ABSTRACT
Adverse immunological responses may be anaphylactic (IgE mediated) or anaphylactoid (non-IgE mediated and often following first exposure to the trigger agent). Anaphylactic reactions occur following ‘classical’ pathway complement activation. Previous exposure to the antigen with antibody formation is required. ‘Alternative’ pathway activation occurs when the trigger activates the cascade directly; previous exposure to the antigen is not necessary (e.g. reactions to drugs, dextrans or contrast media). Reactions to drugs may also occur as a consequence of direct activation of mast cells by the drug (pharmacological histamine release) and do not involve complement activation (e.g. after administration of certain muscle relaxants).
