Heme 04: Podcast - Lymphoid Tissue Histology

Front 1

What are the lymphoid tissues?

Back 1

- Lymph node
- Spleen (particularly the white pulp)
- Mucosa-associated lymphoid tissue (MALT)
- Thymus

Front 2

What are the types of structures in the Lymph Node?

Back 2

- Vascular structures
- Lymphatics
- Hilum
- Capsule
- Subscapular sinus
- Sinus
- Paracortex
- Follicles

Front 3

What are the vascular structures in the lymph node?

Back 3

- Primary vein
- Primary artery → gives rise to different tributaries

Front 4

What are the lymphatic structures in the lymph node?

Back 4

- Afferent lymphatics
- Efferent lymphatic

Front 5

What is the function of the Afferent lymphatics?

Back 5

Carry lymph fluid from other portions of body to LN to be filtered

Front 6

What does lymph fluid contain?

Back 6

- Ags (bacteria, foreign substances, viruses)
- Inflammatory cells (macrophages and dendritic cells)

Front 7

How does the lymph fluid (cells and acellular material) enter the LN?

Back 7

In lymph fluid via afferent lymphatics

Front 8

What is the function of the Efferent lymphatics?

Back 8

- Where filtered lymph fluid exits the LN
- Carries lymph fluid from LN back through the thoracic duct system

Front 9

What structures are found ini the hilum of the LN? How can you differentiate them?

Back 9

- Vein: thin walled
- Artery: thicker walled
- Efferent Lymphatic: relatively thin walled wiht many cells in its lumen

Front 10

What is found in the Efferent Lymphatics?

Back 10

Lots of lymphocytes (vs afferent lymphatic) that are picked up through transport through the LN

Front 11

Where do afferent lymphatics branch first upon entering the LN?

Back 11

Branches in the subscapular space

Front 12

What covers the lymph node?

Back 12

Very thin fibrous capsule

Front 13

What is found under the thin fibrous capsule? What is it made of?

Back 13

Subscapular Sinus
- Space is created by very thin walled ECs composing this lymphatic sinus

Front 14

What do the subscapular sinuses give rise to?

Back 14

- As they dive into the parenchyma even further they give way to the Cortical Sinuses
- Cortical sinuses give way to medullary sinuses in central LN

Front 15

What do the cortical and medullary sinus contain?

Back 15

- Mostly acellular material (mostly material that needs to be filtered or presented to immune cells)

- Only cells you'd expect to see are APCs (macrophages and sometimes some lymphocytes)

Front 16

What are the pink areas?

Back 16

Sinuses (cortical and medullary

Front 17

What are the components of the LN architecture?

Back 17

- Paracortex
- Follicular structures

Front 18

Where is the paracortex of the LN? Structure?

Back 18

- Interfollicular area (between the follicles)

- Generally very vascular
- Predominance of T cells

Front 19

What is found in the follicular structures?

Back 19

B cells (where development occurs)

Front 20

How can you differentiate a benign LN from a malignant LN?

Back 20

- Benign LN: intact architecture
- Malignant LN: disturbed or distorted architecture

Front 21

What are the layers of the follicle?

Back 21

- Germinal center (central)
- Mantle zone (outside germinal center)
- Marginal zone (outermost)

Front 22

What happens in the germinal center of a follicle?

Back 22

- Where significant B cell development occurs
- Frequently where B cells encounter Ag and proliferate in response to antigen

Front 23

What happens in the mantle zone of a follicle?

Back 23

B cells reside here

Front 24

What happens in the marginal zone of a follicle?

Back 24

B cells reside here

Front 25

What components of the follicle do you see in a normal LN?

Back 25

- Frequently see germinal center and mantle zone
- Less frequently see a marginal zone (more common to see it in the spleen follicle)

Front 26

What happens in the first step of B cell development?

Back 26

Naive B cells enter LN
- Never encountered Ag
- Exist in mantle zone

Front 27

What happens in the second step of B cell development, after naive B cells enter the LN?

