Laboratory Activity 3b – Principle of Antigen-Antibody Reaction Flashcards
CATEGORIES OF SEROLOGIC TESTS:
1. Tests to detect unknown antibodies in serum (specimen) using a [?] (reagent)
2. Tests to detect unknown antigen (specimen) using a [?] (reagent)
known commercial antigen
known commercial antiserum
ANTIGEN-ANTIBODY REACTIONS:
• Forces that participate in antibody-antigen interaction
• Affinity and Avidity
• Specificity and Cross-reactivity
• Zone of Equivalence and Zonal Phenomena
Forces that participate in antibody-antigen interaction
o Electrostatic forces (Ionic bonds)
o Van der Waals Forces (London dispersion forces)
o Chemical Bonds
Chemical Bonds:
• Hydrogen bonding
• Hydrophobic bonding
• Hydrophobic bonding does not involve
Covalent bonds
Factors affecting forces of attraction:
• Physiologic pH
• Salt concentration
• Temperature
• The binding strength between an epitope and its corresponding complementary site of the antibody
o Affinity
• Strength of bond between antigen and antibody
o Avidity
• Sum of affinities for all the antigen-binding sites in one antibody molecule
o Avidity
refers to the antibody’s greatest affinity for a particular antigen
o Specificity
refers to the antibody’s greatest affinity for a particular antigen
o Specificity
occurs when the antibody combines with an antigen that is structurally similar to the immunogen that stimulated the antibody production or the antigen the antibody has the greatest affinity for
o Cross-reactivity
o The [?], or level, of antibodies in serum can be measured by using known antigens
titer
• Area where antigens and antibodies are approximately equal and visualization of the reaction is optimized by either agglutination or agglutination
Zone of equivalence
concentration of the antibody exceeds that of the antigen in solution
Prozone phenomenon
concentration of the antigen exceeds that of the antibody in solution
Postzone phenomenon
o Specific recognition and combination of antigen and antibody
Primary phenomena
Conformations of the amino acid chains resulting from interchain hydrogen bonding
Secondary phenomena
o Precipitation, agglutination, complement fixation
Secondary phenomena
o In vivo reactions; e.g., inflammation, phagocytosis, deposition of immune complexes, immune adherence, chemotaxis
Tertiary phenomena
o Involve the folding of polypeptide chains through hydrophobic and hydrogen bonds
Tertiary phenomena
o Association of polypeptide subunits to form one protein
Quaternary
o Some are useful diagnostically
Tertiary phenomena
o Measured more readily
Secondary phenomena
