An update on molecular cat allergens: Fel d 1 and what else? Chapter 1: Fel d 1, the major cat allergen

Background

Cats are the major source of indoor inhalant allergens after house dust mites. The global incidence of cat allergies is rising sharply, posing a major public health problem. Ten cat allergens have been identified. The major allergen responsible for symptoms is Fel d 1, a secretoglobin and not a lipocalin, making the cat a special case among mammals.

Main body

Given its clinical predominance, it is essential to have a good knowledge of this allergenic fraction, including its basic structure, to understand the new exciting diagnostic and therapeutic applications currently in development. The recent arrival of the component-resolved diagnosis, which uses molecular allergens, represents a unique opportunity to improve our understanding of the disease. Recombinant Fel d 1 is now available for in vitro diagnosis by the anti-Fel d 1 specific IgE assay. The first part of the review will seek to describe the recent advances related to Fel d 1 in terms of positive diagnosis and assessment of disease severity. In daily practice, anti-Fel d 1 IgE tend to replace those directed against the overall extract but is this attitude justified? We will look at the most recent arguments to try to answer this question. In parallel, a second revolution is taking place thanks to molecular engineering, which has allowed the development of various forms of recombinant Fel d 1 and which seeks to modify the immunomodulatory properties of the molecule and thus the clinical history of the disease via various modalities of anti-Fel d 1-specific immunotherapy. We will endeavor to give a clear and practical overview of all these trends.

An update on molecular cat allergens: Fel d 1 and what else? Chapter 1: Fel d 1, the major cat allergen

Background

Cats are the major source of indoor inhalant allergens after house dust mites. The global incidence of cat allergies is rising sharply, posing a major public health problem. Ten cat allergens have been identified. The major allergen responsible for symptoms is Fel d 1, a secretoglobin and not a lipocalin, making the cat a special case among mammals.

Main body

Given its clinical predominance, it is essential to have a good knowledge of this allergenic fraction, including its basic structure, to understand the new exciting diagnostic and therapeutic applications currently in development. The recent arrival of the component-resolved diagnosis, which uses molecular allergens, represents a unique opportunity to improve our understanding of the disease. Recombinant Fel d 1 is now available for in vitro diagnosis by the anti-Fel d 1 specific IgE assay. The first part of the review will seek to describe the recent advances related to Fel d 1 in terms of positive diagnosis and assessment of disease severity. In daily practice, anti-Fel d 1 IgE tend to replace those directed against the overall extract but is this attitude justified? We will look at the most recent arguments to try to answer this question. In parallel, a second revolution is taking place thanks to molecular engineering, which has allowed the development of various forms of recombinant Fel d 1 and which seeks to modify the immunomodulatory properties of the molecule and thus the clinical history of the disease via various modalities of anti-Fel d 1-specific immunotherapy. We will endeavor to give a clear and practical overview of all these trends.

Conjunctival allergen provocation test : guidelines for daily practice

Conjunctival allergen provocation test (CAPT) reproduces the events occurring by instilling an allergen on the ocular surface. This paper is the compilation of a task force focussed on practical aspects of this technique based on the analysis of 131 papers. Main mechanisms involved are reviewed. Indications are diagnosing the allergen(s)-triggering symptoms in IgE-mediated ocular allergy in seasonal, acute or perennial forms of allergic conjunctivitis, especially when the relevance of the allergen is not obvious or in polysensitized patients. Contraindications are limited to ongoing systemic severe pathology, asthma and eye diseases. CAPT should be delayed if receiving systemic steroids or antihistamines. Local treatment should be interrupted according to the half-life of each drug. Prerequisites are as follows: obtaining informed consent; evidencing of an allergen by skin prick tests and/or serum-specific IgE dosages; being able to deal with an unlikely event such as acute asthma exacerbation, urticaria or anaphylaxis, or an exacerbation of allergic conjunctivitis. Allergen extracts should be diluted locally prior to administration. Positive criteria are based on itching or quoted according to a composite score. An alternative scoring is based on itching. CAPT remains underused in daily practice, although it is a safe and simple procedure which can provide valuable clinical information.

