Cell Mediated Immunity I and II - Activation of T cells and Differentiation and Function Flashcards
what occurs when naive mature T cells are presented iwth Ag?
they are activated and they give instruction to proliferate into a clone army and differentiate into effector cells (that recognize the same Ag)
what cytokines induce maturation of DC?
TNF alpha and PRR ligation
what 3 signals are essential for T cell activation?
- antigen presentation
- co-stimulation
- cytokine
what cells are responsible for providing 3 signals for T cell activation/DC maturation
APC/DC
describe signal 1 of T cell activation
Ag binds to MHC on immature DC or PAMP binds to PRR (proteoglycan)
what cells can activate DC
macrophages and neutrophils can produce TNF alpha to activate the immature DC
how are signal 2 costimulators induced?
microbe components or cytokines
what are the costimulators for signal 2?
B7 (CD80, CD86)
what occurs once B7 stimulates APC?
cytokine production from APC, and matures APC!
what do signals 1+2 do?
signal proliferation (clone army)
what does signal 3 do?
signal differentiation into effector cells
what occurs once an Ag is recognized by Cd4/8?
activates CD4/CD8 associated Lck (tyrosine kinase) which phosphorylates ITAMs of CD3 and Zeta chains
what do phosphorylated ITAMs do?
recruit ZAP-70 which phosphorylates LAT
what activates ZAP-70?
phosphorylated ITAM
what does LAT do?
activates Ras pathway and phospholipase C (PLC)
describe the Lck pathway
- Ag activates Lck
- Lck phosphorylates ITAM
- ITAM recruites ZAP70
- ZAP70 phosphorylates LAT
- LAT activates Ras and PLC
- Ras does MAPK pathway
- PLC makes DAG and IP3
- IP3 triggers cytosolic calcium increase which increases transcription factors
what does IkB do?
is bound to and inhibits NFkB
what occurs when PKC is activated ?
PKC activates IkB kinase, which phosphorylates IkB, releasing NFkB
what occurs when NFkB is released?
moves into nucleus and promotes transcription – increases inflammation and T cell reactivity
what do glucocorticoids do?
block NFkB activation via inhibiting Lck action (suppresses TCR mediated calcium signaling)
what do the cytosolic Ca ions do?
bind calmodulin, which activates calcineurin
what does Ca bound calmodulin do?
activates calcineurin, which removes inhibitory phosphates from NFAT
what does calcineurin do?
removes inhibitory phosphates from NFAT
what does NFAT do?
migrates to nucleus to activate gene expression, increases survival cytokines
MOA of cyclosporine?
inhibits calcineurin activity to prevent NFAT activation and stop T cell response
end product of MAPK pathway
AP-1
what does MAPK activate?
JNK and ERK which leads to the expression of c-Jun and c-Fos
what is AP-1
C-Fos and C-Jun together which enhances transcription of genes related to cytokine differentiation, proliferation, and apoptosis
what cytokine is associated with clonal expansion?
IL-2/CD25
what does IL-2 do?
- clonal expansion
- induces survival
- prepares cells for differentiation
how does IL-2 enhance survival
- induces expression of anti-apoptotic proteins (BCL)
2. increases gene expression of IL-2 receptor alpha chain CD25
what is IL-2’s receptor?
CD25
how does IL-2 prepare cells for differentiation
promotes gene expression of CD40L and cytokine receptors for Th1 and Th2 responses
what does CD40 do?
increases signal 2 and 3 (DC cytokines and costimuation)
what helps to decrease T cell division?
increased CTLA-4 and PD-1 action
how do memory T cells live 30-40 years?
maintain IL-7R expression (survival factors)
describe effector T cells
- loses IL-7R
- loses CCR7 (so it can leave)
- leaves to the lymph nodes to infiltrate the tissues immediately then undergoes apoptosis
describe the naive T cell
in the spleen, liver or LN and has IL-7R
what does a naive T cell differentiate into
effector and memory T cell
what does CCR7 do?
signals to go and stay in lymph node
what occurs if you get rid of CCr7?
cell can leave lymph node
describe memory T cell
retains IL-7R, can differentiate again into central and effector memory T cells
describe central memory T cell
CCR7 positive, so stays in the lymph node as a reservoir, but can be activated to make more effector memory cells if needed
describe effector memory T cell
CCR7 negative, so it leaves the lymph nodes to infiltrate tissue during local recall response
what T cell does IL-12 make ?
Th1 cells
what T cell does IL-4 make?
Th2 cells
what T cell does IL-6 and TGFbeta make/
Th17 cells
what cytokines does IL-12 promote?
- IL-2
- IFN-gamma
- TNF alpha
what cytokines does IL-4 promote
- IL-4
- IL-5
- IL-13
what cytokines does IL-6 and TGF beta promte?
- IL-17
2. IL-22
what major cytokines does Th1 secrete?
- IL-2
- IFN gamma
- TNF alpha
what does IL-2 do?
- proliferation of T cells
2. activation of NK cells
what does IFN gamma do?
activates macrophages (M1) to increase ROS/RNS production (phagocytosis) and induces MHC I to increase antigen presentation
how do Th1 cells activate macrophages?
