B-Lymphocytes Flashcards
What condition does the absence of B and T cells cause?
Severe combined immune deficiency (SCID)
What is the major difference between innate and adaptive immunity?
Innate doesn’t have memory and requires more time to respond to an antigen for the first time
What is the difference in the type of epitope B and T cells recognise?
T cells recognise sequences of amino acids, B cells identifies the 3D tertiary structure
What is a BCR?
B cell receptor, a membrane bound version of the cells antibody
How many transmembrane domain does a BCR have?
2
What is found next to a BCR? Describe the structure. What function does this carry?
A disulphide linked heterodimers Igalpha and Igbeta that have an Ig like fold. The tail of membrane-bound Ig is too short to signal, so instead it interacts with intracellular signalling molecules when the BCR binds with an antigen
What process generates Antigen Receptor Diversity? How does this work in the light chain?
Recombination. The germ-line DNA encoding for the B cell has a lot of variability. As B cells develop they get rid of a lot of variable units and leave a few V and J regions at random (LIGHT CHAIN). Then the B cell has a variant version of the gene, unused DNA is looped out and removed.
What happens to unused DNA during B cell recombination?
Unused DNA is looped out and removed.
What is the enzyme that allows recombination? What proteins does it contain? What genes encode these? What does deficiency in these genes lead to?
\V(D)J recombinase. Rag1 and Rag2. The Rag genes. SCID
How many variable units do people have in B cell germline DNA? How many in kappa and how many in lambda?
70, 40 and 30.
What process generates Antigen Receptor Diversity? How does this work in the heavy chain?
Recombination. The germ-line DNA encoding for the B cell has a lot of variability. As B cells develop they get rid of a lot of variable units and leave a few V, D and J regions at random (HEAVY CHAIN). Then the B cell has a variant version of the gene, unused DNA is looped out and removed.
Which chain undergoes recombination first, heavy or light?
Heavy
What are the three possible pathways once a B cell meets its antigen?
Affinity maturation, memory cell or plasma cell
Is an antigen enough to activate a naive B or T cell?
No they also need costimulation
Where would an accessory signal for a B cell come from? (2) What are the differences between these two sources of co-stimulation?
Microbial constituents (thymus independent) - only produces IgM and recognises PAMPS/polysaccharides such as LPS and HAS NO MEMORY, or a T helper cell (thymus dependent) memory and all Ig classes
Describe how a B cell is activated by a T helper cell
An antigen is taken up by both a B cell and a dendritic cell. The B cell then becomes an APC, presenting it on it’s MHC II. The dendritic cell does the same. The T helper recognises this through it’s TCR, the population expands and it moves to the lymph nodes where it binds with and activates the B cell.
What happens after a T helper cell activates a B cell?
T helper secretes cytokines/lymphokines after recognising the antigen on the self MHC class II. This stimulates the B cell to either differentiate into plasma cells secreting soluble BCR’s or memory cells.
What decides the Ig class? What drives this?
Types of cytokines, different ones will switch the constant region of the antibody. The T cell drives this class switching
What is activation-induced deamination? Explain
This causes point mutations in the VDJ variable region which causes small changes in the B cell variable region. AID takes the DNA and changes the C in GC to an A, so that in the next generation you get a T on the opposite strand. This improves antibody response. This means that antibodies are better for second exposures and onwards.
Which virus can cause a B cell to become cancerous?
Epstein-Barr
