L10 Flashcards
What are the functions of a T Cell?
Direct immune response: CD4 orchestrate response
Kill virally infected cells: Antibodies cannot cross cell membrane of virus infected cells and CD8 recognises and kills them
How are T cells generated?
T cell precursors from BM
Gestation -> migrate from BM to thymus
Thymus specially adapted for education of thymocytes: Select useful and remove self reactive
Describe the T cell receptor?
Constant region interacts with lymphocyte
Variable region interact with antigen
Variable region produced by somatic recombination
How do T Cells recognise antigens?
• T cells are antigen specific
Antigen recognised is peptide processed from intact antigen
Peptide presented by major histocompatibility molecule
What is the Class I pathway?
• Virally infected cell is synthesising viral proteins
• Pass through ER and Golgi -> cytoplasm
Assembled into virus particles
• Sample of protein in cytoplasm passed into proteasome - tubular organelle lined with enzymes
• Proteins degraded into peptides and transported back into ER by TAP transporter
In ER, the peptides are loaded onto MHCI molecule
• CD8 with correct receptor can recognise peptide as foreign and kill target cell
MHCI groove contains self peptide in healthy cell
How do CD4 cells recognise antigens?
• Antigen presented by MHC class II molecule
• Antigen only presented by specialised antigen presenting cells
Antigen taken from extracellular space
What is Class II pathway?
Macrophages and dendritic cells sample antigens from extracellular space by endocytosis and phagocytosis
Antigens degraded into peptides and loaded onto MHCII
B cells can only present antigens that
bind to their antibody receptor
What is the relationship between CD4 and B cells?
• B cells recognise antigen by antibody receptors and internalise it
• Presented to T cells as peptide with MHCII
• T cells provide signals to B cells via cytokines and juxtacrine signalling
This stimulates the T cell, which then stimulates the B cell appropriately
What is the relationship between CD4 and macrophages?
Macrophage infected with mycobacterium tuburculosis – unable to kill organism
TB peptides presented with MHCII on surface
TB-specific CD4 T cell recognises TB, and provides help to macrophage (cytokines and juxtacrine signalling)
T cells and clonal selection
• T cells with receptor of best fit will be selected for survival and their numbers increase
• After infection, a few will remain as long-lived memory cells
T cells do not mutate receptors like B cells
T cells and memory
Primary infection: Naive CD4 and CD8 response. Clonal selection of most responsive clones
Resolution of infection: Most antigen-specific CD4 and CD8 cells die off, but some remain as memory cells
Secondary infection: Pre-existing memory T cells respond more rapidly and robustly
