classical pathway of complement activation

C1r is a highly specific serine protease initiating the classical pathway of complement activation during immune response.

PTX3 activates the classical pathway of complement activation and facilitates pathogen recognition by macrophages and DCs.

IgG and IgM antibodies bind to these antigens to form complexes that activate the classical pathway of complement activation to eliminate cells presenting foreign antigens (which are usually, but not in this case, pathogens).