Lymphoid Tissues

Question 1

What is meant by a primary lymphoid organ?

Answer 1

Organs where lymphocytes are produced - Lymphopoieses

Question 2

List 3 primary lymphoid organs

Answer 2

Thymus
Bone marrow
Foetal liver

Question 3

What is the adaptive immune system compromised of?

Answer 3

T cells (CD4, CD8, T regulatory cells)
B cells (B lymphocytes and plasma cells)

Question 4

What are the hallmarks of adaptive immunity?

Answer 4

Specificity

Memory

Question 5

What do BCR and TCR stand for respectively?

Answer 5

B cell receptors

T cell receptors

Question 6

What do CD4 (T-helper cells) do?

Answer 6

Produce lots of cytokines which guide B cells and other T cell responses

Question 7

What do CD8 (cytotoxic T cells) do?

Answer 7

Actively kill foreign antigen expressing cells

Question 8

What is the primary site of haematopoiesis?

Answer 8

Bone marrow

Question 9

What are the roles of the red and yellow bone marrows respectively?

Answer 9

Red - Produces blood cells

Yellow - Fat stores

Question 10

What are immature T cells known as?

Answer 10

Thymocytes

Question 11

Where do immature T cells migrate from the bone marrow to?

Answer 11

Thymus

Question 12

Where do B cells migrate to in the immature stage for differentiation?

Answer 12

Spleen

Question 13

Describe what is meant by ‘repertoire’ in terms of lymphocytes?

Answer 13

The range of genetically different BCRs or TCRs in a given host.
The larger the repertoire, the more threats can be recognised.

Question 14

What is thymic involution?

Answer 14

The shrinkage of the thymus with age → associated with a change in structure and a reduced mass

Question 15

Where is the thymus?

Answer 15

On top of heart, above lungs in the thoracic cavity

Question 16

What are the 3 steps in the stepwise differentiation of T cells?

Answer 16

Positive selection - can the T cell receptor signal? (Does it see the MHC receptors on the surrounding cells?)
Negative selection - does it react against our own body (if does react against self-antigens then it undergoes selective apoptosis)
Final selection and exit

Question 17

What is meant by a secondary lymphoid organ?

Answer 17

Where lymphocytes can interact with antigens and other lymphocytes to guide their activation and differentiation

Question 18

List some secondary lymphoid organs

Answer 18

Spleen
Lymph nodes
Appendix
Mucosal associated lymphoid tissue

Question 19

How are lymphoid tissues connected?

Answer 19

Via the lymphatic system and the blood

Question 20

Where in lymph nodes generally are the T cells found relative to B cells?

Answer 20

T cells - Towards inside (further from the marginal sinus)

B cells - Towards outside (closer to marginal sinus)

Question 21

What do the words afferent and efferent refer to respectively?

Answer 21

Afferent - Into (lymphatic vessels)

Efferent - Out of (lymphatic vessels)

Question 22

What is it that makes the spleen so good at filtering antigens from the blood?

Answer 22

It is highly attached to the arterial circulation via the splenic artery

So it can filter blood rapidly and in large numbers

Question 23

How is the spleen different to other secondary lymphoid organs?

Answer 23

Not a discrete tissue contains lymphoid compartment (white pulp) that is located within red pulp of spleen

Question 24

What are Peyer’s patches and where are they found?

Answer 24

Specialised secondary lymphoid tissues
Found below epithelium of the ileum of the small intestine
Specialised Microfold (M) cells sample antigen directly from lumen and deliver it to antigen presenting cells

Question 25

Define a germinal centre

Answer 25

Anatomically restricted site where B cells undergo mutation and selection to generate high affinity antibodies

Question 26

Describe how lymphatic drainage occurs at gut associated lymphoid tissue

Answer 26

Intraepithelial lymphocytes enter villi These are drained to mesenteric lymph node The afferent lymphatic vessels at Peyer’s patches pick these up The follicle is highly enriched with B cells and contains a high frequency of germinal centres

Question 27

Why is the intestine so enriched for these germinal centres?

Answer 27

High amount of antigen being provided in the form of microbial products from the microbiota of the intestinal wall tract

Question 28

What is the Waldeyer ring and what is it comprised of?

Answer 28

Immune tissue specialised in antigen encounter Pharyngeal, tubular, palatine and lingual tonsils encircle the oral and nasal cavity - form the Waldeyer ring Contains its own squamous epithelium and lymphoid follicles containing large germinal centers

Question 29

How do specific T cells become activated by their specific antigen which is in a different part of the body?

Answer 29

Each naive T cell recirculates once every 24 hours They enter lymph nodes via lymphatics vessels Become activated by binding to antigens encountered in SLO Either retained and differentiated in SLO or Leave via efferent lymphatic vessel Travel from SLO to site of inflammation in periphery (inflammatory signals)

Question 30

What are the 2 steps involved in extravasation of naïve T cells into lymph nodes?

Answer 30

Selectin binding Integrin binding CCR7 and CCL21 (chemokine) interaction

Question 31

Define antigen presentation

Answer 31

The display of peptides in the major histocompatibility complex (MHC) I or II proteins such that the T cell receptor can attempt to bind them.

Question 32

How do dendritic cells transport antigens from site of inflammation to the secondary lymphocyte tissues?

Answer 32

Once dendritic cells uptake antigen They migrate out of the inflamed tissue Carry antigen towards the T cells and B cells via lymphatics

Question 33

How else can the antigens be transported to the secondary lymphatic tissues?

Answer 33

Eventually, if in large enough numbers the antigens will flow into the lymphatics, as the fluid is drained from the tissues, to be trafficked through to the secondary lymphoid tissues.

Question 34

Where are lymphoid tissues particularly found?

Answer 34

At barrier surfaces, such as the lungs, gastrointestinal tract and the skin.

Question 35

What structures provide lymph nodes with physical protection?

Answer 35

Tough outer capsule | Surrounded by specialised fatty deposits

Question 36

What allows easy flow of lymphocytes in and out of lymph nodes?

Answer 36

Good lymphatic and blood vessel supply

Question 37

What is contained in the cortex and paracortex of a lymph node?

Answer 37

Cortex - B cells | Paracortex - T cells and dendritic cells, also contains high endothelial venues

Question 38

How do lymphatic vessels enter lymph nodes?

Answer 38

Enter at the outer edge between capsule and cortex | Penetrate deep within the nodes via conduits

Question 39

What is meant by Cluster of Differentiation (CD)?

Answer 39

Internally recognised standard for the systematic naming of proteins used in the phenotyping of hematopoietic cells.