Antigen recognition (8) Flashcards
What complex recognises and aligns the RSSs adjacent to the gene segments to be joined?
RAG1 RAG2 complex.
What three steps occur once RAG1 and RAG2 have recoginsed and aligned RSS sequences?
- Endonuclease activity introduces 2 ssDNA breaks close to RSSs.
- A DNA hairpin is created at the segments to be joined and a flush ds break at the end of the heptamers.
- Blunt ends ligated to form a signal joint. Nicked sequence is repaired to form the coding joint.
How can sequence variability be achieved in the coding joint?
It can be nicked at various points and TdT can add or removed nucleotides.
Where does antigen independent B cell differentiation take place?
Bone marrow.
How many nucleotides can TdT add?
Up to 12. these form the N region.
When does TdT add nucleotides?
During heavy chain rearrangement. This happens in the antigen independent stage in the bone marrow.
What are the three stages of antigen independent B cell differentiation?
- Heavy chain gene rearrangement
- Light chain gene rearrangement
- Selection against self.
When is IgM expressed in B cell differentiation?
After light chain rearrangement in the bone marrow.
What happens in the secondary lymphoid tissue?
Somatic hypermutation- antigen dependant B cell differentiation.
What is expressed in antigen dependant B cell differentiation?
Virgin/ naive B cells express IgM or IgM and IgD.
Where does somatic hypermutation occur, apart from in mature B cells?
Throughout rearranged V regions. In mature B cells it seems to cluster around CDRs.
What is affinity maturation and where does it take place?
The selection of high affinity receptors. It takes place in the 2ndry lymhoid tissue.
What is thought to introduce mutations in somatic hypermutation?
AID- Activation Induced cytidine deaminase.
What happens in class switching?
Same recombined V regions associate with different constant region genes.
What is the purpose of class switching?
To allow for different loclisation or the induction of different effector functions.
What is specifically retained in class switching?
The antigen.