Adaptive immunity - Part 2 Flashcards
Where do T cells develop?
T cells are derived from haematopoietic stem cells that are found in the bone marrow. The progenitors of these cells migrate to and colonise the thymus. T cell gene rearrangement takes place in the Thymus.
Where do B cells develop?
B cells develop in the bone marrow, then head to the spleen where they undergo further differentiation
What is the name of the process that allows B cells to produce many different antibodies with different variable regions, from the same genome?
Immunoglobulin gene rearrangement
The first step in gene rearrangement is called DJ recombination and targets the D (diversity) and J (Joining) genes.
One repeat sequence is left in place for each gene, and the other repeat sequences are put into a loop. Which proteins excise this loop of repeat sequences that are not needed?
RAG proteins
The second step in gene rearrangement involves which region of an ab?
The variable region. This second step is called VDJ recombination
Are the genes coding for antibodies the only ones that can rearrange?
No, T cell receptor genes can also rearrange. The TCR is very similar to an immunoglobulin, but they remain membrane bound, and are only found in T cells.
What is the key to adaptive immunity?
Gene rearrangement, that can only take place in T and B cells!
After gene rearrangement, antibodies are cell membrane bound. When the variable region binds to an antigen, it triggers the B cell to divide and proliferate. What is this process called?
Clonal expansion
What is the purpose of clonal expansion?
It allows the b cell with the correct antibody for a specific antigen, to proliferate. The other B cells that have not bound an antigen will die
Do cytotoxic T cells recognise antigens directly?
No, they recognise pathogen proteins displayed on the surface of infected cells. MHC proteins are important for displaying parts of pathogen proteins on the infected cells’ plasma membrane.
T-cell help is needed for a B cell to proliferate. The B cells can present bits of the specific antigen it recognises which will bind to a T cell receptor. There is then co-stimulation of the T cell, which uses which ligand?
CD40 ligand
Which cytokines does the T cell secrete after co-stimulation with the CD40 ligand, to cause B cells to proliferate?
IL-4 drives memory B cells
IL-10 drives plasma B cells
Which type of B cell keeps its antibody attached to its cell membrane?
Memory B cells
This is important to keep stimulating the T helper cells.
Which type of B cells no longer have a membrane bound immunoglobulin, but secrete it into the blood?
Plasma cells
What is isotype switching?
Another recombination event that occurs after VDJ switching. It changes the class of immunoglobulin eg. IgE, IgM, IgA, by switching the constant region.
