B cell immunity

Question 1

What are the two types of B cell activation?

Answer 1

T-dependent and T-independent responses

Question 2

What is a T-dependent B cell response?

Answer 2

A response where B cells require help from T helper cells CD4+ for antibody production

Question 3

What is a T-independent B cell response?

Answer 3

A response where B cells are activated directly by antigens without T cell help producing mainly IgM - this is faster than a T-dependant response which can be useful for microbial antigens

Question 4

Where does B cell activation occur?

Answer 4

In secondary lymphoid tissues like lymph nodes and spleen

Question 5

What is the role of B cell receptors BCRs?

Answer 5

They bind antigens and initiate B cell activation

Question 6

What happens when a B cell binds an antigen (in terms of T cells)?

Answer 6

The antigen is internalized degraded to short polypeptides and bind to an MHC class II molecule, which presents the antigen fragments to T helper cells

Question 7

What is linked recognition?

Answer 7

A process where B cells and T cells recognise different epitopes of the same antigenic complex and interact - they must have both come into contact with the same antigen for this to occur

Question 8

How do T helper cells activate B cells?

Answer 8

By the binding of CD40 ligand to the CD40 on the B cell and by production of cytokines that stimulate B cell proliferation antibody production somatic hypermutation and class switching

Question 9

What is somatic hypermutation?

Answer 9

A process where point mutations occur in the antibody genes, where the mutations that occur in the variable region of the antibody increase antibody affinity.

Question 10

What is affinity maturation?

Answer 10

The selection of B cells producing high-affinity antibodies during somatic hypermutation in germinal centers

Question 11

What enzyme is required for somatic hypermutation?

Answer 11

Activation-Induced Cytidine Deaminase AID

Question 12

What is class switch recombination?

Answer 12

A process that changes the antibody class produced for example from IgM to IgG IgA or IgE while retaining antigen specificity

Question 13

How does class switching occur?

Answer 13

Through recombination of the heavy chain constant region guided by switch regions and regulated by T cell cytokines

Question 14

What are switch regions in class switching?

Answer 14

GC-rich DNA regions that are about 2-10 kb long, near constant region genes that enable recombination during class switching

Question 15

What is the role of cytokines in class switching?

Answer 15

Cytokines produced by T cells regulate which antibody class is produced for example IL4 promotes IgE, Transforming Growth Factor Beta and IL5 promotes IgA1, Inteferon Gamma produces IgG3

Question 16

What is the primary antibody response?

Answer 16

The initial response to an antigen characterized by IgM production with lower affinity

Question 17

What is the secondary antibody response?

Answer 17

A faster stronger response with higher antibody affinity and different classes mainly IgG

Question 18

What are germinal centers?

Answer 18

Structures in lymphoid tissues where B cells undergo somatic hypermutation affinity maturation and class switching

Question 19

What are plasma B cells?

Answer 19

B cells that are specialized for antibody production often migrating to the bone marrow or inflamed tissues

Question 20

What is the importance of immunological memory?

Answer 20

It allows for a faster and more effective secondary response to previously encountered antigens

Question 21

What are the two types of T-independent antigens?

Answer 21

TI1 bacterial LPS activating through TLR4 and TI2 repeated antigen structures causing BCR cross-linking

Question 22

What is the basis of conjugate vaccines?

Answer 22

Attaching polysaccharides to protein carriers to promote T-dependent B cell responses

Question 23

What is the role of AID in class switching?

Answer 23

It introduces mutations in switch regions to facilitate recombination/loop out parts of the DNA resulting in antibody class change

Question 24

What happens in the dark zone of germinal centers?

Answer 24

B cells undergo somatic hypermutation leading to affinity maturation (an increase in the affinity of the antibody molecule for antigen)

Question 25

What is the role of MHC class II in B cell activation?

Answer 25

It presents processed antigens to T helper cells facilitating their interaction and activation

Question 26

What type of antibody is primarily produced in T-independent responses?

Answer 26

IgM which has lower affinity compared to T-dependent responses

Question 27

What is a naïve B-cell?

Answer 27

B-cells that have matured but not encountered the antigen yet are considered naïve B-cells.

Question 28

What are the two phases of the Primary B cell response?

Answer 28

Phase 1: B cells that encounter antigen and activated by T cells form a primary focus
Leads to production of plasma cells and prompt secretion of IgM
Phase 2: Some activated B cells form germinal centres, - which are areas of proliferating B-cells and a small number of T-cells; This results in B-cell modifications such as somatic hypermutation and class switching to produce a more effective immune response

Question 29

Why do plasma cells have large amounts of endoplasmic reticulum?

Answer 29

Endoplasmic reticulum is key to production of proteins which is what makes up antibodies.

Question 30

What is the proportion of B to T cells in the Germinal centres?

Answer 30

90% proliferating B cells, 10% T cells

Question 31

What causes swollen lymph nodes/tonsils?

Answer 31

Germinal centres are dynamic and can grow when there is an infection.

Question 32

What occurs in the light zone of the Germinal Centres?

Answer 32

Class-switching.

Question 33

How is the affinity of an antibody increased for an antigen?

Answer 33

Hypermutation of the Variable regions of the antibody via single nucleotide/amino acid changes via AID

Question 34

What is the role of AID in Somatic Hypermutation?

Answer 34

AID changes the cytosine in DNA to uracil by deamination, which triggers base pair mismatch and repair.

Question 35

What does Somatic Hypermutation require for testing?

Answer 35

Requires antigen which is delivered to the germinal centre, B-cell antibodies are tested against antigen and the B-cell that produces the highest affinity antibody is selected.

Question 36

What is looping out?

Answer 36

The DNA for different antibody classes is all on one gene, looping out is the removal of the beginning genes to reach the gene that produces the desired class.