Uses of the ELISA process

 

How the ELISA process is used in Pregnancy Tests

(Information from http://www.whfreeman.com/kuby/content/anm/kb07an01.htm)

 

§         Human Chorionic Gonadotropin (hCG) is secreted by the developing placenta after fertilization

 

§         ELISA test, or Enzyme Linked Immunosorbent Assay, is used to detect small amounts of hGC in urine.

 

§         Pregnancy tests use 3 different antibody preparations (zones):

o       Reaction Zone (with soluble mouse monoclonal anti-hCG antibody-enzyme conjugates)

o       Test Zone (with immobilized polyclonal anti-hCG antibodies and dye substrate)

o       Control Zone (with immobilized goat ant-mouse antibodies and dye substrate)

 

§         Negative Test:

1.      Dip test strip in urine sample (with no hCG)

2.      Sample drawn by capillary action up to the test strip to the Reaction Zone

3.      Soluble anti-hCG antibody-enzyme conjugates are dissolved, capillary flow continues

4.      Antibody-enzyme conjugates flow past immobilized polyclonal hCG antibodies and dye substrate in Test Zone

5.      In Control Zone, monoclonal mouse conjugates bind to immobilized goat anti-mouse antibodies

6.      Anti-mouse antibodies bind to the antibody-enzyme conjugate to activate dye substrate

7.      Negative test has 2 areas without dye, with the Control Area colored

 

§         Positive Test:

  1. Dip test strip in urine sample (with hCG)
  2. Sample drawn by capillary action up to the test strip to the Reaction Zone
  3. hCG binds with anti-hCG antibody-enzyme conjugates
  4. hCG bound antibody-enzyme conjugates are dissolved and carried along
  5. In Test Zone, hCG molecule binds to the polyclonal hCG antibodies
  6. In Control Zone, unbound monoclonal mouse conjugates bind to the immobilized goat anti-mouse antibodies
  7. Fixed enzymes activate dye substrate in Test and Control Areas
  8. Positive Test has 1 area without dye, with the Test and Control Areas colored

 

How the ELISA process is used in HIV Tests

(Information from http://www.nyscience.org/whataboutaids/protect/test/content.html)

 

  1. A blood sample is taken from a person. If the person is infected with HIV, the blood contains HIV antibodies, made in response to the proteins on the HIV virus.
  2. The person's blood is added to laboratory HIV virus. There are special shapes called HIV antigens on the surface of the laboratory HIV virus.
  3. If someone is infected with the HIV virus, HIV antibodies in the blood attach to the antigen on the surface of the laboratory HIV virus.
  4. A chemical is added that attaches to the HIV antibody-antigen complex. The chemical turns yellow if HIV antibodies are present in the blood. The yellow color indicates that a person is infected with HIV.

 

(Information from http://www.msichicago.org/ed/AIDS/hivtst2.htm)

 

Antibodies are found in serum that has been separated from the red blood cells. During an ELISA test, this serum is placed in a tiny well containing a plastic bead coated with the proteins of HIV. Among these proteins are antigens. If there are any HIV antibodies in the serum, they will bind to the HIV antigens on the bead. An indicating substance is then added which will turn yellow if any binding has taken place. This multi-layer process can be visualized as in the diagram below.

 

If the test is negative, and the patient may have been exposed to HIV, it is wise to test again in six months. The negative result may simply mean that antibodies have not yet been produced. If the test is positive, it is repeated. If the second test is positive, the Western Blot is performed.