Linking Innate and Adaptive Immunity 1

Question 1

what does it mean when dendritic cells are “homing” to the lymph node?

Answer 1

migrating

Question 2

how do dendritic cells migrate to a lymph node?

Answer 2

via lymphatic vessel

Question 3

what allows DCs to migrate?

Answer 3

once PRRs are activated, they express receptors that target them to lymphoid tissue

Question 4

what are the 3 signals of antigen presentation?

Answer 4

1. ACTIVATION: present epitope via MHC to TCR
2. SURVIVAL: activated DCs express costimulatory molecules B7.1/CD80 or B7.2/CD86 to CD28 on T cell
3. DIFFERENTIATION: activated DCs release cytokines to tell T cell what to differentiate into

Question 5

what are 2 types of T cells?

Answer 5

1. CD4 / Th
2. CD8 / Tc

Question 6

what are the 5 results of PAMPs-induced PRR signaling in DCs?

Answer 6

1. increased expression of receptors that target DCs to lymphatics for migration
2. reduction in receptors that naive cell needed, like PRRs
3. increased processing of antigen so it can be presented
4. induced expression of co-stimulatory molecules
5. increased expression of MHC molecules

Question 7

why are co-stimulatory molecules only expressed once DCs are activated?

Answer 7

naive DCs don’t require signal 2 (survival), only required when needs to interact with T cell

Question 8

why is expression of MHC molecules increased when DCs are activated?

Answer 8

multiple types of MHCs are expressed to increase the possibility for MHC:peptide combinations which increases efficiency for finding a matching T cell

Question 9

ultimately, what is the result of PAMPs-induced PRR signaling in DCs?

Answer 9

activated DC is now capable of priming naive T cells

Question 10

what does it mean when DCs are able to prime naive T cells?

Answer 10

first contact that the T cell has with its antigen

Question 11

what are the 2 characteristics of an unactivated/immature DC?

Answer 11

1. Many dendrites
2. can phagocytose

Question 12

why do unactivated/immature DCs have many dendrites?

Answer 12

want to see whole environment to find something to phagocytose

Question 13

what happens to the DC when it becomes activated and is travelling thru the lymphatic vessel?

Answer 13

it loses its dendrites (becomes rounder) and is no longer phagocytic

Question 14

what 2 things happen to the activated DC when it is in lymphoid tissue?

Answer 14

1. express peptide:MHC and costimulatory molecules
2. interacts with T cell

Question 15

what are the 2 types of DCs?

Answer 15

1. conventional dendritic cell
2. plasmacytoid dendritic cell

Question 16

what are the 4 characteristics of a conventional dendritic cell?

Answer 16

1. travels to lymphoid tissue once activated
2. activates T cells in lymphoid tissue
3. classic APC
4. phagocytic

Question 17

what are the 3 characteristics of a plasmacytoid dendritic cell?

Answer 17

1. stays at site of infection - NEVER migrates
2. high levels of PRRs
3. secretes cytokines (type I IFN) to amplify local response

Question 18

does 1 DC activate 1 or many T cells? why?

Answer 18

activates many T cells because has many MHC

Question 19

what happens to the T cell once it becomes activated?

Answer 19

differentiates

Question 20

what 2 other lymphoid organs have the same function/events as the lymph node?

Answer 20

1. spleen
2. Peyer’s patch

Question 21

how do DCs enter the lymph node?

Answer 21

via Afferent lymphatics

Question 22

how do T and B cells enter the lymph node?

Answer 22

via diapedesis thru High Endothelial Venules (HEV

Question 23

what are HEVs?

Answer 23

post-capillary venules found in lymph nodes –> part of blood circulation

Question 24

what are the 2 times that DCs transfer their antigen to resident DCs in the lymph node?

Answer 24

1. if antigen is from virus that kills DCs during phagocytosis
2. if cDCs are absent, antigen taken up by macrophages (APCs) for transport and then antigen transferred

both can stimulate naive T cells

Question 25

how do naive lymphocytes scan for their specific antigen that they can respond to?

Answer 25

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

Question 26

how do T cells exit the lymph node? and when?

Answer 26

exit via efferent lymphatics

when T cell doesn’t encounter the antigen and if becomes activated + proliferates

Question 27

what happens to the T cell when it encounters an antigen presented by DC?

Answer 27

T cell stays in lymph node until activation and proliferation is complete

Question 28

why does the adaptive response take so long? (2)

Answer 28

1. proliferation takes a long time
2. T cells must remain in lymph node until proliferation is complete

Question 29

what are effector T cells?

Answer 29

T cells that have been proliferated/selected for and can have an effect on the adaptive immune response

Question 30

what happens if the T cell doesn’t encounter an antigen?

Answer 30

leaves lymph node via efferent lymphatics

Question 31

OVERALL PATH OF DCs BEING ACTIVATED THEN MIGRATING

Answer 31

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

Question 32

OVERALL PATH OF T CELLS

Answer 32

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