Oral food challenge in children: an expert review

Oral food challenges are indicated for the diagnosis of food allergy and the double-blind, placebo-controlled oral food challenge is considered the gold standard diagnostic method in children with suspected food allergy. This practice parameter for oral food challenges in children was prepared by a workgroup at the request of the French Society for Allergology and Clinical Immunology (SFAIC) and the French Paediatric Society for Allergology and Pulmonology (SP2A). We aimed to develop practical guidelines for oral food challenges in children for the diagnosis of suspected food allergy or the evaluation of food tolerance. We also considered the safety measures to be implemented during testing and management of the potentially serious allergic reactions that may arise during the test. The strength of the recommendations was established, using the GRADE evidence-based approach. We considered four issues: (1) the selection of children for oral food challenges (indications and contraindications); (2) the procedure used (material, where the test should be carried out, technique and management of reactions); (3) interpretation of the test and (4) consequences of the test.

Le test de provocation conjonctival : recommandations pratiques pour le diagnostic des conjonctivites allergiques

The diagnosis of ocular allergy, which has become a real public health problem occurring in 25% of the general population and continues to rise, requires allergic testing. Skin and blood tests combined with interviewing the patient demonstrate sensitivity to one or more antigens. However, while allergic testing and interviews generally reveal the cause of the symptoms, only the conjunctival provocation test (CPT) provides clear evidence of a functional relation between the conjunctival pathology and exposure to the antigen. Since there is still no validated consensus regarding the criteria for positivity of the CPT in routine practice, the working group attempted to establish the major guidelines for conducting the test, to standardize approaches and pinpoint areas of uncertainty. The group established a consensus regarding the conditions for using the test (patient selection, allergens to be tested, usable concentrations, the test protocol, the signs and symptoms to be assessed, interpretation of results, follow-up) and identified two distinct patient groups (outpatients and hospitalized patients) in whom test-taking conditions are different. The outpatient group includes patients suffering from benign forms of conjunctivitis (acute, seasonal, or chronic) and those sensitive to the usual allergens (mainly domestic and airborne). In these cases, the test is given in a medical setting with an allergologist or an ophthalmologist who instills the drops relatively rapidly. The criterion for positivity is the extent of the pruritus. On the other hand, in the hospital population, which is composed of patients suffering from vernal conjunctivitis, the attempt to establish the triggering factor requires a more elaborate protocol carried out in an ophthalmologic setting and based on the association of a range of clinical and biological factors. The deliberations of the working group should lead to the standardization of the CPT procedure for diagnostic purposes.

High magnesium concentration in vitro decreases human leukocyte activation

In view of experimental data suggesting that pharmacological magnesium (Mg) therapy could be expected to temper hypersensitivity, the aim of the present study was to assess the effect of in vitro high Mg concentration (8 mmol/l vs. 0.8 mmol/l) on human leukocyte activation. The first experiment in nine healthy volunteers was performed on total leukocyte suspension containing 82 +/- 4 per cent of neutrophils. The results demonstrate the inhibitory effect of high Mg concentration as shown by the significant reduction of superoxide anion production following phorbol myristate acetate (PMA) or formyl-methionyl-leucyl-phenylalanine (fMLP) activation. Moreover, neutrophils activated with fMLP showed an increased respiratory burst when incubated in low Mg concentration (0.2 mmol/l) as compared to normal Mg concentration (0.8 mmol/l). Similarly, high concentration of Mg resulted in a significant reduction in superoxide anion production by eosinophils in response to PMA in five eosinophilic patients. In patients showing Hymenoptera venom hypersensitivity, high Mg concentration resulted in a significant reduction of sulphidoleukotrienes production by leukocytes in response to venom allergen (six patients) or in response to zymosan activated particules (fourteen patients). Taken together, the results suggests that Mg acts via a non specific mechanism and appears to be non specific to a particular cell type. As Mg counteracts calcium in many physiological and pathological processes, it is reasonable to hypothesise that extracellular Mg can diminish leukocyte activation by its calcium antagonism.

