Lung Immunology and allergic airway disease Flashcards
List 3 allergic airway diseases
Divided into upper and lower airways:
Upper airways: allergic rhinitis
Bronchi: asthma
Alveoli: allergic alveolitis
What are the two different types of hypersensitivity reactions
Immunological
(“Allergy”)
Non-immunological
Describe immunological hypersensitivity reactions
IgE-mediated atopic diseases hayfever eczema asthma
Non-IgE-mediated
allergic diseases
(e.g. Farmers lung
Describe non-immunological hypersensitivity reactions
Intolerance
(e.g.food)
Enzyme deficiency (e.g.lactase DH def
Pharmacological
e.g. Aspirin hypersensitivity
What is allergy
Allergy is an exaggerated immunological response to a foreign substance (allergen) which is either inhaled, swallowed, injected, or comes in contact with the skin or eye.
Allergy is a mechanism (not a disease). Allergic mechanisms play an important role in some diseases all the time, and in others for some of the time.
Define allergy
An exaggerated sensitivity resulting from a heightened or altered reactivity of the immune system in response to external substances
Define hypersensitivity
Hypersensitivity-An umbrella term to describe an exaggerated sensitivity to any agent irrespective of the mechanism.
Describe the biphasic response to allergies
Type of response is important
Early- sneezing, eyes watering
later- nasal congestion
Describe type 1 immunity of mammals
Mammals protect themselves against viruses, bacteria, fungi and protozoa by mounting a type 1 immune response. This involves the recruitment of T helper type 1 (Th1) and Th17 cells, cytotoxic T cells, IgM, IgA and IgG subclasses.
Describe type 2 immunity of mammals
Type 2 immunity, on the other hand, protects against helminths (“worms”) and ectoparasites (“ticks”) and is mediated by Th2 cells, IgE and IgG1 antibodies as well as components of the innate immune system including epithelial barriers, innate lymphoid cells, eosinophils, mast cells, basophils and activated macrophages.
Cross-reactivity of IgE can cause allergies- dysregulation of IgE response
Outline the pathophysiology behind seasonal allergic rhinitis
1st step is sensitisation- allergen leaks through damages nasal mucosa/epithelia - already disrupted
Captured by a dendritic cell
Migrates to draining lymph nodes
Go to innate cells- such as ILC-2s
Help DC maturation and can help prime T cell into TfH or Th2
TfH can then prime B cells- proliferation and differentiation into plasma cells which express IgE
IgE bids to FceR receptors on mast cells and basophils
When the allergen crosslinks- degranulation- histamine release
What are the pro-allergic cytokines released by Th2 cells
IL-5,4 AND 13
There will also be lots of eosinophils (IL-5 is a survival factor for eosinophils)
What can we do in patients with allergic airway disease
Lung cell biopsy
Immunohistochemistry to challenged individuals- if allergic- lots of IL-4,5 + Th2 cells
Define atopy
Atopy – An hereditary predisposition to produce specific IgE antibodies to common aeroallergens
Describe atopy
Atopy is the hereditary predisposition to produce IgE
antibodies against common environmental allergens
The atopic diseases are allergic rhinitis, asthma and atopic eczema
Allergic tissue reactions (in atopic subjects) are characterised by infiltration of Th2 cells and eosinophils
Why do atopic conditions arise
Atopic (IgE-mediated) allergic conditions arise when individuals produce increased amounts of immunoglobulin E (IgE), a class of antibody which binds strongly to specific receptors (termed FcεR1 and FcεR2) found on mast cells (specialised cells found in connective tissue and airways), blood basophils and dendritic cells.
How does atopy differ to allergy
Sensitised but not allergic- they have the IgE antibodies in peripheral blood or skin-prick test (flare will be produced if allergic)
But exhibit no symptoms when exposed to the allergen
Describe ILC-2 cells
Like lymphocytes but have no TCR
Release IL-4 and IL-5