Term
| What is the basic structure of an immunoglobulin? |
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Definition
| Gamma globulin plasma proteins made up of 4 polypeptide chains, 2 light (L) & 2 heavy (H). Glycosylated |
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Term
| What is the basic definition of an antibody? |
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Definition
| An immunoglobulin that binds a specific antigen |
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Term
| Explain the distinction between an antigen and an immunogen |
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Definition
Antigen (Ag): A substance that can be bound by an antibody
Immunogen: A substance that induces an immune response (i.e., specific antibody production or T cell activation). Are usually: Foreign substances E.g., microbial pathogens, proteins from animals, plants, macromolecules or tissues from unrelated persons.
All immunogens are antigenic but not all antigens are immunogenic |
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Term
| Explain the basics of the antigen-antibody interaction |
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Definition
Immune complex: product or complex formed when Ab binds Ag
-Held by Hydrogen bonds and hydrophobic interactions
-Classic receptor-ligand interaction |
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Term
| What is the Kaff constant? |
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Definition
For the antigen-antibody complex there is an
Equilibrium equation: Ag + Ab <====> Ag.Ab;
The Kaff (affinity constant) = [Ag.Ab]/{[Ag]x [Ab]}.
Kaff (or simply Affinity) measures:
*Tightness of the binding - increases over time
*Stability of the Ag.Ab complex |
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Term
| What is the significance of the immune complex? |
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Definition
Formation is first step in its host defense function;
-High affinity Abs are better in vivo for host defense
-May lead to tissue destruction/disease. E.g. vasculitis, glumerulonephritis |
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Term
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Definition
| An antigen that doesn't illicit a immune response |
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Term
| How can antibody measurement be used as diagnostic tool |
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Definition
-Exposure to an infectious agent (e.g., HIV, anthrax)
- Evidence of immunity; immunization efficacy (e.g., tetanus)
- Certain autoimmune diseases. E.g. Lupus, Grave’s disease)
- Allergic reactions to substances. (Eg., food, pollens)
- Immunodeficiency
- Malignant lymphoid diseases: Monoclonal gammopathies (e.g., Multiple myeloma, Bence Jones proteins, Waldenstrom’s macroglobulinemia). |
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Term
| What are the basics of ELISA? |
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Definition
| In ELISA an unknown amount of antigen is affixed to a surface, and then a specific antibody is washed over the surface so that it can bind to the antigen. This antibody is linked to an enzyme, and in the final step a substance is added that the enzyme can convert to some detectable signal. Thus in the case of fluorescence ELISA, when light is shone upon the sample, any antigen/antibody complexes will fluoresce so that the amount of antigen in the sample can be measured |
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Term
| What are the functions of antibodies? |
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Definition
- Neutralization of infectious agents or toxins
-Immune phagocytosis
-Complement activation
-Antibody dependent cellular cytotoxicity (ADCC)
-Enhancement of Ag presentation, T cell activation & Immune reactivity
Antibodies are able to perform these different functions in part because of their diversity in binding specificity (> 10^6 specificities) |
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Term
| What are the structural characteristics of an Ig molecule? |
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Definition
General Structure: 4 polypeptide chains- 2 L (~23Kda each), 2 H (~45Kda each)
- Maintained by disulfide bonds and noncovalent forces
- L chains designated kappa and lambda. Either 2 kappa chains or 2 lambda chains per Ig, NEVER one of each.
- Domain organization (100-110 aa/): stability/function
-Fab fragments (Ag-binding frag), Fc fragment & Hinge region |
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Term
| What are the results of Ig cleavage by papain and pepsin? |
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Definition
Papain cleaves Ig's into three molecules - 2 Fab fragments and 1 Fc fragment
Pepsin cleaves Ig's into one Fab fragment and many small pieces of the Fc fragment |
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Term
| Explain the different regions of Ig's |
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Definition
Comparing the amino acid sequences of different Ig molecules of a given class (e.g., IgG) reveals:
a. Variable regions: In the amino-terminal domains of L and H chains. Harbors binding site for Ag.
b. Hypervariable (HV) regions or complementarity determining (CD) regions. 3 HV regions in VL; 3 or 4 HV in VH. Sites of contact with the Ag.
c. Constant regions: In the C-terminal domains of L chains or the second, third and forth domains of the H chains (i.e., CL and CH). |
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Term
| What is the significance of the different regions on Ig's? |
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Definition
| SIGNIFICANCE: Diversity of antibodies is due to the V regions. Production of diverse Ig's with unique V region sequences enables an individual to respond to all possible Ag's he/she will confront in a life-time. |
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Term
| How are immunoglobulins classified? |
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Definition
Based on the type of H chain (amino acid in the C domains)
-Classes: 5 major H chain classes:
Gamma = IgG
Mu = IgM
Delta = IgD
Alpha = IgA
Epsilon = IgE |
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Term
| What are the immunoglobulin subclasses? |
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Definition
Only present in IgG and IgA
IgG = 4 subclasses (i.e., IgG1, IgG2, IgG3 and IgG4)
IgA = 2 Subclasses (i.e., IgA1 and IgA2) |
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Term
| What are the basics of the structural differences of different classes of Ig's? |
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Definition
The amino acid differences in the H chain causes variability in the heavy chain length, disulfide bonds, and hinge regions.
(Don't need to know structural specifics) |
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Term
| What are the polymeric forms of Ig's? |
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Definition
Individual Ig molecules of a particular class are joined by disulfide bonds to form a multimer
The J chain joins two of the molecules
Present in Pentameric IgM and dimeric IgA.
Some antibodies function better in this form.
Secretory IgA are dimers with an additional glycoprotein (secretory component) derived from the receptor on epithelial cells. |
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Term
| What are some of the unique characteristics of IgG? |
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Definition
- Contains 4 subclasses
- most populous Ig in serum
- significantly longer half life than other Ig's (3 weeks)
- it can cross the placenta |
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Term
| What are the genes that encode for Ig's? |
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Definition
3 separate gene clusters in humans (FIG 3.15):
-The kappa gene cluster (chr. 2) encode kappa L chains
-The lambda gene cluster (chr. 22) encode lambda L chains
-The H gene cluster (chromosome 14) encode the H chains |
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Term
| How are the different components of Ig's encoded for? |
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Definition
- Several gene segments (distinct exons) in each cluster
- kappa or lambda chains: A collection or library of V genes (> 50), and ~ 5 J genes encode the V domains; single genes ( C gene) encode the C regions.
- H chains: A library or collection of V genes, about 30 D genes (D for diversity), and a number of J genes encode the V domains; single genes encode the C regions of the different H chain classes and subclasses |
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