lecture 4- T cell activation Flashcards
how are T cells activated?
DC in the sites of infection take up antigens –> when triggered by PAMPs and inflammation, DC migrate to draining lymph node –> they undergo maturation, enhancing ability to present antigen and activate T cells –> when they get to lymph nodes, they interact with T cells in a dynamic process
what is a naive T cell
has left thymus, prior to recognition of antigen and activation, needs several signals (MHC peptide and costimulation) to become activated, will die within weeks without antigen stimulation
what is an effector T cell
activated cell, antigen-experienced, needs only one signal to respond (MHC peptide), short lived
what is a memory T cell
antigen experienced, in a “primed and ready state,” long-lived, requires only one signal to be re-activated
describe the signals needed for a naive T cell to be activated
need a minimum of 2 signals
1- specific MHC-peptide
2- costimulation through B71/B72 and CD28
. CD28 is expressed by T cells
. B71 and B72 are expressed by antigen-presenting cells
. together, they are the second signal to activate
B71 and B72 are ___ that are uniquely expressed by ___, ___, and ___ when they have been activated by infection or inflammation
costimulatory molecules
Dendritic cells, B cells, macrophages (APC’s)
what molecules stabilize the interaction between B cells and APC’s
adhesion molecules
when T cells are being activated by DC, ___ forms at site of T cell and APC interaction
immune synapse
what happens when T cells recognize their cognate antigen?
TCR activated with MHC-peptide –> TCR initiate signaling cascade through CD3, then CD4 comes in and provides another part of signaling network, immune synapse forms at site of T cell/APC interaction, they remain in sustained interaction for many hours (up to and beyond 24 hrs) –> T cell disengages, divides and emigrates from lymph node to seek out infected cell in periphery
signaling at the cell membrane through signaling molecules through ___ leads to ____…
calcium flux leads to general activation of TF’s –> gene expression including cell division, proliferation, differentiation and taking on different effector functions
describe structure of immunological synapse
structure that forms between T cell & APC
- the external core (p-SMAC) contains adhesion molecules
- the central core (c-SMAC) has signaling molecules
once a T cell is activated, it needs help from what to proliferate?
cytokine needs to help it to proliferate, most impt. cytokine is IL-2
- structure of IL-2 has 2 chains in its receptor, its receptor goes from low to high affinity when its 3rd chain is added
what happens when T cell receives the first signal only without the second costimulatory signal?
T cell becomes anergic (period of unresponsiveness, then death)
what happens when T cell receives signal signal of costimulation only?
no effect on T cell
name the CD4 helper T cell subsets
Th1
Th2
Th17
Treg
Tfollicular
