hypersensitivites SDL

Question 1

discuss phase pne of type one hypersensitivity

Answer 1

• sensitisation phase
• allergen exposure via respiratory or skin
• antigen presenting cells capture antigens
• causes naive T cells to differentiate into T helper 2 cells
• release cytokines causing B cell proliferation
• class switch for B cells from IgM to IgE
• type 1 = increased IgE
• IgE binds to mast cells
• these relocate to near where the allergen was first encountered

individual now sensitised, this phase has NO clinical signs

Question 2

discuss phase 2 of a type 1 hypersensitivity

Answer 2

• same allergen encountered as in phase 1
• primed IgE coated mast cells bind to antigen of allergen
• release of cytoplasmic granules (histamine, heparin, serotonin)
• breakdown of mast cells
• = pruritis, broncho-constriction and oedema
• all occurs within 15 minutes
• immediate hypersensitivity
• late phase will occur within 4-24 hours and includes eosinophils seen on cytological exam

Question 3

give 2 examples of type 1 hypersensitivity

Answer 3

• anaphylaxis
• atopic dermatitis in cats

Question 4

what organs are typically effected in anaphylaxis

Answer 4

lungs typically bur liver in dogs

Question 5

how is anaphylaxis treated

Answer 5

• epinephrine to relax muscles
• IV fluids
• corticosteroids

Question 6

how is atopic dermatitis treated as a type 1 hypersensitivity

Answer 6

• lifestyle changes
• glucocorticoids

Question 7

what is a type 2 hypersensitivity

Answer 7

• mediated by IgG antibodies circulating in blood that recognise antigens on a cell surface or in the space between cells
• intrinsic or extrinsic antigens
• activates classical complement pathway
• destroys/dysfunctions cells
• extrinsic (drug reaction) is ok
• intrinsic (ion channels or hormone receptors) reactions are concerning
• impacts cellular adhesion, nutrition and waste disposal

Question 8

give example of type 2 hypersensitivites

Answer 8

myasthenia gravis
- neuromuscular disorder
- auto-antibodies against neuromuscular junction
- onset @ 6 months

Question 9

what is a type 3 hypersensitivity

Answer 9

• immune complex hypersensitivity
• formation of immune complexes
• subsequent tissue deposition
• activation of the complement system
• complement chemotactic for neutrophils
• neutrophils are unable to inget the complexes that are stuck in the blood vessel walls
• release toxic granule contents in the tissue = severe tissue damage
• 2 subtypes: antibody excess (lots of IgG) or antigen excess (less IgG but high amounts of antigens)
• small complexes can lead to capillary deposition leading to vasculitis

Question 10

give 2 examples of type 3 hypersensitivities

Answer 10

• equine recurrent airway obstruction (sensitivity to mouldy hay and dust) characterised by flared nostrils,, tachypnoea, cough and a heave line
• canine blue eye cuased by adenovirus (excess antibody or vaccine) leading to inflammation and oedema of the cornea

Question 11

what is type 4 hypersensitivity

Answer 11

• cell mediated NOT antibody mediated
• prolongd onset (24-72 hours)
• sensitisation phase via antigen specific T cells generated
• re-exposure = reactivation of sensitised cells which travel to site of presentation and release interferon gamma and other chemokines. macrophages are recruited, CD4+/8+ and granulopcytes