase in the amount of food tolerated, remains to be defined.     

L'allergie au tournesol et à son huile : rôles du contact,de l'ingestion et de l'inhalation

We report the case of a 5-years old girl with food allergy to sunflower oil. Sensitivity to sunflower oil and seeds was demonstrated by skin tests whereas assays of serum for sunflower-specific IgE were negative. An oral challenge test with 54 ml of sunflower oil was positive. The patient also reacted to cutaneous contact and inhalation of sunflower seeds. Depending on the route of contact –– skin contact, ingestion or inhalation –– sunflower oil and seeds can trigger symptoms such as urticaria, erythema, vomiting, dyspnea or fatigue.     

Allergènes rares de l’environnement intérieur

Allergens rarely present in the indoor environment are not sufficiently recognized. The prevalence of sensitization to these allergens depends on the geographic and climatic characteristics of the habitat as well as on the lifestyle of the inhabitants. Their sources are diverse: allergens of animal (mites, other insects, mammals, etc.) or vegetal origin. Sensitization to rare allergens should be established by a well-documented clinical history, by immunological tests and by the effects of avoidance. A general review of rare allergens and/or some new airborne allergens present in the indoor environment will be presented.     

Anesthésie de l’asthmatique

The asthmatic patient is at risk of bronchospasm during anaesthesia. The risk increases in severe asthma. Uncontrolled asthma is the main risk factor. The preoperative evaluation of asthma control is therefore necessary and if possible the patient will be prepared with bronchodilators and steroids. Locoregional anaesthesia will always be preferred to a general anaesthesia during which endotracheal intubation can induce bronchospasm. Inhaled anaesthetics are well tolerated, in being bronchodilators. Ketamin and benzodiazepines can be used. Propofol and opioids are usually well tolerated in asthmatics. Among myorelaxants, these without histamine release effect will be preferred. During local anaesthesia, lidocain can be used. Its bronchodilator effects are considered. The preventive and a fortiori curative use of beta-2 agonists agents are the treatment of choice of perioperative bronchospasm, associated to steroids.     

Allergie à la farine de blé chez l’adulte

The clinical manifestations of allergy to wheat flour are similar to those of allergies to other foods. In adults, food-dependent exercise-induced anaphylaxis, chronic urticaria, and gastrointestinal food allergies (that is, irritable bowel syndrome, eosinophilic colitis, ulcerative colitis) are the most frequently described clinical manifestations of allergy to wheat. Wheat isolates, used as binders and emulsifiers in the food industry, are neo-allergens resulting from chemically induced desamidation of wheat gluten (heating at high temperature in an acidic medium). Wheat isolate allergens can induce severe systemic reactions (e.g., urticaria) and anaphylactic shock. Diagnosis consists of three steps: a suspicion based on the patient's history, identification of the allergen by skin testing and by laboratory tests, and confirmation by oral challenge or by an avoidance regime.     

Asthme sévère : particularités pédiatriques

Severe asthma in children is defined by the persistence or exacerbation of asthmatic symptoms or persistence of bronchial obstruction in spite of treatment that is considered to be optimal. Management requires, first of all, that cases of false asthma, asthma lacking appropriate treatment, poor compliance and/or preventive education, asthma made worse by the persistence of an unrecognized factor and/or asthma that has not been treated must be recognized. Severe asthma calls for evaluation in specialized centers where the importance of bronchial inflammation and airway remodeling can be appreciated. That evaluation is based on data obtained by broncho-alveolar lavage and endobronchial biopsy; non-invasive methods such as measurement of exhaled NO and thoracic tomodensitometry are still being evaluated.     

Pollution de l’air et asthme de l’enfant

The prevalence of asthma and allergic diseases doubled during the last quarter of the 20th century, particularly among children and adolescents. Given this fact, we cannot attribute this increase exclusively to genetic factors. Environmental factors to which it has been attributed include exposure to allergens and to airborne physicochemical pollutants, and changes in the characteristics of respiratory infections in young infants. In this review, we will point out the role of exposure to air pollutants and their interaction with other environmental factors. Whereas concentrations of the ‘classical’ air quality indicators (SO₂, CO) have more or less decreased steadily in developed countries, asthma prevalence has increased during the same period. However, the relation between the increase incidence of asthma and atmospheric pollution should be examined with the knwoledge that there has been an increase in new forms of pollution, in particular, ultrafine particles. There are at present many experimental studies which show that urban pollution (especially that associated with diesel exhaust particles) elicits chronic oxidative stress, bronchial hyperreactivity and allergic inflammation. Several epidemiological studies suggest that there is an association between the density of automobile traffic and the prevalence of respiratory symptoms, especially asthma and allergic rhinitis. Exposure to automobile traffic-related pollutants during early infancy may accelerate or even provoke, among genetically susceptible subjects, bronchial inflammatory processes which could contribute to the increase in the incidence of asthma in industrialized countries.     

Lymphocytes T et allergie alimentaire

The pathogenesis of food allergy was, in the past, focused on atopy, IgE and auxiliary lymphocytes responsible for class switching. Nevertheless, some allergic reactions induced by foods do not involve IgE. Mechanisms of breaking tolerance and cell mechanisms at the level of the gut mucosa are now better understood. This analysis of the involvement of lymphocytes in food allergy will begin with comments on presentation of antigens in Peyer's patches, followed by comments on a recognition mechanism involving surface receptors and regulation by chemokines. In association with intestinal immunity, regulatory T cells have a central role in the induction of immunization or tolerance to foods.