Basics of B-cells

Question 1

What are B-cells?

Answer 1

B-cells are a cell of the adaptive immune system, functioning in antibody production and as antigen presenting cells

Question 2

What are immunoglobulins?

Answer 2

Antibodies - Antigen specific proteins, produced by B cells and plasma cells

Question 3

Describe the composition of an antibody

Answer 3

They are a complex of 4 polypeptide chains; 2 heavy chains and 2 light chains

Question 4

What are the 5 types of antibody?

Answer 4

• IgM - Mu heavy chain
• IgG - Gamma heavy chain
• IgA - Alpha heavy chain
• IgE - Epsilon heavy chain
• IgD - Delta heavy chain

Question 5

What are the 2 types of light chain?

Answer 5

Kappa
Lambda

Question 6

What are the 5 types of heavy chain?

Answer 6

Mu
Gamma
Alpha
Epsilon
Delta

Question 7

Where does initial antibody production occur?

Answer 7

In the bone marrow under the control of the microenvironment

Question 8

What region of an antibody binds to antigens?

Answer 8

Variable region

Question 9

What are the 3 main parts of the antibody variable region?

Answer 9

Variable
Diversity
Joining

Question 10

How does the body produce millions of types of antibodies specific to different antigens?

Answer 10

There are millions of combinations of VDJ segments

Question 11

What are the 2 types of immunoglobulin production?

Answer 11

Polyclonal
Monoclonal

Question 12

What is the normal type of immunoglobulin production?

Answer 12

Polyclonal

Question 13

What is meant by polyclonal immunoglobulin production?

Answer 13

The immunoglobulin array is produced by many different plasma cell clones

Question 14

What are some stimuli of polyclonal immunoglobulin production?

Answer 14

Infection
Autoimmunity
Malignancy
Liver disease

Question 15

What is monoclonal immunoglobulin production a marker of?

Answer 15

Underlying B-cell or plasma cell disorders

Question 16

What is meant by monoclonal immunoglobulin production?

Answer 16

This involves the immunoglobulin array being produced by a single B-cell which has undergone clonal expansion and must have prevented all others from dividing

This results in the production of identical antibodies, known as paraproteins, with the same structure and specificity

Question 17

What are paraproteins?

Answer 17

These are identical copies of the same antibody, produced by the same clonal B-cell

Question 18

How are types of immunoglobulin detected?

Answer 18

Serum electrophoresis

Question 19

How does serum electrophoresis work?

Answer 19

Immunoglobulins are detected by serum electrophoresis, in which a voltage is applied across a gel with the serum sample

The separated serum proteins appear as distinct bands or zones

This is then classified against a known result

Question 20

What are some causes of paraprotein formation?

Answer 20

• MGUS
• Myeloma
• Amyloidosis
• Lymphoma
• Solitary or extra-medullary plasmacytoma
• CLL
• Waldenstroms macroglobulinaemia

Question 21

What is meant by somatic hypermutation?

Answer 21

This is the production of many B-cells with a huge number of mutations in production of antibodies

Those with high affinity for antigens survive and proliferate, while those with poor affinity undergo apoptosis

This is somatic so only affects the VDJ segments and doesn’t affect germ-line DNA, so is not passed on

Question 22

What are some histological features of plasma cells?

Answer 22

• Eccentric “Clock face nucleus” on H&E staining
• Open chromatin (Synthesising mRNA)
• Plentiful blue cytoplasm with lots of protein
• Pale perinuclear area due to golgi apparatus

Question 23

What are Bence-Jones proteins?

Answer 23

These were proteins found in warming the urine of patients with bone pain and oedema in the 1800s
This was later confirmed to be immunoglobulin light chains

Question 24

What causes the presence of Bence-Jones proteins in the urine?

Answer 24

When immunoglobulins are synthesised in plasma cells, excess light chains are formed which are secreted into the plasma
In cases of increased immunoglobulin synthesis, more moves into the blood and so is excreted into the urine