CH.8 – T cell mediated immunity
Part 1: T cell activation
- Myeloid Dendritic cells take up antigens at site of infection (present Ag in MHC in cell surface
= matured Dc*) and carry them to secondary lymphoid tissues for presentation to naive T
cells
*Maturation of Dc change their form – when non-self Ag + MHC in grows “fingers” that allow it present
Ag for as many T cells as possible
- CD4 T cell activation = Ag+MHCII (Dc uptakes Ag by receptor mediated endocytosis of
bacteria, Micropinocytosis or Phagocytosis of environment that brings organisms along)
- CD8 T cell activation = Ag+MHCI (Dc uptakes Ag when viral DNA gets inside during a viral
infection and by cross-presentation)
Note: all somatic cells express MHC I
- In T cell area: TCR matches Dc’s MHC:Ag = stays there (if not it goes back to circulation)and
TCR signals T cells to prepare for activation
- 2 receptors have to bind for activation/proliferation to occur:
1) TCR:MHC
2) CD28:B7 (co-stimulator found in APC only expressed when presenting non-self Ag)
Note: regulation of T cell proliferation→ CTLA4:B7 (binds B7 better than CD28) = inhibition of
naive T cell activation to prevent overproduction
- IL-2 expressed when TCR binds to APC and gets activated → signal for T cell to proliferate
(autocrine signaling)
Note: In the case of viral infections, viruses can block CD8 activation by inactivating Dc’s ability to
activate them with just MHC1 & B7 binding→ CD4 cells assistance (both cd4 & cd8 have to bind to
mhc): secretion of IL-2 activates CD8
- Propagation and maturation of effector T cells: Dc Bound activated T cells proliferate and
all clones remain attached to DC which secretes cytokines that tell them which type of effector
T cell to become.
- CD8 cytotoxic T cells: directly killed infected cells (only when is very obvious since it causes
so much damage in the process) by secreting cytotoxins that will poke holes on membranes
and induce apoptosis
- CD4 effector T cells: assistance of immune system in clearing infections without directly
attacking pathogen
, -
Th1 Th2 Th17 Tfh (follicular T Treg (regulatory T
cell) cell)
cytokine IL -12 (APC) IL -4 IL-6 IL-6 TGF-b
secreted IFN-gamma (NK TGF-b IL-21
causes its cells) IL-23
differentiation
cytokines IL-2 IL -4 IL-17 IL-21 TGF-b
secreted by it IFN-gamma IL-5 IL-22 IL-10
function of cell activate response against enhance activate B cells suppress other
macrophages & parasites neutrophils effector T cells
promote response
differentiation of
more TH1
Part II: Effector T cells
- differentiates effector t cells leave lymph node and travel to sites of infection
Note: Effector T cells don't need CD28:B7 binding to recognize Ag (work faster)
- When cognate pair with target cell is formed Effector t cells release cytokines that alter cell
behavior (CD4 & CD8) or cytotoxins that kill target cells (CD8)
TH1
Part 1: T cell activation
- Myeloid Dendritic cells take up antigens at site of infection (present Ag in MHC in cell surface
= matured Dc*) and carry them to secondary lymphoid tissues for presentation to naive T
cells
*Maturation of Dc change their form – when non-self Ag + MHC in grows “fingers” that allow it present
Ag for as many T cells as possible
- CD4 T cell activation = Ag+MHCII (Dc uptakes Ag by receptor mediated endocytosis of
bacteria, Micropinocytosis or Phagocytosis of environment that brings organisms along)
- CD8 T cell activation = Ag+MHCI (Dc uptakes Ag when viral DNA gets inside during a viral
infection and by cross-presentation)
Note: all somatic cells express MHC I
- In T cell area: TCR matches Dc’s MHC:Ag = stays there (if not it goes back to circulation)and
TCR signals T cells to prepare for activation
- 2 receptors have to bind for activation/proliferation to occur:
1) TCR:MHC
2) CD28:B7 (co-stimulator found in APC only expressed when presenting non-self Ag)
Note: regulation of T cell proliferation→ CTLA4:B7 (binds B7 better than CD28) = inhibition of
naive T cell activation to prevent overproduction
- IL-2 expressed when TCR binds to APC and gets activated → signal for T cell to proliferate
(autocrine signaling)
Note: In the case of viral infections, viruses can block CD8 activation by inactivating Dc’s ability to
activate them with just MHC1 & B7 binding→ CD4 cells assistance (both cd4 & cd8 have to bind to
mhc): secretion of IL-2 activates CD8
- Propagation and maturation of effector T cells: Dc Bound activated T cells proliferate and
all clones remain attached to DC which secretes cytokines that tell them which type of effector
T cell to become.
- CD8 cytotoxic T cells: directly killed infected cells (only when is very obvious since it causes
so much damage in the process) by secreting cytotoxins that will poke holes on membranes
and induce apoptosis
- CD4 effector T cells: assistance of immune system in clearing infections without directly
attacking pathogen
, -
Th1 Th2 Th17 Tfh (follicular T Treg (regulatory T
cell) cell)
cytokine IL -12 (APC) IL -4 IL-6 IL-6 TGF-b
secreted IFN-gamma (NK TGF-b IL-21
causes its cells) IL-23
differentiation
cytokines IL-2 IL -4 IL-17 IL-21 TGF-b
secreted by it IFN-gamma IL-5 IL-22 IL-10
function of cell activate response against enhance activate B cells suppress other
macrophages & parasites neutrophils effector T cells
promote response
differentiation of
more TH1
Part II: Effector T cells
- differentiates effector t cells leave lymph node and travel to sites of infection
Note: Effector T cells don't need CD28:B7 binding to recognize Ag (work faster)
- When cognate pair with target cell is formed Effector t cells release cytokines that alter cell
behavior (CD4 & CD8) or cytotoxins that kill target cells (CD8)
TH1
