6. Antibody: Genetics and Structure Flashcards
What are the 4 groups of receptors that the immune system uses to recognise pathogens?
Pattern recognition receptors, major histocompatibility complexes, T-cell receptor, Antibody (BCR)
Which type of immune response cells are PRRs present on?
Both innate and adaptive - Charlie you cheeky fucker!!
They were initially discovered on the innate response though
What do PRRs recognise?
PAMPs and DAMPs - produced by host cell in response to infection
How many different MHCI and MCHII molecules are there?
3 of each - A, B, C
How do MHC vary between people? What MHC is common in white (pantone: Blanc de Blanc 11-4800) people
Vary hugely, HLA is most common for white peeps
Where is the T cell receptor found?
Only on the surface of T cells, highly specific, many different TCRs and BCRs can be made
Describe the structure of the antibody?
2 heavy (50kDa), 2 light (25kDa) chains, stable disulphide bond between L and H, variable region have 3 hyper variable regions (CDRs)
What is another name for the hyper variable region?
Complementarity determining region
What are the 2 different types of constant region light chain in an antibody?
Kappa and Lambda constant regions
What are the 5 different classes of heavy chain?
IgG, IgM, IgE, IgA, IgD
How many different immunoglobulin gene loci are there on how many different chromosomes? How are the heavy/light chain genes arranged on the chromosomes?
3 different gene loci on three different chromosomes
Heavy: genes linked together side by side on chromosome 14
Light: lambda light chain genes on chromosome 22, kappa on chromosome 2
What does the heavy chain immunoglobulin gene loci consist of?
5’ - 40 variable region gene segments then 27 diversity genes segments, then 6 joining gene segments then 9 constant region segments - 3’
What is the difference between the gene loci of heavy and light chains?
The light chain genes do not have diversity gene segments (only V, J and C)
How is the antibody developed (how are the genes chosen)?
In a random way - as B cell develops in bone marrow starts to recombine heavy chain of Ig genes - 1/27 D segments is taken and randomly placed next to one J segments (this forms a loop), a random V gene is then picked and placed to D/J to form a continuous loop of DNA (this produces the variable region of the antibody)
The constant region genes are then selected
How does the variability in encoding of CD1/CD2 and CD3 vary?
CD1 and 2 is encoded by only V gene segment whereas CD3 is encoded by V, D and J been segments so much more variable
How many subclasses of antibody are there? What are they?
9 - IgG has 4 subclasses 1-4, IgA has 2 subclasses 1-2, IgM/E/D have no subclasses
How many steps are there in the gene rearrangement process of the light genes compared to the heavy?
2 rather than 3 because light genes have no D segment
What enzymes cause V-D-J recombination?
Rag1 and Rag2 (recombination activating genes), recognise nucleotide sequences that flank the VDJ protein exons
What are Recombination Signal sequences? What is their sequence?
Regions of nucleotide that are recognised by RAG1 and RAG2
Heptononomer sequence: 5’-7nucleotides-spacer-9nucleotides-3’ (Spacer isn’t conserved)
As D is join gin to J need 5’ signal on every J and 3’ signal on every V segment
What is the molecular mechanism of gene recombination (e.g. enzymes)?
Sequences put next to each other, junction is cut using DNases and then DNA ligated back together using DNA ligase
What is the order of gene segments combining?
D and J joined first, then V joined to DJ
What four other methods increase the antibiotic diversity?
- Recombinatorial inaccuracies - exact place of which D joins to J and V to DJ can vary
- N-nucleotide addition - after DNA cut but before stuck together the terminal dNTP transferase transfers the N nucleotide (?)
- Different Chain combinations
- Somatic hypermutations - DNA changes when B cell divides
What do antibodies do the B cells initially make?
IgM and IgG - class switching allows them to synthesise others
How do B cells switch from producing to IgM to IgE?
Recombination process in the heavy chain - initially heavy chain recombines D to J then V to DJ to give variable region and begins off making IgM but when it class switches there is a similar process (cmu to c epsilon - DNA looping etc) but different enzymes involved (not RAG1/2) and different nucleotide sequences involved (switch sequences).
Where are the switch sequences present on the antibody gene?
Immediately upstream of each C region - but not one upstream of C delta (C mu and C delta are always transcribed together hence why cell always has IgM and IgD on surface)
What are the 5 methods of generation of TCR diversity? What 2 diversity generating methods are used in BCRs but not TCRs?
- Multiple germ line genes
- V-J and V-D-J recombination
- Recombinatorial inaccuracies
- N-nucleotide addition
- Chain combinations
What are the names of the subclasses of IgG in mice?
1, 2a, 2b, 3
Which constant region of the heavy chains code for IgG, IgA, IgM, IgD, IgE?
G: lambda A: alpha M: mu D: delta E: epsilon
Describe the structure of the antibody
2 Light chains with variable & constant regions, 2 heavy chains with variable & constant regions and a hinge region at the point where the arms may wobble and flop around like used condoms in a coastal breeze
What are the subclasses of human IgG?
1, 2, 3, 4
Which immunoglobulin molecules may become polymeric?
Secretory IgA (IgA at mucosal surfaces): dimer (linked together by J chain)
Circulating IgM: pentamer
What is the immunoglobulin domain structure?
4 beta strands form a beta sheet, 3 beta strands form another beta sheet (hydrophobic AA) so the two chains come together and are further held by a disulphide bond (very stable)
Hypervariable regions come out of these beta strands - may vary in shape and length
