Transcript Hypersensitivity reactions

Hypersensitivity refers to an inappropriate or undesirable immune
response ( damaging immunological reactions to extrinsic antigens)
Hypersensitivity reactions require a pre-sensitized (immune) state of
the host, genetically susceptible individual called atopic individuals.
Immediate hypersensitivity or allergy due to overproduction of
IgE antibody on mast cells or basophiles
The initial response, characterized by vasodilatation, vascular
leakage, & smooth muscle spasm,
Rapid reaction : the reaction usually takes 5 - 10 minutes from
the time of exposure to the antigen, although sometimes it may
have a delayed onset (10 - 12 hours).
Immediate hypersensitivity is mediated by IgE.
The primary cellular component in this hypersensitivity is the
mast cell or basophil.
Allergy disease are common about 15-20%of the population
Prick test is used to detect type I “ wheal and flare”
Diagnostic tests for immediate hypersensitivity include skin (prick and
intradermal) tests
Allergic asthma
Allergic dermatitis
Anaphylaxis case
Bee sting
Asthma is defined as increased irritability of the bronchial tree with paroxysmal
narrowing of the airways.
which may reverse spontanously or after treatment. Rarely, symptoms persist for
days, leading to respiratory failure and even death.
Features
-Increased irritability of bronchi causes bronchospasm
-Paroxysmal attaches
-Over distended lungs
-Mucus plugs in bronchi
-Enlarged bronchial mucous glands
Classification
There are five major clinical categories of asthma
► atopic
► non-atopic
► aspirin-induced
► occupational
► allergic bronchopulmonary aspergillosis.
Acute attacks are characterized by
- a feeling of tightness in the chest
- difficulty in breathing
- particularly in exhaling which accompanied by loud
wheezing and coughing
Pathogenesis of allergic asthma. Inhalation of allergen causes degranulation of mast
cells bearing specific IgE molecules. Release of vasoactive substances from the
cells causes bronchial constriction, oedema and mucus hypersecretion.
SRS-A = slow –reacting substance of anaphlylaxis
ECF-A = eosinophil chemotactic factor of anaphylaxis
PAF = platelet activation factor
Tracheal mucus plug in death from status asthmaticus.
This cast of the bronchial tree is formed of inspissated mucus and was coughed
up by a patient during an asthmatic attack. The outpouring of mucus from
hypertrophied bronchial submucosal glands, the bronchoconstriction, and
dehydration all contribute to the formation of mucus plugs that can block
airways in asthmatic patients
Histological section of lung at autoopsy showing occlusion of airways by oedma and
mucus plugs accompanied by alveolar distension with entrapped gas.
The lumen (top) of this small bronchus containing exudate in which there are many cells mostly
leukocytes. The epithelial lining consist of large mucus secreting cells. The epithelial basement
membrane is thickened and the smooth muscle of the wall is hypertrophied ,eosinophil leukocytes
and lymphocytes are also present in the wall.