Hypersensitivity Flashcards
Type 1 Hypersensitivity: IgE-mediated hypersensitivity
- IgE can trigger degranulation of antigen-sensitised mast cells
- Process:
1+ Primary exposure to allergen activates B cells to form allergen specific IgE-secreting plasma cells
2+ The secreted IgE binds to FcEpsilon receptors on mast cells + basophils
3+ Mast cells/basophils become sensitised + degranulate when they come into contact with allergen at later date - Can be localised but can also become systematic anaphylaxis which can be fatal
Type 2 Hypersensitivity: IgG/IgM-mediated hypersensitivity
- Includes transfusion reactions, triggers complement-mediated lysis + ADCC
- Certain drugs + Antibiotics can adsorb non-specifically to proteins on RBC membrane forming a complex that is immunogenic
- Resultant Ab produced are directed against the drug complexed-RBC membrane + promote complement-mediated lysis
- Often leads to progressive haemolytic anaemia
Type 3 Hypersensitivity: Immune complex-mediated
- Likely caused by large immune-complexes
- Accumulation of large immune-complexes in the circulation/in certain tissues ie skin, joints, kidney glomerules can have pathophysiological consequences due to activation of complement system
- Can occur during recovery from bacterial infection or after receiving horse antiserum for tetanus/diptheria
- Can also be caused by persistent occupational exposure to antigen
Type 4 Hypersensitivity: Delayed-type/T cell-mediated hypersensitivity
- Persistent T cell-mediated immune response following chronic/repeated exposure to intracellular microorganism/chemicals that can modify “self” ie by binding to skin cells
- 3 steps:
+ Sensitisation phase
+ Effector phase
+ Granuloma formation
Protein allergens associated with Type 1 hypersensitivity
- Proteins: Foreign serum, vaccines
Granule mediators/content
- Histamine
- Serotonin
- Prostaglandins
- Eosinophil chemotactic factor
- Neutrophil chemotactic factor
Granule effectors
- Smooth muscle cells
- Blood vessels
- Mucous gland
- Blood platelets
- Sensory-nerve endings
- Eosinophils
Haemolytic Disease of the Newborn
- An example of a type 2 hypersensitivity reaction, can be prevented with Rhogam which can prevent B-cell activation + memory cell formation
- Mother must be treated with Anti-Rh IgG within few days of giving birth
Symptoms of Type 3 hypersensitivity
- Fever
- Weakness
- Rashes
- Oedema
- Arthritis from complex deposition in synovial joints
- Vasculitis from complex deposition in arteries
- Glomerulonephritis from complex deposition in glomerulus
Farmer’s lung
- Disease commonly found in people who handle hay + compost
- Caused by immune response to repeated exposure to antigens, found in mold spores of hay, crops + animal feed
- Deposition of immune complexes in alveoli, causing chronic inflammation + fibrosis
Pigeon-fancier’s lung
- Similar to Farmer’s lung but immune response is to mouldy detritus in pigeon lofts
Intracellular bacteria that induce Type 4 hypersensitivity
- Mycobacterium tuberculosis
- Mycobacterium leprae
- Listeria monocytogenes
- Brucell abortus
Intracellular fungi that induce Type 4 hypersensitivity
- Pneumocytosis carinii
- Candida albicans
- Histoplasma capsulatum
- Cryptococcus neoformans
Intracellular parasites that induce Type 4 hypersensitivity
- Leishmania sp.
Intracellular viruses that induce Type 4 hypersensitivity
- Herpes simplex virus
- Variola (smallpox)
- Measles virus
Contact antigens that induce Type 4 hypersensitivity
- Picrylchloride
- Hair dyes
- Nickel salts
- Poison ivy
- Poison oak
Plant pollen allergens associated with Type 1 hypersensitivity
- Rye grass
- Ragweed
- Timothy grass
- Birch trees
Drugs associated associated with Type 1 hypersensitivity
- Penicllin
- Sulfonamides
- Local anesthetics
- Salicylates
Foods associated associated with Type 1 hypersensitivity
- Nuts
- Seafood
- Eggs
- Peas, beans
- Milk
Insect products associated with Type 1 hypersensitivity
- Bee, wasp + ant venom
- Cockcroach calyx
- Dust mites
Other allergens associated with Type 1 hypersensitivity
- Mold spores
- Animal hair/dander
