What may control the distribution of membrane receptors?
cytoskeleton
What is the immunological synapse?
organised structure at the interface between a lymphocyte and an APC or target cell
What is the general function of the immunological synapse?
transger of information
What is the function of the central SMAC?
recognition, co-simtulation and signalling
What is the function of peripheral SMAC//
adhesion
What does SMAC stand for?
aupra-molecular activation complex
What causes the formation of SMACs on both the T cell and APC?
receptor-ligand interactions
What organelles play key roles in IS formation?
cytoskeleton and microtubule-organising centre
What are the proposed funhction of the immunological synapse?
signal amplification and integration; co-stimulation; cytotoxicity; directed secretion; protein transfer adn signal termination
What is the function of the adhesion molecules in the SMAC?
affinity for a TCR to its pMHC is low; so need adhesions to form a stable association allowing hte T-cell to inspect the peptides
Which integrins appear important for lymphocyte adhesion?
LFA-1; VLA-4
What enzyme is thought to be invovled in changing the integrin adhesiveness on T cells?
small GTPase Rap1
What tyhpe of signalling is the change in integrin adhesivenesss on T cells known as?
inside-out signalling
What is the dSMAC?
distal SMAC
What interactions take place in the dSMAC?
filamentous actin; CD43/CD45
What initiates the formation of the IS?
TCR engagement; co-stimulation; chemokines
What are the 4 specific stages of IS formation?
initial adhesion; TCR t riggering; organisation; stabilisation
What is the ligand for LFA-1?
ICAM-1
What is the ligand for LFA-3?
CD2
What is CD43 thought to bind to?
E-selectins; ICAM-1
What is the distribution of surface molecules and domains on resting T cells?
uniform
What is the function of polairsation in the immunological synapse?
allows the establishment of a sensory contact with APC and early junction formation
What is hte earliest biochemical event in TCR signalling?
tyrosine phophorylation of ITAM sequences
What protein is activatede once Lck mediated phosphorylation of ITAMs has taken place
ZAP-70
What proteins are recruited after the activation of ZAP-70?
LAT and SLP-76
What proteins are activated and play a role in cytoskeleton reoganisation?
Vav and WASP
What is the function of cytoskeletal rearragments in the IS?
leads to recruitment of other TCRs and rafts and to synapse organisation
What is the function of stabilisation as the last process of the IS?
allows sustained signallling and optimal activation
What is the difference between the IS in CD4 and CD8 cells?
CD8 cells have an dditional secretory pocket- a mechanism of target killing
What is the difference between the extracellular domains of the y, d and e cahins o f the CD3 and the x chains?
the y, d and e chains have extracellular Ig-like domains whereas the x have only a hort extracellular domain
What parts of CD3 does the alpha chain of the TCR interact with?
one CD3d:CD3e dimer and one x dimer
What parts of the CD3 does the beta chain of the receptor interact with?
onw CD3y: CD3e dimer
What mediates the interactions between CD3 dimers and chains of the TCR?
recpirocal charge interactions between basic and acidic intramembrane amino acids
What is the function of the CD3 and TCR interactions?
stabilises the alpha and beta chains during production in the ER and allows transportation to the plasma membrane
How many ITAMs does the TCR contain?
10- each y, d and e has one ITAM and each x chain contains 3
How many yrosine residues does each ITAM contain?
2
What polypeptides are required for BCR transport and signalling?
Iga and Igb
How does the Iga:Igb heterodimer associate with the BCR?
hydrophilic rather than charge interactions
What is a microcluster?
small numbers of TCRs found in the zone of contact between the TCR and APC
How is Lck activity regualted?
allosterically by phosphosporlation of a tyrosine in its carboxy terminus by C-temrinal Src kinase (Csk)- the phosphotyrosine interacts with Lcks SH2 domain keeping it in a closed conformation
What allows Lck to become primed (not in an inactive conformation)?
dephosphorylation of the tyrosine or engagment of the SH2/SH3 regions
What does full activation of Lck require?
Lck autophosphorylation of a tyrosine in its kinase domain
What is phosphorylation of LCk counteracted by in nonstimulated lymphocytes?
tyrosine phosphatase CD45- releases the kinase domain of Lck
What is required to stabilise the activated form of Lck and lead to ITAM phosphorylation?
antigen receptor activation
What protein tyrosine kinases are involved in the phosphorylation of ITAMs in B cells?
Fyn, Blk and Lyn
What is recruited to phosphorylated ITAMs in B cells instead of ZAP-70?
Syk
What is the idfference between Syk and ZAP-70?
ZAP-70 required additional acivation by Lck phosphorylation whereas Syk is activated by binding to the phosphorylated site
What is the B cell co-receptor formed of?
CD19; CD21 and CD81
What is the function of the cytoskeletal protein talin?
connects LFA-1 to the actin cytoskeleton
How does polarisation of a T cell begin?
local reorganisation of the cortical actin cytoskeleton at the site of contact
What does the reorganisation of cortical actin cytoskeleton at site of contact cause?
reorientation of the micro-tubule organising centre and golgi apparatus
How does the TCR control delivery of effector signals?
induces tight binding of effector cells to their target cells to create narrow space in which effector moelcules can be concentrated; focues delivery of effector molecules at site of contact by reorientation of secretory apparatus; triggers synthessi or release of the effector molecules
What are TCR-enriched microvesicles?
post-signalling extracellular products of T cell activation that retain pMHC binding competences
What mediates the initial binding of an effector T cell to its target?
LFA-1 and CD2
What do LFA-1 and CD2 bind to?
ICAM and CD58
What causes the transient interaction between adhesins on the T cell and its target cell to increase in affinity?
recognition by antigen
What 3 broad categories of receptor does the immunological synpase integrate?
antigen (TCR); adhesion and costimulatory/checkpoint
How is the immune synapse organised?
into a bull’s eye structure with a central TCR-MHC interaction cluster surrounded by adhesion molecules and a dsital ring that includes CD45
Why do adhesion molecules segregate laterally in the immune synapse?
the intercellular link formed by the interaction between LFA-1 and ICAM-1 is much longer than that between TCR-MHC
What are teh 3 supramolecular activation clusters?
central; peripheral and distal regions
What is the central cluster separated into?
signalling zone and secretory zone
Which APCs do T cells bind when moving around?
to each antigen presenting cell
Why has it been difficult to figure out exactly what each adhesion molecule does?
there is a lot of synergy between them
What does CD2 on the T cell bind to on the APC?
CD58
What suggests a redundancy in hte function of the adhesion molecules?
people lacking LFA-1 have normal T clel repsonses and mice lacking CD2 do as well
What is the transient binding of naive T cells to APCs crucial for?
providing time for a T cell to sample large numbers of MHC molecules for the presence of its cognate antigenic peptide
How is the immunological synapse formed?
when binding to their antigenic p/MHC, TCRs and their associated co-receptors cluster at the site of cell-to-cell contact
What happens if there are defects in Wasp?
results in inability for the cell to become polarised, as WAsp protein is an important intermediary between TCR and cytoskeleton- needed for peoper release of effector molecules —immune deficiency syndrome
What effect doesreorganisation of the actin cytoskeleton at the site of contact have?
reorientation of hte MTOC, and the golgi apparatus, focusing exocytosis of cytotoxic granules derived from the golgi and cytokines
How does the TCR control the delivery of effector signals?
induces tight binding of effector cells to their targets to create narrow space in which effector molecules can be concentrated; focuses delivery of molecules to site of contact by reorientation of the secretory apparatus and triggers synthesis/release of the molecules