Hypersensitivity Flashcards
What is type I hypersensitivity
Allergy
What is the definition of hypersensitivity
A state of altered reactivity in which the body reacts with an exaggerated immune response to a foreign agent
What is an allergen
An antigen that causes an allergic reaction
What types of reaction is a type 1 hypersensitivity reaction
IgE mediated reaction
What immune cells are involved in type 1 hypersensitivity reaction
Mast cells
Basophils
Give some examples of type 1 hypersensitivity reaction
Atopy
Anaphalaxis
What type of reaction is type II hypersensitivity
Cytotoxic responses
What immune cells are involved in type II
NK cells
Complement
T cells
What is an example of type II
Haemolytic anemia
What reaction is type III hypersensitivity
Immune complex responses
What immune cells are involved in type III
Complement
Neutrophils
What is an example of type III
Serum sickness
What type of reaction is type IV
Cell mediated response
What immune cells are involved in type IV
T cells
Macrophages
Give examples of type IV
Sracoidosis
TB
Crohn’s disease
What is anaphylaxis
Actuate serious allergic response
What are allergens
Can be proteins, have ability to elicit an immune response
What are happens
Any small molecule that can be recognised by a specific antibody but cannot elicit an immune response
What are the main roles of mast cells and basophils
- immune cell recruiter
- neurotransmitter
- vasodilator
- endothelial constrictor
- bronchoconstrictor
Give some cutaneous atrophy examples of type I hypersensitivity reactions
Localized
- allergic rhinitis (hay fever)
- atopic dermatitis (allergic eczema)
- asthma (Lower respiratory tract)
What is systemic anaphylaxis
Anaphylactic shock throughout the whole body
Give some examples of allergy tests
- skin prick and patch test
- blood test - measures IgE in the blood
- food challenge
Name some drugs that can be taken for allergies
- anti histamines
- epinephrine
- hydrocortisone
- cromoglycate
Function of antihistamines
Compete with histamine receptors
Function of epinephrine in anaphylactic shock
Best immediate treatment, reverses effect of granules (vasoconstriction, relaxes muscles)
Name immunological treatment for allergies
- hypo or de sensitisation
- IgE or IgG production
What is the mechanism for epinephrine
— stimulation of adrenoreceptors
- improves blood pressure
- reverses peripheral vasoconstriction
- causes bronchodilation
- reduces inflammatory mediator response
What does type II arise from
Antigen-antibody complex arising
IgG and IgM binding to antigenic cell
Type II hypersensitivity is lysed by
- membrane attack complex formation (complement)
- antibody dependent cell mediated cytotoxicity (natural killer cells or CD8 + T cells)
- common example - transfusion reactions/autoimmune haemolytic anaemia
Describe what happens when mismatched blood type is transfused in an individual
The body attacks the red blood cells, immune cells recognise the antibodies on the blood cells as a foreign invader and attack them
Describe type III hypersensitivity
- involves reactions against soluble antigens circulating in serum
- antibody - antigen immune complexes are deposited in organs which leads to - complement activation, neutrophil recruitment, inflammation mediated damage
What are some examples of type III hypersensitivity
- Arthus reaction
- serum sickness
- oral erythema multiforme (EM)
What happens during rheumatoid arthritis
Immune complexes deposited in tissues activate a complement which attracts neutrophils to the site
What are some examples of type III hypersensitivity reactions
- arthus reaction (localised hypersensitivity reaction)
- antibody - antigen complexes are localised
- can arise from injected particles (eg booster vaccines) or inhaled or injected antigens
Serum sickness is an example of a …. Reaction
Arthus reaction
Describe oral erythema multiforme (EM)
- characterised y crusty blistering of oral mucosa
- caused by deposition of immune complexes (IgM bound immune complexes) in the microvasculature of the oral mucous membrane
- can be acute inflammatory response to viral infections eg HSV
- can be caused by hypersensitivity drugs eg.Trimethroprimsulfamethoxazole which treats UTI’s
Describe type IV hypersensitivity
- T cell mediated hypersensitivity (no antibodies)
- sometimes called delayed hypersensitivity as it takes time to recruit T cells
- localized T cell reaction at site of antigen exposure (eg contract dematitis)
- involves both CD8+ T cells (direct damage of cells - cytotoxicity)
What are some examples of type IV hypersensitivity
- contract dermatitis
- tissue graft rejection
- response to Intracellular pathogens
- orofacial granuloamatus
