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POM 4 Immunology > 4.2 Lymphoid Tissues > Flashcards

4.2 Lymphoid Tissues Flashcards

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1
Q

What are primary lymphoid tissues?

A

The sites of lymphopoiesis

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2
Q

How is lymph formed?

A

Draining of interstitial fluid out capillaries and into lymphatic vessels

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3
Q

What are the 3 primary lymphatic organs?

A

Bone marrow
Thymus
Foetal liver

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4
Q

What cells are of the lymphoid lineage?

A

T cells, B cells and NK cells

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5
Q

Which part of the bone marrow does haematopoiesis occur on?

A

The red part

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6
Q

What does the yellow bone marrow do?

A

Contains mesenchymal stem cells that produce fat, cartilage and bone

Stores fat in adipocytes

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7
Q

Which cells mature in the bone marrow and which part of it?

A

B cells

Yellow marrow in the middle

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8
Q

Which cells mature in the thymus?

A

T cells

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9
Q

What is meant by thymic involution?

A

Shrinking of the thymus with age, leading to reduced T cell output

Functional tissue is replaced with fat

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10
Q

What are the three selection processes which the T cells undergo?

A

Positive, negative and final selection

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11
Q

What is positive selection?

A

Can the T cell receptor (CD4/CD8) signal

If not, the cell is destroyed

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12
Q

What is negative selection?

A

If T cell recognises self antigens, apoptosis is triggered

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13
Q

How do the T cells differentiate into T helper cells and T killer cells?

A

Depending on whether CD4 (helper) or CD8 (killer) has the strongest bond, the T cell will up regulate that one

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14
Q

How does the number of peripheral T cells change with age?

A

Remains the same

Peripheral T cells are maintained by division of mature T cells

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15
Q

Why are older people more vulnerable to new strains of pathogens?

A

Peripheral T cells are maintained by the division of mature T cells outside the central lymphoid organs

Results in less variety of T cells (fewer cells from new lineages)

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16
Q

How do T cells move from their site of production?

A

The thymus releases chemokines which initiates the chemotaxis of T cells from the bone marrow to the thymus

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17
Q

What happens to the thymus during infection?

A

No change

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18
Q

What happens to the bone marrow during infection?

A

Increased white cell production

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19
Q

What are secondary lymphoid tissues?

A

Sites where mature lymphocytes interact with antigens and other lymphocytes

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20
Q

What are some secondary lymphoid tissues?

A

Spleen
Lymph nodes
Appendix
Mucosal associated lymphoid tissue

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21
Q

What are lymph nodes?

A

Highly organised, encapsulated structures located at points of convergence of lymphatic vessels

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22
Q

What are germinal centers?

A

Anatomically restricted site where B cells undergo maturation and differentiation to generate high affinity antibodies

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23
Q

Through what vessel does lymph enter into the lymph nodes?

A

The afferent lymphatic vessel

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24
Q

Why do we have a lymphatic system?