Atopy parameters in asthmatic infants

We evaluated various atopy parameters in 44 asthmatic infants aged 1-3 years: nonspecific parameters (total IgE and eosinophilia), and specific parameters relative to 21 allergens (specific IgE and skin tests), together with tests of leukotriene release by blood leukocytes (cellular allergen stimulation test; CAST) in the presence of a mixture of 21 allergens. Thus far 17 infants have displayed no sign of atopy, but 27 met at least one criterion. Eight met nonspecific criteria, and the others single or multiple criteria. Of the 21 allergens, 20 gave rise to at least one sensitization in this population. The specific IgE was more frequently positive than the skin tests. Dissociations between the two types of specific tests were practically systematic. Different phenotypes based on the chosen parameters were individualized, demonstrating heterogeneity in the expression of atopy in these young infants. The polyvalent CAST was positive only when other criteria of atopy were also positive (specific IgE and/or skin tests), and the range of intensity of the responses obtained supports reactivity rather than sensitization.

[Vernal keratoconjunctivitis in the child. Clinical and complementary study apropos of 22 cases]

PURPOSE

Vernal kératoconjunctivitis was studied in a population of 22 children aged 3 to 14 years and followed up in an allergy and ophthalmology outpatient clinic. The role of allergy and the severity of inflammation where assessed by a systematic exploration, which combined a detailed allergy evaluation and blood and lacrimal sampling.

MATERIALS AND METHODS

Allergy criteria chosen and recorded in 9 cases are: an increase of total IgE over the higher limit for the age, a positive skin prick test to one allergen, a positive serum specific IgE dosage (> 0.35 IU/mL) of specific IgE. Conjunctival allergy was present in 6 of the 9 children with a positive allergenic provocation test, or with a high local production of total IgE and a lacrimal/serum eosinophilic cationic protein ratio greater than one.

RESULTS

Criteria used for supporting the IgE mediated hypersensitivity diagnosis are discussed: they have to be very strict to eliminate false positive results. Allergen involvement can only be evidenced by a specific provocation test. When evidenced as described, limbic or palpebral conjunctivitis had the same frequency. Lacrimal ICAM 1 levels seemed to be higher (p < 0.05) in the severe limbal forms (24.7 +/- 3 pg/mL) than in the palpebral ones (8.1 +/- 6.5 pg/mL). Interpretation of biological parameters evidencing conjunctival inflammation is more difficult.

CONCLUSION

Allergic involvement in child vernal keratoconjunctivitis can only be assessed through a detailed evaluation, leading to a specialised ophthalmic and allergic management. A specific treatment can then be established, based on allergen eviction and possibly on specific immunotherapy (5 cases). H1 antihistamin treatments are dedicated only to children with a positive allergic evaluation.

[Comparison of specific IgE levels versus various milk proteins in 76 eczematous children]

Among 76 eczematous children, we realized a RAST test for whole milk and milk specific proteins: lactalbumin, lactoglobulin and casein. One of these RAST tests, at least, was positive for 27 children. Whole milk RAST test is the most frequently positive (77%) but some non specific reactions seem to interfere: only three children are clinically milk sensitive. Among specific proteins, lactalbumin is more frequently positive (59%) than lactoglobulin (51%) and casein (18%). Eczematous children with positive milk RAST tests, if compared to other eczematous children, have currently more mite allergies and positive egg RAST tests. They have a tendency (non significative) to be more frequently breast fed. The positivity of milk RAST tests seems to belong to a polysensitization and infrequently concerns a clinical allergy.