An immunologist is conducting an experiment to understand precipitation reactions. He notes that on adding excessive amount of antibody to a serum sample containing small amount of antigen, the amount of precipitate formed is less, compared to adding smaller amount of antibody to the same sample. What is this phenomenon called?: (A) Pro-zone phenomenon, (B) Zone of equivalence, (C) Post-zone phenomenon, (D) Flocculation phenomenon
Answer is A. Lattice hypothesis explains this: In precipitation reactions, the amount of precipitate formed is greatly influenced by the relative propoions of antigens and antibodies. Pro-zone phenomenon: It is caused by excessive antibody in the test system. (Weak or even absent precipitation and a false negative test) Zone of equivalence: Antigen and antibody are in optimum propoions and maximum precipitation occurs. Post-zone phenomenon: Presence of excessive antigen in the test system. (Weaker or even absent precipitation) Reference: Ananthanarayan and Paniker&;s Textbook of Microbiology Tenth edition