Immunoglobin Structure Flashcards
Is the immunoglobin isotype (class) determined by the heavy chain or the light chain?
Heavy chain
Differentiate the functionality of the constant region from the functionality of the variable region
Constant Region (Fc): important for biological activity Variable region (Fab): important for antigen binding
How are the different parts of the antibody held together?
Disulfide bonds
What are the two alleles from which the light chains are derived? What it the ratio between the two in a normal individual?
Kappa and lambda in a ratio of 3:1
What are the hypervariable regions of an antibody?
The hypervariable regions are the regions within the variable region of both the light and heavy chain responsible for the specificity of the antibody binding (the residues directly responsible for Ag binding- located in the loops)
They are called CDRs, or complementarity determining regions
Describe the polymeric structure of IgM in the blood.
IgM is a pentamer in the blood (connected with a J-chain)
How many epitopes can an IgM polymer bind?
10- (2x5)
What is the structure of IgA in the blood?
Dimer
What is the concentration of IgD in the blood?
Almost zero- IgD is primarily bound to the surface of B-cells
Which Ig is found in the highest levels in the blood?
IgG1
Which Ig is responsible for allergies?
IgE
Cross-linking of IgE on mast cells leads to degranulation, release of histamine and other substances that mediate allergic reactions
What is the first Ig made in response to an infection?
IgM
Following IgM, which is the next antibody found in the blood following an infection?
IgG
What are three ways by which antibodies mediate humoral immunity/
1) Neutralization
2) Opsonization (promotes phagocytosis)
3) Compliment activation (enhances opsonization)
What is Fc receptor-mediated killing?
Fc receptors on the surface of certain cells (B-cells, follicular dendritic cells, natural killer cells, macrophages, neutrophils, …etc etc) bind to the Fc region of antibodies bound infected cells or extracellular pathogens. This activates the immune to kill the pathogen or infected cell by phagocytosis or antibody-dependent cell-mediated cytotoxicity.
Will an effector cell be activated through binding of just one Fc-receptor an antibody?
No- activation through Fc-receptors requires aggregated Ig.
Cross-linking required!
How long does maternal IgG protect a newborn?
Fully for 3 months, with transient low levels of IgG for up to 1 year
Describe the half-life of serum antibody titers of someone who received a tetanus shot and someone who had measles as a child
Tetanus: half life is 11 years
Measles: Essentially forever
What is IVIG?
A polyclonal antibody used to treat many immune deficiencies and autoimmune diseases
Describe the use of tumor-specific monoclonal antibodies for the treatment of cancer
1) identify a tumor-specific antibody
2) Clone the antibody and clone it
3) Inject the antibody into someone with that tumor, and allow it to bind and activate effector cells to launch an immune response against tumor cells
