Lymphoid System

Question 1

Where do B cells differentiate?

Answer 1

BM

Question 2

Where do T cell differentiate?

Answer 2

Start in BM, continue in thymus

Question 3

Where does activation occur?

Answer 3

Secondary lymphoid organs (LN, spleen, tonsils) and lymphoid tissues in non-lymphoid organs

Question 4

Is lymphocyte differentiation Ag dept?

Answer 4

NO

Question 5

Blast transformation

Answer 5

result of lymphocyte activation, cell enlarges to become immunoblast and divides repeatedly

Question 6

Thymus is what kind of organ?

Answer 6

Lymphoepithelial organ

Question 7

Development of thymus

Answer 7

development begins at about 5wks of gestation, from the endodermal epithelium of 3rd pharyngeal pouch, bi-lobed organ migrates into superior mediastinum of thorax at approx 7wks

Question 8

Thymic epithelial cells/epithelioreticular cells

Answer 8

initially exclusively makes up thymus, connected by desmosomes, first prothymocytes push between these cells and for sheets connected by tight junctions, eventually thymic epithelial cells will become stromal cells of thymus
found in both cortex and medulla, large pale cells with euchromatic nuclei, have tonofibrils composed of cytokeratin tonofilaments
Not phagocytic

Question 9

Capsule of thymus

Answer 9

dense irregular CT with type I collagen and reticular fibers

Question 10

Septa of thymus

Answer 10

sheets of CT that extend inwards from capsule, incompletely subdivide the two lobes into many lobules

Question 11

Cortex of thymus

Answer 11

dark-staining region of each lobule, contains more lymphocytes (dark staining), partially surrounds medulla

Question 12

Medulla of thymus

Answer 12

pale inner region of each lobule, continuous throughout organ, contains more macrophages that lymphocytes

Question 13

Stroma of thymus

Answer 13

formed by thymic epithelial cells, ONLY PRESENT IN THYMUS

Question 14

Presence of tonofibrils composed of cytokeratin tonofilaments helps to identify what?

Answer 14

TECs as epithelial cells vs CT

Question 15

Cortical TECs

Answer 15

Type 1-3

Question 16

Type I TEC

Answer 16

line inner surface of capsule, cover CT septa, surround cortical blood vessels

Question 17

Type II TEC

Answer 17

nurse cells, stellate cells whose long processes are connected by desmosomes, form nests for thymocytes, participate in positive selection

Question 18

Type III TEC

Answer 18

at corticomedullary boundary, connected by tight junctions, also important for + selection

Question 19

Medullary TECs

Answer 19

Type 4-6

Question 20

Type IV TEC

Answer 20

layer just deep to type III, joined by tight junctions

Question 21

Type V TEC

Answer 21

approximately equal to nurse cells, for meshwork throughout medulla, particulate in - selection

Question 22

Type VI TEC

Answer 22

arranged in concentric layers to form Hassall’s corpuscles, evidence they may contain thymic stromal lymphopoietin that activates thymic dendritic cells

Question 23

Thymocyte migration path

Answer 23

1. corticomedullary boundary to outermost cortex, just beneath capsule
2. back to corticomedullary boundary
3. back to medulla
4. leave organ as mature naive T cell and migrate to secondary lymphoid organ

Question 24

Tingible body macrophages

Answer 24

Macrophages that have phagocytosed apoptotic cells in cortex

Question 25

blood-thymus barrier

Answer 25

tight in cortex and leaky in medulla

Question 26

Involution of thymus

Answer 26

thymus is fully function and formed at birth, reaches max weight at puberty, then decreases, some functional tissue throughout life

Question 27

DiGeorge syndrome

Answer 27

congenitial defect involving malformation of structures derived from 3rd (thymus) and 4th pharyngeal pouches, pt cant product normal T cells

Question 28

Difference between stroma of thymus and LN

Answer 28

Epithelial stroma in thymus | CT stroma w/ reticular fibers in LN

Question 29

Do afferent lymphatics have valves?

Answer 29

yes, to prevent backflow, so due efferent lymphatics

Question 30

Hilus of LN

Answer 30

where efferent lymphatic vessels leave

Question 31

Where are nodules present in LN?

Answer 31

Outer cortex contains lymphoid nodules (primary or secondary), paracortex and medulla do not

Question 32

Pathway of lymph flow

Answer 32

afferent lymphatics, subcapsular sinus, trabecular, sinuses, medullary sinuses, efferent lymphatic vessel

Question 33

Difference between sinuses and lymphatics?

Answer 33

sinuses dont have valves but are very leaky

Question 34

Where are HEVs

Answer 34

postcapillary venules found in paracortex of LN

Question 35

T cell and B cell regions of the LN

Answer 35

T cell regions are paracortex and internodular cortex | B cell regions are lymphoid nodules

Question 36

Daughter cells of b cell immunoblasts

Answer 36

Memory B cells or plasmablasts

Question 37

Plasmablasts function?

Answer 37

secrete Ab into medullary sinuses or leave node via efferent lymph and travel to other organs

Question 38

Secondary nodule

Answer 38

contains mantle of small memory b cells or inactive B cells pushed aside by germinal center, germinal center contains light-staining activated B cells which move from dark to light zones

Question 39

Names for B cells in dark and light zones

Answer 39

dark - centroblasts | light - centrocytes - interact with FDC, mitosis decreases, negative selection

Question 40

FDC form what? and function as?

Answer 40

Stroma of primary and secondary nodules, not true APCs, bind immune complexes for long periods of time

Question 41

Causes of lymphadenopathy

Answer 41

immune reactions, microbial infection, primary malignancies of LN, replication of metastatic malignant cells

Question 42

Follicular hyperplasia

Answer 42

Ab production predominates, but paracortex does not greatly increase in size, ex: rheumatoid arthritis

Question 43

Paracortical hyperplasia

Answer 43

cell-mediated response predominates, with relatively few secondary nodules developing, ex: viral infections

Question 44

Dual roles of spleen

Answer 44

1) white pulp - filtered antigens from blood and initiates immune response 2) red pulp - destroys old/damaged RBCs

Question 45

Hilus of spleen vs LN

Answer 45

Spleen hilium is where blood vessels enter and leave, LN hilium is only where efferent lymphatics leave

Question 46

Splenic capsule

Answer 46

dense irregular CT that contains some myofibroblasts, covered by mesothelium

Question 47

Splenic trabeculae

Answer 47

composed of CT that extends inward from capsule

Question 48

White pulp

Answer 48

is not continuous, organized around central artery, contains PALS (contains mostly T cells - thymus dept region and DCs) and lymphoid nodules (embedded in PALS, B cell regions, contain FDCs, these nodules push central artery to edge of white pulp)

Question 49

Red pulp

Answer 49

``` splenic sinuses (contain blood) highly permeable sinusoidal capillaries splenic cords (bilroths cords) sites where old RBCs are destroyed, mixed cell population ```

Question 50

Marginal zone

Answer 50

surrounds white pulp, separating it from red pulp, initiates immune response, B cells present here do not recirculate

Question 51

Open or closed circulation in spleen?

Answer 51

In humans - open

Question 52

causes of splenomegaly

Answer 52

diseases involving excessive destruction of RBCs, certain lysosomal storage diseases