Binding of antibodies to red blood cells activates the classical pathway of the complement system.

The classical pathway can also be triggered by binding of C1 to some types of structures on the target microbe.

The classical pathway is triggered by activation of the C1-complex.

C4b and C2b then bind together to form C3-convertase, as in the classical pathway.

The classical pathway is inhibited by C1-inhibitor, which binds to C1 to prevent its activation.

Thus, pathways that are near the classical pathway interact constructively to build up amplitude.

Peptides are processed and presented by two classical pathways:

The protein encoded by this gene is part of the classical pathway of complement system.

These fragments form during the classical or lectin pathway of the complement.

It is a membrane protein and regulates also C5 convertase of the classical and alternative pathway.