11 - Allergy Flashcards
1
Q
Allergy
A
- The inappropriate reaction of the immune system to a substance (allergen)
- One of four types of hypersensitivity reactions of the immune system
2
Q
Examples of allergens
A
Pollen, animal dander, dust mite, food, stings
3
Q
Hypersensitivity
A
- Refers to undesirable immune reactions produced by the normal immune system
- Requires a pre-sensitised (immune) state of the host
- Four types based on the mechanisms involved and time taken for the reaction
4
Q
Type 1 hypersensitivity reaction
A
- Allergies
- Mediated by IgE antibodies, with mast cell activation the major final effector
- Individual had to become sensitised to the allergen by producing IgE antibodies against it
- Subsequent exposure leads to symptoms
5
Q
Type 2 hypersensitivity reaction
A
- Antibody-mediated destruction of cells by IgG and IgM antibodies through complement activation, Antibody-dependant cellular cytotoxicity (ADCC) and Opsonisation
- e.g. Grave’s disease, Myasthenia Gravis.
6
Q
Type 3 hypersensitivity reaction
A
- Immune complexes are formed when antibody
binds with antigen and are usually removed by
macrophages after complement activation - Persisting immune complexes can be deposited
in blood vessels and in a range of tissues and
organs; and cause inflammation – vasculitis,
glomerulonephritis, arthritis, SLE
7
Q
Type 4 hypersensitivity reaction
A
- Delayed type
- excessive T cell activation
- Hypersensitivity reactions are mediated by T cells (primarily Th1 subtypes, but also Th17 and CD8)
- Antigens are processed and presented to T cells by APCs (sensitization). This is followed by an effector phase upon re-exposure to the antigen
8
Q
Symptoms of allergic reaction
A
hives, swelling of lips eyes or face, vomitingm wheeze
9
Q
Allergic reactions
A
- Development of symptoms following exposure to allergen
- Can be IgE or non IgE mediated
- Can range from mild to severe (anaphylaxis)
- Can affect multiple body systems
10
Q
Anaphylaxis
A
- Severe reaction of rapid onset, involving multiple organ systems which results in circulatory collapse and drop in BP
- Can be fatal
11
Q
Development of an allergy
A
- Requires pre-sensitisation to the allergen
- Once sensitised (immunised), every following exposure to the allergen elicits the allergic reaction
12
Q
Immunology of an allergic response
A
- After a B cell comes into contact with an allergen exposed T cell it will differentiate into an antibody secreting plasma cell
- IgE antibodies produced by the plasma cell will bind to the surface of mast cells
- Upon subsequent allergen exposure, IgE antibodies on the surface of mast cells become cross-linked by the allergen
- Mast cells then degranulate –> release of vasoactive amines, lipid mediators, enzymes, cytokines, chemokines
13
Q
Two phases of allergic response
A
- Early (minutes): Classic allergic reaction, hypotension
- Delayed (hours): late phase reaction, Eosinophil infiltration, Neutrophil infiltration, late phase reaction, Fibrin deposition
14
Q
Classification of allergic reactions
A
- Immediate (<1hour): anaphylaxis hypotension, wheezing - IgE
- Accelerated (1-<72hours): swelling, wheezing - IgE
- Late (>72 hours): rash, cytopenias , hypersensitivity (organ involvement) - non IgE
15
Q
Common allergic disorders
A
- Allergic rhinitis (hay fever)
- Asthma
- Food allergy
