Flashcards in Hypersensitivity Deck (18)
Here's a mnemonic for remembering the types of hypersensitivity:
3) Immune Complex mediated
What mediates type 1 hypersensitivity?
Why does Type 1 hypersensitivity occur?
Due to a genetic predisposition aka Atopy.
Some Th cells are genetically hypersensitive to certain non-harmful antigens e.g. pollen or nuts
What are the phases of a type 1 reaction?
What happens to kick off the sensitisation phase of type 1 reactions?
1st encounter of allergen:
APC activates a predisposed Th cells which converts into a Th2 cell and release interleukins 4 & 5
During the sensitisation phase what happens to IL-4 & 5?
IL-4 makes B cells class switch to IgE which then attaches to Mast cells, priming them.
IL-5 activates granulocytes like eosininophils
The reaction phase of type 1 reactions is split into Early and Late, what happens in the early reaction phase?
Exposure to allergen triggers immediate degranulation of mast cells --> Histamine --> Inflammation
What happens in the late reaction phase of type 1 reactions?
~10hrs later ILs activate Th cells & other immune cells e.g. eosinophils and basophils are drawn in.
This creates further inflammation and priming of mast cells (hence the idea is that each exposure is worst than the last)
What's the Atopic Triad?
Atopic Dermatitis (Eczema)
Hayfever (Allergic Rhinitis)
How do we test for Atopy?
Skin prick testing
Serum Tryptase (spikes right after a reaction)
How do we treat type 1 reactions?
Anaphylaxis is a severe life threatening type 1 reaction, what are the symptoms?
Tightening of Face
Swelling & oedema
Constriction of airway
What happens in a Type 2 Hypersensitivity reaction?
Defective B cells release tissue-specific Abs that attach to antigens on our host cells, triggering opsonisation.
This ends up in complement activation AND Ab mediated cytotoxicity against your own cells
Give some examples of Type 2 reactions?
Blood transfusion reactions (ABO mismatch)
Autoimmune Haemolytic Anaemia
What are the 2 types of type 2 reaction?
Intrinsic - Abs attach to antigens normally made in the body
Extrinsic - Abs attach to antigens from outside the body (e.g. penicillin bound to RBCs)
In both cases the antigen is still attached to host tissues
What happens in type 3 reaction?
Plasma cell presents an abnormal antigen on its MHC and bind to Th cells by CD4/CD40 ligand bonds.
Cytokines are released causing the plasma cell to change its immunoglobulin class.
Abs then bind to circulating antigens, forming complexes that are deposited throughout the body triggering an immune response
What happens in type 4 hypersensitivity?
Starts like type 1 (using Th cells and APC in lymph nodes) but it lacks the genetic predisposition and happens much slower (~48hrs)
End up with slow inflammation and tissue damage