B Lymphocytes Flashcards
What is the difference between the types of epitopes recognised by B cells and T cells?
T cells = sequences
B cells = structure (tertiary)
Describe the structure of the B cell receptor and how it transmits signals into the cell.
The BCR is a membrane-anchored antibody
It is associated with two transmembrane domains called Ig-alpha and Ig-beta which have cytoplasmic tails that are long enough to transmit a signal to the inside of the cell
Antigen binding to the BCR causes a conformational change, which drives signaling via the Ig-alpha Ig-beta heterodimer
What is the process by which B cells and T cells generate the variety in their receptors/antibodies?
Immunoglobulin Gene Rearrangement
Describe the generation of variation in the light chain.
There are 70 different V and J regions
The B cell begins with germline DNA and it cuts out various V and J regions at random leaving only a few
This means that there is a large number of different combinations of segments forming a large number of different antigen specificities
Different splicing patterns give rise to more variation
Describe the generation of variation in the heavy chain.
Gene rearrangement is the same – the only difference is that the heavy chain also has a D region and has several different constant regions (determines class)
What enzyme is involved in the removal of unused segments of DNA?
V(D)J Recombinase
What gene encodes this enzyme and what disease is caused by the deficiency of this gene/enzyme?
Rag gene - SCID
What determines the class of the immunoglobulin?
The constant region of the heavy chain
In what order does the gene rearrangement take place?
The heavy chain undergoes rearrangement before the light chain
What three things can happen to B cells once they’ve recognised their antigens?
Become Plasma cells
Become Memory cells
Somatic Hypermutation and Affinity Maturation
What is the general rule about B cell and T cell activation?
It needs co-stimulation to be activated – antigen alone is not enough
What are the two pathways by which B cell production is achieved?
T dependent and T independent
Describe the T independent pathway.
This is associated with long polysaccharides with a repeating subunit
The repeating unit can bind to several BCRs and drive cross-linking
There will also be PAMPs such as LPS that provide co-stimulation
Describe the T dependent pathway.
Dendritic cells and B cells take up the antigen at the same time
B cells process and present the antigen on MHC Class II
Dendritic cells also present the SAME antigen on MHC Class II to a T helper cell
The T helper cell becomes activated and undergoes clonal selection
The T helper cell then moves to the lymph nodes, comes into contact with the B cell and activates it
Describe the process of immunoglobulin class switching.
T helper cells (once bound to the B cell) can release various cytokines – depending on the cytokine released, the immunoglobulin class can be switched
