Lecture 6 Flashcards
Compare antibodies and immunoglobulins
Antibodies and immunoglobulins are the SAME THING
they were originally discovered in blood serum and termed “immunoglobulins”
In which “migrating group” are most Antibodies found?
the 3rd and slowest migrating group
named “gamma globulins” bc gamma is the 3rd letter in the greek alphabet
List the effector properties of antibodies (7 of them)
Direct antibacterial activity
Activation of complement
Reduced damage to host from the inflammatory response
Toxin neutralization
Immunomodulation
Organized T cell response
Opsonization
“DARTIOO Mnemonic”
Describe the structure of an antibody, including the types of interactions that hold them together. (be specific)
Abs have a basic unit of 4 polypeptide chains (2 light “L chains” and 2 heavy “H chains”) that are bound together by covalent disulfide bridges AND noncovalent interactions
Compare the functions of the V and C regions of an antibody. Which chains are these regions found on?
V regions contain the Ag-binding site
C regions determines the fate of the Ag
V and C regions are found on both the L chains and and H chains on an antibody
What results after IgG is proteolytically cleaved by Papain? (describe what is left)
2 “Fab fragments”: fragment Ag-binding, Fab
1 Fc fragment: Fragment crystallized, Fc
What results after IgG is proteolytically cleaved by Pepsin? (describe what is left)
A single, bivalent antigen-binding fragment F(ab’)2
(Pepsin cuts lower than papain on the “stalk” of the Y shaped antibody, so the Fc fragment cannot form and the excess just becomes peptide fragments)
State how many different types of antibody H chains there are AND how many different types of antibody L chains. Which of the types of L chains is primarily found to comprise Ab’s?
5 different types of H chains
2 different types of L chains
(the Kappa chain is what is primarily found to comprise Abs)
Gamma is the other L chain that sometimes occurs
For the following types of antibody H chains, state the corresponding class of antibody that they will form: Mu:
Delta:
Gamma:
Epsilon:
Alpha:
Mu: creates Igm
Delta: creates IgD
Gamma: creates IgG
Epsilon: creates IgE
Alpha: creates IgA
Describe CH1, CH2, VH, and VL domains of Abs (where they are found, their size, how their structure maintains it’s integrity)
both H-chains and L-chains have intrachain disulfide bridges every 90 AA’s.
These disulfide bridges create polypeptide loops (CH1,CH@,CH, and VL domains) that are 110 AA’s long
what determines the biological properties of an antibody? (biological properties are what occurs AFTER the ag has already bound to an antigen)
The type of heavy chain it has (Mu, Delta, Gamma, Epsilon, Alpha)
State the 6 members of the Ig superfamily proteins, then state the 3 functions they are all involved in
IgG
TCR (T cell receptor)
Class I MHC
CD4 (coreceptor of T cells found on Helper T cells)
CD28 (costimulatory receptor on T cells)
ICAM-1 (adhesion molecule)
All of these are involved in: recognition, binding, or adhesion
Compare secreted IgG and Membrane-bound IgG (differences and similarities)
Secreted IgG: Has 2 “CH domains” and it’s heavy chain ends in “tail pieces” (caps that let it float freely)
Membrane-bound IgG: Has 3 “CH domains” and it’s heavy chain ends in a C-terminal transmembrane and cytoplasmic portion (anchor’s it to a B cell)
Both:
Have Ag-binding sites formed by the juxtaposition of VL and VH domains
Describe the importance of “Hinges” on Ab’s and delineate which domain of an Ab a hinge can be found
Hinges are present on all Ab’s and provide Ab’s the flexibility to be able to bind to epitopes that occur in different spacing, depending on the molecule they are present in.
hinge regions are located between the CH1 (closest to variable region) and CH2 (on other side of hinge from CH1) domains of Ab’s
Explain how the following principles can affect the recognition of an antigen by an antibody:
Conformational determinant:
Linear Determinant:
Neoantigenic determinant (created by proteolysis):
Conformational Determinant: An antigen that was previously bound to an antibody, could lose it’s binding affinity with the Ab if it is denatured (bc the antigen is a protein)
Linear Determinant: An antigen that was bound to an Ab, that denatures into 2 separate (linear) proteins, may bind to 2 different antibodies now
(before denaturation, one of the potential binding sites for an Ab was covered)
Neoantigenic determinant (created by proteolysis): an antigen that did NOT bind with an Ab at first, could have a binding site that binds to the same Ab, after it is exposed by proteolysis. (a lot like "unmasking" the Ab binding site on the antigen)
Define “affinity” as it relates to antibodies, and explain what determines an antibodies level of affinity
Affinity: the tightness of Ag-Ab binding
the higher the binding constant is, the stronger the affinity of the Ag-Ab complex (high binding constant = less likely to dissociate the Ag-Ab complex)
Compare the affinity of Abs formed in the primary response to an antigen with Abs formed by a memory response to an antigen.
Abs formed in the primary response to an antigen have a low affinity
Abs formed by a memory response to an antigen have a high affinity
Describe a type of infection where a high affinity of Abs is critical to being able to neutralize the antigens rapidly, at low titer levels.
When the antigen is a Toxin or virus
Define “Valence” as it pertains to antibodies and explain how it directly affects another property of Antibodies
Valence: the maximum # of antigenic determinants (Ags) with which a single antibody can react
This has a direct affect on the “binding affinity” of an Ab, because having 2 or more binding sites for the same antigen on an Ab can “dramatically increase the affinity it has for that antigen”.
If a single molecule can bind to 2 molecules of Ag or 2 identical sites on the same particle, then what would it’s valance be?
2
Define Avidity as it pertains to Abs. What are the 2 factors that the level of Avidity is dependent upon?
Avidity: give a measure of the overall strength of an Ab-Ag complex
it is dependent on the “affinity of the Ab for the epitope” and the “Valence of both the Ab and the Ag”
State the corresponding level of Avidity for the following valence values
Monovalent:
Bivalent:
Polyvalent:
Monovalent: low
Bivalent: high
Polyvalent: very high
Describe the level of affinity IgM has and also describe the avidity of it. explain.
Igm has a low affinity, however it has a very high avidity, which makes it extremely effective in neutralizing microorganisms
Igm can still have such an impressive avidity, despite low affinity for it’s individual bonds because it has a large number of binding sites (basically a lot of weak interactions (10 to be exact) create an overall strong interaction)
Compare IgG and TCR’s in terms of
Ag-binding site:
Ag that may be bound:
Antigenic determinants recognized:
Ag-binding site:Both have 6 total CDR’s (complementarity-determining region)
IG’s have 3 CDR’s in VH and 3 CDR’s in VL domains
TCR’s have 3 CDR’s in V-alpha and 3 CDR’s in V-beta domains
Ag that may be bound:
IG’s recognize proteins, lipids, polysaccharides, etc.
TCR’s recognize Peptide-MHC complexes
Antigenic determinants recognized:
IG’s recognize Linear and conformational determinants of various molecules
TCR’s recognize only 2-3 AA residues of a peptide bound to an MCH molecule
