Lynphoid Tissues

Question 1

What are the hallmarks of adaptive immunity?

Answer 1

Specificity and memory

Question 2

To what extent are b and T cells specific?

Answer 2

Each cell has the ability to express only one type of cell receptor (BCR/TCR) that is unique. The DNA sequence that codes it is unique, as is the antigen it can recognise

The gene that encodes the TCR allows up to 10e15 different unique sequences

Question 3

How do b and T cells make so many different antibodies?

Answer 3

B CELLS
The shape of the antibody is determined by the variable region. Diversity is generated in the early stages of development. There are multiple copies of V, D and J genes. These are rearranged. The heavy chain also has its own V and J genes. There are also additional nucleotides added between these genes by the enzyme TdT, changing the structure of the variable region. When a B cell binds the shape of the variable region can alter in a process called somatic hypermutation, randomly mutating the variable region.

T CELLS
These work in a similar way only they don’t have antibodies

Question 4

What is primary lymphoid tissue?

Answer 4

Where lymphocytes are produced

Lymphopoiesis (b, T and natural killer cells)

Eg. Bone marrow, thymus, foetal liver

Question 5

What makes up the adaptive immune response?

Answer 5

B and T cells

They have unique BCRs and TCRs

Question 6

What receptors do T helper cells have?

Answer 6

CD4

Question 7

What receptors do cytotoxic T cells have?

Answer 7

CD8

Question 8

What happens to white cell production during infection?

Answer 8

Increased

Question 9

Where are B cells and their repertoire produced?

Answer 9

In the bone marrow , however final maturation can occur in the periphery (eg spleen)

Question 10

Where are T cells produced?

Answer 10

In the Thymus,

Migrate there from the bone marrow

Question 11

How do T cells develop?

Answer 11

Stepwise.

An immature thymocyte undergoes positive selection in the vortex of the thymus.

Then negative selection occurs. Checks that the T cell doesn’t react to self antigens. If they do, they undergo apoptosis

Then final selection and exit

Question 12

What happens to the thymus with age?

Answer 12

It’s output declines. The medulla is slowly replaced by adipose tissue

Question 13

Why are secondary lymphoid tissues necessary?

Answer 13

1.5e9 T cells per L of blood

5L of blood in bod

7.5e9 in all blood

Blood only contains 2% of all T cells

So 7.5… x 50 = 3.75e11 T cells in total

However they may only be one T cell that has a specific receptor, so this must be transported to a place where it can induce a response

Remeber T cell repertoire is about 10^15 minimum

Question 14

What is secondary lymphoid tissues

Answer 14

Where lymphocytes can interact with antigens and other lymphocytes

Question 15

What are some secondary lymphoid organs?

Answer 15

Spleen

Lymph nodes

Appendix

Mucosal associated lymphoid tissues

These are distributed around the body.
Interconnected by the lymphatic system and the blood. They can be discrete organs, or distinct regions within a tissue. All highly organised structures.

They all bring cells into close proximity with antigens

Question 16

What is the structure of lymph nodes?

Answer 16

Distinct zones for T cells and B cells

Have afferent and efferent lymph (in/out)

Also arterial and venous connections

Google a picture

Question 17

What is the structure of the spleen

Answer 17

Similar to lymph nodes

Distinct B and T zones

Afferent and Efferent lymph

Arterial and venous connection

HOWEVER

More of an arterial connection

Unlike nodes, the whole organ is not specialised for this purpose. Only the white pulp of the spleen (which is inside the red pulp)

Question 18

Where are epithelial barriers found?

Answer 18

Abundant Around the external facing membranes, such as the GI tract, and lining the oesophagus

The skin acts as the first line of defence as a physical barrier

Also abundant in areas that might have high levels of antigens. Such as peyers patches (specialised secondary lymphoid tissues) below the epithelium of the illeum of the small intestine
They are highly enriched with B cells and contain lots of germinal centres

Question 19

What is a germinal centre

Answer 19

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

Question 20

What is the structure of the tonsils (also a secondary lymphoid tissue)?

Answer 20

They encircle the oral and nasal cavity. Forming the waldeyer ring

They, like the peyers patches, have lots of lymphoid follicles which contain large germinal centres and lots of B cells

Question 21

How do antigens and activated B and T cells get into the lymphatic system?

Answer 21

Drained from between tissue cells into the lymph

2-3 litres of lymph are returned to the blood every day via the superior vena cava

Question 22

How often do naive T and B cells circulate?

Answer 22

Once every 24 hours

Question 23

How does extravisation of naive T cells occur?

Answer 23

Look at inflammation, pretty much the same just different molecules involved

Question 24

What are dendritic cells?

Answer 24

Professional Antigen presenting cells