Lymphocytes Flashcards
How do B lymphocytes produce antibodies?
Upon antigen activation, B lymphocytes differentiate into plasma cells to produce antibodies. Antigens need to bind to the antigen receptor placed on plasma cells in order to start secreting soluble antibodies.
How is antibody diversity generated?
Antibodies are coded with many gene segments. Each heavy chain have 3 segments (V,D AND J). The V domain has 50 different segments, 25 different D and 6 joining segments. Therefore there can be any combination of VDJ domains.
This governs the 3D shape that is formed to create this antibody.
With the kappa light domain, there is no diversity segment- just purely- Vk and Jk segments- DNA is spliced, mRNA is formed and we now have a polypeptide
How are the antibody classes produced?
All B cells are created by making IgM- when a secondary response is triggered and the same antigen is produced, class switching occurs. They can switch into IgG, IgA, IgE and they will retain the same VH and VL domains of the original IgM therefore have the same antigen specificity
What is the TCR?
It is receptor found on the surface of T cells that bind to antigen peptide complex that are associated with MHC.
Structurally, it looks very similar to the Fab (top) fragment of an antibody. Any TCR on a particular cell will be the same however the receptors of the T cell from one to another differ. They have an alpha chain and a beta chain that is linked together with disulphide bonds.
On one segment we have variable alpha linked to constant alpha- we then have disulphide bonds linking beta and alpha chains. The variable beta is linked to constant beta.
At the tips of the variable domains, we have hyper variable loops or CDR- these form the antigen binding site which will be able to detect the MHC and antigen complex.
If it is an MHC class 1- it will be recognised on the cytotoxic T cell
What are the two major classes of T cells
Helper T cells have their T cell receptors associated with CD3+CD4 cell surface proteins.
Cytotoxic T cells have their T cell receptors associated with CD4+CD8 cell surface proteins
What does a normal T cell receptor complex contain
Alpha and Beta chains that make up the TCR
CD3 cell surface
What are CD4 and CD8 cells needed for
When T cells and the MHC molecules come together, the CD4 and CD8 cells mediate additional contact with antigen presenting cells (have MHC on its cell membrane) molecules.
Explain the complex of TCR, MHC, CD3/CD4
If CD3 and CD4 are involved, were aware that it is is a helper T cell and therefore the MHC molecule it must have would be class 11. The MHC molecule presents the antigen peptide to the T cell receptor of the helper T cell.
Pairing of these accessory molecules stabilises interaction and provides co-stimulation to the helper T cell-
After antigen binding, what do helper T cells do?
They secrete growth factors called cytokines. Helper T cells produce interferon gamma which then acts on the antigen presenting cell that releases the interleukin 1 (cytokines).
Some CD4/ T cells- secrete cytokines that favour macrophage activation. other CD4/T cells secrete cytokines that stimulate B cells to produce antibodies
Explain the complex of TCR, MHC, CD3/CD8
Cytotoxic T cells recognise the class MHC molecule having foreign antigenic peptides causing the viral and cellular proteins to break down. The bridge the virally infected cell to the cytotoxic T cell.
After binding, cytotoxic T cells release perforins which forms pores in the target cell which release other damaging enzymes.
