Immunology Chapter 5
Define "epitope" (or "determinant") and explain how it is different from "antigen"
They represent a small portion of most antigens. An antigen as a whole may float around, but the epitope is the area that interacts with the antibody.
True or false, antibodies are divided into classes and subclasses based on differences in heavy chain C regions.
True, antibodies are separated into classes, known as isotypes, and subclasses.
What does polyvalent (or multivalent) mean and what are some examples?
Typical of carbohydrates, lipids, and nucleic acids; it is when they typically repeat the same epitope
Relate avidity to valency
Valence is the number of bonds (monovalent, bivalent, polyvalent) while avidity looks at the overall strength?
How does Fab compare to F(ab')2?
When an antibody is cleaved by a protease called Pepsin, the F.A.B. regions are separated from the F.c. region and is now called F.a.b. prime; the two "branches" are linked together.
How can some epitopes be only in the natively folded protein
When denatured, the epitope structure is lost
How can some epitopes be both in a native or denatured protein
When in native protein, the epitope is accessible. When the protein denatures, it's okay because the epitope is still functional and accessible
Describe the forms of Ig formed during Mature B-cell formation.
A mature B cell develops a "delta" heavy chain for I.g.D. along the membrane with the I.g.M. Activated B cells stop expressing membrane-bound immunoglobulin and then becomes an antibody secreting Plasma Cell which secretes classes of antibodies that are post-translationally altered.
What are monoclonal antibodies and how are they made?
A pure collection of identical antibody molecules with the same specificity as they originated from a single B-cell clone.
What is the neonatal Fc receptor and what is it's significance?
A receptor that is found in many types of cells, such as epithelial cells. Its known to bind and transport I.g.G. into cells for recycling?
Describe the forms of Ig formed during Immature B-cell formation
A stem cell has no receptor. A Pre-B cell has a cytoplasmic "mew" heavy chain with surrogate light chains. An immature B-cell has the final form of "kappa" or "lamda" light chains to complete the membrane bound receptor.
Describe the antigen-binding site of an antibody
A variable domain from the heavy chain, and another from the light chain, come together to make an antigen-binding pocket.
Describe signal induction as a monoclonal antibody mechanism of action.
Activation of a cell when receptors are bound by monoclonal antibodies which induce signaling that makes the cell change its function or differentiation.
Contrast affinity vs. avidity
Affinity is the strength of binding between one antigen binding site and one epitope. Avidity is the overall strength of attachment, not just between one antigen and one epitope.
Where does an antigen specifically bind to an antibody?
An antigen binds to the antigen-binding region, which is where the variable domains are found.
What are antibodies and where are they found?
An effector molecule of the humoral response. Small circulating proteins found in body fluids.
Describe ligand blockade as a monoclonal antibody mechanism of action
Bind to ligand, blocking its ability to bind receptor
Describe receptor blockade as a monoclonal antibody mechanism of action
Bind to receptor, blocking its ability to bind ligand
Describe receptor downregulation as a monoclonal antibody mechanism of action
Bind to receptor, inducing endocytosis of receptor and reduction of receptor number
Describe complementarity-determining regions
C.D.R.'S are another term for Hyper-variable loops. They extend from the two variable domains and interact with the target antigen
How can some epitopes be produced new after processing (e.g., proteolysis)
Cutting up of the protein that has no epitope, a new epitope can be formed.
What DNA regions code for the components of VDJ recombination
DNA in a chromosome has gene clusters that code for components of heavy and light chains. Variable, or V, clusters; D clusters; and joiner, or J, clusters. Along with the constant, or C, clusters.
What are alternate names for antibodies?
Gamma globulins or immunoglobulins
What are the 5 major types of immunoglobulin classes, and how is this determined?
IgG, IgM, IgA, IgE, IgD. The F.c. region of an antigen determines what class an antigen will be.
What are some examples of proteins within this superfamily?
IgG, class 1 MHC for antigen presentation, CD4 for t-cell activation.
Where does somatic recombination, or VDJ recombination, occur?
In the bone marrow. The process is meant to increase the diversity of antigens and epitopes.
How does a membrane-bound antibody (e.g., IgM, IgD) differ in structure compared to a secreted antibody?
In the c-terminal, the membrane bound antibody has one more domain than the secreted antibody.
How can some epitopes be only in a denatured protein
In the folded protein, the epitope is hidden away and inaccessible. When the protein denatures, the epitope becomes accessible
Describe the regions of the antibody
In this Y-shaped structure, the F.a.b. regions are identical and made up of variable and constant domains which bind to specific antigens. The F.c. region determines the class of the antibody, and is in charge of the effector function.
Describe antibody activation of complement
It can activate by the classical pathway of complement. leading to inflammation, opsonization, and lysis of the target microbe.
Why does IgG have such a long half-life?
It can bind to the neonatal F.c. receptor on various cells. It is recycled as it processes through the endosome?
What is the function of the hinge region of an antibody?
It is a semi flexible connector between the f.c. portion of an antibody and the f.a.b. portions.
Describe the immunoglobulin IgA isootype
It is secreted as a dimer. 10-to-15% of serum is made up of it, but it is the most abundant in the body. Its half-life is 4-to-7 days. It canNOT activate complement. It canNOT cross the placenta. It can neutralize bacterial toxins. And its function is to be secreted in mucosal surfaces to prevent microbial attatchment; it is also the main antibody found in breast milk.
