Lecture 3 Flashcards
What is antibody valence?
the number of antigens one antibody molecule can bind to. For example, a trivalent antibody can simultaneously bind to three copies of the antigen it recognizes.
what is antibody affinity?
Affinity measures the strength of interaction between an epitope and an antibody’s antigen binding site. It is defined by the same basic thermodynamic principles that govern any reversible biomolecular interaction: KA = affinity constant.
precipitation vs. agglutination
The large immune complexes that are formed at or near equivalence (where ratios of antigen to antibody are optimal) tend to become insoluble and fall out of solution. When the antigen is a molecule, the phenomenon is called precipitation; when it’s a cell or cell-sized particle, it is called agglutination.
Distinguish the five classes of immunoglobulins in terms of:
passage across the placenta
IgG. It is the only class that passes the human placenta from mother to fetus (active transport required
IgM is the only antibody made by the fetus
Distinguish antibodies based on: ability to activate complement
IgM. oldest antibody; first seen in blood after immunization; great capacity to activate complement; two adjacent Fcs are needed to get the complement cascade started, and IgM always has five adjacent. It can be as much as 500 times more efficient than IgG at activating complement. Why, then, even bother to have IgG? One reason is that IgM, being so large, is viscous in solution; if we had only IgM at the same molarity as we have IgG we would scarcely be able to pump our blood.
IgG: It takes two IgGs close together to activate the first component of complement, so this will only happen if the density of epitopes on the antigen is high enough for that to occur (remember, binding a single epitope should be enough to allow an IgM molecule to activate complement).
IgA: is some monomer and dimer IgA in the plasma, where it can bind pathogens and activate complement (by the alternative pathway).
Distinguish antibodies based on: involvement in allergic diseases
IgE. Because its Fc end binds to a corresponding receptor on mast cells and basophils, forming a trigger for these histamine-loaded cells, this antibody is the cause of immediate hypersensitivity or allergy (see Type I Immunopathology). Why does it exist? Resistance to parasites, where it triggers the mast cells to release not only histamine, but eosinophil chemotactic factor. Eosinophils are uniquely effective at killing parasites.
Distinguish antibodies based on: “first line of defense”
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Antibody that is most resistant to enzymatic degradation?
IgA. Secretory Component protects the IgA from digestion in the gut, and makes it work well as our first line of immunological defense against invading organisms.
Describe a quantitative precipitin test where amount of antigen/tube is varied while antibody/tube is constant.
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