C3b
Chapter: 2
One of the split products of the activated form of the complement protein, C3. It binds to and, thereby, opsonizes bacteria, making them easier for neutrophils and macrophages to ingest (phagocytose). Ingestion is enhanced, because both neutrophils and macrophages have receptors for C3b on their surfaces. When a particle becomes bound to the surface of a phagocytic cell, it is easier for the phagocyte to ingest it.