Lymphatics & Regulation

Question 1

What is a lymphoid follicle?

Answer 1

• an island of follicular dendritic cells within a sea of B cells
• located in all secondary lymphoid organs

Question 2

Whats the difference between antigen presenting dendritic cells and follicular dendritic cells?

Answer 2

• dendritic cells are produced in bone marrow, while FDCs take their place in the lympoid organs during embryogenesis
• Dendritic cells present to T cells via MHC, FDCs display antigen to B cells

Question 3

How does a follicular dendritic cell become “decorated” with antigens?

Answer 3

• its receptors bind complement fragments

- picks up and retains the ospsonized antigen (can also retain invaders opsonized by antibodies)

Question 4

Where are HEVs located?

Answer 4

Paracortex of the lymph node

Question 5

Are dendritic cells a part of the innate or adaptive immune system?

Answer 5

Innate

Question 6

Where are the T cells located in the lymph node?

Answer 6

Paracortex

Question 7

Which part, light or dark, of a germinal center contains the proliferating B cells?

Answer 7

Light

Question 8

How do APCs and lymphocytes know where to go within a lymph node and when to go there?

Answer 8

• Follicular dendritic cells in a lymph node produce a chemokine called CXCL13
• Naive B cells are attracted to this chemokine
• if B cell finds its cognate, it downregulates CXCL13, and upregulates CCR7
• CCR7 detects a chemokine produced in region where activated Th cells and B cells meet

Question 9

What cytokines does the Regulatory T cell produce? What do they do?

Answer 9

IL-10 binds to T cells to block co-stimulatory signals

TGF-beta

Both restrain the immune system

Question 10

What receptor does B7 on APCs bind to on Th cells (stimulatory or inhibitory)?

Answer 10

CD28 = stimulatory

CTLA-4 = inhibitory

*CLTA-4 works by antagonizing the CD28 activation signal within the T cell

Question 11

Where is the CTLA-4 receptor kept on a naive T cell? When active?

Answer 11

• naive = kept inside cell

- When activated, CTLA-4 is moved to the surface of the cell

Question 12

Which has a higher affinity for B7 on T cells, CD28 or CTLA-4?

Answer 12

CTLA-4 (1000x higher)

Question 13

What do M cells do?

Answer 13

• enclose antigens of the intestinal lumen in endosomes
• transport antigens to Peyer’s Patches
• concentrate the efforts of a Peyer’s patch on potential pathogens

Question 14

Describe dendritic cells in the spleen?

Answer 14

• inactive reside in marginal sinus
• take up foreign antigens or get infected by pathogens
• Display MHC I/II
• Once activated, travel to PALS where T cells have gathered

**Th cells activated by dendritic cells move from PALS to lymphoid follicles to activate B cells

Question 15

What stimulates Th 17 cells?

Answer 15

-IL-6 in concert with TGF-beta

**remember, TGF-beta also stimulates Treg cells

Question 16

What happens when Natural Killer cells die off after an infection has been battled?

Answer 16

• NK cells secrete IFN-gamma, which activates macrophages

- NK cells die, no more IFN-gamma to activate macrophages, so they simmer down

Question 17

What is Activation-induced cell death (AICD)?

Answer 17

-process by which obsolete T helper cells are eliminated

How it works:
-CTL’s have Fas-L

• when T cells are activated, they become increasingly more sensitive to ligation of Fas proteins
• CTL’s kill 90% of the obsolete active T cells