Immunology Part 5 Flashcards
What do activated B cells do?
- Produce short-lived plasma cells
- Low affinity, antigen-specific antibodies are secreted
Activated B cells can also produce memory B cells, these product high affinity antigen specific antibodies
Describe the recognition function of antibodies
The variable regions allow binding to antigen
Describe the effector function of antibodies
Clearance mechanisms mediated interaction of the constant region with effector molecules
- complement
- Fc receptors
What is the role of IgM?
Serves as the B cell antigen receptor
-activates b cells
First Ig produced in immune response
(mmmmneong)
What is the function of IgM?
Pentamier in plasma and secretory fluids;
- agglutination (immune complex formation)
- complement system activation
What is agglutination?
When an antibody cross-links multiple antigens forming a clump of antigens
What is agglutination mediated by?
Specific antigen binding to IgM and IgG antibodies
What does agglutination do?
Increases the efficacy of microbial elimination by phagocytosis
What initiates complement system in the classical pathway?
Specific antigen binding to IgG and IgM antibodies
What happens when a specific antigen binds to IgG and IgM antibodies?
Induces a conformational change in the constant regions of IgM and IgG heavy chains which exposes multiple binding sites for C1, the first component of the Classical Activation pathway of the Complement System
Describe the structure and abundance of IgG?
most abundant in human serum (normally)
dominant Ig type produced during a secondary memory response
What are the functions of IgG?
Agglutination Complement system activation Foetal immune protection Neutralisation Opsonisation Natural Killer cell activation
Which antibodies are transported across the placenta into foetal blood?
IgG
What is neutralisation?
- Prevents pathogens from infecting host cells
- Prevent toxins from disrupting normal cell function
What triggers neutralisation?
Binding of high affinity neutralising antibodies to antigens is protective
IgG
Also dimeric IgA (in secretions)
What is opsonisation?
Enhanced phagocytosis of encapsulated bacteria
What initiates opsonisation?
Specific antigen binding
What mediates opsonisation?
Special Fc receptors that bind specifically to the constant region of the Iggamma chain of IgG
Describe natural killer cell activation in antibody-dependant cell mediated cytotoxicity?
NK cells Fcgamma receptor binding to IgG on infected cell can trigger apoptosis of infected cell
What is the function of IgD?
In membrane-bound form serves as b cell antigen receptor (monomer)
Functions to activate B cells
What is the second must abundant serum Ig?
IgA
What is the monomeric form of IgA?
Present in serum
functions to activate B cells
What is the dimeric form of IgA
Present in secretory fluids
functions;
-neonatal defence
-neutralisation at mucosal sites
What is the role of IgE?
Trigger allergic response
How are antibodies of the same specificity but different Ig class produced?
During B cell activation, B cells can switch the Ig heavy chain constant region gene segment that they use
Retain the original Ig heavy and light chain gene hypervariable gene segments
Process is induced by the specific cytokines
Describe the effector functions of activated CD4+T cells?
Produce helper t cells which produce
- TH1
- TH2
- Tfh
- Th17
- TREG
What is the role of Th1 Cells?
Killing of intracellular bacteria
What is the role of Th2 cells?
Killing of helminths
What is the role of Tfh cells?
B cell co-activation
What is the roll of Th17 cells?
Killing of extracellular pathogens
What is the roll of regulatory T cells?
Lymphocyte suppression
What do effector Th cells do?
Stimulate other immune cells
- CD4+T
- CD8+
- macrophage
- B cell
How do effector Th cells help T cell responses?
They secrete interleukin 2 which stimulates proliferation and differentiation of antigen-activated T cells (and antigen-activated B cells)
How do effector Th1 cells help macrophages?
Effector TH1 cells migrate from secondary lymphoid tissues into infected tissue sites.
TH1 cells are re-activated by tissue-resident macrophages in an antigen-specific manner
TH1 cells express co-stimulatory molecules (e.g. IFNg) that hyper-activate macrophages, enhancing their killing activities and pro-inflammatory cytokine production.
How do tFH cells help B cells?
help B cells respond effectively to protein antigens (they provide Signal 2)
- protein antigen bound to BCR is internalised
- antigen is degraded and peptides are presented on the B cell surface in complex with MHC-II
- effector Tfh move into B cell zone of lymph node, they are re-stimulated by B cells in an antigen-specific manner and start to express co-stimulatory molecules
- re-activated effector Tfh cells stimulate the B cell to clonally proliferate
- the re-activated effector Tfh cells secrete cytokines that activate the B cell and stimulate the germinal centre response
What is the germinal centre response?
B cell proliferation Differentiation into Plasma cells Differentiation into Memory B cells Ig heavy chain class switching Generation of high affinity antibodies
Describe the pathway of CD8+ cells effector function?
Produce cytotoxic T lymphocytes and kill infected host cells
What do CTLS do?
CTLS exit lymph nodes, migrate to sited of infection, recognise and kill infected tissue cells in an antigen specific manner
Describe the process of CTL killing?
- CTL recognises and binds to virally infected cell via MHC i
- CTL programs target for death, inducing DNA fragmentation
- CTL migrates to new target
- target cell dies by apoptosis
How do CTLs and NK cells kill infected host cells?
Release perforin and granzyme molecules from granules
Perforin: polymerises to form pore in target membrane
Granzymes: serine proteases which activate apoptosis once in the cytoplasm of target cell
Granulysin: induces apotosis
What is Fas ligand mediated killing?
Externally driven apoptotic signals which initiate caspase cascade and apoptosis
