IgG and IgM activate which complement pathway?

The classical pathway of complement activation is initiated when antibodies, specifically IgG and IgM, bind to antigens on the surface of pathogens. This binding leads to the formation of an immune complex, which subsequently activates complement component C1. The classical pathway is a crucial part of the immune response, as it enhances phagocytosis, promotes inflammation, and leads to the lysis of pathogens.

IgM, being a pentamer, is particularly effective at complement activation, as it can bind multiple antigens and initiate the pathway efficiently. IgG, while a monomer in its basic form, can also effectively activate the classical pathway once it forms a complex with an antigen. This mechanism is significant in generating a robust immune response and is crucial for the elimination of pathogens from the body.

Other pathways, such as the alternative pathway and lectin pathway, utilize different mechanisms and factors for activation and do not rely specifically on antibody-antigen interactions to the same extent as the classical pathway. Opsonization is a process by which pathogens are marked for phagocytosis but is not a standalone pathway of complement activation.