Facteurs de risque de l’allergie alimentaire sévère

Asthma is the main risk factor for severe, potentially fatal food allergy reactions. Peanut and tree nuts are the main foods involved in these reactions. Consequently, any asthmatic individual with a food allergy must be controlled perfectly by daily treatment. Other risk factors for severe allergic reactions are parallel medications (especially aspirin, beta-blockers and angiotensin enzyme inhibitors), physical effort, food consumption outside the home, mastocytosis, hidden allergens, and a combination of such associated factors. Better patient education and, in addition, risk prevention, particularly away from home, in restaurants and at school, should reduce the frequency of severe food allergic reactions. Collection of data concerning food allergies will allow better identification of the individuals at risk and development of targeted preventive measures.     

Intérêt des allergènes recombinants pour la prise en charge de patients allergiques : cas cliniques

Allergen extracts used in diagnosis by clinicians are manufactured from crude source materials. These extracts contain a number of allergenic proteins and their composition can vary. The employment of molecular biological methods in the field of allergy has led to the production of recombinant allergens from a variety of sources. Their use has allowed us to improve our understanding of allergenic proteins, to define families of allergens, to explain allergenic cross-reactions, and to show that pollen sensitivity profiles vary as a function of the geographic region in which individuals live. As a result, in the 21st century reasoning on the molecular scale should be included in patient management. In 2005, the clinician has at his disposal the level of specific IgE with 27 recombinant allergens from 7 different allergenic sources. The use of these materials can, in certain cases, allow us to have a more precise diagnosis and to orient the therapeutic decision more accurately. Three observations made in our consultation service are described to illustrate the contribution of these new diagnostic methods.     

Devenir des allergènes dans le tube digestif

Mechanisms by which food allergens sensitize atopic individuals still remain unclear. However, most of them are thought to sensitize via the gastrointestinal tract. Due to the very acidic conditions in the stomach and the intense proteolysis occurring in the stomach and in the intestine, only small amounts of intact or immunologically active proteins are taken up by the gut mucosa. This suggested that food allergens are, at least partially, resistant to gastro-duodenal digestion in order to be able to sensitize the mucosal immune system. As a result, several in vitro models have been developed to evaluate the stability of potential allergens to digestion. Indeed, resistance to digestion is part of the premarketing allergenicity assessment of newly expressed proteins in genetically modified crops. However, some food allergens are rapidly and extensively degraded during digestion, whereas some other food proteins that are resistant to digestion are not allergenic. It has been shown that degradation products, i.e. peptide fragments of various sizes, produced during the digestion of a protein may keep (part of) the allergenicity of the native protein. In addition, other factors may interact as to make a food protein an allergen, such as the structure and composition of the food matrix, technologic processing including cooking of the whole food that contains the allergens. Some studies also suggested that the biological property of a protein to be an allergen can influence its mode and route of transport across the intestinal epithelial barrier, which may have a profound impact on the immune responses thus generated. It is noteworthy that a pregastric absorption also occurs, i.e. in the oral cavity, which explains the occurrence of symptoms few minutes after ingestion of food allergens.     

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.     

Devenir des allergènes dans l’arbre respiratoire

The role of allergens as a trigger for bronchial symptoms has always appeared to be deeply linked to their ability to get into the respiratory tract. Interest in large diameter particles has focussed essentially on their capacity to reach the lower airways. The recent demonstration of the effect of aerosols of allergen-loaded pollen particles of a respirable size supports this hypothesis. Nevertheless, the exact site of allergen deposition leading to asthma symptoms is still not known. Studies carried out with allergen bronchial challenge tests using particles of different sizes have lead to a better understanding of the associated pathophysiological phenomena. Thus, the role of large-diameter particles could be more important than previously thought. Indeed, the results obtained provide support for the importance of these particles and their proximal deposition in the immediate bronchial response.     

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.     

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.     

Allergènes recombinants et immunothérapie

The development of new immunotherapy techniques using products produced by molecular biology requires that their efficacy be controlled by appropriate clinical trials. An outline of the principal molecules derived through fundamental research during the past few years will include recombinant allergens corresponding to natural allergens that are pertinent because of their high prevalence of sensitivity, hypoallergenic derivatives of recombinant allergens (polymers, fragments, molecules with mutations or amino acid deletions), hybrid molecules, T-cell epitopes, B-cell epitopes, and molecules conjugated with CpG or other co-stimulants. The biological activity of a large number of these molecules has been demonstrated in vivo. The selection of candidate molecules for immunotherapy will depend first of all on the results of preliminary open studies on a limited number of patients. Here, we report the results of five double blind immunotherapy studies, in which the control group received placebo, and in two studies another group was treated with natural extract. The most statistically significant clinical results were observed with unmodified recombinant allergens, without occurrence of severe systemic reactions. In these five studies, there was a significant increase in the level of specific IgG with the natural allergen and with the recombinant allergens. Decrease in skin test responses in the treated groups relative to the placebo group was significant in two of the three studies. Studies including a greater number of patients are now needed to meet the demands of regulatory requirements for clinical development of recombinant allergens.     

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.     

Les recombinants des panallergènes polliniques : application à l’interprétation des polysensibilisations

Multiple pollen sensitization is frequently encountered in patients who present with seasonal allergic respiratory symptoms. This regularly leads the allergist to question the significance of skin and laboratory test results because such results make it difficult to differentiate between cross-reactions and co-sensitization. Assays for specific IgE with recombinant panallergens, such as those in the profilin or polcalcin families, the results of which are now available in clinical practice, may lead to a better interpretation of such cases.     

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.     

Les allergènes de l’arachide et des fruits à coque

The foods contain several hundreds of proteins for which only a small number, called allergens, is responsible for allergic reactions. The edible tree nuts (almond, walnut, cashew, Brazil nut, macadamia nut, pecan, Nangai nut, pistachio, pine nut, chestnut and coconut) consist of approximately, 15% of proteins. The objective of this review is to present, from a biochemical point of view, the allergens of these nuts known at the present time and to discuss what this type of information can bring in the comprehension of the mechanisms of cross reaction.     

Mesure des allergènes de pollens d’arbre dans l’air (bouleau, olivier)

The information provided by pollen counts cannot be ignored by allergists and allergic individuals, but the divergence sometimes observed with clinical observations has led the réseau national de la surveillance aérobiologique (RNSA) to initiate the monitoring network of allergens by immunosampling (Monalisa) project. Moreover, some recent papers has shown the influence of pollution in the region and even of the year on the content in pollen allergens, particularly that of birch pollen. Thus, the goal of the Monalisa project was to set up a measuring system based on an immunological method that would result in validation of this new way of measuring airborne pollen counts. This European Life Environment project includes nine partners: Bertin Technologies (France), RNSA (France), NPARU (England), UCO (Spain), UTU (Finland), UAM (Poland), UEVORA (Portugal), AIA (Italy), and Meteoswiss (Switzerland). The results obtained during the 2006 season and then in the 2007 campaign, after modifications made in the sampler, were not very good. The principal results concern the measurement of birch and olive allergens, captured essentially in the prepollination period and sometimes in the postpollination period. Detection of these allergens may be due either to their presence on submicroscopic particles emitted independently of pollination, these allergens cross-reacting with birch and olive allergens. The difficulties encountered in this study lead us to say that pollen counts, phenological observations and clinical data are still the best way to assess the effects of airborne pollen.     

Les allergènes du grain de blé

Wheat is a major dietary cereal, which can cause respiratory, contact and food allergies. Wheat grain contains a large panel of proteins with very particular structures and functions. This review will consider diverse wheat grain proteins and summarize recent work on wheat grain allergens.