Adaptive immune response; B cells

Question 1

What is the BCR?

Answer 1

a membrane bounds version of the antibody molecule and the variability is generated through genetic recombination. V region of BCR recognises native (unprocessed) antigen. BCRs have two heavy chains (identical) and two light chains.

Question 2

How many constant regions does IgM and IgE have?

Answer 2

4

Question 3

How many constant regions does IgA/G/D have?

Answer 3

3

Question 4

How is the BCR membrane bound?

Answer 4

When an antibody is acting as a BCR, a transmembrane sequence anchors it to the plasma membrane, these are hydrophobic amino acids with a short intracellular tail.

Question 5

Describe light chains.

Answer 5

They are smaller than heavy chains and have two domains, variable and constant. The class of antibody is determined by the constant regions.

Question 6

What does the Cmu gene cause?

Answer 6

The immunoglobulin to be IgM

Question 7

What does the Calpha gene cause?

Answer 7

IgA

Question 8

What are identical light chains?

Answer 8

Light chains which are identical via the Ckappa or lambda genes (Kappa in IgM)

Question 9

What is clonal selection?

Answer 9

Selection of the B cell through the antigen selecting the most appropriate B-cell and clonal proliferation occurs. Clonal selection occurs via complementary shape binding between the antigen and the BCR on that particular B cell. B cell becomes activated and clonal proliferation occurs.

Question 10

Do B cells differentiate after activation?

Answer 10

Yes, some B cells differentiatie into plasma cells which are the effector cells producing (secreting) plasma antibodies= a polyclonal antibody. These plasma cells have more cytoplasm and a rough ER due to protein synthesis. Memory cells are also produces that persist in the circulation after infection and re-encounter of the complementary antigen re-initiates proliferation and differentiation of the memory cells into plasma cells; the secondary immune response; faster response and more specific

Question 11

What do polyclonal antibodies do?

Answer 11

They specifically bind to the initiating antigen; opsonisation, neutralisation of toxins.

Question 12

What are the five classes of antibody?

Answer 12

IgG, A, E, M, D

Question 13

What is the first sign that a lymphocyte is becoming a B cell?

Answer 13

The recombination of immunoglobulin genes

Question 14

Which antibodies do naive B cell co-express?

Answer 14

IgM and IgD, specific for the same antigen.

Question 15

Name other surface B molecules

Answer 15

Igalpha, Igbeta, CD19 and CD20 (both are B cell markers) and CD40.

Question 16

True or false, B cells can class switch independently?

Answer 16

False, B cells require help from Th cells for class switching.

Question 17

How is class switching mediated?

Answer 17

By the interaction between cell surface molecules on B cells and receptors on T cells; soluble cytokines also facilitate class switching. Th2 are the most efficient at class switching as these have CD28, TCR and CD40L which bind to B7, pMHC-II and CD40 respectively. There is mutual activation between B and Th cells. Cytokines cause direct class switching during maturation in the bone marrow. The class of antibody produced is determined by which cytokines are produced by Th cell. for example IL-14/13 cause B cells to class switch to IgE

Question 18

What accompanies antigen-induced proliferation?

Answer 18

Somatic hypermutation of the rearranged antibody variable region genes; B cells have reduced DNA repair mechanisms for the variable region of the genes to enable high diversity of the variable region. Regulatory regions on the gene which flank the variable region specify the mutation site; not completely random. Multiple consequences of somatic hypermutation, but survival of the B cell is dependent on the affinity of the BCR to the antigen.

Question 19

What is the second function of B cells?

Answer 19

They are also professional APCs, a cell that can use MHC-II to rpesent peptides to CD4 T helper cells. Include dendritic cells and macrophages, dendritic cells are required for antigen presentation to naive T cells. B cell activation of T cells is similar to T cell activation of B cells. BCR binding to antigen can be endocytosed.

Question 20

Does the BCR transduce a signal to the B cell?

Answer 20

No; the short cytoplasmic tail of BCR is too short to be phosphorylated by tyrosine kinases. A singal is transduced by the BCR-associated Igalpha and Igbeta molecules which have disulphide bonds. ITAMs are present on cytoplasmic tails of Igalpha and Igbeta. Src family of tyrosine kinases initiate cell signalling through phosphorylation of the tyrosine domains of Igalpha and Igbeta.

Question 21

Can the B cell response be T cell independent?

Answer 21

Yes, through T-cell independent antigens such as LPS and other structures that have repeated structures. Cross linking of these polysaccharides to BCRs oversomes the requirement of T cell help. Class switching cannot occur via this method -efficient IgM response. However for most cells B cell response is T-cell dependent. The T cell provides second signals for B cell activation.

Question 22

What is the T cell response?

Answer 22

Cell mediated immunity for intracellular infections

Question 23

What is the B cell response?

Answer 23

Humoral immunity for extracellular infections.