Lecture 9: T-Cells Flashcards
What are CD4 and CD8?
Markers on the surface of all leucocytes (T cells).
What is the role of CD4+ T (helper) cells?
CD4 ‘helper’ T cells help orchestrate innate response by presenting antigen to innate immune cells and B cells.
What is the role of CD8+ T (effector) cells?
Cytotoxic T cells (CD8 cells) recognise infected cells (viruses hidden within cells) and kill them.
Where are T cells formed?
T cell precursors are produced in the bone marrow and migrate to the thymus for maturation. T cells become ‘educated’ so non-react or self-reactive T cells are removed.
Why do T-cells mature in the thymus and no the bone marrow?
The thymus is specially adapted for the education of thymocytes; T cells ae exposed to certain proteins which educate them to be reactive at appropriate times.
How is the T cell receptor formed?
The variable region of the T cell receptor interacts with the antigen.
How is the variable region of T cells formed?
The variable region is produced by somatic recombination between T cell receptor gene segments (similar process to antibody formation).
How does the T cell recognise the antigen?
T cells recognise peptides of antigens which have been processed and presented by antigen presenting cells (APCs) in their histocompatibility molecule. The T cell receptor binds to the peptide and at the same a T cell surface glycoprotein also attaches to the histocompatibility molecule of the APC.
How do CD8+ cytotoxic T cells destroy infected cells?
CD8+ cytotoxic T cells recognise infected cells due to markers on their surfaces and destroy them
Describe the antigen processing class I pathway of CD8+ T cells
Direct infection of cells causes viral peptides to be loaded onto histocompatibility complex class I, so they can be presented to CD8 T cells. CD8 T cells with the correct receptor can recognise the peptide as foreign and kill the target cell.
Describe the antigen processing class II pathway of CD4+ T cells
Macrophages and dendritic cells phagocytose antigens from the extracellular space which are degraded into peptides and loaded onto MHC class II molecules. Passing CD4+ T cell with correct receptor recognises peptide-MHCII complex and activates response.
How does the major histocompatibility complex differ between health and infected cells?
In infected cells, the major histocompatibility complex presents a virus peptide. In a healthy cell, the major histocompatibility complex will contain a self-peptide.
How do CD4+ and CD8+ cells differ?
CD4+ helper T cells recognise processed peptide antigen in MHC class II of specialist APCs, whereas CD8+ cytotoxic T cells recognise peptide in MHC class I. With the APCs used to activate CD4+ T cells, the antigen is taken up from the extracellular space rather than from direct infection of the cell.
How do B cells act as ‘professional’ APCs for CD4+ T cells?
Antigen receptor on B cells can attach to passing antigens, internalise and degrade them into peptide fragments, and present them in MHC class II for recognition by CD4+ T cells.
How do CD4+ T cells help B cell maturation?
T cell binds to antigen peptide in MHC class II molecule on B cell and triggers T cells to provide signals to B cells via cytokines and juxtacrine signalling.
