Exam 2 (Lecture 14.5) - Immunodiagnostics Flashcards
Draw an ELISA to detect an antigen (e.g. a virus), properly label all reagents, and interpret a positive and negative result. Please note: when drawing or describing and ELISA, you must describe and give the name of your conjugate; we want to know that you understand what the conjugate is.
Done
Draw an ELISA to detect antibodies, properly label all reagents. Provide 2 or 3 explanations for what a positive antibody test can mean.
Done
Explain the differences in interpretation of a positive antigen test and a positive antibody test.
Positive Antigen Test:
- Antigen is present (animal is infected)
Positive Antibody Test:
- Antibody is present, could be from:
- Prior infection
- Vaccine
- Maternal antibodies
Describe a lateral flow immunoassay (lateral flow chromatography) and the basic differences (e.g., a detection system) compared to an ELISA-based assay.
1) Sample containing antigen flows through nitrocellulose membrane within test cassette (in an ELISA, sample flows across a test strip)
2) Conjugate pad: contains blue beads and antibody to the antigen covalently bound to red beads (conjugate)
3) Test pad: Antibody to the blue bead immobilized in nitrocellulose membrane
If antigen is present, it will bind to the Ab that’s covalently bound to the red beads from the conjugate pad and will continue to flow to test pad where antigen-antibody complex will bind to immobilized Ab.
Explain what the precipitate is in a precipitation assay, what the equivalence zone means, and why there is no precipitate when there is antibody excess or antigen excess.
Precipitate = forms when soluble Ag and Ab covalently bind together at optimal proportions
- cross-linking occurs, creating a clump of Ag/Ab
Equivalence zone:
- Optimal Ag/Ab interaction and max precipitation
- When Ab or Ag is in excess, there is not enough
visible cross-linking to form a visible precipitate
Define titer and describe, in general, how a titer is determined.
Measuring levels of a specific antibody in a sample, using serial dilution to determine levels.
The last dilution that gives a reaction in the immunological test being used.
Draw the last well of an ELISA test showing positive for Feline Immunodeficiency Virus antibody. Be sure to draw the antigen-binding site of antibody binding to its epitope. Label all molecules. Remember you must name your conjugate.
Done
What does a positive FIV antibody test mean?
It means that the cat is infected with FIV (once infected, always infected); in cats 9+ years of age, there is a possibility that the + antibody result is due to vaccination (vaccine was discontinued in US in 2015, but still used in Australia so patient history is important).
