Manifestations of Type I Reaction
المؤلف:
APURBA S. SASTRY , SANDHYA BHAT
المصدر:
Essentials Of Medical Microbiology 2021
الجزء والصفحة:
3rd edition , p195-196
2025-09-21
417
Manifestations are grouped into immediate and late.
Immediate Manifestations
Systemic anaphylaxis It is an acute medical emergency condition, characterized by severe dyspnea, hypotension, and vascular collapse leading to death at times.
- It occurs within minutes of exposure to allergen and unless treated promptly, may lead to fatality
- Allergens: Wide range of allergens have been shown to trigger anaphylaxis in susceptible humans, including the venom (from bee, wasp, and ant stings); drugs (such as penicillin, insulin), antitoxins, seafood and nuts
- Epinephrine (adrenalin) is the drug of choice for systemic anaphylactic reactions.
Localized anaphylaxis (atopy)
Here, the reaction is limited to a specific target tissue or organ, mostly the epithelial surfaces at the entry sites of allergen. These allergies afflict more than 20% of people. They almost always run in families (i.e. inherited) and are collectively called atopy. Examples include:
- Allergic rhinitis (or hay fever): It is the most common atopic disorder, affecting 10% of the population. This results from exposure to airborne allergens with the conjunctiva and nasal mucosa leading to appearance of various symptoms such as ↑watery secretions of the conjunctiva, nasal mucosa, and upper respiratory tract, as well as sneezing and coughing
- Asthma: It is the second most common atopic manifestation. It differs from hay fever in involvement of lower respiratory mucosa, resulting in contraction of the bronchial smooth muscles and airway edema, ↑mucus secretion; all together leading to bronchoconstriction and dyspnea. The stimulus may or may not be an allergen. Accordingly, asthma can be classified as:
- Allergic asthma: It is induced by air-borne or blood borne allergens, such as pollens, dust, fumes, insect products, or viral antigens
- Intrinsic asthma: It is independent of allergen stimulation; induced by exercise or cold.
- Food allergy: Various foods also can induce localized anaphylaxis in atopic individuals. The food allergens (e.g. nuts, egg, seafood, etc.) can either stimulate the mast cells lining gut mucosa to cause GI symptoms such as diarrhea and vomiting or may be carried in the blood stream to distant sites (e.g. when the allergen is deposited on skin, causes local wheal and flare like reaction called atopic urticaria (or hives)
- Atopic dermatitis (allergic eczema): It is an inflammatory disease of skin that is frequently associated with young children with family history of atopy. It often develops during infancy, manifested as erythematous skin eruptions which are filled with pus. The skin lesions have an increased response of TH 2 cells and eosinophils
- Drug allergy: Various drugs (such as penicillin, sulfonamides, etc.) may produce type I hyper-sensitivity responses which may be either local reactions or even sometimes produce systemic anaphylaxis.
Late Manifestations
The immediate phase of type 1 reaction is followed, 4–6 hours later, by an inflammatory response. This phase lasts for 1–2 days and leads to tissue damage.
- Mediators: They are released in acute phase along with cytokines (IL-3, IL-5, IL-8), ECF and NCF; induce recruitment of various inflammatory cells, such as neutrophils, eosinophils, macrophages, and lymphocytes, etc. Among the infiltrates, eosinophils and neutrophils predominate; each accounting for 30% of the total inflammatory cells influx
- Eosinophil influx: It is favored by ECF (eosinophil chemotactic factor), IL-5 and GM-CSF. Eosinophils express Fc receptors for IgG and IgE and thus bind directly to antibody-coated allergens. This in turn causes release of toxic granules from eosinophils which contribute to the chronic inflammation of the bronchial mucosa that characterizes persistent asthma
- Neutrophil infiltration: It is induced by NCF (neutrophil chemotactic factor), and other cytokines such as IL-8. Activated neutrophils release various mediators which further potentiate inflammatory tissue damage and thickening of basement membrane.
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