1. Gel Diffusion (Immunodiffusion) By Group 7

2. What is it? A technique for detecting antigen-antibody interactions based on the theory of double diffusion originally described by Oudin and Ouchterlony. The formation of antigen and antibody complexes can be influenced by a number of factors: relative concentration of antigens and antibodies, ionic strength of the buffer, pH, and temperature.

3. How does it work? The bloodstain being tested and the human antiserum are placed in opposite wells on a plate covered in a gel called agar. If it is human blood, the antigens and antibodies are drawn together and form a line of precipitation. A method called the electrophoretic method can be used to make the antigens and antibodies move toward each other. When this is used, an electric potential is added to the gel medium. A specific reaction is characterized by a precipitation line forming between the well containing the blood and the well containing the human antiserum.

4. Examples The image below is of an immunodiffusion test for Coccidiomycosis (left) and Histoplasmosis (right). Well 3 on the left represents a patient positive for coccidiomycosis (presence of an F band). Wells 2 and 3 on the right represent patients positive for histoplasmosis. Well 2 contains both H and M bands, well 3 only has an M band. For histoplasmosis, the H band is usually only present in clinically active cases, the M band occurs in acute and chronic cases, or in individuals after skin testing with histoplasmin. The immunodiffusion procedure is used to identify Blastomycosis, Coccidiomycosis, Histoplasmosis, and Aspergillosis.

5. Examples An example would be in Knee replacements when patients need to have muscles placed back together. Doctors will add antigens and antibodies together to form a bond and conjoin the muscles back together.

7. Pros/Cons Pros • Sensitive • Extracts from mummies four to five thousand years old have given positive reactions with this test • Easy to perform • A reliable procedure that is useful for detecting a specific antibody or antigen Cons • Does not individualize the blood sample • Takes a while to perform • Most take about 24 hours to conduct

8. Review Questions How is the test performed? What result does the test give if the extracted bloodstain is human? What is the electrophoretic method? How long does it take for results to appear? How sensitive is the test?

9. Works Cited http://www.engin.umich.edu/~cre/course/lectures/twelve/exam2.htm http://www.piercenet.com/instructions/2160268.pdf http://armymedical.tpub.com/MD0838/MD08380070.htm http://www.cfsph.iastate.edu/HPAI/resources/Presentations/AGID%20Overview-D.Senne.pdf http://books.google.com/books?id=kPLyt8b_44gC&pg=PA193&lpg=PA193&dq=immunodiffusion+techniques&source=bl&ots=pLYTRf7ZRd&sig=FicTJldzfSmBZNt2nfpEOrVDpRM&hl=en&sa=X&ei=yZBbUc7HMMeqywHjzYCwAQ&ved=0CDUQ6AEwATgK#v=onepage&q=immunodiffusion%20techniques&f=false http://www.dshs.state.tx.us/lab/serology_id.shtm