Lymphoid Anatomy

Question 1

central lymphoid organs

Answer 1

thymus and bone marrow

Question 2

peripheral lymphoid organs

Answer 2

adenoid, tonsil, lymph nodes, appendix, spleen, mucosal

Question 3

B and T cells originate where

Answer 3

bone marrow

Question 4

B cell mature where

Answer 4

bone marrow and are continually produced even in adults

Question 5

where do T cell mature

Answer 5

thymus-slows down as individuals age but T cell numbers are maintained outside the central lymphoid organs

Question 6

adaptive immunity occurs when

Answer 6

a lymphocyte meets its corresponding antigen in the peripheral lymphoid tissue

Question 7

purpose of lymphoid tissue

Answer 7

Supports lymphopoiesis
Supports development of incredibly diverse repertoire of antigen-specific lymphocytes
Critically important for both central & peripheral tolerance
Provides sustaining signals for lymphocyte survival

Question 8

central lymphoid tissue purpose

Answer 8

Responsible for lymphopoiesis
Responsible for central tolerance
B cells: Bone Marrow
T cells: Thymus

Question 9

peripheral lymphoid tissues purpose

Answer 9

Mixture of B & T cells
Supports circulating lymphocyte survival
Activation of naïve lymphocytes
Peripheral Tolerance

Question 10

Stromal cells

Answer 10

Stromal cells in the bone marrow, are critically important to B cell development. Provide maturation factors such as FLT3 ligand, IL-7, Stem-Cell Factor (SCF) & CXCL12

Question 11

final stage of immature B cells developing to mature B-cells occurs where?

Answer 11

peripheral lymphoid organs

Question 12

Central Tolerance

Answer 12

immature B cells in the BM are tested for reactivity to self antigens or auto reactivity and are eliminated if autoreactive

Question 13

thymus cortex

Answer 13

the outer cortical region; contains only immature thymocytes & scattered macrophages; most t-cell development occurs here

Question 14

thymus medulla

Answer 14

the inner region; more mature single positive thymocytes, dendritic cells & macrophages

Question 15

lack of Thymus

Answer 15

no T cell development despite lymphoid progenitors

Question 16

young vs old thymus

Answer 16

The thymus is fully developed at birth
Rate of T-cell production is greatest before puberty
After puberty, the thymus begins to shrink & the production of new T cells is lower but not entirely absent

Question 17

when does the beta chain rearrangement of the T-cell receptor take place

Answer 17

during the double negative phase

Question 18

when does the alpha chain rearrangement take place

Answer 18

during the puble positive phase

Question 19

T-cell development relays on

Answer 19

timely expression of various surface and signaling molecules

Question 20

thymic cortal stroma

Answer 20

network of epithelia where the T cell precursors reside; provides unique microenvironment for T- cell development (like B cell stromal cells); has epithelial cells with long branching process that express both MHC I and MHC II on their surface.

Question 21

corticomedullary junction of the thymus

Answer 21

where the t cell progenitors enter

Question 22

positive selection

Answer 22

if the double positive T cell does recognize self-peptide;self-MHC complexes, than it will drop one of the co-receptors and become either CD4+ or CD8+ single positive T-cells and migrate to the medulla

Question 23

Negative selection

Answer 23

If the single positive T-cell recognizes self-peptide:self-MHC too strongly, then it will undergo apoptosis. If it does not it will be exported from the thymus to the periphery

Question 24

central tolerance

Answer 24

98% of thymocytes that develop in the thymus also die in the thymus by apoptosis. includes positive and negative selection

Question 25

antigens and APCs enter the lymph node through

Answer 25

afferent lymphatics into the paracortical areas

Question 26

APCs and lymphocytes are attracted to the lymph nodes by

Answer 26

chemokines

Question 27

High endothelial Venules (HEV)

Answer 27

how naive lymphocytes get into the lymph node, located in paracortical area

Question 28

follicules of lymph node

Answer 28

where B cells are located in a lymph node

Question 29

cortex of lymph node

Answer 29

outer area of the lymph node where the follicules are

Question 30

paracortical area (of lymph node)

Answer 30

aka deep cortex; where the T cells are diffusely scattered; also where free antigen gets “trapped” on resident DCs and macrophages; also where migrating DC’s bring their antigens. Great meeting spot for T cells and APCs so T cells can become activated.

Question 31

germinal centers

Answer 31

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

Question 32

Spleen functions in immune responses to

Answer 32

blood born pathogens (not in the tissues); (especially good at responding to encapsulated bacteria)

Question 33

secondary function of the slpeen

Answer 33

dispose of old red blood cells

Question 34

Red pulp

Answer 34

majority of the spleen; sites of red blood disposal

Question 35

white pulp

Answer 35

collection of densely packed lymphocytes surrounding the arterioles running through the spleen

Question 36

periarteriolar lymphoid sheath (PALS)

Answer 36

sheath of lymphocytes around an arteriole; mainly T-cells

Question 37

follicules (of spleen)

Answer 37

adjacent to the PALS; contain B cells, may be germinal centers

Question 38

Marginal zone

Answer 38

surrounds the follicle; contains macrophages and resident, non-circulating B cells which are sensitive to circulating bacterial peptides

Question 39

what do macrophages and DCs within the marginal zone do

Answer 39

filter blood-borne microbes, soluble antigens, and antigen:antibody complexes which migrate to T cell areas and activate T cells after filtration

Question 40

When they become activated (in the LN), T cells and B cells both

Answer 40

move to the border of the follicle and T-cell zone, & T cells can provide their helper function to B cells

Question 41

Peripheral tolerance

Answer 41

In the absence of an infection, mature B & T cells that encounter a strongly cross-linking antigen in the peripheral lymphoid organs will undergo clonal deletion or anergy

Question 42

Peyer’s patches structure

Answer 42

Peyer’s Patches have the structure of lymphoid follicles with parafollicular regions & germinal centers. However they are not encapsulated & have lymph & blood-independent entry of antigen from the lumen