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ANTIGEN ANTIBODY REACTIONS. By. Dr. Emad AbdElhameed Morad. Lecturer of Medical Microbiology and Immunology. characters. Highly specific. The antibody can react only with the antigen which induced its formation.
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ANTIGEN ANTIBODY REACTIONS By Dr. Emad AbdElhameed Morad Lecturer of Medical Microbiology and Immunology
characters • Highly specific. The antibody can react only with the antigen which induced its formation. • These interactions are used invitro for identification of either antigen or antibody (serological reactions). • In these tests, one of the reactants is known and the other is unknown. • Serological reactions are also used to determine the amount of antibodies in the patient serum (antibody titer).
At higher antibody levels (antibody excess) or higher antigen levels (antigen excess), the reaction may not occur. The reactions occurs only when both antigen and antibody concentrations are optimal (prozone effect).
Forms • Antigen antibody interactions my take several forms: • Agglutination: if the antigen is particulate. • Precipitation: if the antigen is soluble. • Complement fixation. • Toxin antitoxin neutralization. • ELISA • Immunofluorescence • Radioimmunoassay
Agglutination • It is a form of antigen antibody reactions when the antigen is in the form of particles such as cells or microorganisms. • Types: Direct Passive (latex)
Direct • Example: blood grouping.
Passive (latex) • Agglutination reaction in which inert particles called latex beads are coated with either antigen or antibody. • Example: anti streptolysin “O” test (ASOT). In this test, latex beads are coated with streptolysin “O” toxin and mixed with the patient serum for the presence of antibodies (ASO antibodies).