Labeled Immunoassays and Techniques Quiz

Labeled Immunoassays

• Measure small or low concentrations of antigens and antibodies
• Use various labeling techniques, including:
  • Radioactivity
  • Enzymes
  • Chemiluminescence
  • Fluorescence

Types of Immunoassays

• Competitive
• Noncompetitive
• Heterogenous (requiring separation)
• Homogenous

Antibody Requirements

• Must be specific to the antigen in question
• Must have a high affinity for the antigen

Radioimmunoassay

• Based on competition between labeled and unlabeled antigen for a limited number of antibody-binding sites

Noncompetitive Indirect Enzyme Immunoassays (e.g., ELISA)

• Antigen is bound to the solid phase
• Antibody is detected
• A second enzyme-labeled antibody is added after binding occurs

Capture Assays

• Antibody is bound to the solid phase
• Any patient antigen is allowed to bind or be captured
• A second labeled antibody is added that binds to patient antigen, forming a "sandwich"

Fluorochromes

• Fluorescent compounds that absorb energy from an incident light source and convert it to light of a longer wavelength

Immunofluorescent Assays

• Direct immunofluorescent assays:
  • Antigen detection through a specific antibody labeled with a fluorescent tag
• Indirect immunofluorescent assays:
  • Original antibody is unlabeled
  • Incubation with antigen is followed by addition of a second fluorescent-labeled anti-immunoglobulin that detects antigen–antibody complexes

FPIA (Fluorescent Polarization Immunoassay)

• A type of homogeneous fluorescent immunoassay