Final answer:
The complement system can be activated through three pathways: classical, alternative, and lectin.
Step-by-step explanation:
The complement system can be activated through three pathways: the classical pathway, the alternative pathway, and the lectin pathway.
In the classical pathway, complement activation is triggered by the binding of an antibody to an antigen on a pathogen. This pathway is dependent on the adaptive immune response.
The alternative pathway does not require antibody activation. It involves the spontaneous breakdown of C3 and the binding of C3b to the surface of the pathogen.
The lectin pathway is triggered by the binding of certain acute-phase proteins called lectins to pathogen surfaces. This pathway is involved in the innate immune response.