Type I Hypersensitivity Reactions (Type I HSR)
What are the features of HSR in general?
1. over-reaction of the immune system in the absence of danger
2. Undesired reactions produced by the normal immune system
3. Under some circumstances, immunity, rather than providing protection, produces ...
1. over-reaction of the immune system in the absence of danger
2. Undesired reactions produced by the normal immune system
3. Under some circumstances, immunity, rather than providing protection, produces damaging,
discomfort-inducing and sometimes fatal results
what are the 4 types of hypersensitivity reaction based on?
1. immunological mechanism
2. time frame
What are the immune reactant, antigen, effector mechanism, example of HSR associated with Type I
HSR?
What is the definition of type I hypersensitivity reaction?
AKA: IgE mediated HSR, immediate HSR, anaphylaxis, allergy, atopy
- an undesirable immune reaction to harmless environmental substances; non protective
what is the severity of type I HSR?
ranges from simple irritation such as running nose, breathing difficulty or even death due to
asphyxiation.
what does chronic manifestation of Type I HSR lead to?
accumulation of Th2 and eosinophils- thus it is described as cell-mediated- one form of the type IV
reactions
what is an allergen?
harmless environmental substance that induces an allergic response
what is anaphylaxis?
a rapidly progressing, could-be life-threatening allergic reaction
what is atopy?
familial predisposition of certain individuals to react against common foreign substances in an
uncommonly excessive way
when does anaphylaxis occur?
, when a patient with immediate hypersensitivity is exposed to the relevant allergen entering the
circulation rapidly like in bee sting, injection of penicillin, ingestion of allergen. Response can be local
initially or can become generalized leading to generalized urticaria and/or bronchospasm
What are the components and mechanisms of Type I HSR?
1. Allergen: Harmless environmental substance- T dependent antigen
2. Immune Reactants: Antibody IgE
3. Effector Cells: Mast Cells, Basophils, activated Eosinophils (in chronic allergy)
- indirect: APC, Th2 CD4, B cells
4. Mechanism: activation and degranulation of the effector cells resulting in the release of biologically
active compounds- resulting in tissue damage or interference with normal function
what are the characteristics of common allergens?
1. LMW proteins (10-40 kD)
2. diffusible, soluble, stable
3. must contain peptides that bind to hot MHC class II molecules
4. many have been cloned and expressed
5. most are enzymes
what inhaled materials are examples of common allergens?
1. plant pollens
2. dander of domesticated animals
3. mold spores
4. feces of very small animals like dust mites
what injected materials are examples of common allergens?
what ingested materials are examples of common allergens?
1. food
2. PO drugs
what HSR are contacted materials associated with ?
type IV HSR
what are contacted materials that are examples of common allergens?
1. plant leaves
2. industrial products made from plants
3. synthetic chemicals in industrial products
4. metals
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