A

More tissue is filtered than reabsorbed during tissue perfusion

Lymphatics return fluid to the systemic circulation

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25
What are the functions of the spleen?
1. Store of platelets 2. Reacts with blood borne antigen 3. Removes defective RBCs from circulation
26
What forms the first line of defense against infection?
Epithelial barriers
27
What is the significance of the location of lymphoid tissues?
They are spread around the body and interconnected via lymphatic system and blood Thus they bring cells in close proximity to antigens
28
What are gut associated lymphoid tissue called?
Peyer's patches – specialised secondary lymphoid tissues
29
Where are Peyer’s Patches Found?
Below the epithelium of the ileum of the small intestine
30
What are 2 features of Peyer's patches?
Many B cell follicles with germinal centres Areas between follicles occupied by T cells
31
Why are there a lot of germinal centers and secondary lymphoid tissues in the gut?
High amount of **foreign antigens** in the form of microbial products from the **microbiota** of the **intestinal tract**
32
What happens in the red pulp of the spleen?
Red blood cells are destroyed
33
What is a periarteriolar lymphoid sheath?
Area of white pulp surrounding arteries running through the spleen Highly populated with T cells
34
Which special cells do gut associated lymphoid tissues contain?
M cells
35
What do M cells do?
Take up small amounts of **gut antigen** Resident **dendritic cells** in Peyer's patch present antigen to **T cells** B cells react and produce **IgA antibodies** which are secreted into the gut lumen
36
What do the IgA antibodies made in the gut do?
They **prevent** microorganisms in the gut from **sticking** to the gut epithelium, and can also **neutralize toxins and viruses**
37
What forms the Waldeyer ring?
The pharyngeal, tubular, palatine and lingual tonsils
38
What are the tonsils made of?
Epithelial cells that phagocytose bacteria and transfer antigens to macrophages that act as APCs
39
How are tonsils involved in lymphatics?
Many lymphoid follicles with large germinal areas for **B cell priming**
40
Why is the waldeyer ring an ideal environment for the immune system to encounter antigens?
Food, bacteria and things we breathe in pass the oral pharyngeal section very often, therefore more antigens
41
Why do lymph nodes swell during an infection?
**B cell follicles** of the lymph nodes **expand** as the B cells proliferate to form germinal centers, amd the entire lymph node enlarges
42
Where do naive Lymphocytes go after they are produced?
They enter into the blood stream and migrate to the **peripheral lymphoid tissues**
43
How long does it take for a T cell to recirculate?
24 hours
44
How do T and B cells get inside the lymph nodes?
They enter via high endothelial venules
45
Where are high endothelial venules found?
In T cell zones of the lymph nodes
46
Which organ is mainly associated with filtering antigen out of blood?
Spleen
47
What are the four steps of T cells getting inside the lymph nodes?
1. Rolling (along endothelial surface) 2. Activation 3. Adhesion 4. Transendothelial migration
48
What molecule on T cells results in the **rolling** of the T cell before it enters the T cell zone of the lymph nodes?
**L-selectin** on T cell
49
What molecules binds to L selectin?
CD34
50
What chemokines are involved in activating LFA-1?
**CCR7** on T cells recognises **CCL21** on the endothelium of the high endothelial venule
51
What happens when LFA1 is activated?
The affinity for ICAM-1 and ICAM-2 is increased
52
What does ICAM allow?
The migration of the lymphocytes through the blood vessel wall
53
What are dendritic cells?
Potent **antigen presenting cells** that pick up and bring antigen from **sites of infection** to **secondary lymphoid organs**
54
How do dendritic cells help with the adaptive immune response?
They **pick up antigens** and present them to T cells in secondary lymphoid organs to **activate the T cells**
55
How do dendritic cells display the antigens?
Through MHCII molecules
56
What stimulates dendritic cells to engulf pathogens?
PAMPs at the site of infection stimulate the **pattern recognition receptors** on the dendritic cell Thus the cell engulfs the pathogen and degrades it
57
What does receptor-independent macropinocytosis allow dendritic cells to do?
Take up extracellular material like virus particles and bacteria
58
**Summarise** the transport of lymphocytes and antigens in the lymphatics and blood stream
**Free antigens** and **dendritic cells** travel from the site of infection to the lymph nodes through the **afferent lymphatic vessel** **Activated lymphocytes** proliferate and differentiate, becoming **effector cells** **Effector cells** leave the lymph nodes via the **efferent lymphatic vessel** They are carried by the blood to **tissues** where they will act
59
What is an example of a dendritic cell?
Langerhans cells in epidermis
60
Describe what is meant by 'repertoire' in terms of lymphocytes?
The range of **genetically distinct** BCRs or TRCs present in a given host The larger the repertoire, the more threats can be recognised
61
What enables a variety of B cell receptors?
Immature B cells undergo VDJ recombination
62
Where in lymph nodes generally are the T cells found relative to B cells?
T cells - Towards inside (further from the marginal sinus) B cells - Towards outside (closer to the marginal sinus)
63
What is it that makes the spleen so good at filtering antigens from the blood?
It is **highly attached** to the arterial circulation via the **splenic artery** So it can filter blood rapidly and in **large numbers**
64
What does lymph do?
Transports dietary lipids, drains interstitial fluid and facilitates immune responses
65
What are the 2 steps involved in extravasation of naïve T cells into lymph nodes?
Selectin binding Integrin binding
66
Define antigen presentation
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
67
How do dendritic cells transport antigens from site of inflammation to the secondary lymphocyte tissues?
Once dendritic cells uptake antigen They migrate out of the inflamed tissue Carry antigen towards the T cells and B cells
68
How do lymph nodes, the spleen and mucosal associated lymphoid tissues all function?
They trap **antigens** and **APCs** from sites of infection in order to **present antigens** to migratory lymphocytes Thus they induce an **adapative immune response**

POM 4 Immunology (14 decks)

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