Functional Lymphoid Anatomy

Question 1

What are the central (primary) lymphoid organs?

Answer 1

Bone Marrow (b-cells)
Thymus (t-cells)
–>lymphopoiesis
–>central tolerance

Question 2

What are the peripheral (secondary) lymphoid organs?

Answer 2

Lymph Nodes, Spleen, Mucosal Associated Lymphoid Tissue

• ->activation of naive lymphocytes
• ->peripheral tolerance

Question 3

What do stromal cells do?

Answer 3

provide signals that direct the development of progenitor cells and eventually b-cells

Question 4

What is central tolerance?

Answer 4

Immature B-cells in the BM are tested for reactivity to self antigens
-eliminated if autoreactive

Question 5

HOw do mature B-cells leave the marrow?

Answer 5

via sinusoids that enter the central sinus and are carried by the venous blood supply to the spleen

Question 6

What is in the thymic cortex of the thymus?

Answer 6

outer cortical region

• contains only immature thymocytes and scattered macrophages
• most T-cell development occurs here
• double negative t-cells

Question 7

What is the corticomedullary junction?

Answer 7

where T-cell progenitors enter

Question 8

What is the medulla?

Answer 8

Inner region

-more mature, single positive thymocytes along with the dendritic cells and macrophages

Question 9

What is the thymic cortical stroma?

Answer 9

network of epithelial where T cell precursors reside

• provides unique microenvironment for T-cell development
• has epithelial cells with long branching processes that express both MHC 2 and 1

Question 10

What are the steps of T-cell development?

Answer 10

1. double negative -proliferate vigorously and CD3 negative
2. Receptor rearrangement –>CD3+ and CD4 CD8 double positive
3. Positive Selection–>CD8 or CD4
4. Negative selection: must not recognize self too much

Question 11

Where do T cells encounter foreign antigens?

Answer 11

In the peripheral lymphoid organs

Question 12

Does lymphoid tissue provide sustaining signals to lymphocytes that do not encounter their specific antigen immediately?

Answer 12

yes so they will continue to survive and recirculate

Question 13

Are peripheral lymphoid tissues dynamic?

Answer 13

yes
B-cell follicles of a lymph node will expand during infections to form germinal centers and the entire lymph node enlarges

Question 14

What is homing of lymphocytes and other cells to specific regions of peripheral tissues mediated by?

Answer 14

chemokines

Question 15

What is lymph?

Answer 15

extracellular fluid from tissues

Question 16

How do antigens get to the lymph nodes?

Answer 16

Free antigen or antigen on an APC travel from site of infection through the afferent lymphatic vessels into the draining lymph nodes

Question 17

WHat happens once the antigen or APCs get to the lymph node?

Answer 17

antigen-specific lymphocytes are activated

• 1 week later, the activated lymphocytes and its clones leave via efferent lymphatic vessels
• to the bloodstream via the thoracic duct and back to the site of infection

Question 18

What is steady-state?

Answer 18

naive lymphocytes that do not recognize their antigen leave via efferent lymphatics and recirculated until they meet their match or die

Question 19

What are High Endothelial venules (HEV)?

Answer 19

How naive lymphocytes get into lymphoid

-located in paracortical areas

Question 20

What are the follicles of the lymph node?

Answer 20

where B cells are located in lymph node

Question 21

What is in the outer cortex of the lymph node?

Answer 21

follicles

Question 22

What is the paracortical area?

Answer 22

• deep cortex where the T cells are diffusely scattered
• where free antigen gets trapped on resident DCs and macrophages
• where dendritic cells bring their antigens
• –>meeting spot for T cells and APCs so T cells can become activated

Question 23

What are germinal centers?

Answer 23

where activated B cells undergo intense proliferation and differentiation into plasma cells with the help of T helper cells

-somatic hypermutation, and class switching

Question 24

Is the spleen directly connected to the lymphatic system? What type of pathogens does it respond to?

Answer 24

no
collects antigens from the blood
-involved in immune responses to blood-borne pathogen (not tissue)

Question 25

Where do lymphocytes enter and exit the spleen?

Answer 25

exist first in marginal sinus then migrate to appropriate areas of the white pulp
-probably leave via venous sinuses in the red pulp

Question 26

What is the secondary function of the spleen?

Answer 26

Disposal of old RBCs

Question 27

What is the red pulp?

Answer 27

majority of the spleen, sites of RBC disposal

Question 28

What is the white pulp?

Answer 28

lymphocytes surrounding the arterioles running through the spleen

Question 29

What is periarteriolar lymphoid sheath?

Answer 29

Sheath of lymphocytes around an arteriole; mainly T cells

Question 30

WHere are the follicles in the spleen what do they contain?

Answer 30

• adjacent to the PALS

- contain B cells-may be germinal centers

Question 31

Where is the marginal zone what does it do?

Answer 31

surrounds follicle

-contains macrophages and resident non circulating bcells

Question 32

What do blood-borne microbes, soluble antigens and antigen:antibody complexes do in the spleen?

Answer 32

Get filtered from the blood by macrophages and immature dendritic cells within the marginal zones
-then they migrate to the Tcell area and activate T cells (PALS)

Question 33

What do Peyer’s patches contain?

Answer 33

1) Microfolds (M) cells: specialized epithelial cell which directly collects antigen from the lumen
2) Follicle: large central dome of B cells, surrounded by smaller numbers of T cells
3) Resident DCs present antigen to T cells
4) B-cells tend to commit to producing IgA (germinal centers)