Linking Innate and Adaptive Immunity 1 Flashcards
what does it mean when dendritic cells are “homing” to the lymph node?
migrating
how do dendritic cells migrate to a lymph node?
via lymphatic vessel
what allows DCs to migrate?
once PRRs are activated, they express receptors that target them to lymphoid tissue
what are the 3 signals of antigen presentation?
- ACTIVATION: present epitope via MHC to TCR
- SURVIVAL: activated DCs express costimulatory molecules B7.1/CD80 or B7.2/CD86 to CD28 on T cell
- DIFFERENTIATION: activated DCs release cytokines to tell T cell what to differentiate into
what are 2 types of T cells?
- CD4 / Th
- CD8 / Tc
what are the 5 results of PAMPs-induced PRR signaling in DCs?
- increased expression of receptors that target DCs to lymphatics for migration
- reduction in receptors that naive cell needed, like PRRs
- increased processing of antigen so it can be presented
- induced expression of co-stimulatory molecules
- increased expression of MHC molecules
why are co-stimulatory molecules only expressed once DCs are activated?
naive DCs don’t require signal 2 (survival), only required when needs to interact with T cell
why is expression of MHC molecules increased when DCs are activated?
multiple types of MHCs are expressed to increase the possibility for MHC:peptide combinations which increases efficiency for finding a matching T cell
ultimately, what is the result of PAMPs-induced PRR signaling in DCs?
activated DC is now capable of priming naive T cells
what does it mean when DCs are able to prime naive T cells?
first contact that the T cell has with its antigen
what are the 2 characteristics of an unactivated/immature DC?
- Many dendrites
- can phagocytose
why do unactivated/immature DCs have many dendrites?
want to see whole environment to find something to phagocytose
what happens to the DC when it becomes activated and is travelling thru the lymphatic vessel?
it loses its dendrites (becomes rounder) and is no longer phagocytic
what 2 things happen to the activated DC when it is in lymphoid tissue?
- express peptide:MHC and costimulatory molecules
- interacts with T cell
what are the 2 types of DCs?
- conventional dendritic cell
- plasmacytoid dendritic cell
what are the 4 characteristics of a conventional dendritic cell?
- travels to lymphoid tissue once activated
- activates T cells in lymphoid tissue
- classic APC
- phagocytic
what are the 3 characteristics of a plasmacytoid dendritic cell?
- stays at site of infection - NEVER migrates
- high levels of PRRs
- secretes cytokines (type I IFN) to amplify local response
does 1 DC activate 1 or many T cells? why?
activates many T cells because has many MHC
what happens to the T cell once it becomes activated?
differentiates
what 2 other lymphoid organs have the same function/events as the lymph node?
- spleen
- Peyer’s patch
how do DCs enter the lymph node?
via Afferent lymphatics
how do T and B cells enter the lymph node?
via diapedesis thru High Endothelial Venules (HEV
what are HEVs?
post-capillary venules found in lymph nodes –> part of blood circulation
what are the 2 times that DCs transfer their antigen to resident DCs in the lymph node?
- if antigen is from virus that kills DCs during phagocytosis
- if cDCs are absent, antigen taken up by macrophages (APCs) for transport and then antigen transferred
both can stimulate naive T cells
how do naive lymphocytes scan for their specific antigen that they can respond to?
they spend hours in the secondary lymphoid organs (lymph nodes) but if there’s no match, they exit and restart the search at a different lymph node
therefore, they are constantly travelling to search for their antigen
how do T cells exit the lymph node? and when?
exit via efferent lymphatics
when T cell doesn’t encounter the antigen and if becomes activated + proliferates
what happens to the T cell when it encounters an antigen presented by DC?
T cell stays in lymph node until activation and proliferation is complete
why does the adaptive response take so long? (2)
- proliferation takes a long time
- T cells must remain in lymph node until proliferation is complete
what are effector T cells?
T cells that have been proliferated/selected for and can have an effect on the adaptive immune response
what happens if the T cell doesn’t encounter an antigen?
leaves lymph node via efferent lymphatics
OVERALL PATH OF DCs BEING ACTIVATED THEN MIGRATING
Immature DC has many dendrites –> capable of phagocytosis
PAMP binds PRR on DC leads to:
- increased receptors for migration
- decreased receptors needed for naive cell
- increased antigen processing
- increased MHC
- increased co-stimulatory molecules
Now DC can prime naive T cells (i.e. T cell can meet antigen)
DC travels thru lymphatic vessels and loses dendrites and ability to phagocytose
DC enters lymph node (or Peyer’s Patch, spleen) thru AFFERENT LYMPHATIC VESSEL
DC expresses MHC molecules and costimulatory molecules and interacts w T cell
OVERALL PATH OF T CELLS
Constantly traveling and searching –> T cell enters lymph node via diapedesis thru HIGH ENDOTHELIAL VENULE
- if no match –> exit thru EFFERENT and restart search or die
- if match –> stay in lymph node until complete proliferation then exit thru EFFERENT
