Antigen and Antibody Testing Flashcards
How do we diagnose an infection?
Look at clinical signs
Detect pathogen (antigens)
Detect host response to pathogen (antibodies)
Methods of detecting Pathogen (antigens)
ELISA
Culturing
PCR
Lateral flow devices
Latex agglutination
Culturing
Detects virus growth
Shows cytopathic effect (haemagglutination)
Pros of Culturing
○ Allows further characterisation of virus
Can understand if gone under antigenic drift
○ Can use in future vaccines
○ Can test for antibiotic sensitivity
Limitations of Culturing
Slow to do
Pros of PCR
- PCRs are sensitive
- Can detect presence of pathogen after it has been cleared
Pros of latex agglutination
Instant result
Limitations of latex agglutination
Less accurate
Pros of sandwich/capture ELISA
More easily detect presence of IgM
More accurate
Timing of IgM - primary immune response
Pros of competitive ELISA
Multi-species test
Not specific
Which ELISA test for testing antibodies?
Indirect
Which ELISA test for testing antigens?
Direct
Agglutination inhibition Test
○ Some viruses can agglutinate red blood cells
○ Premix virus with antibody
Blocks ability of virus to bind to RBC
Inhibition of agglutination if only virus present
Single radial haemolysis
○ Tests for antibodies which lyse cells via complement
○ Sheep RBCs sensitised with virus
○ If the sample added to the agarose contains antibodies against the virus:
As antibodies diffuse for agarose the interaction between the complement added and the antibodies will lyse the sheep RBCs
* See zones of lysis
Complement Fixation
○ Relies on ability of antibodies to lyse sensitised RBCs
○ If serum with antibody in it mixed with antibody and complement in there
○ The antibodies will bind up the complement so no free complement available
○ If no antibodies specific to the antigen the complement will still be available
Mix with sheep RBCs
If no free complement = lysis of cells = antigen present
