Allergy and Hypersensitivity Flashcards
What is the definition of an allergy?
Disease following a response by the immune systen to an otherwise innocous antigen
What is the definition of ‘Hypersensitivities’?
Harmful immune responses that produce tissue damage
What immune reactant causes a type 1 hypersensitivity reaction?
IgE
What is the effector mechanism for a type 1 hypersensitivity reaction?
Mast cell activation
What is an example of a type 1 hypersensitivity reaction?
Allergy, asthma
What immune reactant is involved in the type 2 hypersensitivity reaction?
IgG
What are the five main classes of immunoglobulins?
- IgG
- IgM
- IgD
- IgA
- IgE
What immunoglobulin has the highest concentration in the bloodstream?
IgG
What immunoglobulin has the shortest half-life?
IgE (2 days)
What immunoglobulin has the longest half-life?
IgG (21 days)
What does IgE trigger?
Mast cell degranulation
What cells produce IgE?
Plasma B cells in lymph nodes or locally at site of unflammation
What route is thought to favour IgE production?
Transmucosal
What do CD4+ T cells do?
They produce IL4 cytokines that favour IgE responses
What cells force B cells to switch the isotype of the Ig they secrete from IgM to IgE?
Th2 T cells
What are some of the common inhaled allergens?
- Plant pollens
- Dander of domesticated animals
- Mold spores
- Feces of very small animals (e.g house dust mites)
What injected materials are a source of allergy?
- Injected venoms
- Vaccines
- Drugs
- Therapeutic proteins
What ingested materials can be a source of allergy?
- Food
- Orally administered drugs
What contacred materials can be source of allergy?
- Plant leaves
- Industria; products made from plants
- Synthetic chemicals in industrial products
- Metals
What are some of the common features of inhaled allergens?
- Proteins induce T cell responses
- Allergens are often proteases
- They often favour IL4 producing CD4 T cells
- They can diffuse out of particle (highly soluble)
- They are highly soluble
- They can survive dessictation (dry) (stable)
What is the allergen produced in feces of house dust mites?
Der p 1
How do Der p 1 allergens work?
- Can cleave tight junctions between epithelial cells in airway, thus enhancing access
- Der p 1 then taken up by Dendritic cells, presented to T cells which become Th2, and cause B cells to secrete IgE
What is the pathway of allergies from when the substance enters to when IgE is produced?
- Crosses lung tissue
- Antigen presenting cells (APC) e.g dendritic cells or macrophages
- Processed by by protoletic enzymes typically
- Presented as antigenic peptides on MHC molecules
- T cells will be activated and coordinate with B cells the production of IgE
- IgE binds to mast cells
What is the most important factor in what symptoms occur in the allergic reaction?
Location and distribution
What is the name of the allergic response to inhaled antigens which affect nasal epithelium?
Allergic rhinitis
What can allergen induced degranulation further down the respiratory tract result in?
Allergic asthma
What does allergic asthma include?
- Bronchial constriction
- Increased secretion of fluid and mucus trapping inhaled air
- ## Chronic inflammation may ensue with presesence of Th2 T cells, eosinophil, neutrophils
What causes the second decrease in FEV1 in asthmatics?
Influx of inflammatory cells and influx of fluid and therefore oedema
What is the first appearence of a skin allergy referred to as?
Wheal and Flare, first appearing within a few minutes as a result of vasodilation after Mast cell degranulation, localised redness
What happens roughly 8 hours after the ‘wheal and flare’ which is a result of a skin allergy?
More diffuse oedema at site due to influx of lymphocytes and other leukocytes, attracted by cytokines
What are the two main symptoms of ingested allergens?
- Diarrhea and vomitting
What happens if an ingested allegen enters the bloodstream?
- Generalised disseminated rash, Urticaria (hives)
- severe cases life threatening generalised anaphylaxis can occur
What do mast cell granules contain?
- Lipids
- Leukotryienes
- Histamine
- Prostaglandins
- Heparin
What cytokines amplify Th2 response?
IL-4 and IL-13
What chemokine attracts macrophages and neutrophils?
MIP-1alpha
What are the two main types of treatment of allergies?
- Desensitisation
- Blockade of effector pathways
What is the aim of allergy treatments?
- Shift from IgE dominated to IgG dominated
What does injecting patients with higher and higher doses of allergen cause?
A gradual shift from Th2 to Th1 T cells
What is the dosage for adrenaline?
0.3mg in adults (0.15 in children)
What are the hypotheses for having increased allergy levels in developed countries?
- Exposure to infectious diseases in childhood decreases allergy chances
- Early childhood exposure to Th1 inducing pathogen may prevent bias towards Th2 responses later decreasing allergy responses
- Increased pollution levels decrease asthma levels
- Allergies and athma lower in areas with high helminth burdens
What kind of organism is IgE thought to fight against?
Helminths
Promotion of what type of cells favours IgE response?
Th2 T cells
