wk2: AED - Immunopath Allergic Response Flashcards
Outline the 6 steps for the general mechanism of allergic response
- First exposure to allergen
- Antigen activation of TH2 cells + stimulation of IgE class switching in B cells
- Production of IgE
- Binding of IgE to FCeR1 on mast cells (sensitises them)
- Repeated exposure to allergen
- Activation of mast cell: release of mediators
What 3 mediators do activated mast cells release?
Vasoactive amines
Lipid Mediators
Cytokines
In what phase of allergic reaction do mast cells release vasoactive amines and lipid mediators? (When)
Immediate hypersensitivity reaction (minutes after repeated exposure to allergen)
In what phase of allergic reaction do mast cells release cytokines? (when)
Late-phase reaction (2-4 hours after repeated exposure to the antigen)
Why are TH2 cells important for the allergic response?
Because they drive IgE production
Describe the 2 phases of an allergic reaction
Immediate phase, followed by late-phase reaction which involves recruitment of eosinophils (sometimes neutrophils)
What mediates activation of mast cells?
IgE antigen complex
By what process is degranulation triggered?
Transduction
What does a mast cell release when it degranulates? [3]
Histamines, Proteases, and Chemotactic factors (ECF, NCF)
What part of the mast cell is responsible for the release of secondary mediators?
Membrane phospholipids
What secondary mediators do membrane phospholipids drive?
drives the arach. acid pathway and platelet-activating factor
Where is the H1 receptor expressed? What does activation of the H1 receptor cause?
In nerve terminals (e.g. sensory nerves of conj.). Activation cases nerv stimulation - e.g. conjunctival itching
Where is the H2 receptor expressed? What does activation of the H2 receptor cause?
In the smooth muscle of blood vessels (e.g. walls of conj. vessels). Activation causes vasodilation - e.g. cause of conj. redness
Which phase of allergic reaction is more severe? Immediate or Late-phase
Immediate is more severe
What is a histopathological sign of an allergic reaction?
Eosinophils present in the epithelium
What is the difference between what neutrophils and eosinophils ingest?
Neutrophils ingest cellular debris, Eosinophils ingest antigen-antibody complexes
Does the presence of presence of eosinophils mean there’s a parasitic infection?
Not always. In non-parasitic infections, the eosinophils come in thinking there’s a parasite even if there isn’t
What happens to a parasite before being ingested by eosinophils?
It gets coated in antibody: marking it for the eosinophil to come eat
What do eosinophils do in a mast cell/IgE-mediated response to small antigens?
They arrive at the site but then are bystanders because there are no antigen-antibody complexes for them to ingest
What type of cell can be used as a diagnostic tool for IgE-mediated responses?
Eosinophils
What is the difference between delayed hypersensitivity (Type IV) and an allergic response?
DTH is not IgE mediated or immediate
Note: some drugs such as penicillin or atropine can stimulate immediate IgE reactions, however most drugs show delayed response - not clear why