4 - Immune system III: Immune Processes Flashcards
How is antigen presented to T cells via MHC molecules?
- TCR binds antigen presented on MHC Major Histo-Compatibility group proteins
- MHC are membrane bound glycoproteins
- MHC-I is express by all nucleated cells
- MHC-II is expressed by specialised antigen presenting cells
- CD8+ CTLs recognise MHC-I & antigen presented by infected cells
antigen presenting cells
dendritic cells, macrophages, B cells
- Phagocytes
- Migrate from site of infection to lymphoid tissues
- Display processed antigen to naïve helper T cells
- Important in triggering a Primary immune response
Antigen presenting cells phagocytosis
- Macrophages can present antigen but are less able to activate naïve T-cells than DCs
- Important in activation of the secondary immune response
B cells as APC
- B cells bind antigen via B cell receptor
- Receptor & antigen endocytosed
- B cells present antigens via MHC II to helper T cells with same epitope recognition
- Activated helper T cell secretes cytokines
- Cytokines activate B cell to produce memory B cells and plasma cells.
humoral immunity
- b cell mediated
- antibody-antigen mediated
- phagocytosis and complement-mediated killing
clonal selection
The process by which an antigen selectively binds to and activates only those lymphocytes bearing receptors specific for the antigen.
The selected lymphocytes proliferate and differentiate into a clone of effector cells and a clone of memory cells specific for the stimulating antigen.
basic humoral response
- Free pathogen binds to B cell receptor (specific epitope recognition).
- B cell activated to produce clones of plasma cells and memory B cells
- Antibody production from plasma cells.
- Elimination of pathogen.
- BUT In order to be fully activated, B cells also need activation from TH cells
humoral response full
- Macrophage or dendritic cell phagocytoses pathogen
- Antigen processed in macrophage or DC & presented on surface via MHC II
- Specific helper T 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 presented 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.
opsonisation
enhancement of phagocytosis
how do antibodies mediate antigen inactivation
- neutralisation
- agglutination of antigen bearing particles
- precipitation of soluble antigens
- complement fixation
what is complement?
a pathway composed of >30 different soluble proteins in the blood
- activated via 3 different pathways: classical, lectin, alternative
membrane attack complex (MAC)
complement system components assembled to form pores in membranes of invading cells
cell-mediated response
- Infected cell presents antigen on MHC I to CTL
- T cell receptor (TCR) binds presented antigen
- CD8 binds to MHC I (MHC I on all somatic cells)
- TC cell activated
- Perforin – forms pores in target cell membrane
- Granzymes – initiate apoptosis in target cell
role of granzymes
initiate apoptosis in target cell
role of perforin in CMR
forms pores in target cell membrane
