Hypersensitivity 1 Flashcards
What are hypersensitive reactions?
Hypersensitive reactions = excessive immune responses that cause damage
What are examples of antigens involved in hypersensitive reactions?
- Infection
- Harmless environmental substances
- Self-antigens
What are the 4 different types of hypersensitivity?
- Type I (Immediate)
- Type II (cell-bound antigen)
- Type III (immune complex)
- Type IV (Delayed)
Describe the process of influenze causing hypersensitivity?
- Virus damaged epithelial cells in respiratory tract
- Sometimes triggers exaggerated immune response
- High levels of cytokine secretion (cytokine storm)
- Cytokines attract leukocytes to the lungs, triggering vascular changes that lead to hypotension and coagulation
- In severe influenza, inflammatory cytokines spill into systemic circulation causing effects in remote parts of body, such as brain
Describe the process of dust causing hypersensitivity?
- Able to enter lower extremities of respiratory tract which are rich in adaptive immune response cells
- Can mimic parasites and stimulate antibody response
- If dominant antibody is IgE may trigger immediate hypersentivity, which manifests as allergy symptoms such as asthma or rhinitis
- If dominant antibody is IgG may trigger a different kind of hypersensitivity, such as farmer’s lung
Describe the process of nickel causing hypersensitivity?
Sometimes smaller molecule diffuse into the skin and can act as haptens (small molecule irritants that bind to proteins and elicit immune response), triggering delayed hypersensitive reaction – example is nickel causing contact dermaititis:
- Drugs administered orally, by injection or onto surface of body can elicit hypersensitivity reaction mediated by IgE or IgG antibodies or by T cells
- This is common, and even small doses can be life-threatening (idiosyncratic adverse drug reactions)
What is type I hypersensitivity?
Immediate hypersensitivity reaction to environmental antigens mediated by IgE
- Degranulation of mast cells and eosinophils
How quick is the onset of type I hypersensitivity?
- Within minutes of exposure
What is type 1 hypersensitivity basically?
An allergy
What is another word for allergy?
Atopy
What are some presentations of type 1 hypersensitivity?
- Anaphylaxis
- Angioedema
- Urticaria
- Rhinitis
- Asthma
- Dermatitis
- Eczema
What is the atopic march?
Different presentations of type 1 hypersensitivty come and go at different ages
What are allergens?
Allergens = antigens that trigger allergic reactions
How can people be exposed to allergens?
- Inhalation, ingestion, contact or administered as drugs
What immunoglobulin mediates type 1 hypersensitivity?
IgE is required for type 1 hypersensitivity:
- B cells produce it when co-stimulated with IL-4 (secreted by TH2 cells)
Describe the mechanism of type I hypersensitivity?
- Release of mediators that cause allergic symptoms
- Mast cells are resident in many tissues
- Eosinophils migrate to tissues where type 1 hypersensitivity reaction is
- Mast cells initiate allergic symptoms after allergen and IgE interact – mast cells have receptors for IgE and FcεRI
Describe the symptoms for anaphylaxis?
Describe the symptoms for asthma?
Describe the symptoms for rhinitis?
Describe the symptoms for urticaria?
Describe the symptoms for angioedema?
Describe the symptoms for atopic eczema?
Describe the epidemiology of allergies?
Very common, up to 40% population:
- Runs in families
- Prevalence rising
Describe the genetics of allergies, and name 2 genes to be aware of?
Polymorphism, but we are aware of 2 genes:
- Filaggrin
- Expessed by keratinocytes and involved in maintaining epithelial barriers, moisturising surfaces and controlling pH
- Polysaccharide
What is the most serious type of allergy?
Anaphylaxis
Describe the mechanism of anaphylaxis?
- Mast cells produce prostaglandins and leukotrienes through the cyclooxygenase and lipoxygenase pathways
- Causes vasodilation and increased vascular permeability
- Shift of fluid from vascular to extra-vascular space resulting in fall of vascular tone
- Severe drop in blood pressure
- In the skin, mast cells release histamine further contributing to welling and fluid shift
Describe the mechanism of rhinitis?
- Mast cells degranulate in nasal mucosa
- Vasodilation and oedema in nose causes nasal stuffiness and sneezing
- Leukotrienes increase mucous secretion, causing discharge
- In lungs, leukotrienes cause smooth muscle contractions reducing airflow
Describe the mechanism of asthma?
- Exposure to antigen triggers airway obstruction characterised by wheezing within seconds
- Symptoms improve after an hour or so as immediate response dies down
- Severe hours after acute episode, the airway in bronchi may deteriorate again due to migration of leukocytes into bronchi in response to cytokine
- This late phase can last for several hours
Describe the treatment of allergies?
- Prevention
- Desensitisation (allergen immunotherapy)
- Drug treatment
- B2-adrenergic agonist
- Drug – salbutamol
- Effect – mimics effect of sympathetic nervous system, preventing smooth bronchial muscle contraction in asthma
- Epinephrine (adrenaline)
- Effect – stimulates both alpha and beta-adrenergic receptors, decreases vascular permeability, increases blood pressure and reverses airway obstruction
- Anti-histamines
- Effect – blocks specific histamine receptors
- Indication – allergies that affect skin, nose and mucous membranes
- Specific receptor antagonist
- Effect – blocks effect of leukotrienes
- Corticosteroids
- Effect – can prevent the immediate hypersensitivity reaction, the late phase and chronic allergic inflammation
- B2-adrenergic agonist
What test can be performed to determine what antigen somone is allergic to?
Prick test
