The Antigen-Antibody Reaction Flashcards
What is affinity?
the initial force that exists between an antibody Fab site and one epitope on the corresponding antigen
What are Van der Waals forces?
interaction between the electron clouds of oscillating dipoles (temporary shifting of the electron clouds); dependent on how easily electron distribution can be distorted by an adjacent molecule
What is coulombic attraction (ionic bonding)?
weak attraction force between positive and negative ions which increases as the charges come closer together
What is hydrogen bonding?
involves an attraction between polar molecules that have a slight charge separation, and in which the positive charge resides on a hydrogen ion
What are hydrophobic forces?
hydrophobic groups in nonpolar molecules associate with one another, squeezing water out as they do so, therefore being held more firmly together; estimated to be up to 50% of the total strength of antigen-antibody bonds
What is avidity?
the sum of all attractive forces between antigen and antibody; measure of overall stability of the complex, which is essential to the detection of an unknown
What effect does the kind and concentration of electrolyte present have on precipitation or agglutination?
saline is commonly used, as it is capable of reducing (neutralizing) the net negative charge in solution, which reduces the repulsion of molecules
What is the optimal pH for most serological procedures?
6.5-8.5
How does temperature affect precipitation and agglutination reactions?
the visible stage of serologic reactions is usually accelerated as temperature rises from 0C to 20-30C; however, some antigen-antibody complexes only react at very low temperatures (cold agglutinins)
What effect does agitation have on antigen-antibody reactions?
accelerates the visible state of the reaction by providing increased opportunity for contact between the antigen and antibody
What is the Law of Mass Action?
free reactants are in equilibrium with bound reactants
What does the equilibrium constant (K) represent?
the difference in the rates of the forward and reverse reactions; can be seen as a measure of the “goodness of fit”, and depends on the strength of the bonds within the antigen-antibody complex
What is the equation for finding K, and what do each of the factors represent?
K = K1/K2 = (AgAb)/(Ag + Ab); (AgAb) is the concentration of the antigen-antibody complex in mol/L, and the individual Ag and Ab factors represent the concentrations of antigen and antibody, respectively, in mol/L
What is the general rule of antigen-antibody complexes regarding avidity?
as avidity increases: 1. the tendency of the complex to dissociate decreases, and 2. the value of K2 decreases as K1 increases
How does the value of K relate to precipitation or agglutination testing?
the higher the value of K, the higher the amount of antigen-antibody complex, and therefore the more visible/easily detectable the reaction is
What is the Lattice Hypothesis of Marrack?
most widely favored antigen-antibody complex hypothesis today; based on assumptions that each antibody molecule must have at least two binding sites, and antigen must be multivalent; therefore, antigen-antibody aggregates consist of a lattice or framework of alternating antigen and antibody molecules
What is the prozone phenomenon?
if there is an excess of antibody, there will not be enough antigen to cause precipitation, leading to false negatives
If prozone phenomenon is suspected, how can one resolve the discrepancy?
dilute out patient antibody and perform the test again
What is the zone of equivalence?
as the optimal proportions of antigen and antibody are reached, stable lattice structures are formed and precipitate out to their maximum; required for detectable precipitation reactions
What is the postzone phenomenon?
if there is an excess of antigen, all of the antibody will be bound before a precipitate can be formed (the excess antigen does not allow for the formation of the lattice); leads to a false negative
How is the postzone phenomenon resolved?
test is repeated with a new patient specimen collected about a week later; this allows for further production of the antibody in the patient (if test is still negative, it is likely the patient does not actually have the antibody)
What is neutralization?
the ability of an antibody to diminish or abolish some biologic property of the antigen other than its antigenicity
What is antigenicity?
the toxicity or infectivity for cells, or the enzymatic activity of a given antigen
When would a neutralization test be performed?
commonly used on toxins, viruses, and enzyme or enzyme-like antigen, but it can be performed on most infectious agents
