has part has part immune effector process activation of immune response complement activation complement response GO:0006956 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. Reactome:R-HSA-166658 complement activity complement cascade humoral immune response protein activation cascade