Which components of the complement system are most likely to coat a cell?

The complement system is a critical component of the immune response, playing a key role in opsonization, inflammation, and the lysis of pathogens. Among the options provided, C3b and C4b are some of the most important molecules involved in coating (or opsonizing) cells. Opsonization enhances the recognition and ingestion of pathogens by phagocytes.

C3b is particularly important as it binds to the surface of pathogens and facilitates their clearance by immune cells such as macrophages and neutrophils. This process enhances phagocytosis, as immune cells have receptors that specifically recognize and bind to C3b-coated pathogens.

While C4a does play a role in inflammation, it is not typically involved in opsonization to the same extent as C3b, making C3b the stronger candidate when focusing on components that actively coat cells for the purpose of opsonization.

Thus, the association of C3b with coating cells and facilitating their recognition and clearance by immune cells is the underlying reason that makes this the correct choice.