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2.1 Molecular Immunology > Practical 1: The Thymus > Flashcards

Practical 1: The Thymus Flashcards

1
Q

List the two primary lymphoid organs

A

Thymus

Bone marrow

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2
Q

Describe the location of the thymus

A

Anterior mediastinum
Resting on the heart

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3
Q

Describe the anatomical structure of the thymus
(4)

A

Bi-lobed
Protected by adipose tissue
Held in place by a ‘stalk’
Good blood supply - blood vessels in and out

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4
Q

List the parts of a thymic lobe
(4)

A

Capsule
Cortex
Medulla
Septum

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5
Q

Describe the histological structure of the thymus
(5)

A

Surrounded by a connective tissue capsule which forms extensions called septae in the tissue

Septae divide the thymic tissue into lobes and lobules

The outer darker staining region is the cortex (more cells = more nuclei here to stain darker)

The inner lighter staining region is the medulla

Blood vessels can be seen in the septae

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6
Q

When does involution begin?

A

Soon after birth but really progresses after puberty in adolescence

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7
Q

Define a primary lymphoid organ

A

Primary lymphoid organs are responsible for the maturation of an immune cell population

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8
Q

What cell do T cells develop from?

A

T cell progenitor - produced in bone marrow then travels to thymus in circulation

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9
Q

What happens to T cells after they have matured?

A

They leave the thymus and move to the secondary lymphoid tissues

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10
Q

Define a secondary lymphoid organ

A

Secondary lymphoid organs increase the chances matured immune cells have at meeting an antigen

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11
Q

What is another name for septae?

A

Trabecula

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12
Q

What are mitotic bodies?

A

Cells undergoing mitosis

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13
Q

What type of cells are found in the cortex?

A

Mitotic bodies are found, especially neat the edge

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14
Q

Mitotic bodies are found in the thymus, what does this indicate?

A

Proliferation occurs in the thymus

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15
Q

What is the cortical-medullary junction?

A

This is where the cortex and medulla meet

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16
Q

What is found at the cortical-medullary junction?

A

Specialised vessels called post capillary vessels are found here

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17
Q

Briefly describe the movement of a progenitor T cell into the thymus
(5)

A

Progenitor T cell leaves bone marrow

Cell travels to thymus via circulation

Cell enters thymus at cortical-medullary junction

Cell travels to outer region of cortex in nearest lobule via post capillary vessels

Double positive naive T cells mature here and gain a receptor

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18
Q

What is meant by T cell maturation?

A

T cells get their T cell receptor

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19
Q

What does the T cell receptor consist of?

A

Two chains of proteins

20
Q

What are the two types of T cell receptors?

A

alpha-beta

gamma-delta

21
Q

What are the thymus cells called?

A

Thymocytes

22
Q

What CD molecules are naive T cells positive for?

A

They are double positive, positive for both CD4 and CD8

23
Q

What happens to a T cell after it gains it’s receptor?
(5)

A

It begins to move back towards the cortical-medullary junction

As it moves it must undergo positive selection in the cortex

After reacting with a MHC (Class I or II) it moves to the medulla

Here, any cells that react to self are killed

Very few cells make it to the junction but they leave here and move to secondary lymphoid organs

24
Q

Describe positive selection of T cells
(5)

A

T cells with a receptor must meet a MHC molecule in the cortex

The receptor must react with either MHC Class I or MHC Class II

T cell keeps CD8 and loses CD4 (-helper) if reacts with MHC Class I (all nucleated cells)

T cell keeps CD4 and loses CD8 (-cytotoxic) if it reacts with MHC Class II (APCs)

T cell will only get the signal to survive if it reacts with MHC

25
Q

What happens if a T cell reacts with MHC Class I?

A

T cell will keep it’s CD8 and lose its CD4

T cell will become a cytotoxic T cell

26
Q

What happens if a T cell reacts with MHC Class II?

A

T cell will keep it’s CD4 and lose its CD8

T cell will become a helper T cell

27
Q

Where does positive selection take place?

A

Cortex

28
Q

Where does negative selection take place?

A

Medulla

29
Q

Describe negative selection
(2)

A

T cell moves to medulla where mTECs test T cells for self receptors

Any thymocytes with a high-affinity for self are killed

30
Q

What are mTECs?
(3)

A

Medullary thymic epithelial cells

They are bone-marrow derived APC e.g. macrophages or DENDRITIC CELLS

They are responsible for negative cells

31
Q

What are AIREs?
(3)

A

Autoimmune regulatory epithelial cells

A subtype of mTECS - mTECs with better antigen presentation

Have peripheral tissue antigens for self which can be shown to T cells before they leave the thymus

32
Q

What cells are responsible for positive selection?

A

CTECs

33
Q

What cells are responsible for negative selection?

A

MTECs

34
Q

What percentage of thymocytes become T cells?

A

2 %

35
Q

What do APECED stand for?

A

Autoimmune
Polyendocrine
Candidiasis
Ectodermal
Dystrophy

36
Q

What is APECED?
(3)

A

Two mutated AIRE genes, not functioning properly

Therefore T cells are never negatively selected properly

Results in autoimmunity where the cells attack multiple organs

37
Q

Where is AIRE located?

A

Chromosome 21

38
Q

What is meant by the ‘starry sky’ in the thymus?

A

Apoptosis of thymic cells by macrophages

39
Q

What is thymic involution?

A

Thymus is invaded by adipose tissue

Loss of significant thymic tissue to adipose tissue

40
Q

What does thymic involution look like?

A

Only ‘islands’ of thymic tissue remain

41
Q

What are Hassall’s corpuscles?

A

mTECs that no longer express AIRE but instead produce whirls - mTECs are old

42
Q

How do you identify a Hassall’s Corpuscle?

A

Found more so in the medulla than cortex

Have no lumen

Red colour

No erythrocytes

43
Q

What is produced by Hassall’s Corpuscles?

A

Thymic stromal lymphopoietin

44
Q

Give one function of TSLP

A

Activation of thymic dendritic cells

45
Q

What increases involution?

A

Acute involution caused by stress, cancer, disease, pregnancy and lactation

46
Q

Why were different strains of mice used in the Miller Paper?
(2)

A

A strain A mouse would accept a graft from strain A mouse because the MHC molecules would be the same

But a strain A mouse would not accept a graft from strain B mouse if mouse A has a functioning T cell population because the different MHC molecules should be recognised as antigen

47
Q

What were the conclusions of the Miller Paper?
(2)

A

When thymus removed at birth a strain B mouse accepted a skin graft from a strain A mouse

Therefore there was no T cell population as the skin graft would have been rejected otherwise

2.1 Molecular Immunology (19 decks)

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