To what RBC cell surface receptor does the opsonin C3b on immune complexes bind for transport to the liver?

The correct answer involves understanding the role of opsonins, specifically C3b, in immune complex transport to the liver. C3b is a fragment of the complement system that binds to pathogens or immune complexes to enhance their clearance from circulation. This process is important for maintaining body homeostasis and preventing the accumulation of potentially harmful immune complexes.

C3b binds to specific receptors on the surface of red blood cells (RBCs) to facilitate the transport of these immune complexes to the liver for clearance. The receptors involved in this transport include CR1 (Complement Receptor 1) and CD35, which are the same molecule but can be referred to by these different names.

CD35 acts as a receptor for C3b, allowing the RBCs to bind to the immune complexes. As such, the interaction of C3b with these receptors enables the immune complexes to be taken to the liver, where they can be processed and eliminated by phagocytic cells. Therefore, both CD35 and CR1 are integral to this transport mechanism, confirming that the correct answer spans both options A and C, which describe the same receptor.

By facilitating this interaction, the immune system ensures that potentially damaging immune complexes do not persist in the bloodstream, thus