T - Cells Flashcards
What are lymphoid progenitor cells?
- Gives rise to Lymphocytes
- 20-30% peripheral blood white cells
- 6-10 microns in diameter with large nucleus, small halo of cytoplasm
- Upon stimulation by Ag become EFFECTOR CELLS or MEMORY CELLS
- 2 main types: T cells and B cells
- (T-lymphocytes and B-lymphocytes)
- Early developmental stage, cells pass to Thymus – become T cells or stay in Bone marrow – become B cells
Describe the maturation of T-cells in the thymus
- T cells mature in the thymus.
- Immature T cells develop in the bone marrow then migrate to the thymus to encounter self-antigen.
- During this process, many T cells die by apoptosis leaving just those that can generate a useful response to infection.
T - cell subsets:
Describe T-helper cells (express CD3 AND CD4)
Cytotoxic T-cells (Express CD8 AND CD3)
Regulatory T-cells (mainly CD4+ and CD8+)
y/s T-cells
They can also form memory cells the two groups are Th1 and Th2.
Define from previous lecture + they can also form memory cells.
Able to affect the immune system response by either suppressing them or activating them through direct cell contact or by secretions of soluble factors (cytokines)
T-cell receptors are formed of y/s chain that recognises lipid antigens
Describe the structure T-cell receptor
Dimeric molecule; ab or gd chains covalently linked by S-S
Each chain has a variable and constant Ig like domain
The variable region has hypervariable regions which are the antigen binding sites
Associated with the signalling complex CD3
CD3 is the identifier of the T cell
What is MHC: The Major Histocompatibility Complex?
MHC is a way which alpha-beta T cells (CD4 and CD8+) can recognise there antigen.
There are two types MHC class 1 and MHC class 2.
MHC 1 is expressed on nucleated cells and can see if a cell is infected with a virus
MHC 2 is expressed on professional antigen presenting cells, they cause the immune response by activating T-cells
Describe antigen processing and presenting to CD4 cells
- Extracellular uptake of antigen into a vesicle in the APC.
- Processing of proteins in lysosomes and endosomes.
- Biosynthesis occurs and transport of MHC class 2 to endosomes.
- Peptides combine with MHC class 2
- Expression of the peptide-MHC complex on the surface of the cell.
Describe antigen processing and presenting to a CD8 cells
On image
Describe dendritic cells
- Irregularly-shaped cells in most tissues
- DC usually myeloid derived (can be myeloid/lymphoid)
- When immature, DCs capture Ag (foreign material) and migrate to LYMPHOID TISSUES where they mature and effectively ‘present’ or ‘show’ antigen to T cells (T lymphocytes)
- Subtypes: include, Langerhans cells (skin), Interdigitating, plasmacytoid and ‘follicular DCs’ (actually fibroblasts)
- Only APC that can present to naïve T cells
What are some other antigen-presenting cells?
• Tissue specific DC: o Langerhans cells in skin o Interstitial DC in dermis o Blood myeloid DC o Plasmacytoid DC o Blood monocyte derived DC • Macrophages • B-cells • Endothelial cells under some conditions
What do CD4 T cells do?
- Recognise a peptide in the binding groove of MHCII
- T-helper cells: produce a cytokine profile which directs the immune response to a particular outcome.
- T-regulatory cells: responsible for ending an immune response
What do CD4+ Th1 cells do?
Help to activate the cellular immune response
What do CD4+ Th2 cells do?
Help to activate the humoral response
What do CD4+ Th17 cells do?
- Help to protect the gut mucosa
- Recruits neutrophils to sites of infection
- Th17 response effective against extracellular bacteria and fungi. Effective in promoting neutrophil mediated inflammation and helping Th1 cells to induce phagocytosis and subsequent killing of pathogens
What CD4+ Treg cells do?
- Maintain immune tolerance and suppress immune responses
- Produce anti-inflammatory cytokines IL10 and TGFb.
- Also has contact-dependent immunosuppressive effect
- Tregs inhibit the effector functions of CD4+ and CD8+ T cells. Also inhibit antigen presentation function of B cells and other APC.
What do CD8+ cytotoxic T-cells (CTL) do?
- Eliminate intracellular infections
- Also has role in anti-tumour immunity and rejection of transplants.
- Kill infected cells in an antigen-specific and cell-contact dependent manner.
