Antibody Function Flashcards
epitope
the part of the antibody that actually interacts with the antigen, usually 10-20 amino acids long. Also known as antigenic determinant. Proteins have several epitopes which bind to different antibodies.
antibody valence
The valency of antibody refers to the number of antigenic determinants that an individual antibody molecule can bind. The valency of all antibodies is at least two (divalent) and in some instances more (multivalent).
affinity
The strength with which an antibody molecule binds an epitope (= antigenic determinant) is called its affinity
precipitation
large immune complexes that are formed at or near equivalence tend to become insoluble and fall out of solution, when the antigen is a molecule, it is called precipitation.
agglutination
large immune complexes that are formed at or near equivalence tend to become insoluble and fall out of solution, when the antigen is a cell or cell-sized particle, it is called agglutination
Distinguish the five classes of immunoglobulins in terms of: passage across the placenta, ability to activate complement, involvement in allergic diseases, “first line of defense”, and most resistant to enzymatic digestion: IgG
most abundant immunoglobulin in blood, only class that passes the placenta (mother –> fetus, requires active transport), comes up later than IgM after primary immunization, but levels go higher and last longer, plasma life= 3 weeks, phagocytic cells have receptors for the Fc of bound IgG –> opsonizing. It takes 2 IgG’s close together to activate complement.
Distinguish the five classes of immunoglobulins in terms of: passage across the placenta, ability to activate complement, involvement in allergic diseases, “first line of defense”, and most resistant to enzymatic digestion: IgM
first immunoglobulin seen in blood after immunization, decavalent, but shape rarely allows more than 2 of its 10 binding sites to interact with antigenic determinants. Best at complement because it always has 2 adjacent Fc’s to begin complement cascade. IgM is viscous in solution (because of its size), so if we only had IgM we couldn’t pump our blood. There are no useful IgM receptors on phagocytes. IgM is the only antibody made in the fetus
Distinguish the five classes of immunoglobulins in terms of: passage across the placenta, ability to activate complement, involvement in allergic diseases, “first line of defense”, and most resistant to enzymatic digestion: IgA
made by plasma cells in lymphoid tissues near mucous membranes, assembled into dimer by the adition of the J chain while in plasma cell and then secreted into interstitial space. Adjacent epithelial cells have receptors for IgA which binds to them and is taken up and moved to the luminal side. IgA is exocytosed, still bound to receptor which is now called Secretory Component (SC). SC protects IgA from digestion in the gut and works as our first line of immunological defense against invading organisms
Distinguish the five classes of immunoglobulins in terms of: passage across the placenta, ability to activate complement, involvement in allergic diseases, “first line of defense”, and most resistant to enzymatic digestion: IgD
only important role is as a B cell receptor
Distinguish the five classes of immunoglobulins in terms of: passage across the placenta, ability to activate complement, involvement in allergic diseases, “first line of defense”, and most resistant to enzymatic digestion: IgE
its Fc adheres to mast cells and basophiles –> trigger these histamine loaded cells, causes immediate hypersensitivity or allergy. Important for resistance to parasites when it triggers mast cells to release eosinophil chemotactic factor –> eosinophils come and kill parasites
Describe a quantitative precipitin test where amount of antigen/tube is varied while antibody/tube is constant. Draw a graph which compares, on the ordinate, amount of precipitate obtained, with amount of antigen added/tube. Identify the zones of antigen and antibody excess, and equivalence.
Quantitative precipitin test: mix the antigen and antibody in different ratios and see how much precipitate is form. Relative antigen or antibody excess the amount of precipitate is less because the complexes are smaller and not every molecule may get bound
Sketch the lattices obtained in antigen or antibody excess, and at equivalence, using Y as antibody and + as antigen.
Sketch these
Discuss why a line of precipitate may form in agar gel when antigen and antibody diffuse towards each other.
Precipitate forms in the agar when the antigen and antibody meet at optimal proportions (more immune complex forms and precipitates out of solution). This technique is called Immunodiffusion
Compare and contrast precipitation and agglutination in terms of the nature of the antigens involved, and sensitivity of the tests.
- Precipitation: large immune complexes that are formed at or near equivalence tend to become insoluble and fall out of solution, when the antigen is a molecule, it is called precipitation.
- Agglutination: large immune complexes that are formed at or near equivalence tend to become insoluble and fall out of solution, when the antigen is a cell or cell-sized particle, it is called agglutination. More readily detected than precipitation so the agglutination test is MORE sensitive
Discuss how complement plays roles in both innate and adaptive immunity.
The alternative pathway seems to be a more primitive, early, less-specific sort of defense, since it can work even without waiting for antibody to be made. There is also the lectin pathway of complement activation, truly part of innate immunity. The lectin pathway is mediated by mannose-binding protein, MBP or MBL, a lectin. Lectins are proteins that bind (usually foreign4) carbohydrates. MBP binds certain mannose–containing structures found in carbohydrates of bacteria but not humans.
