L19- B and T cell co-operation- Germinal centres, affinity maturation of the B cell response and immunological memory

Question 1

What is the main lymphoid organ and what percentage of the total lymphocyte load does it contain at any one time?

Answer 1

The spleen and it contains about 20% of the total lymphocyte load.

Question 2

What happens to the spleens function in immunity over time?

Answer 2

As we age we aquire protective immunity, this means that the spleen becomes less active as we age as there is sterilising immunity in the blood.

Question 3

Where are most lymphocytes found?

Answer 3

If not in the liver then most are found either in MALT or lymph nodes.

Question 4

Why can antibiotics cause disease in the gut?

Answer 4

They can sometimes destroy protective bacterial colonies known as commensals which results in other bacteria being able to grow such as clostridium difficile

Question 5

What prevents maternal lymphocytes from rejecting the foetus as it contains paternal MHC molecules?

Answer 5

Lymph nodes prevent the mothers lymphocytes from entering the foetal haemoglobin

Question 6

Which T cells are crucial for the preservation of commensal bacteria and prevent them being attacked by the immune system?

Answer 6

T regulatory cells downregulate responses towards them. As well as protecting our own tissues from attack by the immune system.

Question 7

If negative selection in the thymus gets rid of self-reactive cells then why are T reg cells required.

Answer 7

Body tissue antigens can sometimes become modified by their environment resulting in an immune response. T regs often do this with cancer cells with modified antigens, this prevents the immune system from damaging them.

Question 8

What are the two main areas of the spleen and what are their functions?

Answer 8

The red pulp that is a series of sinusoids lined with macrophages where the blood flow is slow whose function is to phagocytose pathogens in the blood.
The white pulp is the area where CD4 T and B cells can collaborate to produce antibodies.

Question 9

What happens during a primary CD4 T cell dependent antibody response?

Answer 9

Dendritic cells present antigens to CD4 T cells to prime them. B cells that bind foreign proteins through their B cell receptors then migrate to to the primed T cells. if the CD4 T cell recognises peptides presented by the B cell then it will help it to proliferate to produce plasmablasts that secrete antibodies. The plasmablasts differentiate into plasma cells that produce antibody for around a week before they die. These antibodies are mainly IgM and are of low quality (do not bind strongly).

Question 10

Why are B and T cells segregated into separate areas within the lymph node?

Answer 10

This is so they are separate for B cells to undergo somatic mutation in the germinal centre of the B follicle.

Question 11

What is the name of the gene which codes the B cell immunoglobulin receptor (B cell receptor)?

Answer 11

The AID gene, it is responsible for for somatic mutation as well as switching B cells from producing IgM to other types of antibodies.

Question 12

Which types of B cells become long lived and reside in the bone marrow?

Answer 12

IgG and IgA

Question 13

Which type of B cell lives in the lamina propria of the gut?

Answer 13

Predominately IgA

Question 14

Which is the most abundant Immunoglobulin? and what is its main role?

Answer 14

IgA and it is very important for dampening the immune response to commensal bacteria.

Question 15

What is the most important immunoglobulin and why?

Answer 15

IgG as it is smaller than IgM and can get to places that IgG cannot. It has a much longer half life than IgM or IgA which means that it can provide protection to newborns for at least 6 months by transferring maternal IgG

Question 16

What is the first stage of a T and B cell memory?

Answer 16

Pre-existing antibodies produced by long lived plasma cells in the bone marrow alert the immune system. Memory B cells in the germinal centre then make IgG and IgA antibodies very quickly.

Question 17

What actions do memory T and B cells coordinate?

Answer 17

The CD4 T cells and the B cells collaborate to coordinate T cell dependent antibody responces.

Question 18

Which gene co-ordinates the germinal centre environment?

Answer 18

LTBR (lymphotoxin beta-receptor gene)

Question 19

How do memory T and B lymphocytes move from the blood into the lymph node?

Answer 19

Through specialised post capillary venules called high endothlial venules. The memory cells constantly circulate between lymph nodes in order to encounter antigens.

Question 20

What are natural antibodies and how are they produced?

Answer 20

They are IgM antibodies that are produced independent of antigen by B cells called B1 cells. These do not require secondary lymphoid organs to produce antibodies.

Question 21

What are T cell independent antibodies and how do they work?

Answer 21

These are antibody responses that do not require CD4 T cell help, they are mainly from bacterial or viral cell walls. These are often quicker than T dependent responses.