Allergy : An Overview Salwa Hassan Teama. Allergy. Allergy refers to certain diseases in which immune responses to environmental antigens cause tissue inflammation and organ dysfunction. Hypersensitivity and sensitivity are synonyms for allergy.
Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.
Allergic Reaction Its overreaction to a harmless substance(an allergen)
This harmless substance that is contacted through the skin,
inhaled into the lungs, swallowed, or injected.
Type I hypersensitivity is also known asimmediateoranaphylactichypersensitivity. The reaction may involve skin (urticaria and eczema), eyes (conjunctivitis), nasopharynx (rhinorrhea, rhinitis), bronchopulmonary tissues (asthma) and gastrointestinal tract (gastroenteritis). The reaction may cause a range of symptoms from minor to death. The reaction usually takes 15 - 30 minutes from the time of exposure to the antigen, although sometimes it may have a delayed onset (10 - 12 hours). Immediate hypersensitivity is mediated byIgE.
Type II hypersensitivity is also known as cytotoxic hypersensitivity and may affect a variety of organs and tissues. The antigens are normally endogenous, although exogenous chemicals (haptens)which can attach to cell membranes can also lead to type II hypersensitivity.
Type IV hypersensitivity is also known ascell mediatedordelayed type hypersensitivity.
e.g. Rhinitis, asthma and eczematous dermatitis occur in significant number of patients without atopic IgE mediated allergy.
e.g. Mast cells may be triggered by other stimuli such as exercise, emotional stress, chemicals.These reactions, mediated by agents without IgE-allergen interaction, are not hypersensitivity reactionsalthough they produce the same symptoms.
Histamine:This mediator acts on histamine 1 (H1) and histamine 2 (H2) receptors to cause: contraction of smooth muscles of the airway and GI tract, increased vasopermeability and vasodilation, nasal mucus production, airway mucus production, pruritus, cutaneous vasodilation, and gastric acid secretion.
Proteoglycans:Proteoglycans include heparin and chondroitin sulfate. The role is unknown; heparin seems to be important in storing the preformed proteases and may play a role in the production of alpha-tryptase.
Chemotactic factors:An eosinophilic chemotactic factor of anaphylaxis
causes eosinophil chemotaxis; an inflammatory factor of anaphylaxis
results in neutrophil chemotaxis. Eosinophils release major basic
protein and, together with the activity of neutrophils, cause significant
tissue damage in the later phases of allergic reactions.
Allergic Rhinitis:Most common clinical expression of atopic hypersenstivity . IgE mediated allergy localized in the nasal mucosa and conjunctiva. Pollens and fungal spores, dust and
animal danders usual atmospheric allergens.
Allergic asthma (IgE mediated allergy in bronchial mucosa)
Allergen exposure results in bronchoconstriction, and patients may report shortness of breath (e.g., difficulty getting air out), wheezing, cough, and/or chest tightness.
Long-term allergen exposure can cause chronic changes of increased difficulty breathing and chest tightness, and the patient may give a history of repeated rescue inhaler use or reduced peak flows.
Localized IgE reactions in the gut to an ingested food. Gastrointestinal loss of serum proteins and blood leading to edema and anemia. Rare in adult but more common and transient in children.
Particular attention should be given to:
Food Allergy may be defined as a complex of clinical syndromes (sick all over) resulting from the sensitization of the patient to one or more foods, in which symptoms manifest locally in the GI tract or in other remote organs.
Any symptom can be associated with food allergy or intolerance. By identifying and eliminating or treating food allergies, many of our insolvable chronic health problems can be improved or eradicated.
Some reactions are classically allergic(immediate reactions alone),or may reflectdelayed IgE-mediated mechanisms.
Immunologic response to a food protein.This overreaction can cause symptoms from the mild (hives) to the severe (anaphylactic shock) upon subsequent exposure to the substance. An actual food allergy, as opposed to simple intolerance due to the lack of digesting enzymes, is indicated by the production of antibodies to the food allergen, and by the release of histamines and other chemicals into the blood.
Respiratory(hay fever, asthma, bronchitis, recurring ear infections, sinus conditions, rhinitis, laryngitis, allergic sore throat, hoarseness);digestive (gastroenteritis, irritable bowel syndrome, celiac disease, inflammatory bowel disease, diarrhea, constipation, colic, malabsorption);cerebral(headaches, dizziness, sleep disorders, learning disorders, tension-fatigue syndrome, foggy thinking, irritability,depression);skin-related(dermatitis, eczema, angioedema, hives, rashes);or related toother body systems(arthritis, myalgia, urinary irritation, conjunctivitis, edema, hypoglycemia, diabetes, overweight, underweight, premenstrual syndrome, and fatigue.
Respiratory symptoms:Sneezing, runny nose , stuffy nose wheezing, watery eyes, persistent cough, bronchitis, itchy feeling in the mouth or throat.
Skin affection:Red, sandpaper-like facial rash, dry scaly, itchy skin (mostly on face), swelling in hands and feet, puffy eyelids, dark circles under eye, tongue soreness and cracks, sore throat.
Behavior changes:fatigue, migraine, headaches, hyperactivity, crying, irritability, anxiety, crankiness, sore muscles and joints.
GIT Symptoms:burn like rash around anus, vomiting, constipation , abdominal discomfort, mucous diarrhea, intestinal bleeding poor weight gain,bloating, gassiness, excessive spitting up.
The 6 most common food allergens are peanuts, shellfish, fish, eggs, milk, soy, and wheat. the most common food allergies present in children aremilk,eggs,andpeanuts
Certain foods can cross-react with latex allergens. These foods include banana, kiwi, chestnut, avocado, pineapple, passion fruit, apricot, and grape.
Many adverse reactions to foods do not involve IgE antibodies. They are often called food “sensitivities” or “intolerances.” The absence of IgE does not make them any less real; other immune mechanisms, such as IgG antibodies, immune complexes, or cell-mediated reactions are involved instead. These reactions can happen quickly or can be delayed for two to seventy-two hours or longer.
About 95% of IgG-mediated reactions are not fixed. Therefore, after several months of avoidance, problem foods can be reintroduced into the diet in moderate amounts without causing symptoms as long as they are not eaten too frequently.
IgE-mediated allergies are easily detected by standard blood or skin tests. The reactions happen rapidly, usually within a few minutes of exposure to inhaled substances or eating a food.
The cutaneous and intradermal allergy testing
The cutaneous test (prick test, puncture test epicutaneous test) is used routine diagnosis in atopic or anaphylactic diseases. A single drop of concentrated aqueous allergen extract placed on the skin which is then pricked lightly with a needle point at the center of the drop. After 20 minutes the reaction is graded and recorded.
Negative and positive control should be included.
Negative results should be repeated using the intradermal skin
test (intracutaneous test). Food skin tests have a higher false-positive rate than skin tests for aeroallergens, but negative food skin test results can be helpful in excluding IgE-mediated allergies.
Test For Drugs
Spirometry or pulmonary function testsoffer an objective means of assessing asthma.