T cell mediated immunity Flashcards
Compare and contrast antigen receptors of T and B cells
B cells can directly identify antigen in its native form
T cells must have antigen presented to them by a plasma cell prior to activation
T cell receptor made from 2 transmembrane glycoprotein chains - alpha and beta - each chain has a constant and variable domain ; 1 antigen combining site consists of variable parts of each chain ; cytoplasmic tail on cell interior ; no capacity to cause activation of cell
B cell receptor made from 4 chains - 2 heavy and 2 light ; 2 antigen combining sites
What kind of pathogens and leukocytes/components of immune system are responsible for : a) intracellular vesicular infections and b) intracellular cytosolic infection
A) bacteria and helper T cells
B) viruses and interferon/natural killer/cytotoxic T cells
Role of CD4 T helper cells
Aid B cells in antibody production
Aid macrophages in phagocytosis
Role of CD8 cytotoxic cells
Kill infected cells q
What determines if an immature T cell becomes a cytotoxic or helper cell?
Type of human leucocyte antigen presented to it on the antigen presenting cell
For a T cell to become a TC cell, antigens must be presented on class I of MHC
for a T cell to become a TH cell, antigens must be presented on class II of MHC
Describe the structures of MHC I /II molecules
MHC class I - made up two chain - alpha and microglobulin beta chain ; alpha chain has 3 domains - α1 , α2 and α3 ; peptides from antigen loaded onto α1 and α2 domains
MHC class II molecule made up two chains - alpha and beta ; both chains have two domains ; peptide binding grove consists of α1 and β1 domains
Describe CD8 T cell activation
Antigen on MHC class I of antigen presenting infected cell binds to T cell receptor
CD8 coreceptor on T cell surface binds to α3 domain of MHC class I = activation
Describe CD4 T cell activation
Antigen on MHC class II of antigen presenting cell binds to T cell receptor
CD4 coreceptor interacts with β2 domain of MHC class II = activation
specificity of T cells
Only T cell with comp receptor for antigen will respond to the MHC proteins
How does the immune system ensure that’s the right type of antigen is presented on the right class of MHC?
For cytosolic Infections , the antigen is broken down into peptides in a proteosome then these are transported to the ER where they are loaded onto class I proteins
For extracellular infection , antigen enters cell and is enclosed in a phagosome then broken down into peptide fragments ; Class II protein has invariant chain blocking the peptide binding groove ; peptide added to MHC class II only once it is enclosed in a new vesicle together with the peptide fragments
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Describe the function of dendritic cells
Involved in the later adaptive response
Antigen carriage by dendritic cells to lymphoid tissue
leads to activation of naive T and B cells and antibody production
recirculation back to site of infection
Cytokines And disease
Overproduction of cytokines can lead to diseases such as psoriasis , arthritis , colitis etc
Role of Th2 cells
Involved in type 1 allergic responses
Produce IL-4 which activates mast cells via action of B cells
produce IL-5 which activates eosinophils
Role of Th1 cells
Macrophage activation via interferon-γ
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