IgE channels and allergies Flashcards
What is an allergy?
Disease following an immune response to an allergen
What immunoglobulin is most associated with allergies?
IgE
What is a hypersensitivity reaction
Inappropriate or exaggerated immune response that causes inflammation, tissue damage and disease.
What is the end result of sensitization to an allergen
Production of allergen-specific IgE and up-regulattion of T helper cells
How are allergens sampled in the lungs
Dendritic cells sample in the airway lumen or tissue itself if the allergen has transferred through disrupted epithelium.
Where do dendritic cells migrate to and mature
Migrate to the regional lymph nodes or local mucosa, where they present allergen derived peptides on their MHCII complexes to naive T cells.
What is required to be present for maturation of naive T cells to T helper cells
IL-4 (enhanced by engagement of notch on the surface of T cells with Jagged on dendritic cells).
What is the result of T helper cell interaction with B cells
Cause them to mature into plasma cells and undergo immunoglobulin class-switch recombination
What is immunoglobulin class-switch recombination in the context of asthma
Plasma cells’ gene segments encoding Ig heavy chains are rearranged so IgE antibodies are produced.
What do circulating IgE receptors bind to after reaching the interstitial fluid?
Allergen specific or non-specific IgE binds to the high affinity receptor for IgE on tissue resident mast cells. FcεRI
Does sensitisation produce any symptoms
No
Give an example of how the T helper cell response to allergens can be treated
IL-4 receptor dosage binds IL-4, inactivating naturally occurring IL-4 without cellular activation.
What needs to occur for an active response of a mast cell
Binding of two IgE antibodies by the antigen on the mast cells surface
What do mast cells do when activated
Release preformed mediators and increase the synthesis of many cytokines, growth factors and chemokines.
What is the result of mast cell activation
Bronchoconstriction, vasodilation, increased vascular permeability, increased mucous production
How does mast cell activation contribute to the late phase transition
Promoting the influx of inflammatory leukocytes: By upregulating adhesion molecules on vascular endothelial cells. But also by secreting chemotactic mediators, especially leukotriene B (LTB) and prostaglandin D2 (PGD2) and chemokines such as IL-8
What innate immune cells are present in the late phase reaction
Neutrophils, eosinophils, basophils, monocytes
What adaptive immune cells are present in the late phase reaction
Antigen stimulated T-cells.
What is the action of neutrophils in the late phase reaction
Release of elastase - promotes the activation of matrix metalloproteinases (MMPs) and the subsequent degredation of type III collagen
What is the action of eosinophils in the late phase reaction
Release basic proteins that can injure epithelial cells
What are other late phase reaction results
Bronchoconstriction, increased mucus production
What do B2-adrenoceptor agonists do
salbutamol, relax smooth muscle, inhibit mast cell degranulation and inhibit mucus secretion.
What do corticosteroids do
repress transcription of newly synthesised mediators like chemokines, other cytokines and prostanoids by the inhibition of COX2 induction.
What is the action of Omalizumab/ Zolair
IgE antibody - blocks IgE receptors from binding to mast cells.
Very costly, must be injected, and has no effect on mast cells that already have IgE associated with them.
What subunits make up the tetrameric FcεRI receptor
one alpha, one beta, two gamma
What regulates the synthesis of FcεRI
IL-4 produced by TH2cells
What is the importance of the FcεRI beta and gamma chains
They contain the ITAMs (immunoreceptor tyrosine based activation motif) - These are required for initiation of signalling
How to ITAMs induce signalling
Tyrosines in ITAMs are targets for phosphorylation by Src tyrosine kinases and subsequent SH2 domain binding of intracellular signalling molecules
What is the role of the beta subunit of the FcεRI
amplifies signalling and stabilises cell surface expression
What is the role of the gamma subunit of the FcεRI
Provides scaffold, ensuring the receptor can reach the cell surface.
What us the result of cross linking of two IgE FcεRIs
Association of the src family kinase: LYN, specifcally to the beta chain (Also Fyn)
what is the action of LYN kinase
Phosphorylates FcεRI beta and gamma ITAMs, creating a high affinity docking site for lyn and syk (SH2 domain containing).
