Hypersensitivity Clinical Correlations Flashcards
Hypersensitivity reactions
Excessive, undesirable reaction produced by the normal immune system
- exaggerated and harmful response
- mild to life threatening
Sensitizaiton
Initial exposure to an antigen
- subsequent exposure to the same antigen results in hypersensitivity
Type 1
Immediate!
- minor symptoms to death
- present 15-30 min after antigen exposure
Type 1 - phase 1
Sensitization
- antigens encountered at mucosal and cutaneous surfaces
- IgE production to inital encounter
- asymptomatic
Type 1 - phase 1 example
DC within the bronchial epithelium encounters an inhaled antigen --> DC travels to lymph node to signal Th2 --> IL-4, 13 induces a humoral response --> B cells are directed to a class switch to IgE production --> IgE binds to tissue mast cells, where they reside at mucosal/cutaneous surfaces at the original site of encounter = sensitization
Type 1 - phase 1 summary
- mediated by IgE
- primary cellular component is the mast cell
Type 1 - phase 2
Re-exposure
- exposure to the same allergen = cross linking (occurs when antigen is bound by 2 or more IgE)
- initiates signal pathway in mast cells and triggers degranulation
Mast cell degranulation
Release of cytokines (IL-4,5,6 and inflammatory mediators)
- results in pruritus, bronchoconstriction, and vasodilation
Type 1 active substances
- histamine!
- heparin
- leukotrienes
- prostaglandin D2
- platelet activating factor
- eosinophil chemotactic factor
Clinical consequence of mast cell degranulation
Immediate hypersensitivity (occurs within 15-20 min)
- vasodilation/vascular permeability = tissue edema
- bronchoconstriction (smooth muscle contraction)
- interaction with local nerves = pruritis
- platelet aggregation
Type 1 - late phase
Occurs 4-24 hrs after antigen exposure
- recruitment of eosinophils and macrophages into the tissue
Presence of ______ is the hallmark of type 1 hypersensitivity
Eosinophils!
Majority of type 1 reactions are ______
Localized
- skin: dermatitis
- respiratory: asthma, allergic rhinitis
- intestinal tract: food allergy
Type 1 - systemic reactions
Often involve drugs or insect stings
- causes anaphylactic reaction
Anaphylactic reaction signs
- bronchoconstriction and dyspnea
- hypotension
- tachycardia
- vomiting/diarrhea
- dizziness
Anaphylactic reaction treatment
- epinephrine
- fluids
- oxygen
- antihistamines
- steroids
- supportive care
Feline Asthma
Lower airway disease, limiting airflow due to reduced airway diameter
- airway inflammation
- accumulating airway mucus
- airway smooth muscle contraction
What 2 cells play an important role in feline asthma?
Interactions between T cells and eosinophils
Feline asthma treatment
Need to address inflammation and bronchoconstriction
- steroids and bronchodilators
Adverse vaccine reactions
Due to IgE mediated degranulation of mast cells located in the skin = histamine and leukotriene release to deeper skin layers
- causes angioedema, urticaria, and pruritis
Type 2 hypersensitivity
Aka cytotoxic or antibody mediated hypersensitivity
- affects variety of organs
- involves destruction of a target cell and the sensitization is to an antigen displayed on the surface of that target cell
Type 2 - antibody production
Produced to endogenous antigens or exogenous substances (haptens) which attach to cell membranes and cause subsequent tissue damage
- mediated by IgG or IgM (with or without complement involvement)
Type 2 - pathophysiology
Rapid destruction occurs via activation of classical complement pathway and formation of MAC
- takes longer when target cell destruction involves NK cell destruction or macrophage phagocytosis of the antibody dependent cell mediated pathway
Type 2 - examples
- IMHA
- transfusion reactions
- myasthenia gravis
- pemphigus
