ELISA- HIV test

• What can an indirect ELISA test be used to do?

  To see if a patient possesses antibodies to the HIV virus
• What is STEP 1?

  HIV antigen is bound to the bottom of a well in a well plate
• Describe a well plate?


  A plastic tray with many circular pits in it
• What is STEP 2?

  A sample of the patient's blood plasma is added to the well

  If there are any HIV-SPECIFIC ANTIBODIES these will bind to the HIV antigen stuck to the bottom of the well

  The well is then washed out to remove any unbound antibodies
• What are HIV-specific antibodies?


  Antibodies against HIV
• What may the sample of the patient's blood plasma contani?


  several different antibodies
• What is STEP 3?

  -A secondary antibody, that has a specific enzyme attached to it, is added to the well

  -This secondary antibody can bind to the HIV-specific antibody (primary antibody)

  -Well is WASHED OUT to remove any unbound secondary antibody

  -If there is no primary antibody in the sample, all of the secondary antibody will be washed away
• What is STEP 4?

  -A solution is added to the well, the solution contains a substrate, which can react with the enzyme attached to the secondary antibody and produce a coloured product
• What is indicated if the solution changes colour?

  The patient has HIV-specific antibodies in their blood and is infected with HIV
• Why are the WASHING steps IMPORTANT?

  To ensure unbound antibodies are not left in the well which could affect the results

  eg unbound secondary antibodies could cause the test to appear positive when there are no HIV antibodies present
• If the ELISA test was negative, what would there be?


  No colour change because there would be NO HIV-specific antibodies for the secondary antibodies to bind ti