Final answer:
CR-1 can act as an opsonin and induce phagocytosis by binding to C3b, making the correct answer A and C. Opsonins mark pathogens for phagocytosis, which is essential for the innate immune response.
Step-by-step explanation:
The correct answer to the question about the role of CR-1 is d. A & C. CR-1 can function as an opsonin when it acts to mark antigens for phagocytosis by immune cells like neutrophils. This is because opsonins coat the surface of pathogens with molecules that aid in their recognition and engulfment by phagocytes. Clathrin, on the other hand, plays a different role by stabilizing the inward facing surface of the plasma membrane during the formation of vesicles that engulf the antigen.
Phagocytes such as macrophages, dendritic cells, and neutrophils have receptors that recognize and bind to the Fc portion of IgG molecules, allowing them to attach to and engulf pathogens that have been tagged by opsonins. This process is a crucial part of the innate immune system's immediate response to invading pathogens.