Adaptive Immunity T Cells 1 Flashcards
What cell do T and B lymphocytes develop from?
What do myeloid pluripotent cells develop?
Lymphoid pluripotent cell.
All other blood cell types.
What are the two main types of T cell?
- T helper cell (Th)
- Cytotoxic T cell (CTL)
What cells do T Helper cells activate and how do they do this?
They activate T cells, B cells, dendritic cells, granulocytes (stimulates monocytes to develop into macrophages) and macrophages.
They activate by cytokines releases from the Th cell.
What innate cells are good for stimulating the adaptive immune response?
Dendritic cells and macrophages.
What are cytokines?
What do they do to a cell?
Cytokines are secreted proteins including growth and differentiation factors as well as chemoattractants.
They bind to specific receptors on target cells and initiate cell signalling. This triggers the target cell to express genes for cell activation and proliferation, production of more cytokines and cell migration.
What is the role of cytotoxic T lymphocytes?
What are the 3 ways that cytotoxic T cells achieve this?
They recognise cells that are infected by intracellular pathogens and induce apoptosis of that cell.
- Secretion of tumour necrosis factor which is a cytokine
- Cytotoxic T cell secretes perforin and granzymes
- Direct binding of the T cell Fas ligand to the ‘death receptor’ called Fas. Fas ligand is a cell-membrane bound homologue of TNF.
These all activate caspase proteases to induce apoptosis.
How do T cells recognise the antigens?
T cells all express an antigen receptor composed of 2 polypeptides.
Each T cell has a receptor of unique specificity.
This T cell receptor will not bind directly with the antigen. It will only bind to fragments of the antigen that are presented on the MHC on the surface of the target cell. These fragments are made by intracellular proteases that degrade antigens of infections micro-organisms.
Why is it important that T cells bind to MHC and not the antigen directly?
They come in close contact with cells that release cytokines to activate T cells. This ensures the cytokines are specifically targeted to the cells they are going to affect. Also comes into close contact with target cells which are the recipient for cytokines secreted by T cells.
This ensures that the cytokines are targeted towards the correct cells.
Explain the structure of a T cell receptor
- formed of 2 polypeptides anchored in the cell membrane
- most T cells have alpha and beta polypeptides but some have gamma and delta
- each polypeptide have 2 immunoglobulin domains
- membrane distal domains (from alpha and beta chains) form the single antigen binding site.
What is MHC 2 structure?
How is MHC 1 different?
Two polypeptides of similar size that are anchored to the cell membrane.
Both have a membrane proximal immunoglobulin domain but form a single antigen binding domain together.
Beta chains form a relatively flat base for a grove formed by two long alpha helixes shown red. The antigen is bound in this groove.
MCH 1 - only one peptide anchored in the membrane. The MHC 1 alpha chain is longer and included membrane proximal immunoglobulin like domain but also forms the entire antigen binding region (similar to MHC2). Smaller beta 2 microglobulin is not membrane anchored but forms a single immunoglobulin like domain which supports the antigen binding domain.
How does the T helper cell bind to the MCH 2 complex?
Th cell bind via T cell receptor to the MHC 2 complex.
T cell receptor of MHC 2 is associated with CD4 which binds to MHC 2.
The antigen binding site on the MHC 2 is formed by loops between beta strands at the top of the T cell receptor which make contact with the antigen and the alpha helixes of the MHC2.
CD4 glycoprotein is included which is a protein forming part of the T cell receptor complex on helper T cells. CD4 has 4 immunoglobulin like domains that bind to MHC class 2 proteins which gives a stronger attachment than the T cell receptor alone.
What is the role of CD4 for T helper cells?
CD4 transmits part of the activating signal to the T helper cell.
What is the structure of CD3 and what is it for?
CD3 is another component of the T cell receptor complex. Once the receptor has bound to the MHC complex, CD3 transmits the activating signal to the T cell.
Its made of 6 transmembrane proteins surrounding the antigen receptor.
How does antigen recognition occur when with CTL cells?
CD8 and its structure
CTL binds to MHC 1 complex with peptide.
TCR of CTL is associated with CD8 which binds to MHC 1.
CD8 is a dimer. The polypeptide comprises of a single immunoglobulin like domain on a long stalk.
CD8 binds only to the MHC class 1 protein part of the MHC 1 complex increasing the affinity of binding of the T cell receptor and transmits part of the activating signal to the cytotoxic T cell.
What is the main role of CD8 and CD4?
Increase binding of T cell receptor to MHC 1 or 2.
