Which factor speeds up C3b deposition on pathogen surfaces?

The correct answer is the factor that facilitates the acceleration of C3b deposition on pathogen surfaces. This factor is known as Properdin, or Factor P. Properdin stabilizes the alternative pathway C3 convertase, leading to an increased formation of this enzyme complex. By stabilizing the C3 convertase, Properdin enhances the cleavage of C3, which subsequently promotes the deposition of C3b onto the surface of pathogens. This process is crucial in complement activation, which is an essential part of the immune response against infections.

The specificity of Properdin's role in enhancing C3b deposition distinguishes it from other factors involved in the complement system. While Factor H and Factor I are important in regulating the complement cascade—including the inactivation of C3b—neither directly accelerates its deposition on pathogen surfaces. Factor C does not serve a recognized role in this context. Understanding the function of Properdin helps clarify its importance in enhancing immune responses by promoting the opsonization of pathogens, thereby marking them for destruction by immune cells.