T cell releases IFN gamma and it binds to macrophage, which makes CD40L bind to CD40. both of these induce killing
when do effector T cells release cytokines?
only when TCR is re-engaged in the tissue
what does TNFalpha do?
- increases vascular permeability of endothelia via loosening tight junctions
- induces adhesion molecules
- promotes apoptosis of infected cells
what are the major cytokines produced by Th2 cells?
- IL-4
- IL-5
- IL-13
what does Il-4 do?
promotes IgE production in B cells, which then bind to mast cells and eosinophils (degranulate)
what does Il-5 do
recruits and activates eosinophils
what does IL-13 do?
- increases mucus and peristalsis in intestines
2. activation of M2 macrophages (wound healing, suppresses inflammation)
what do M2 macrophages do?
woundhealing and antiinflammatory
what are the major cytokines produced by Th17 cells?
- IL-17
2. IL-22
what does IL-17 do?
- acts on tissue cells and leukocytes to increases IL-1, IL-6, TNFalpha, chemokines and colony stimulating factors
- these recruit and activate neutrophils and other inflammatory cells
what does IL-22 do?
- acts on tissue cells to enhance defensins (antimicrobial peptides to increase barrier protection)
- enhances wound healing (M2)
effector functions of CD8 Tc cells?
secrete cytotoxkins and cell-cell contact interactions to eliminate infected host cells
what are CTL?
cytotoxic T lymphocytes are activated and differentiated CD8 T cells
what do CTL do?
- release cytotoxins to induce apoptosis
2. ligate to death receptors (upregulate Fas)
what cytotoxins do CTL release to induce apoptosis?
- perforin
- granzyme to activate caspases, DNAse
- caspases to induce DNA fragmentation
how does Fas work
Fas ligand binds Fas receptor, establishing DISC (death inducing signaling complex).
DISC cleaves caspase-8, which then cleaves effector caspases.
what do effector caspases do?
induce DNA fragmentation and apoptotic body formation (blebbing)
what if Fas is downregulated?
no killing
what if perforin is downregulated?
no killing
what survival signals block receptor mediated apoptosis? (aka Fas)
cytokines and NFkB signals induce c-FLIP expression
what does c-FLIP do?
outcompetes caspase-8 binding to FADD, blocking apoptosis! it also blocks TNFalpha mediated apoptosis
what is receptor mediated apoptosis?
Fas-Fas ligand binding
describe TNFalpha signaling
- TNFalpha binds its receptor
- triggers complex 1 formation
- triggers NFkB signaling
- activates inflammation and inhibits apoptosis by c-FLIP
what does NFkB do?
- cytokine production
- adhesion molecule regulation
- ROS and NO induction
inflammation
describe TNFalpha action on endothelial/immune cells
they have high TNFR1 on the surface, which means if TNFalpha is there, c-FLIP is released and it survives. if low, other stimuli induce anti-apoptotic factors
what occurs on virus infected host cells or cancer cells?
there are low levels of TNFR1 on surface and more complex II (killing), so the low level of TNFalpha binding means low c-FLIP == they die
what is the most common antiapoptotic protein in the face of T cell activation stress?
Bcl-2 family! they can make you survive
what occurs in stressed cells (bc of T cell activation)
MOMP and effector caspases are activated to lead to apoptosis
what is MOMP
mitochondrial outer membrane permeability - poking holes in membrane of mitochondria leading to apoptosis
what can block MOMP???
BCL-2!!!
how does Bcl -2 block MOMP>?????
decreases available Bax/Bax proteins for Bid-mediated MOMP formation aka no pore!
what can increase Bcl-2 expression?
IL-2, IL-7 and growth factors
describe the process of MOMP
- activated caspase 8 cleaves Bid
- Bid displaces Bax and Bak from their inhibitor Bcl-2
- Bid oligomerizes Bax and Bak into the outer membrane of the mitochondria
- pore formed makes cytochrome C leak out into cytosol
5, cytochrome C binds APAF-1 (apoptosome) - apoptosome cleaves caspase 9
- caspase 9 activates effector caspases (apoptosis)
describe CD8 response to tumor
- cell injury or death at tumor site generates signals to mature the DC
- DC process Ag and transport to LN
- DC present tumor peptide Ag to naive T cells (signal 1) and signals 2+3 happen
- tumor specific CTL generated
2 mechanisms of T cell death
- passive cell death
2. activation induced cell death
what is passive cell death
the cell is deprived of growth factors and IL-7 (survival signals) leading to MOMP (mitochondria dies, decreases ATP, cell dies)
what is activation induced cell death
cytokine driven expression of receptors and ligands for cell death leading to death receptor mediated apoptosis (FAS)
what drives expression of Fas and FasL expression on activated T cells?
IL-2
what finally allows Fas to kill the cell?
few days after Ag, IL-2 levels decrease and c-FLIP levels drop == no protection, and FasL and Fas bind. apoptosis
what happens to effector T cells if threat has established a chronic infection?
exhausts T cell, leading to microbial/cancer persistence (herpes, hepatitis, cancers)
what is altered in exhausted T cells?
effector functions and chromatin patterns
what happens if you administer blocking antibodies?
CTL cytotoxicity returns, but it is limited to the functions previously induced ( because no change in gene expression or proliferation)