Back 27

Upon Ag presentation / exposure:
- B cells migrate into germinal center
- Germinal center is where B cell development, somatic hyper-mutation, and proliferation occurs

Front 28

What happens in the third step of B cell development, after naive B cells are exposed to Ag and enter germinal center?

Back 28

- B cells are ready to proliferate
- B cell proliferation occurs in germinal center (becomes very crowded area of follicle)

Front 29

What happens in the fourth step of B cell development, after B cells proliferate in germinal center?

Back 29

- B cells migrate out to reside within marginal zone (not easily visualized)
OR
- B cells traverse into blood

Front 30

What is the most crowded part of the follicle of a LN?

Back 30

Germinal center (central part)

Front 31

What is the thin rim around the germinal center of a LN follicle?

Back 31

Mantle Layer (very dark, dense small cells)

Front 32

What can the germinal center be divided into morphologically?

Back 32

Light Zone

Dark Zone

Front 33

What happens in the light zone of the germinal center?

Back 33

- Number of smaller cells ("centrocytes")
- Less proliferative (haven't gone onto gain proliferation capacity because they haven't been completely Ag stimulated)

Front 34

What happens in the dark zone of the germinal center?

Back 34

- Contains large proliferating cells ("centroblasts")
- More dispersed, delicate chromatin (more blast-like)

Front 35

Is it reactive or malignant to have light zone / dark zone polarity in a LN?

Back 35

Normal reactive morphology contains polarized follicle w/ designation into dark and light zones

Front 36

Where are centrocytes found? What do they look like?

Back 36

- Light zone
- Smaller cells
- Coarser and condensed (purple) chromatin
- Irregular nuclei

(cells are just being stimulated and just starting to undergo processes of Ag exposure)

Front 37

Where are centroblasts found? What do they look like?

Back 37

- Dark zone
- Open and delicate chromatin
- Nuclei not very purple
- Characteristic blastoid chromatin pattern (more immature)
- Larger cells (2-3x size of smaller centrocytes)
- Lots of cytoplasm

(these cells are proliferating)

Front 38

What is the term for the macrophages found in reactive LN follicles?

Back 38

Tingible Body Macrophages

Front 39

When do Tingible Body Macrophages appear?

Back 39

When there's cell turnover or cell proliferation (eg, during reactive process)

Front 40

What is the term for the dendritic cells found in reactive LN follicles?

Back 40

Follicular Dendritic Cells

Front 41

What is the function of Follicular Dendritic Cells?

Back 41

- Stromal component / meshwork
- Form framework of follicle (and germinal center)

Front 42

What is found in the mantle zone layer?

Back 42

- Naive B lymphocytes that haven't encountered Ag yet
- This is where B cells originally reside before they encounter Ag and migrate into germinal center

Front 43

What is found in the paracortex?

Back 43

- Predominantly houses T cells (helper and cytotoxic)
- High endothelial venules
- Dendritic cells and macrophages

Front 44

What are High Endothelial Venules? Where are they found?

Back 44

- Lined by plump, cuboidal endothelial cells
- Lumen within central portion

- Found in paracortex

Front 45

What is the function of High Endothelial Venules in the Paracortex?

Back 45

- Important role in migration of lymphocytes to and from the LN
- Allow lymphocytes to ENTER the LN

Front 46

What does the teal arrow represent?

Back 46

High Endothelial Venule

Front 47

What does the small purple arrow represent?

Back 47

Normal T cell

Front 48

What do the red arrows represent?

Back 48

Thin walled vessels

Front 49

What does the circled structures represent?

Back 49

Several larger cells w/ big prominent nucleoli

Front 50

What happens to the lymph node in patients w/ viral syndrome?

Back 50

- LN paracortical area frequently becomes hyperplastic or reactive appearing
- T cells play an important role in mediating viral infections

Front 51

What are the compartments of the spleen?

Back 51

- Red pulp
- White pulp

Front 52

What happens / is found in the Red Pulp of the spleen?

Back 52

- Filters blood and RBCs
- Majority of the splenic parenchyma

Front 53

What happens / is found in the White Pulp of the spleen?

