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Reagents Used In Detecting Antigen-Antibody Reactions3. Reagents Used In Detecting Antigen-Antibody ReactionsSaline Isotonic saline is the basic medium in which cells are suspended. Agglutination owing to IgM antibodies can occur in this medium. The pH of the saline medium should be 6.8 to 7.2. Bovine albumin The presence of albumin in the reaction mixture reduces the zeta potential by dispensing sodium ions and thus raising the dielectric constant of the medium. This causes red cells to move closer together and allows IgG molecules to cause agglutination. Enzymes Proteolytic enzymes such as papain, bromelin, trypsin and ficin have been used to enhance agglutination. They act by removing sialic acid from the red cell membrane, thereby causing a decrease in the red cell surface charge. This subsequently causes a reduction in zeta potential and facilitates the agglutination by IgG molecules. Enzymes are known to destroy M,N,S, Fya and Fyb receptor sites and should not be used when testing for these antigens. Low ionic strength salt (LISS) solution Reducing the strength of the suspension medium causes decrease in the ionic strength around the antigen sites and thereby increases the antibody uptake, both the speed of uptake as well as the quantity of antibody. The LISS reagent hence helps in the sensitization phase of agglutination reaction and does not have any effect on the subsequent agglutination reaction. Macromolecular potentiating medium Several synthetic potentiating media have been described e.g. polyvinyl pyrrolidone, dextran and gum acacia. These have a tendency to cause rouleaux formation and have not gained general acceptance in routine serology laboratories. These substances act by causing reduction in zeta potential. However, polybrene (hexadimethrine bromide) has been used successfully in automated serology. Anti-human globulin serum Agglutination of sensitized cells can be caused by the addition of anti-human globulin serum. AFIG makes bridges between IgG molecules attached to red cells and brings about agglutination. This is the most common method used in immunohaematology for detection of antigen-antibody (IgG) reaction
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