Paper
Antigen-Antibody Interaction
Published Nov 1, 2000 · Mary Culp
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Abstract
The purpose of this experiment is to illustrate how antigen-antibody interactions can be applied to the study of evolution. Antigens are substances that stimulate an immune response from the body. There are two general categories of antigens: pathogens and allergens (Karp 1996). Pathogens include viruses, bacteria, fungi, protozoan parasites and toxins. Allergens include pollen, spores, and food additives. Antibodies are globular proteins produced by B lymphocytes that bind to an antigen and target the antigen for destruction. Antibodies are located in interstitial fluid and plasma and are mostly effective against pathogens that have not invaded host cells. The Ouchterlony test is a double diffusion method on an agar plate that clearly shows any reaction between antigens and antibody (Ouchterlony & Nilsson 1973). Antigens and antibody are inoculated onto an agar plate into separate wells where they diffuse through the medium. As long as the pore sizes within the agar gel substance are large enough, an assumption is made that diffusion of randomly moving particles can freely occur. The agar must be an inert material that does not react with the testing materials. If the antibody recognizes and binds to an antigen on the plate, a white precipitate will form. The precipitate itself is too large to continue to diffuse-once a precipitate is formed, it is stationary. The antigens for this experiment are albumins from various ungulates: horses, pigs, cows and sheep. Albumins are small globular proteins isolated from blood. Albumin is produced by the liver and participates in homeostasis by influencing the osmotic balance of plasma. Antiserum is a liquid containing antibodies that have been exposed to a specific antigen. For example, antihorse serum includes antibodies that will react against antigens isolated from a horse. Antisera were purchased from Sigma, a chemical supply company (PO Box 14508, St. Louis, MO 63178, USA; 800-325-3010). Students learn in lecture and lab that an outstanding characteristic of antibodies is their property of specificity. The general hypothesis being tested is: a specific antigen will react with a specific antibody that has been formed against it, and form a precipitate. Therefore, horse albumin should react only with anti-horse serum, pig albumin with anti-pig, and so on. The results can be used to support the current classification of the ungulates at the order and suborder level. To accomplish this, students must become informed about the following subjects:
Antigen-antibody interactions can help support the current classification of ungulates at the order and suborder levels by forming white precipitates when specific antibodies bind to specific antigens.
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