Immunology 4 Flashcards
What do B cell receptors do?
(4 marks)
- Recognise a specific antigen e.g. peptide/ whole molecule
- Activate opsonisation
- Can kill pathogen by neutralisation or agglutination
- Variable region binds and recognises antigen
What is the difference between a B cell that is secreted or membrane bound?
(2 marks)
Secreted B cell will become an anitbody
Membrane bound B cell is a B cell receptor
What does the structure of BCR antibodies consist of?
(2 marks)
- Two heavy chains and two light chains which contain a disulfide bond
- Heavy and light chains have 3 constant regions therefore it is a conserved sequence
Which part of the anitbody is ‘flexible’?
(2 marks)
Hinge region is flexible and so is antigen binding region ot reach chains
What are the heavy and light hcains encoded by?
- Light chain is encoded by either kappa or lamda
- Heavy chain is encoded by genes (on image) that translate into different antibodies
What does a T cell do and is it membrane bound or not?
(2 marks)
- It IS membrane bound
- Recognises peptide on either MHC I/II molecules
How is diversity achieved in TCR’s and BCR’s to keep up with ever changing pathogens?
(5 marks)
- Genetic recombination
- Transcribe different combinations of GENE EXONS
- B cells shuffle gene exons encoding BCR’s/ antibodies
- T cells shuffle gene exons encoding TCRs
- Somatic cell is able to alter DNA permanently
A. What do each of the letters stand for below? (5 marks)
AND
B. What do they do in transcription and translation? (3 marks)
A.
- L - Leader
- V - Variable
- D - Diversity
- J - Joining
- C- Constant
B.
- L - takes light chain to surface after DNA been transcribed inot RNA and translated inot polypeptide chain
- Folds to form ligth chain and variable region will be sat on antigen binding site
- Heavy chain: when protein folds up V, J and D folded to sit on antigen binding site
To make one light chain what does a B cell need to transcribe?
(3 marks)
- 1x variable exon
- 1x joining exon
- 1x constant exon
To make one heavy chain what does a B cell need to transcribe?
(4 marks)
1x variable exon
1x diversity exon
1x joining exon
3x constant exons
Where does genetic recombination occur in BCR’s?
- Variable region of BCRs
- Each BCR gene has multiple copies of ‘variable’ gene exons
How does BCR create diversity with its exons?
(2 marks)
- Has multiple copies of eaxh exon, BUT it only needs one of each
- Able to take one of them and create a specific antibody
- Shown in image below through difference in exons
How many copies does the BCR gene contain of:
- Variable regions
- Diversity regions
- Joining regions
(3 marks)
- V: 40 regions
- D: 23 regions
- J: 6 regions
How many copies of variable and joining regions are present in lamda light chain and kappa?
(4 marks)
- k - v: 38 and j: 5
- l - v: 30 and j: 3
How many regions are in the β and α chains of a TCR?
(5 marks)
- β:
- V - 52
- D - 2
- J - 13
- α:
- V - 80
- J - 61
Roughly how many different anitbodies are there per person?
>1011
How do you get mass variability/ unique antibodies in T and B cells?
(10 marks)
- RAG (recombination activating gene) - randomly binds to intron between exons in V and J regions
- RAG bound to specific 12 pair sequence in J region and specific 23 pair sequence in V region
- RAG only binds to 12 & 23 sequences specifically so wont create e.g. 2 J/ V regions
- Recombination brings exons of V region 4 and 2 together and chunk of DNA excised off and permanently changes DNA in cell
- Between exon 4 and 2 brought together, get random addition of nucleotides - increases variability more in b cell genes
- B/T cells that do this intorduce variable nucleotides between these exons - so shuffled and genes are added and random nucleotides
- DNA stitched togehter and then get ‘imprecise coding’ = random addition of nucleotides
- DNA transcribed to RNA - and other parts of exons tagging along now spliced out of mRNA bringing C region up to J & V region
- mRNA translated into protein
- Light chain protein folds up and forms antibody and random AA, nucleotides etc. sat right on antigen binding site
- Creating unique sequence and unique variable region and antibody
What is T and B cell maturation?
(2 marks)
- Where cell goes from lymphoid precursor cell into naive b cell or t cell
- Maturation includes steps to check TCR and BCR functionality
Where does the T cell mature?
In the thymus - which shrinks during adolescence
Summarise T cell maturation.
(but after this PLEASE read the slide there is way more information on there)
(11 marks)
- Lymphoid progenitor cell enters thymus via diapedesis from blood vessel
- Precursor T cell express either CD8 or CD4
- TCR expression induced by Notch signalling from thymic epithelial cell
- VDJ recombination of β chain
- β chain tested - if cant signal will DIE
- VJ recombination of α chain
- CD4 and CD8 expression - T cell double positive
- Recognition of MHC tested
- Depending on MHC affinity T cells become single positive CD8 (MHC I) or CD4 (MHC II)
- Self antigen recognition is tested - can’t bind to MHC cell will die
- Mature T cell leaves thymus and migrates to peripheral lymhpoid tissue and awaits activation
What kind of recombination do the light and heavy cahins of BCR undergo? What is the receptor for BCR at recombination stage?
(2 marks)
- Undergo VDJ recombination
- IgM
Where does B cell maturation occur?
Bone marrow
Summarise B cell maturation
(after please read the slide - way more info)
(9 marks)
- Lymphoid progenitor mature into B cells in bone marrow
- B cells develop into pro B cells, pre B cells and then immature B cells
- Rearrangement of the Ig heavy chain occurs first with VDJ recombination, in pro B cells
- Heavy m chain is tested (45% b cells die here made faulty b cell receptor)
- Pre-B cells then undergo V-J rearrangement of the Ig light chain
- IgM expressed on surface
- Self antigen recognition tested
- IgD expressed on surface - if b cell can’t recognise IgM
- Mature B cell leaves bone marrow and migrates to peripheral lymphoid tissue and awaits activation.
