Lymph node development

Question 1

What is the hallmark feature of secondary lymph organs?

Answer 1

Highly ordered compartmentalization of T and B cells and also myeloid cells.

Question 2

What is the role of (non-hematopoietic) lymph node stromal cells?

Answer 2

Maintain LN integrity and function, play a role in organogenesis and support immune responses.

Question 3

What two cells types lead to LN organogenesis in humans and around what weeks?

Answer 3

Lymphoid Tissue Inducer (LTi) and Lymphoid Tissue organizer (LTo) around weeks 8 to 11 of gestation

Question 4

LTi cells have a CD45 marker. What does that mean?

Answer 4

They are hematopoietic stem cells.

Question 5

What two transcription factors lead to the formation of LTi cells?

Answer 5

Id2 and RORyt.

Question 6

What are CXCR5 and CCR7?

Answer 6

Chemokine receptors.

Question 7

Do LTo cells have a CD45 marker? What does that mean?

Answer 7

They do not, LTo are non-hematopoietic / non-stem cells.

Question 8

What chemokines bind to CCR7?

Answer 8

CCL19 and CCL21

Question 9

How do LTi cells induce LTo cells?

Answer 9

LTi cells produce lymphotoxin, which binds to LTbR on LTo.

Question 10

What chemokines does CXCR5 bind?

Answer 10

CXCL13

Question 11

What do CXCR5 or CXCL13 deficient mice develop?

Answer 11

They lack most LNs

Question 12

What do CCR7 or CCL19/21 deficient mice develop?

Answer 12

Develop all LNs, but they are smaller and badly organized.

Question 13

Briefly describe the steps of LN development.

Answer 13

LTi cells are found in the fetal liver. They travel to spots called “LN Anlagen” which are line ‘nests’ where Lymph Nodes will develop. LTi cells that travel to those nests start recruiting LTo cells that are of mesenchymal (mLTo) or endothelial origin (eLTo). LTo cells then create a feed-forward loop that recruits more LTi cells.

Question 14

Which molecule and where is suggested to play a role in setting up the LN Anlage?

Answer 14

Lymphotoxin (LT) signaling in mesenchymal cells has been found to potentially play a role in the anlage development.

Question 15

What is the role of High Endothelial Venules (HEV)?

Answer 15

Those are cuboidal cells at the differentiated end of the lymph node venule, which play a role in catching lymphatic cells and transporting them into the LN.

Question 16

What signaling molecules do HEVs need to transport cells to the LN?

Answer 16

They need LTbR signaling by LT from DC.

Question 17

What are the three compartments of the lymph node and what ells does it harbor?

Answer 17

1. Cortex - the outer part of the LN and harbors B-cells within individual B-cell follicles.
2. Paracortex - beneath the cortex in which T-cells and DCs are located
3. Medulla - The basal part of the LN, is where macrophages and plasma cells are found. They also contain sinuses to facilitate lymph flow.

Question 18

What type of cells is important for the migration of specific cells to specific places WITHIN the lymph node?

Answer 18

The Fibroblastic Reticular Cells (FRC).

Question 19

What is PDPN a marker of?

Answer 19

FRC

Question 20

Briefly explain FRC development.

Answer 20

Development of FRC starts when mesenchymal LTo cells transition to the precursor cells in an LT-independent manner. Then The formation of FRC from the precursor requires LT / LTbR signaling.

Question 21

What is CLEC2 important for?

Answer 21

FRCs and LECs both express PDPN in order to bind to CLEC2 on DC. This is important for the transport of DC into the lymph node.

Aka. Important for DC transport into LN.

Question 22

Where are TRCs located, what do they secrete and why?

Answer 22

TRCs are found in the T-cell zones of the LN. They secrete homeostatic CCL19 and CCL21 and mediate the recruitment of CCR7 naive T-cells and DCs to facilitate their interactions.

Question 23

How is a chemokine gradient established in the LN and what is it used for?

Answer 23

LECs (border of the LN) produce a chemokine used in degradation, so once cells enter the LN, they will travel to the highest concentration of their respective chemokine, which will be higher the further away it is from the border of the LN.

Question 24

What happens during loss of LT and TNF?

Answer 24

FDC (FRC for DC) do not develop properly.

Question 25

What is the function of IL-7 and where is it produced?

Answer 25

It is the T-cell survival factor and it is produced in the TRC (T-cell FRC).

Question 26

What factor important to B-cells do FRCs secrete?

Answer 26

FRCs on the outer edge of B-cell follicles secrete BAFF, which is important for B-cell maturation, survival and proliferation.

Question 27

What receptors and chemokines are important for B-cell recruitment by FRC in the LN follicle?

Answer 27

chemokine CXCL13 which attracts CCR5 B-cells.

Question 28

What is the function of LECs and FRCs in the context of CD8?

Answer 28

LECs and FRCs have a secondary anti-self-reactive CD8 control, which presents peripheral tissue antigen on MHC-I. Transcription factor Deaf-1 is important for this process. In the Thymus, gene AIRE is the one doing this.

Question 29

Why is CCL21 expression upregulated during an immune response?

Answer 29

To attract CCR7 expression naive T-cells and DC.

Question 30

Upon antigen uptake, what receptor on DC is upregulated to facilitate transport to LN?

Answer 30

CLEC2 on DC, which binds to PDPN on FRC.

Question 31

What happens when DC bind to FRC during an immune reaction?

Answer 31

The FRCs stretch and lose their tension, expanding the cells and leading to lymph node swelling.

Question 32

Which cells and receptors are important for FRC quiescence?

Answer 32

B-cells and DCs by an LT / LTbR mediated response.

Question 33

Briefly explain B-cell activation with the help of FRC.

Answer 33

T-cells activate B-cells which then migrate to the follicular center and activate the germinal center to produce high-affinity antibodies. FDCs (B-cell FRC) expand in number by differentiation from MRC and express high amounts of CXCL13, BAFF, and IL-6. (these three are important for B-cell survival, recruitment, and growth.)