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.
How do CD4+ T cells help macrophages?
T cell is able to recognise complex of bacterial peptide within MHC class II molecule and activates macrophages by cytokines and juxtacrine signalling.
How do T cells undergo clonal selection and develop memory?
During infection, T cells with receptor of best fit will be selected for survival and their numbers will increase. After the infection, most antigen-specific CD4 and CD8 cells die off, however, a few T cells will remain as long-lived memory cells
What is the difference between the innate and adaptive immune response?
The innate immune response consists of physical, chemical and cellular defences against pathogens, whereas the adaptive immune response utilises specialist and specific immune cells (T-cells and B-cells) to activate a more specific response.
Adaptive immune response involves a pathogen-specific immune response that is hallmarked by the clonal expansion of T and B lymphocytes.
What is the difference between B and T cells?
The key difference between T cells and B cells is that T cells are involved in cell-mediated immunity while B cells produce antibodies which are responsible for humoral immunity.
What is the difference between MCH class I and MHC class II?
MHC class I molecules present antigens that are intracellular or endogenous to CD8+ cytotoxic T cells, whereas MHC class II molecules present antigens that are extracellular or exogenous to CD4+ helper T cells.
