Pollen Allergy - Diagnosis
Allergy to pollen
Pollinosis is an allergic disease caused by the inhalation of antigenic pollen, transported by air currents even at considerable distances from the places where they are produced. The most common symptoms are rhinitis, conjunctivitis and sometimes bronchial asthma. Pollen allergy has a typically seasonal course.
Identification of allergens
Pollen allergy includes a complex of clinical manifestations (asthma, rhinitis, conjunctivitis) supported by immunological hyper reactions and usually associated with inflammatory processes.
The analysis of the allergenic extracts derived from pollens of different species has allowed the identification of numerous allergens, whose characterization was later exploited in allergy diagnostics.
Pollen analysis has shown that antigens are typically low molecular weight proteins or glycoproteins. At first, it was believed that the allergenic epitopes were exposed above all to esin (cell membrane). Subsequently, it was ascertained that most of the allergens were contained within the granule and that, once in contact with a damp surface, it came out very quickly from the pores of the granule. Further electron microscopic studies have shown typical selective locations for different pollen allergens (example: exine, protoplast, intin, etc.). Some allergens are also located in the sporophyte (non-pollen part of the plant), among these we remember the profilin (structural protein and fundamental component of the exoskeleton), present in almost all the plant elements and, at different concentrations, in almost all pollen . For this reason it has been called pan-allergen and is responsible for some cross-reactions in allergic oral syndromes.
To confirm a suspicion of allergy to one or more pollen, a series of diagnostic tests must be performed:
- History. The first diagnostic approach to identify pollen allergy is the specialist allergy examination, during which the doctor can assess any symptoms present with an objective examination . Furthermore, the allergist specialist performs the anamnesis, that is the accurate and careful investigation of the patient's clinical history, which evaluates:
- The incidence in the family of allergic disorders;
- The symptoms of the allergic reaction;
- The way in which allergic reactions occur: when the first attack occurred, how long it lasted, the frequency with which the episodes are repeated, the seasonality of the symptoms and their trend over time;
- Lifestyle, work activity, tendency to suffer from inflammatory respiratory disorders and contracted diseases.
- Skin tests.
- Prick test. To identify the pollen responsible, a drop of pollen allergen extract is placed in contact with the skin and the area is then punctured with a special needle. If the person is allergic to pollens, a characteristic wheal is observed, surrounded by an area of redness. The specialist also evaluates the intensity of the reaction, which is then expressed quantitatively with a series of + signs: it goes from +, to indicate a mild reaction, to ++++, to indicate a very intense reaction. The Prick test is reliable, easily executable and completely painless. The examination can give staggered results if it is performed in the presence of skin diseases or when the person is following a treatment with antihistamines or cortisone drugs.
- Intradermal reaction : it is a Prick test variant, more sensitive but less specific. In this case, the allergen is not applied, but injected into the dermis, using a small syringe. The result is evaluated in the following 24-72 hours: if a reddened swelling appears in the injection site, which may be accompanied by itching, the person is allergic.
- Dosage of specific IgE (PRIST and RAST).
- The PRIST test (or Test of Radio-Immuno-Absorption on Paper) doses the total IgE: a venous blood sample is taken to dose the total IgE (a type of antibody) present in the sample, which in case of allergy are increased. The PRIST test is an important test, but it does not have an absolute diagnostic value: total IgE can indeed increase even in non-allergic persons, for example due to infectious diseases.
- The RAST test (Radio Allergy-Absorption Test) doses the specific IgE: the level of specific IgE produced towards a particular substance is measured in venous blood. The blood collected is put in contact with an allergen: if the blood contains the specific IgE towards the allergen, a bond is established. In a second moment, the blood is put in contact with radioactive anti-IgE antibodies: the higher the radioactivity that is detected, the greater the amount of specific IgE present in the blood.
Blood tests confirm the diagnosis of pollen allergy in association with skin tests.
Molecular diagnostics of pollen allergy
The ISAC test (Immuno Solid-phase Allergen Chip) is a multi-analyte analysis of the specific IgE titre, which allows to dose more than 100 molecules with a single blood sample (includes allergens from eg animal hair, pollen, mites, food or latex). This multiple test (it is a microarray) allows the simultaneous evaluation of specific IgE for single purified, natural or recombinant allergenic molecules (they mimic the allergic source with extreme sensitivity). Furthermore, the ISAC test also helps to detect cross-reactivity allergies.