Describe the immunoglobulin IgD isootype
It is secreted as a monomer that binds surfaces of . 0.2% of serum is made up of it. Its half-life is 2-to-8 days. It canNOT activate complement. It canNOT cross the placenta. It does not neutralize bacterial toxins. And its function is to act as a receptor on B-cells and activate the humoral response.
Describe the immunoglobulin IgE isootype
It is secreted as a monomer. 0.004% of serum is made up of it. Its half-life is 1-to-5 days. It canNOT activate complement. It canNOT cross the placenta. It does not neutralize bacterial toxins. And its function is to be a surface receptor on mast cells and basophils; as well as play a role in allergic reactions and be effective in parasitic worm infection.
Describe the immunoglobulin IgM isootype
It is secreted as a pentamer; with 5 monomers together. 5-8% of serum is made up of it. It has a half-life of 5-to-10 days. It can activate complement. It cannot cross the placenta. It can neutralize bacterial toxins. And it's function is to be the first antibody secreted in the primary antibody response.
Describe the immunoglobulin IgG isootype
It is secreted as a single monomer. It is most abundant in the blood as 80% of serum is made up of it. It has the longest half-life of 7-to-24 days. It can activate compliment. It can cross the placenta. It can neutralize bacterial toxins. And its function is to be the main antibody of secondary antibody response.
How is immune complex formation clinically relevant?
Large complexes can lead to disorders as the large structure can get trapped in blood vessels, joints, etc. and induce an excessive inflammatory response.
Describe under what conditions immune complexes may form
Large complexes form when there's a Zone of Equivalence; in which there is an equal number of antigens to antibodies. Small complexes form in a Zone of Antigen Excess or a Zone of Antibody Excess.
Describe the structure of an antibody
Larger, longer heavy chains and shorter, smaller light chains make up the antibody, and they're held together by disulfide bonds. Immunoglobulin domains line the chains.
What are some monoclonal antibody mechanism of action?
Ligand blockade, receptor blockade, receptor downregulation, cell depletion, signal induction
Describe how monoclonal antibodies, or mAbs, can be engineered to modify effector functions
Mutations in the sequences of the Fc region, which is in charge of effector function, can change effector function. The FcγR region of the Fc binds with natural killer cells, phagocytes, and can activate complement, so altering this can change these effector activities.
Describe the specific interactions (forces) that occur during binding between antibodies and antigens
Noncovalen, reversible interactions. Electrostatic forces, hydrogen-bonds, van der Waals forces, and hydrophobic interactions.
What does it mean if something is immunogenic vs. something that is not?
Not all antigens are immunogenic. If something is immunogenic then it stimulates an immune response?
How do antibodies act as effectors?
Antibodies do not kill microbes directly, but they indirectly mark, clump, coat, activate complement, etc. A microbe binds a B-cell's surface antibody which causes it to secrete antibodies.
What other immune structures (besides secreted antibodies) use the VDJ genetic recombination process to acquire their structure?
Antigen-specific T-cell receptors?
Define antigen
Any substance that can be specifically bound by an antibody, or T-cell receptor.
How is the neonatal Fc receptor action pH-dependent?
Increased acidity causes an increased affinity of the receptor to I.g.G.
Define immunogen
Molecules that stimulate an immune response.
What are haptens?
Small chemicals that may bind to antibodies, but do not result in an immune response on their own; binding to a "carrier", then the combination becomes immunogenic.
Describe hyper-variable loops
Specific regions within the variable domain. They are largely responsible for the variability in antigen binding sites so that there can be a variety of antigen-binding sites in order to account for as many antigens as possible.
Describe antibody opsonization
The "stem", or F.c. region, of the antibody after the antibody binds the antigen, can bind phagocytes to activate it and engulf the target microbe.
Describe antibody-dependent cell-mediated cytotoxicity
The F.c. receptors on a natural killer cell bind the antibody's "stem"
What monoclonal antibody modifications affect half-life?
The FcRn interacts with the neonatal Fc receptor, so mutations in this can affect the half-life. Complete removal of the Fc region can greatly decrease the half-life.
Describe antibody neutralization
The antibodies bind to the pathogen until it is coated. This inhibits the pathogens binding to host cells.
Describe cell depletion as a monoclonal antibody mechanism of action
The antibody binds to antigen on a cell's surface, and interactions with its Fc region can induce destruction through complement, or antigen-dependent cell-mediated cytokineses. This can help in autoimmune therapies.
Describe the overall process of VDJ recombination
The enzymes of a B cell randomly selects one random V, D, J, and C region, and then spliced them together with random nucleotides in between each junction. After the recombination even has occured, this spliced sequence is then transcribed into a heavy chain. The light chain goes through the same thing,, but lacks the D region. Disulfide linkages bring together the chains to make the immunogloulin.
What do the Ig superfamily of proteins have in common?
They all have immunoglobulin domains.
What are advantages of using monoclonal antibodies vs. polyclonal antibodies?
They can be used to ID cell types, in diagnosis, and therapeutic tool
Which "branch" of the immune system do antibodies fit?
They fit into the adaptive branch? As a humoral response.
