CR1 (Complement Receptor 1), also known as CD35. is a transmembrane glycoprotein that plays a critical role in the regulation of the complement system and immune complex clearance. Discovered in the 1970s, it is predominantly expressed on erythrocytes, neutrophils, B cells, and certain dendritic cells. Structurally, CR1 belongs to the complement activation-receptor (CAR) family and contains multiple binding sites for complement components C3b and C4b, enabling it to act as a cofactor in the degradation of these opsonins by factor I. This process helps prevent excessive complement activation and tissue damage.
CR1 on erythrocytes facilitates the transport of immune complexes to the liver and spleen for phagocytic removal, a key mechanism in preventing systemic inflammation. Genetic polymorphisms in CR1 have been linked to diseases such as systemic lupus erythematosus (SLE) and malaria susceptibility, highlighting its dual role in immunity and pathogenesis.
CR1-specific antibodies are valuable tools in research and diagnostics. They are used to study CR1 expression patterns, immune complex handling, and complement regulation. Therapeutically, anti-CR1 antibodies have been explored for targeting drug delivery to CR1-expressing cells or modulating complement activity in disorders like paroxysmal nocturnal hemoglobinuria. However, their clinical application remains under investigation, emphasizing the need for further exploration of CR1's functional diversity and disease relevance.