The complement system can be activated through three distinct pathways: the _classical pathway_, the _lectin pathway_, and the _alternative pathway_. Each of these pathways converges at the activation of _C3_, a central component of the complement system, leading to a cascade of further events.
- Classical Pathway: Initiated by the binding of complement protein _C1q_ to antibodies that are bound to antigens on the surface of a pathogen. - Lectin Pathway: Triggered by the binding of _mannose-binding lectin_ (MBL) to mannose residues on the pathogen surface. - Alternative Pathway: Activated directly by the presence of pathogen surfaces and does not require the presence of antibodies.
