<P> Now these antibodies will encounter antigens and bind with them . This will either interfere with the chemical interaction between host and foreign cells or they may form bridges between their antigenic sites hindering their proper functioning or their presence will attract macrophages or killer cells to phagocytose them . </P> <P> The complement system is a biochemical cascade of the innate immune system that helps clear pathogens from an organism . It is derived from many small blood plasma proteins that work together to disrupt the target cell's plasma membrane leading to cytolysis of the cell . The complement system consists of more than 35 soluble and cell - bound proteins, 12 of which are directly involved in the complement pathways . The complement system is involved in the activities of both innate immunity and acquired immunity . </P> <P> Activation of this system leads to cytolysis, chemotaxis, opsonization, immune clearance, and inflammation, as well as the marking of pathogens for phagocytosis . The proteins account for 5% of the serum globulin fraction . Most of these proteins circulate as zymogens, which are inactive until proteolytic cleavage . </P> <P> Three biochemical pathways activate the complement system: the classical complement pathway, the alternate complement pathway, and the mannose - binding lectin pathway . The classical complement pathway typically requires antibodies for activation and is a specific immune response, while the alternate pathway can be activated without the presence of antibodies and is considered a non-specific immune response . Antibodies, in particular the IgG1 class, can also "fix" complement . </P>

Which of the following steps is not part of the humoral immune response