Human Complement Receptor Type 2 (CR2) Protein

Background

CR2, also known as complement receptor type 2 (CR2) or CD21, is a crucial protein involved in the immune response, particularly in the regulation and activation of B cells and the complement system. It serves as a receptor for fragments of complement component C3, specifically C3d, C3dg, and iC3b, which are breakdown products of C3b, an integral part of the complement system. By binding these complement fragments, CR2 plays a key role in amplifying the immune response and facilitating interactions between the innate and adaptive arms of the immune system. CR2 is predominantly expressed on the surface of B lymphocytes, follicular dendritic cells, and some epithelial cells. Its most well-known function is to enhance B-cell activation by linking the complement system to the B-cell receptor (BCR) signaling pathway. This enhances B-cell sensitivity to antigens, especially during the formation of immunological memory.