T and B Cells Flashcards
Where are T cells derived from and describe their route there after
They are derived from bone marrow stem cells (haematopoietic stem cell). They then arrive in the thymus and spent 1-3weeks undergoing differentiation and proliferation
What are thymocytes?
Early T cells
Describe the education of T cells
Small double positive thymocytes express low levels of TcR. Most TcR’s don’t recognise your own MHC molecules so T cells die because of lack of +ve selection. Cells that do recognise own MHC go on to mature and express high levels of TcR. They loose either a CD8 of CD4 to become single +ve cells. Then underogo -ve selection
What does double positive thymocytes mean?
They express both CD4 and CD8 receptors.
What is negative selection of T cells
This is where T cells that recognise your own MHC receptors with high affinity are eliminated to prevent autoreactive T cellls.
What does MHC stand for?
Major Histocompatibility Complex
Describe features of TcR’s
T cell Receptors. These are similar to antibodies in structure as they are both members of the immunoglobulin superfamily however TcR’s are always membrane bound. They can also undergo chromosomal rearrangement.
What is a main difference between antibodies and TcR’s
The antibody can bind to an antigen that is free in solution or membrane bound whereas TcR’s recognise an antigen when it is bound by an MHC molecule.
Describe the process of antigen presentation
Protein antigen in cell is broken down and the MHC molecule can now present the peptide. This is important as the antibodies cannot get into the cell
Describe features of the MHC class 1 proteins
Made up of a heavy chain and a small Beta2 microglobulin. Groove can hold 8-10 amino acid peptides. These are expressed on almost every cell of your body although in low levels in the CNS and none on RBC’s
Describe features of the MHC class 2 proteins
Made up from two heavy chains (alpha and beta). Groove can hold longer peptides of over 20 amino acids. Expression of these molecules is limited to specialised antigen presenting cells and immune cells. (macrophages/ B and T cells)
What are the MHC class 1 and the MCH class 2 molecules recognised by? (important)
Class 1 - recognised by CD8 T cells.
Class 2 - Recognised by CD4 T cells
MHC class 1 and 2 picks up peptides derived from where?
Class 1 - Internal contents of cells (tells you about internal environment).
Class 2 - External sources (tells you about external environment)
Where do MHC class 1 and 2 meet peptides?
Class 1 - Meets peptides in the endoplasmic reticulum.
Class 2 - Meets peptides in endosomes.
The polymorphic features of MHC molecules means what?
It means that different people will present slightly different peptides to their immune system. This means that organ transplant can be rejected because the organs natural MHC molecules will be picked up by the donors precipitants immune system as foreign.
