8: Lymphatic organs and cell trafficking 🏁

Question 1

What are the organs of the immune system?

Answer 1

central/primary:
- thymus
- bone marrow

peripheral/secondary:
- lymph nodes & lymphatic vessels
- spleen
- tonsils and adenoids
- appendix

Question 2

What are lymphatics for?

Answer 2

• migration
• recirculation

-> collect lymph and cell from tissue and deliver them to blood

Question 3

Give an example of cellular movement by immune cells.

Answer 3

1. DC migrates from tissue to lymph node
2. upon activation B & Tfh cells migrate towards B-T boarder zone to undergo cognate interaction
3. primed effector T cells migrate to inflammation site; Neutrophils, macrophages, etc. follow
4. germinal center B cells are retained till they die or differentiate into memory B cell or plasma cell

Question 4

How does Leukocyte activation influence the movement?

Answer 4

Upon activation the expression of adhesion molecules changes, therefore different receptors are used for recirculation of naive leukocytes and migration of activated leukocytes.

Changes are mainly induced by chemokines (cytokines that induce chemotaxis)

Question 5

What do chemokines do?

Answer 5

mediate chemotaxis and chemokinesis

• chemotaxis: directed migration
  
  1. chemokines mediate the adhesion
  2. chemokines direct the migration towards a conc. gradient
• chemokinesis: random cell movement

Question 6

There are 4 families of chemokines. Name them and explain the nomenclature.

Answer 6

4 families: CXC, CC, C, CX3C

the name comes from the pattern of cysteine residues within the chemokines

Question 7

What are the classifications of chemokines according to their function?

Answer 7

Question 8

Homing of T cell subpopulations.

Answer 8

Skin: CLA+ T cell (CCR10)
Mucosal tissue: α4β7+ T cell (CCR9)
2nd lymphoid organ: CXCR5 T cells and CCR7 T cells
bone marrow: CXCR4 T cell

Question 9

Homing of B cells.

Answer 9

naive B cells in follicle of 2nd lymphoid organ
short-lived plasma cell in extrafollicular area of 2nd lymphoid organ
memory cells and plasma blasts (plasma cell precursors) go into circulation
plasma blasts with CCR9/CCR10 migrate to mucosal tissue
long-lived plasma cells stay in bonemarrow niches

Question 10

What are the changes of chemokine receptor expression over B cell development

Answer 10

naive/memory B cell: CXCR5 & CCR7 (CXCR4 possible)

early plasma blast: chemotaxis towards CXCR3 and CXCR4 ligands, no CXCR5 & CCR7

late plasma blast, plasma cell: CXCR4, no chemotaxis

CXCR3 mediates homing to inflammed tissue
CXCR4 mediates homing to bone marrow niches

Question 11

What are immune privileged sites/tissues?

Answer 11

Eye, brain, placenta (pregnant uterus), ovary, testis, liver (adrenal cortex)

some tumors

meaning: leukocytes have limited or no access to these sites to protect these sites from damage caused by the immune system