What are the different classes of antibodies?
IgG, IgD, IgA, IgE and IgM - these are all isotypes of each other. They are classed according to the heavy chain they contain - alpha, delta, epsilon, gamma or mu
What is the dual biological function of antibodies?
They have a recognition function via binding to antigens by variable region sites
Effector function - the clearance mechanisms are mediated by the constant region
What is the function of IgM?
It activated B cells when membrane bound. First Ig produced in an immune response
When in plasma, it exists as a pentamer and will perform agglutination and activates the complement system
What is agglutination?
The action of an antibody when it cross-links multiple antigens producing clumps of antigens. It is mediated by IgM and IgG antibodies and increases the efficacy of microbial elimination by phagocytosis
How is the complement system activated?
Initiated by specific antigen binding to IgM and IgG antibodies. This induces a conformational change in the constant regions of the heavy chains exposing multiple binding sites for C1, the first component of the complement cascade
What is the function of IgG?
Most abundant antibody in human serum. Dominant Ig in memory immune response. Functions: Agglutination Complement system activation Foetal immune protection Neutralisation Opsonitation NK cell activation
How do IgG antibodies provide foetal immune protection?
The IgG antibodies are transported across the placenta, directly into the foetal blood circulation
How do IgG provide neutralisation?
It is mediated by specific antigen binding. The binding of high affinity neutralising antibodies to antigens is protective. It prevents pathogens from infecting the host. Also prevents microbial toxins from disrupting normal cell function
How do IgG do opsonisaition?
Initiated by specific antigen binding. It is mediated by Fc receptors that bind specifically to the constant region of the heavy chain in IgG. Opsonisation enhances phagocytosis
How are NK cells activated?
Via antibody-dependent cell-mediated cytotoxicity
What is the function of IgD?
When membrane bound acts as a B cell activator
What is the function of IgA
In its monomeric form in serum it activates B cells
In its dimeric form in secretory fluids it provides neonatal defence and neutralization at mucosal sites
What is the function of IgE?
Triggers allergic reactions via the degranuation of mast cells and basophils
What is the process in which the antibodies are made?
IgM is made first in the adaptive response
IgG and other antibodies are then produced later
How are different Ig classes produced?
During B cell activation, B cells can change the Ig heavy chain constant region gene segment that they use. This process is induced by specific cytokines
What are CD4+ T cells?
Helper T cells that regulate the immune system
How do T cells regulate the immune system?
Killing of intracellular bacteria Killing of helminthes B cell co-stimulation Killing of extracellular pathogens Lymphocyte suppression
How do helper T cells stimulate other immune cells?
Cytokines
Receptor : Ligand interactions
How do effector T helper cells help T cell responses?
They secrete IL-2 which is a cytokine that stimulates proliferation and differentiation of antigen-activated T and B cells
How do T helper cells help macrophages?
They migrate from secondary lymphoid tissues into infected tissue sites. They express co-stimulatory molecules such as interferon gamma that will hyper-activate macrophages enhancing their killing ability and pro-inflammatory cytokine production
How do T helper cells help B cells?
They help B cells to respond effectively to protein antigens by providing the second signal they need to activate.
The antigen is internalized by the cell and the peptides are presented on the B cell by MHC 2. T cells ill move into B cell zone of lymph node where they are stimulated by MHC 2 and express co-stimulatory molecules telling the B cell to clonally proliferate. Activated T cell will secrete cytokines to further activate B cell and stimulate 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 Generatino of high affinity antibodies
What is the fate of CD8+ cells?
Turn into cytotoxic T lymphocytes that kill the infected host cell
How do cytotoxic T lymphocytes kill infected host cells?
They exit lymph node and migreate to the site of infection, recognize and kill infected tissues by:
Binding to infected cell
Initiates apoptosis
Migrates to new target
Cell dies. They release toxic molecules into the cell
How does fas ligand kill cells?
Fas ligand binds to fas receptor and initiates apoptosis