WK 2- B CELLS, IMMUNOGLOBULINS AND ANTIGEN RECEPTORS

Question 1

What chains are Ig composed of

Answer 1

Heavy and Light chain->heavy chain composed of variable and constant regions, light chain composed of variable regions

Question 2

What two regions comprise an Ig

Answer 2

Constant region= attached to the membrane of B/T cells

Variable region= attaches to the antigen

Question 3

What are the functions of antibodies

Answer 3

Neutralise microorganisms and toxins, opsonisation and phagocytosis of a pathogen

Question 4

What does the constant region do

Answer 4

The constant region of the antibody determines its isotype and function

Question 5

What are the 5 different classes of Ig

Answer 5

IgA, IgG, IgD, IgE, IgM

Question 6

What Ig is the most abundant in the human body

Answer 6

IgG

Question 7

What is a polymeric immunoglobulin

Answer 7

Have multiple Ig’s joined together by J chains

eg. IgA has 2 molecules

Question 8

What isotypes have subtypes

Answer 8

IgG= IgG1/2/3/4
IgA= Iga1/2

Question 9

What immunoglobulin is the least common in blood

Answer 9

IgE

Question 10

Which Ig molecule has the largest weight

Answer 10

IgM

Question 11

What is a BCR- describe the structure

Answer 11

B cell receptors are present on the cell membrane of a B cell- comprised of

Question 12

What is somatic hypermutation

Answer 12

Occurs after the B cell has encountered an antigen- involves point mutation by AID, occurring to the variable region- the point mutation leads to an increased affinity for the antibody

Question 13

What is VDJ recombination

Answer 13

Occurs in the primary lymphoid tissue- involves mutations to the germline DNA(or V/D/J) that encodes for the variable region- mutations increases the diversity of the variable regions

Question 14

What is isotype switching

Answer 14

Originially B cells have only IgM- when they mature in secondary lymph tissue they receive cytokines from T cells- differing cytokines cause different isotypes to form

Question 15

Where do B cells mature

Answer 15

B cells mature in secondary lymph tissue when they are exposed to antigens

Question 16

What is the process of B cell maturation

Answer 16

bone marrow lymphocyte progenitors receive signals from stromal cells to develop into B cells

1. Progenitor cells undergo somatic recombination(VDJ recombination) of heavy chains to form a precursor B cell
2. The precursor B cell will undergo somatic light chain recombination (VDJ recombination) so that it then becomes an immature B cell
3. Immature B cell will then have an IgM attached to its membrane and leave the bone marrow and migrate to the blood- tested for autoreactivity before they leave the BM
4. From the blood it will move into the lymph tissues
5. In the lymph tissues it will become activated through contact with a CD4 T helper cell
6. Once activated it will move to the dark area of the germinal centre of the lymph and undergo clonal expansion
7. Whilst the B cell is proliferating it will undergo somatic hypermutation which will result in either an increased or decreased affinity for antigens by that B cell
8. Those B cells that recognise the antigen will receive a single to proliferate further, those that do not recognise the antigen will be apoptosed
9. The B cell that has been chosen to proliferate will also undergo class switching (changing of the isotype)
10. After class switching, the B cell with become either a memory B cell, or a long lived plasma cells that secretes antibodies and will migrate back to the bone marrow

Question 17

In which portion of the germinal centre do cells proliferate in

Answer 17

Dark zone