Adaptive immunity 5 Flashcards
what are the basics of T cell activation?
where does this occur?
when a naive T cell encounters its antigen
-> it becomes activated
occurs in the secondary lymphoid tissue
describe what would happen if bacteria were to enter the body via a cut
DCs phagocytose bacteria in the skin and present antigens
- > then migrate to enter a draining lymphatic vessel
- > settle in the T-cell areas
- > CD4+ T cells bind to MHC-II molecules
= activated
-> proliferate and differentiate into effector cells
what is the co-stimulatory signal required for activation of naive T-cells?
what happens if B7 is not present?
when do DCs up regulate this co-stimulatory signal expression?
B7 expressed on professional APCs
binds to CD28
T-cells become anergic
as they migrate to secondary lymphoid tissue
what receptor do all naive T cells express?
what is then expressed when T cells are activated?
what do activated T cells secrete?
low affinity IL-2 receptor
high affinity IL-2 receptor
IL-2
what happens when IL-2 binds to the high affinity receptor?
sends a signal to the T-cell
= induces proliferation
what is required for naive CD8 T cell activation?
stronger co-stimulatory activity
via DCs
or APCs with help of CD8 T-cells
how do cytotoxic T cells kill target cells?
attracted to site of infection by chemokines
detect cells presenting the peptides they have been activated against on MHC-I molecules
CTLs release granzymes at region of contact
- > enter target cell cytoplasm via perforin
- > granzymes induce apoptosis by activating caspases
what other cells does activation produce?
what don’t these cells require?
memory T cells
B7 co-stimulatory signal
what happens when CD4 T cells are activated?
can differentiate into a no. of different cells
e.g. TH1 cells activate macrophages
TFH (T follicular helper) cells activate B cells
what do activated TH1 cells do?
migrate from secondary lymphoid tissue to site of infection
here, resident macrophages are phagocytosing the bacteria
+ presenting on MHC-II molecules
TH1 cell recognises complementary peptide on MHC-II
-> starts to produce cytokines
-> activate macrophages so they’re more effective at killing
AND recruit more macrophages to site of infection
where are TFH cells located?
how do they activate B cells?
secondary lymphoid tissues
- B cell expresses antigen on MHC-II on its surface
2.
what is different about the epitope that an antibody binds to?
why is this?
may be different to the epitope that the TCR binds to
T cell antigens are processed peptides
(even though its from the same bacterium, it may be a different peptide e.g. an intracellular peptide)
what are the different cytokines produced by activated TH1 cells?
what are their effects?
IFN-gamma + CD40 ligands
= activate macrophages + increase killing efficiency
Fas ligand
= kills chronically infected macrophages
-> releases bacteria to be destroyed by healthy macrophages
IL-3 + GM-CSF
= induce macrophage differentiation in bone marrow
chemokines
= attracts macrophages to site of infection
LT + TNF-alpha
= activate epithelium to induce macrophage adhesion + exit from blood vessel at site of infection
what do Tregs do?
what do TH17 cells do?
have suppressive effect on immune responses
- migrate out of secondary lymphoid tissues to site of infection
migrate to infected tissues + interact with cells of immune system
