Immunology - Hypersensitivity Flashcards
What is a hypersensitivity reaction?
Excessive immune responses that cause damage
What are the types of antigen that can be reacted to in hypersensitivity reactions?
Infectious agents
Environmental substances
Self antigens
Type I hypersensitivity
Immediate
IgE antibody
Th2 cells
Type IV hypersensitivity
Delayed hypersensitivity
T cell mediated
CD4+, CD8+ T cells
How is type I hypersensitivity mediated?
through degranulation of mast cells and eosinophils
Effects felt within minutes of exposure
What are allergens?
Antigens that trigger allergic reactions?
Degranulating cells
Release of mediators that cause allergic symptoms
Where are mast cells found?
Reside in many tissues
When do mast cells initiate allergic symptoms?
After allergen and IgE interact
Clinical syndromes of allergy
Anaphylaxis Asthma Rhinitis Urticaria Angioedema Atopic eczema
Symptoms of anaphylaxis
Low blood pressure
Angioedema
Airway obstruction
Pathophysiology of anaphylaxis
Mast cells produce prostaglandins and leukotrienes through the cyclooxygenase and lipoxygenase pathways
Results in vasodilation and increased vascular permeability
Shift of fluids from the vascular to the extra-vascular space resulting in a fall in vascular tone
Severe drop in blood pressure
IN the skin, mast cells release histamine further contributing to welling and fluid shift
Treatment of type I hypersensitivity
β2-adrenergic agonists (asthma) Epinephrine (lifesaving in anaphylaxis) Antihistamines (for skin, nose and mucus membrane affected allergies) Specific receptor antagonists Corticosteroids
What mediates type II hypersensitivity?
Antibodies - IgG or IgM reacting with the antigen present on the surface of cells
What effect does type II hypersensitivity have on cells?
Opsonisation of target cells
Immune mediated haemolysis
What type of hypersensitivity reaction can be caused by transfusion reactions?
Type II
Which antibody is responsible for type III hypersensitivity?
IgG
What is type III hypersensitivity?
Immune complex disease
Immune complex disease in the kidney
Nephrotic syndrome with gradual development of renal failure
Nephritis with rapid onset renal failure
How does type III hypersensitivity cause damage?
Immune complexes of antigen and antibody form and cause damage at the site of production or circulate and cause damage elsewhere
When are delayed hypersensitivity reactions initiated?
When tissue macrophages recognize danger signals and initiate an inflammatory response
Which cells loaded with antigen migrate to local lymph nodes, where they present antigen to T cells?
Dendritic cells
Which factor secreted by both macrophages and T cells stimulates much of the damage in delayed hypersensitivity?
Tumour necrosis factor
Treatment of delayed hypersensitivity
Prevention through avoiding antigens
Anti-inflammatory drugs
Immunosuppressive drugs
