Which complement proteins are important for opsonization?

The correct answer highlights the role of C3b and C4b in opsonization, a crucial process in the immune response. Opsonization enhances the ability of phagocytes to recognize, engulf, and destroy pathogens. C3b, in particular, acts as a powerful opsonin by binding to the surface of pathogens, thereby marking them for phagocytosis. It facilitates the recognition of these pathogens by different types of immune cells, such as macrophages and neutrophils, which express receptors for C3b.

C4b also contributes to opsonization, albeit to a lesser degree than C3b. It can bind to the surface of pathogens and serve a similar purpose in enhancing phagocytosis. The interaction of these complement proteins with the immune cells is fundamental in establishing an effective immune response against infections.

Regarding the other choices, C5a is mainly known for its role as a potent chemotactic factor, attracting immune cells to sites of inflammation rather than directly participating in opsonization. Factor B is involved in the alternative complement pathway and collaborates with other proteins, but it does not serve directly as an opsonin. C1 and C2 are components of the classical complement pathway and play roles in initiating