Block A - lecture 3

Question 1

where does the membrane signalling stop ?

Answer 1

phospholipase c gamma one is where the membrane signalling stops and the signal cascade then enters the cytosol of the cell

Question 2

explain PLC gamma 1

Answer 2

an enzyme and it liberates 2 signalling molecules. PIP2 (Phosphatidylinositol 4,5-bisphosphate) is a membrane phospholipid. PLC gamma one uses PIP2 as a substrate and cleaves the molecule into 2 parts: 1,2 - Diacylglycerol (DAG) and Inositol trisphosphate (IP3)

Question 3

what occurs if there isn’t a calcium signal ?

Answer 3

T cell will not become activated

Question 4

what causes the release of calcium ions from the intracellular stores of T cell ?

Answer 4

IP3 signals the release of calcium from the intracellular stores within the T cell , this leads to an increase in the intracellular levels of calcium within a T cell and leads to its activation.

Question 5

what does DAG activate ?

Answer 5

protein Kinase C

Question 6

what do anti TCR antibodies activate and what occurs ?

Answer 6

Anti TCR antibodies activate the T cell, and this pulls T cell receptors together called ligation

Question 7

what occurs once ligation has occurred ?

Answer 7

once the T cells are ligated this leads to an increase in the calcium production. This process is a fast , not slow

Question 8

does free calcium have much of an effect on T cells alone ? why

Answer 8

The free calcium doesn’t have much of an effect on T cells alone. It requires the calcium to bind to calmodium and this then activates T cells. The calmodium then activates the Calcineurin which is a protein

Question 9

what is calcineurin and mode of action?

Answer 9

Calcineurin removes the phosphate and this translocates the NFATc to the nucleus and it is now NFATn and it is a transcription factor which directly controls gene expression and DNA.

Question 10

explain pathway of DAG

Answer 10

DAG activates protein Kinase C. Protein Kinase C activates I kappa B kinase which leads to the phosphorylation of the I kappa B subunit of NF kappa B. This phosphorylation leads to the disengagement of the NF kappa B and it can translocate into the nucleus to become a transcription factor.

Question 11

Ras/Rac pathway ?

Answer 11

Ras/Rac pathway is a small GTP binding protein. It activates proteins involved in mitogenesis ( cell division). This leads to the activation of MAP and JNK kinases. MAP kinase phosphorylates fos and fos enters the nucleus. JNK phosphorylates jun and this also enters the nucleus. It is these 2 transcription factors that when interaction occurs leads to a pre transcription factor AP-1 complex to form. AP-1 influences gene expression. It is thought that CD28 causes the activation of Ras/Rac pathway

Question 12

when will T cell division not occur ?

Answer 12

T cell division will not occur is the calcineurin pathway doesn’t occur.

Question 13

where does the signal start ?

Answer 13

in the membrane which leads to activation of PLC

Question 14

what generated soluble signal ?

Answer 14

phospholipase C which generated the soluble signal that could enter the cytosol of the cell , this could be DAG or IP3

Question 15

what allows the kinase or phosphatase activity ?

Answer 15

The DAG activates protein Kinase C , while the IP3 mobilises intracellular stores of calcium. This action allows the kinase or phosphatase activity on a transcription factor , which allows it to enter the nucleus of a cell through translocation and gene expression can be modulated.

Question 16

what is the late phase of T cell activation ?

Answer 16

gene transcription phase in the nucleus

Question 17

immediate genes ?

Answer 17

ones that need to be expressed in a very short period of time. These are c – fos and c- myc which are the transcription factors so the signal pathways can occur.

Question 18

early genes ?

Answer 18

nvolved in the function of the T cell and are expressed up to 6 to 12 hours. These includes IL2 , IL 2 receptor alpha chain and cytokines. IL-2 is important as it is the growth factor for T cell division. Cytokines are needed for the CD4 cell as they are the helper cells .

Question 19

late genes ?

Answer 19

MHC, adhesion molecules and VLA (very late antigens). These are involved in housekeeping functions.

Question 20

what is the point of these genes ?

Answer 20

produce a response, T cell proliferation. It is the early genes which expresses IL2 which is critical for the proliferation of the particular T cell that is activated by the pathogen.

Question 21

what stage do drugs target ?

Answer 21

Drugs can target calcium mobilisation so that the IL2 is not expressed and the T cell does not proliferate.

Question 22

is the one activated T cell enough to fight an infection ?

Answer 22

the one T cell that is activated is not enough to fight an infection, so once the antigen is recognised the T cell needs to quickly produce clonal cells through expansion to form a mass of identical cells to fight the pathogen.

Question 23

what is the job of a B cell and how ?

Answer 23

B cells job is to produce antibodies and therefore must recognise a pathogenic antigen and produce an antibody against it.

Question 24

describe the B cell receptor ?

Answer 24

The B cell receptor has a variable region, and it shows structural similarity to an antibody. The B cell contains antibodies embedded in the membrane it is an sIgM as it is a surface IgM , this can also be an mIgM for membrane.

Question 25

is the antibody released into the bloodstream?

Answer 25

The antibody is not released in the bloodstream it is bound for receptors. The receptor antibody is the same antibody that the B cell will produce once activated.

Question 26

in terms of diversity describe the B cell receptors?

Answer 26

On a single B cell there is more than one receptor present, every receptor on the one B cell shows the same receptor type. However, each B cell in the body will show variability in the receptor they show to increase the chance of recognising a pathogen antigen.

Question 27

describe the structure of the B cell receptor ?

Answer 27

The surface IgM has 2 chains an alpha and beta chain on either side of the sIgM. So 4 chains in total. This is the constant region. The antibody part of the receptor stick out of the cell , while the chains face the cytosolic side of the cell , the white lines are the ITAM’s tails.

Question 28

describe the stages of antigen recognition of B cell ??

Answer 28

Antigens recognised on one receptor, will also be recognised on the other receptor. This allows the receptors to move closer together. Lck and fyn are the 2 kinase like proteins that phosphorylate the ITAM’s on the alpha and beta chains that surround the sIgM.

Question 29

TAPA-1

Answer 29

TAPA-1 ( CD81) is a transmembrane spanning protein

Question 30

other associated molecules ?

Answer 30

2 other proteins that are associated with each other are the CD19 and CR2(CD21- cluster designation)

Question 31

CD21 ?

Answer 31

CD21 is a marker on B cells that sticks out the B cell as a receptor which can bind to complement

Question 32

CD19 ?

Answer 32

CD19 is used as a marker for B cells , as it is unique to B cells.

Question 33

what do the adaptor proteins allow ?

Answer 33

The adaptor proteins allow phospholipase C gamma 2 to move close to the membrane and kinases phosphorylate it and it becomes active. This cleaves PIP2 into DAG and IP3 to activate protein kinase C and mobilise intracellular stores of calcium.

Question 34

where is the complement proteins found and role?

Answer 34

In the blood there are circulating protein called complement proteins which, stick covalently to the surface of pathogens, the C3d is a complement which coats the pathogen.

Question 35

role of CR2 ?

Answer 35

the CR2 recognises the C3d coating the pathogen through opsonisation. The CR2 moves forward and binds to the C3 and brings the CD19 and TAPA1 which are involved in the signal pathway of phospholipase C gamma 2.