What is the action of syk
Recruited to the gamma subunit - auto and trans phosphorylates itself to increase its catalytic activity.
What is the name of the scaffold protein that Syk and Lyn also phosphorylate
LAT - linker for activation of T-cells. This co-ordinates the activation of further signalling molecules
What is the action of phosphorylated LAT
Creates a binding site for PLC gamma (phospholipase C gamma) which breaks down P1,4,5 phosphate (a lipid found in the plasma membrane)
What action does hydrolysis of P1,4,5 phosphate have
Forms IP3 - Acts on calcium stores creating a calcium signal
Forms DAG - this acts on PKC, leading to degranulation of mast cells, activation of TFs which produce cytokines/chemokines that mediate the inflammatory response. Also increase COX2 transcription leading to sustained prostaglandin synthesis.
What causes the bent structure of the IgE-Fc
the Cε2 domains fold back and make extensive contact with the Cε3 domains and even touching the Cε4 domains.
What causes a chronic stage immune reaction
Innate and adaptive immune cells take up residence in the tissue itself.
What changes occur to mast cells in chronic immune reactions.
More mast cells develop in the tissue, displaying lots of IgE bound to FcεRI and have an altered anatomical distribution.
What is the result of repetitive epithelial injury
Epithelial - mesenchymal trophic unit (EMTU) becomes established. This is thought to sustain Th2 cell associated inflammation, to promote sensitisation to additional allergens or allergen epitopes.
What are 3 other symptoms of chronic phase immune reactions.
Substantial thickening of the airway walls.
Increased deposition of ECM proteins (Fibronectin and collagen)
Hyperplasia of goblet cells (increased mucus).
What is the role of thapsigargin
Blocks calcium GTPase on the ER so allows for a passive expulsion of calcium from the ER - Calcium influx as a result of CRAC channel function can then be observed by adding calcium to the extracellular compartment.
What is the role of CRAC channels
CRAC channels are calcium release activated channels and re-establish a persistent calcium concentration intracellularly after store depletion. This calcium concentration activates transcriptional pathways required for T-cell proliferation and effector immune function.
How was STIM’s involvement in CRAC channel function found in drosophila
dsRNA treated well plate knocking down the entire genome of the fly in S2 cells. cells were loaded with calcium dye and treated with thapsigargin. STIM knockdown cells exhibited the same properties of the SCID patient T cells, unable to re-establish intracellular calcium concentration when extracellular calcium was reintroduced.
What domains does STIM1 possess and what are their roles
1 transmembrane domain - tethering to the membrane
EF1 and EF2 domains which are calcium sensitive
coiled coil domains CC1 and 2 which are important in protein to protein interactions.
Where is STIM found and what did this mean
The ER, STIM1 is not the drosophila’s version of the CRAC channel but a regulatory protein for CRAC channel function
What happens to STIM1 after induced calcium store depletion
STIM1 translocates to the plasma membrane
How was the human gene ORAI1 investigated
In T-cell line, insertion of a marker for NFkB which in the presence of a calcium signal, translocates from the cytosol to the nucleus.
How was NFkB marker used for ORAI1 investigation
dORAI1 cells were treated with thapsigargin and calcium was reintroduced extracellularly. NFkB was unable to translocate to the nucleus - also seen in dSTIM1 cells.
What is the structure of the ORAI1 gene
4 TMBDs - SCID mutation can be found just inside one of the transmembrane domains.
How can you treat SCID patients
Use the patients own T cells, transfect them with WT ORAI1 protein - rescues CRAC channel function.
What was the mouse mode used for studying CRAC function
CRACM1 deficient mice mast cells showed defective degranulation and cytokine secretion.
How did CRACM1 deficient mice respond to allergens and how were they investigated.
Function of CRACM1 in allergic reactions involving tissue resident mast cells, examined using in vivo IgE mediated model of passive cutaneous anaphylaxis (PCA) *CRACM1
deficiency suppressed PCA.
What is c-kit
A receptor for stem cell factor that is found on the surface of mast cells
what is the role of stem cell factor mediated c-kit activation
Required for maturation of mast cells and in order to stay alive.
