complement activation 2009-12-01T02:47:12Z Any process involved in the activation of any of the steps of the complement cascade, which allows for the direct killing of microbes, the disposal of immune complexes, and the regulation of other immune processes; the initial steps of complement activation involve one of three pathways, the classical pathway, the alternative pathway, and the lectin pathway, all of which lead to the terminal complement pathway. GO:0006956 GO:0006956 IDOMAL:0000810 complement activity complement cascade complement response idomal_namespace host immune effector process