Back 53

- Immune system: lymphoid tissue component of spleen
- Where immune effect occurs
- T cell rich areas and B cell rich areas

Front 54

What is the location rich in T cells in the spleen?

Back 54

Periarteriolar Lymphoid Sheath (PALS) of White Pulp

Front 55

What is the location rich in B cells in the spleen?

Back 55

Follicles of White Pulp (histologically mimic LN follicles)

Front 56

What is found in the Periarteriolar Lymphoid Sheath (PALS) of White Pulp of the spleen?

Back 56

Dominated by helper T cells

Front 57

What is found in the follicles in the white pulp of the spleen?

Back 57

B cells

Front 58

What is in this image?

Back 58

- Arteriole = pink circle in middle
- Lymphocytes = small round blue cells surrounding arteriole (dominated by T cells)
- Splenic sinusoids = red pulp in periphery (contains RBCs, macrophages, and CT)

Front 59

What is in this image?

Back 59

- 3 arterioles (pink areas in center)
- Lymphocytes = pronounced aggregate of small round blue cells surrounding arterioles

* This specimen is from a trauma: RBCs are congesting the red pulp (periphery of PALS) - intensely red areas

Front 60

What does a spleen that has undergone trauma look like?

Back 60

RBCs are congesting the red pulp (periphery of PALS) - intensely red areas

Front 61

What are the components of a follicle in the spleen?

Back 61

- Germinal Center (GC) - central portion of follicle
- Mantle Layer - zone around GC, dark blue
- Marginal Layer - zone peripheral to mantle zone, outermost layer of follicle

Front 62

What is the main difference between follicles in lymph nodes vs spleens?

Back 62

- In spleen the marginal zone is very pronounced
- Unusual to see the marginal zone in a LN unless its very reactive

Front 63

What is found in the germinal center of a follicle?

Back 63

- Centrocytes
- Centroblasts
- Macrophages
- Dendritic cells

Front 64

What characterizes the L side vs R side?

Back 64

- L: normal spleen

- R: spleen w/ lymphoma

Front 65

What are the features of a spleen with lymphoma?

Back 65

- Big nodules of white pulp (purple, looks like lymphocytes)
- Obliteration of architecture (R side) suggests malignancy
- See little red pulp peripherally, but completely lost centrally
- Red pulp replaced by big huge nodules of lymphocytes (obliterates normal)

Front 66

What are the sites of Mucosa-Associated Lymphoid Tissue (MALT)?

Back 66

- GI tract (principle location)
- Respiratory tract
- Oral mucosa
- Ductal mucosa (salivary, breast, etc)

Front 67

Where is there Mucosa-Associated Lymphoid Tissue (MALT) int he GI?

Back 67

Entire tract from stomach to colon
- Pockets of lymphoid tissues that rest right under mucosa

Front 68

Why is it important to have Mucosa-Associated Lymphoid Tissue (MALT) across the entire GI?

Back 68

GI is constantly being bombarded by contents coming through the gut that are foreign to body; very active in what they're encountering (as far as Ags go)

Front 69

What kind of tissue is important to have in ductal mucosa (eg, salivary or breast)?

Back 69

Mucosa-Associated Lymphoid Tissue (MALT) because you may need an antigenic response

Front 70

What is the function of the Mucosa-Associated Lymphoid Tissue (MALT)?

Back 70

- Filters luminal (gut, ducts, cavities) contents
- Carries contents to regional LNs via efferent lymphatics

Front 71

Where are Peyer's Patches? What is the organization?

Back 71

Small Bowel epithelium (bright pink cells)
- Dark blue small lymphocytes are predominantly B cells because it is follicular
- Mantle zone surrounds Germinal Center

Front 72

What kind of tissue lines the oral cavity?

Back 72

Stratified squamous epithelium

Front 73

What is the appearance of Palatine Tonsils?

Back 73

- Look likes a LN at this power
- Contains follicles w/ germinal centres and mantle zones

Front 74

Where is lung Mucosa-Associated Lymphoid Tissue (MALT) located?

Back 74

- Alveolar spaces
- Respiratory epithelium
- Bronchiole epithelium

* MALT is found right under basement membrane of epithelium