Lymphocyte Development in Bone Marrow and Class Switching

Question 1

what myeloid cells

Answer 1

monocytes, macrophages, neutrophils, basophils, eosinophils, erythrocytes, dendritic cells, and megakaryocytes or platelets

Question 2

what are lymphoid cells

Answer 2

T cells, B cells, and natural killer cells

Question 3

what happens to preB cells

Answer 3

undergo Ig gene rearrangement to produce one specific Ig. preB cell-> naive Bcell, expressing cell surface IgM.
go tp secondary lymph organs

Question 4

what happens to preT cells

Answer 4

go to thymus and mature there

Question 5

what are the two broad phases of humoral immunity

Answer 5

recognition phase and activation phase

Question 6

what happens in the activation phase of humoral immunity

Answer 6

bcell clonal expansion
differentitaion (Ig secretion, memory cell, affinity maturation, class switching)

Question 7

what happens to naive bcells

Answer 7

sit in lymphoid organs. On exposure to its specific antigen, become activated.
needs stimulation from CD4+ and cytokines

Question 8

how is activation of bcells regulated

Answer 8

needs stimulation from CD4+ and cytokines

Question 9

what happens to the cells of clonal expansion of bcells

Answer 9

become:

• memory bcells
• plasma ells (Ig secretion)
• affinity maturation
• class switching

Question 10

what happens to the first Ig produced by the Ig produced bt the naive bcell

Answer 10

is expressed as a membrane Ig. acts a receptor to recognise the Ig.
Stimulates signalling pathways to activate the bcell

Question 11

what are the two forms of Ig

Answer 11

membrane bound

secreted into mucosa, circulation, tissue

Question 12

how does the bcell switch being membrane Ig to having plasma secrete Ig

Answer 12

differential splicing of the exons of C segment of RNA

Question 13

what part of the RNA encodes the Fc region

Answer 13

is not coded for by a single exon, but 4 exons that need to be transcribed and then spliced to make mature mRNA

Question 14

RNA polymerase transcribes whole primary transcript. What happens if it is needed to be secreted

Answer 14

translated protein will contain amino acids that make it secreted

Question 15

RNA polymerase transcribes whole primary transcript. What happens if it is needed to be in membrane

Answer 15

RNA polymerase transcribes whole primary transcript. What happens if it is needed to be secreted

Question 16

three ways in which secreted Ig deal with pathogens

Answer 16

neutralisation
opsonisation
activation of complement

Question 17

what is opsonisation

Answer 17

pathogen coated by antibodies.’. flagged.

Fab region binds to antigen, Fc region bind to Fc receptor on a phagocyte, facilitating phagocytosis

Question 18

Role of Ig in neutralisation

Answer 18

antibodies bind to pathogens, this means that the viral particles are prevented from attaching to host cells. Thus viral genome cannot be taken up

Question 19

reason for class switching

Answer 19

B cell antibodies to perform different effector functions and deal better with pathogens
DOES not alter specificity

Question 20

what bit changes when Ig undergoes class switching

Answer 20

Constant heavy chain

CH region

Question 21

what class of Ig is produced first

Answer 21

IgM

Question 22

How is IgD made

Answer 22

made at same time as IgM. Bcell rearranges DNA to bring VDJ segments together.
whole gene is transcribed into primary transcript. RNA splices the unwanted J segments and constant region for mew OR delta heavy chain.

Question 23

how is IgG,IgA,IgM,IgE made

Answer 23

different constant region = different class of antibody. (alternative constant segments)
endonuclease have reconition sites before each heavy chain constant. Will cut a C segment (and Constant heavy chain)
bring that S segment up so its next to VDJ
original VDJ can be transcribed along with new C region 

SO same specific Ig but with different constant heavy chain/different class. No change in light chain

Question 24

Role of CD4+ cell in setiching to IgE

Answer 24

The CD40 ligand on the T cell interacts with CD40 on B cells
The T cell then produces cytokines that tells the B cell what to do
If it secretes IL-4 -> B cell will switch to IgE

Question 25

Role of CD4+ cell in setiching to IgA

Answer 25

The CD40 ligand on the T cell interacts with CD40 on B cells
The T cell then produces cytokines that tells the B cell what to do
If it secrets TGF-b -> B cell will switch to IgA

Question 26

what is affinity maturation

Answer 26

initially antibody have low affinity for their antigen
later in immune response get higher affinity antibodies starting to be produced
secondary immune response = high affinity antibodies straight away released

Question 27

mechanism of affinity maturation

Answer 27

somatic mutations of Ig genes in the variable regions.
Mutations that have given B cell more efficient antibodies will replicate better. Bcells with lower affinity = little stimulation .’. fail to survive.
- preferential selection