Lecture 4 Immune Processes III Flashcards
(25 cards)
How is antigen presented to T cells ?
- Via MHC molecules
- T cell receptors (TCR) binds to antigen presented on MHC
What does MHC stand for?
Major Historical-Compatibility group proteins
What is MHC-I expressed by ?
All nucleated cells
What is MHC-II expressed by ?
Specialised antigen presenting cells
What type of cell and MHC molecules does CD8+ recognise?
CD8+ CTLs recognise MHC-I and antigen presented by infected cells
What type of cell and MHC molecule does CD4+ T helper cells recognise?
They recognise MHC-II and antigen on Antigen presenting cells
3 Antigen Presenting Cells (APCs)
- Dendritic cells
- Macrophages
- B cells
What are dendritic cells function? (5)
- Professional APCs
- Migrate from site of infection to lymphoid tissues
- Display antigen to naive helper T cells
- Important in triggering a Primary immune response
Function of macrophages as APCs
- Can present antigen but less able to activate naive T cells than dendritic cells
- important in activation of the secondary immune response
Function of B cells as APC (5)
- B cells bind antigen via B cell receptor
- Receptor and antigen endocytosed
- B cells present antigens via MHC II to helper T cells with same epitope recognition
- Activated T cell releases cytokines
- Cytokines activate B cell to produce memory B cells and plasma cells
What are the 3 major immune responses?
- Inflammation
- Humoral mediated immunity
- Cell-mediated immunity
What is humoral immunity
- B cell mediated
- Antibody-antigen mediated
- Phagocytosis and complement-mediated killing
Steps involved in clonal selection ?
Humoral response (10)
- Macrophage or dendritic cell phagocytoses pathogen
- Antigen processed in macrophage or DC & presented in surface via MHC II
- Specific T helper cell recognises processed antigen and binds (aided by CD4 binding to MHC II)
- Helper T cell activated
- B-cell phagocytoses BCR & antigen, presents antigen on MHC II
- Helper T cell recognises antigen present enter by B cell
- Cytokines from activated helper T cell fully activate B cell
- B cell activated to produce clones of plasma cells and memory B cells
- Antibody production from plasma cells
- Elimination of pathogen
How do antibodies initiate antigen activation?
- Neutralisation
- Agglutination
- Precipitation of soluble antigens
1,2&3 enhance phagocytosis - opsonisation
- Complement fixation (activation of complement) e.g. MAC leads to cell lysis
What does opsonisation mean?
Enhancement of phagocytosis
3 different pathways of complement activation ?
- Classical
- Lectin
- Alternative
What do all complement activation pathways end with?
All routes end with formation of Membrane Attack Complex (MAC)
What is classical complement activation pathways?
Antibody-activated pathway
How do complements kill cells/complement-mediated lysis?
- Complement bind to antigen-antibody complexes on cell surface
- Complement cascade activated
- Several complement proteins form Membrane Attack Complex (MAC)
- A hole is formed in foreign cell and the cell eventually lyses
Cell type in cell-mediated response
T cell mediated
CTL for cell mediated, aided by t helper cells
What does perforin do?
Forms pores in target cell membrane
What do granzymes do?
Intimate apoptosis in target cell membrane
Cell-mediated response (5)
- Infected cell presents antigen on MHC I to CTL
- T cell receptor (TCR) binds presented antigen
- CD8 binds to MHC I
- CTL cell activated
- Perforin-forms pores in target cell membrane and granzymes initiate apoptosis in target cell