The biochemical events that immediately follow reinjection of antigen into sensitized animals and lead to anaphylactic symptoms or tissue reactions have not been fully elucidated. Among the intermediate steps that have been suggested are the liberation of toxic substances such as “anaphylotoxin” (1), histamine (2, 3, 4), or acetylcholine (5, 6), and activation of enzymes such as proteases (7–15).Theories that antigen-antibody reactions are followed by the activation of proteases have received some experimental support. In 1915 Bronfenbrenner (7) added egg albumin to sera of rabbits that had been sensitized to this protein nine days earlier, and observed that dialyzable nitrogenous material was liberated. He attributed this result to auto-digestion of the serum by “digesting ferments” liberated under these conditions. Analogous results were obtained with other antigens. Jobling, Eggstein and Petersen (8) reported similar experiments and conclusions at about the same time.
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