Which receptor binds to C3b to facilitate phagocytosis of pathogens?

The receptor that binds to C3b to facilitate phagocytosis of pathogens is CR1 (Complement Receptor 1). CR1 is found on various immune cells, particularly on phagocytic cells such as macrophages and neutrophils. It plays a crucial role in the innate immune response by recognizing and binding to C3b that is deposited on the surface of pathogens during the complement activation process.

When C3b binds to the surface of a pathogen, it tags the pathogen for opsonization, which significantly increases the efficiency of phagocytosis. The interaction between C3b and CR1 allows the phagocyte to recognize the pathogen as foreign, leading to its engulfment and subsequent destruction. This function is fundamental in clearing infections and maintaining homeostasis.

The other receptors listed—C3a, CD4, and Fc receptors—are involved in various immune functions, but they do not directly bind C3b to mediate phagocytosis. For instance, C3a is an anaphylatoxin that promotes inflammation, while CD4 is a co-receptor for T cell activation and not involved in opsonization. Fc receptors are important for binding antibodies, facilitating antibody-dependent cellular cytotoxicity, but