title: Complement-induced histamine release from human basophils. II. Mechanism of the histamine release reaction.
abstract: The activation of human serum complement by incubation with zymosan generates C5a which releases histamine from autologous basophils. The characteristics of the C5a-induced histamine release were investigated. It is similar to IgE-mediated reactions in requiring Ca++ and in being inhibited by EDTA. However, it has marked differences from IgE-mediated reactions. C5a, at all concentrations, released histamine completely in less than 2 min. The C5a reaction has a narrow pH optimum that antigen-induced release and occurs well at 17 degrees to 37 degreesC but not at 0 degreesC. The optimal reaction temperature is 25 degrees to 30 degrees C. Unlike the antigen-induced release, no two-stage activation with C5a for the release of histamine could be demonstrated. There was additive release between C5a- IgE-mediated reactions. Leukocytes could be desensitized to the C5a-mediated reaction by 1) incubating the cells at 37 degrees C for 45 min, 2) pretreating the leukocytes with activated serum in the presence of EDTA, and 3) adding the activated serum to the leukocytes at 0 degrees C before transferring to the optimal reaction temperatures. Cells desensitized to the complement-induced release have normal reactions to IgE-mediated histamine release. In parallel experiments, cells from allergic donors desensitized for IgE-mediated reactions by incubation with antigen under sub-optimal conditions release histamine normally upon the addition of C5a. The results indicate that histamine release by C5a involves a mechanism of basophil activation that is different from the pathway involved in the IgE-induced reaction.
mesh_terms: D000941:Antigens; D001491:Basophils / Q000502:physiology*; D002118:Calcium / Q000494:pharmacology; D003182:Complement C5 / Q000502:physiology*; D003165:Complement System Proteins / Q000502:physiology*; D004492:Edetic Acid / Q000494:pharmacology; D006636:Histamine Release; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007770:L-Lactate Dehydrogenase / Q000502:physiology; D007962:Leukocytes / Q000276:immunology; D006109:Poaceae / Q000276:immunology; D013696:Temperature; D013997:Time Factors
chemical_list: D000941:Antigens; D003182:Complement C5; D003165:Complement System Proteins; D004492:Edetic Acid; D007770:L-Lactate Dehydrogenase; D002118:Calcium