016 Antigen recognition by B-cells and antibody Flashcards
What is the side chain theory?
That lymphocytes recognise antigens by the lock and key model
What is Burnetts clonal theory?
That when a B cell is activated by a taget, it is stimulated to divide into cells with identical receptors
What does the BCR complex consist of?
Along with the B cell receptor, it also has a Ig-alpha and Ig-beta chain that are linked by disulphide bond.
What is the function of IgAlpha and IgBeta chains?
They initiate signals into the B cells when the B cell transmembrane antibody binds to the antigen.
What class of antibody is expressed on B cells when they are not yet activated by antigen?
IgM, IgD
Describe the antibody structure on the cell membrane?
Antibody is a dimer molecule; heavy chain and light chain; both chains have a constant a variable region; chains are bound together by S-S bonds
What structures determine antigen specificity on the surface of the antibody?
There are 3 loops CDR1, CDR2, CDR3 on both the light and heavy chains that determine antigen specificity
What is an epitope?
This is the recognisable surface on that antigen in which the antibodies are able to detect.
How is the antigen-antibody complex held together?
Lots of non-covalent bonds (hydrogen bonds, hydrostatic forces, vanderwaals etc)
How many antibodies are able to bind to one antigen?
Multiple antibodies because each antigen has several different epitopes
Where does B cell development occur?
Bone Marrow
Describe the variable region of the heavy chain IgH
Variable region of heavy chain is encoded by 3 sections of 3 genes (V,D,J). The V and D genes contain sequences encoding for CDR1 and CDR2, whilst J genes encode for CDR3. During B cell development, one section is selected from each at random. There are 40 segments in the V section, 27 segments in the D section and 6 segments in the J section.
Describe the variable region of the light chain Igk
Variable region of light chain selects segments from V and D genes from two separate loci.
What may cause additional variability?
RAG-1 and RAG-2 genes encode for recombination activating genes that piece the different segments together. However, this is normally not proof red, and is imprecise causing additional variability through deletion of base pairs or addition of random base pairs.
What is somatic hypermutation
This only occurs in B cells - they are able to adapt according to their environment and undergo class switching. It improves affinity.
