Hypersensitivity and Allergy Flashcards
Atopy is…
A form of allergy in which there is a hereditary or constitutional tendency to develop hypersensitivity reactions in response to allergens (atopens)- individuals with this predisposition, and conditions provoked in them by contact with allergens, are described as atopic
What does an appropriate immune reaction involve
- Involves antigen recognition by cells of the immune system and antibody production
Antigen recognition + ‘danger’ signals =
IMMUNE REACTIVITY
Antigen recognition + no ‘danger’ signals =
Tolerance
What leads to tolerance
Antigen recognition + no ‘danger’ signals
What leads to IMMUNE REACTIVITY
Antigen recognition + ‘danger’ signals
HYPERSENSITIVITY REACTIONS:
Occur when immune responses are mounted against: (3)
- Harmless foreign antigens (allergy/contact hypersensitivity)
- Autoantigens (autoimmune diseases)
- Alloantigens (serum sickness, transfusion reactions, graft rejections)
Immune response against what causes allergy/contact hypersensitivity
Harmless foreign antigens
Immune response against what causes serum sickness, transfusion reactions, graft rejections
Alloantigens
Alloantigens are against what? (3)
serum sickness, transfusion reactions, graft rejections
4 types of hypersensitivity reactions?
- Type I: Immediate Hypersensitivity
- Type II: Antibody-dependent Cytotoxicity
- Type III: Immune Complex Mediated – complex of antibody and antigen causing disease
- Type IV: Delayed Cell Mediated
What is a type 1 hypersensitivity reaction (summarised)
Immediate Hypersensitivity
What is a type 2 hypersensitivity reaction (summarised)
Antibody-dependent Cytotoxicity
What is a type 3 hypersensitivity reaction (summarised)
Immune Complex Mediated – complex of antibody and antigen causing disease
What is a type 4 hypersensitivity reaction (summarised)
Delayed Cell Mediated
Examples of type 1 hypersensitivity? (4)
Anaphylaxis, asthma, rhinitis (seasonal or perennial (long lasting, year round i.e. constant)), food allergies
Explain 2 exposure mechanism of T1 hypersensitivity
1st EXPOSURE:
- Sensitisation (allergy) not tolerance (no allergy)
- Sensitisation involves IgE antibody production
- IgE binds to Mast Cells and Basophils
2nd EXPOSURE:
- More IgE Ab produced
- Antigen cross-links IgE on Mast Cells/Basophils
- Leads to degranulation and release of inflammatory mediators
What Ab does sensitisation involve
- Sensitisation involves IgE antibody production
- IgE binds to Mast Cells and Basophils
What cells do IgE act on in T1 hypersensitivity
Mast Cells/Basophils
Examples of diseases caused by T2 hypersensitivity reactions? (4+3)
- Myasthenia gravis (anti-ACh receptor antibodies)
- Glomerulonephritis (anti-glomerular basement membrane antibody)
- Pemphigus vulgaris (anti-epithelial cell cement protein antibody)
- Pernicious anaemia (antibody mediated blood cell destruction such as below)
- Haemolytic anaemia
- Thrombocytopenia
- Neutropenia
What autoimmune target when attacked causes pemphigus vulgarisms
autoimmune attack of an antibody that cements epithelial cells together
What autoimmune target when attacked causes bullies pemphigoid
antibodies are against basement membrane proteins
Difference between pemphigus vulgarisms and bulls pemphigoid?
the blisters tend to be more robust because they are due to a deeper inflammation in the skin than pemphigus
What is used to test for specific antibodies in T2 HS (2)
- Immunofluorescence
- ELISA (enzyme-linked immunosorbent assay, e.g. anti-CCP cyclic citrullinated peptide antibodies for rheumatoid arthritis)
Examples of diseases caused by T3 hypersensitivity reactions? (3)
- Tissue damage (vasculitis)
Systemic lupus erythematosus (SLE)
Vasculitides (Poly Arteritis Nodosum, many different types)
What causes T3 HS?
- Formation of Antigen-Antibody complexes in blood
Explain mechanism of T3 hypersensitivity reactions (4 stages)
- Formation of Antigen-Antibody complexes in blood they can’t get through small blood vessels very easily
- This causes complex deposition in blood vessels/tissue
- This leads to complement and cell activation
- Activation of other cascades e.g. clotting
- Tissue damage (vasculitis)
Examples of T4 HS reactions? (8)
- Chronic graft rejection
- GVHD (Graft vs host disease)
- Coeliac disease
- Contact hypersensitivity
- Many autoimmune diseases
- Asthma (this and below are Th2 mediated, above is Th1 mediated )
- Rhinitis
- Eczema
3 main varieties of T4 HS reaction?
- Th1
- Cytotoxic
- Th2
What characterises TH1 mediated T4 HS?
Characterised by producing lots of gamma-interferon- the most important type in hypersensitivity reactions
What characterises TH2 mediated T4 HS?
Releases IL-4, IL-5 and IL-13:
Which IFN is most important in hypersensitivity
gamma-interferon
Explain TH2 mediated T4 HS?
- Th2 mediates allergic inflammation e.g. asthma etc.
- Mechanisms involve either a transient antigen presence or a persistent antigen
- T cells then activate macrophages and CTLs
- Much of the tissue damage is dependent upon TNF, hence why neutralising TNF has marked clinical benefits
examples of Th1 mediated diseases in T4 HS? (5)
- Chronic graft rejection
- GVHD (Graft vs host disease)
- Coeliac disease
- Contact hypersensitivity
- Many autoimmune diseases
examples of Th2 mediated diseases in T4 HS? (3)
- Asthma
- Rhinitis
- Eczema
Explain mechanism of T4 mediated HS? (3)
- Transient/Persistent antigen
- T cell activation of macrophages, CTLs
- Much of tissue damage dependent upon TNF & CTLs
What is the antigen in T2 HS reactions?
Cell surface or matrix bound proteins
What is the antigen in T3 HS reactions?
Soluble antigens
What causes asthma? Ig involved, what cell is involved, what is induced, and what does this produce?
caused by IgE binding to mast cells and by the induction of T cells producing Th2 type cytokines