CR1 (Complement C3b/C4b Receptor 1) is a membrane-bound type-I transmembrane glycoprotein that functions as a cellular receptor for complement components C3b and C4b 1. The receptor exhibits wide cellular and tissue distribution, particularly on erythrocytes, monocytes, and immune cells 1. CR1 mediates multiple biological functions including transport of complement-opsonized immune complexes on erythrocytes, enhancement of phagocytosis, and modulation of B-cell differentiation 1. Mechanistically, CR1 regulates complement cascade through decay acceleration activity and co-factor activity, inhibiting classical, lectin, and alternative pathways 2. The receptor contains multiple duplicated domains that bind C3b/C4b ligands, with structural variants like the CR1-B duplication allele increasing the number of binding sites 3. CR1 dysfunction is associated with several diseases. Genetic variants in CR1 are among the strongest genome-wide association signals for late-onset Alzheimer's disease (LOAD), influencing amyloid-β pathology and neuroinflammation 43. Reduced CR1 expression—through genetic variants or epigenetic hypermethylation—characterizes catastrophic antiphospholipid syndrome (CAPS), a complement-driven thrombotic disorder, with CR1 deficiency predicting response to C5 inhibition therapy 5. CR1 polymorphisms and decreased plasma levels correlate with dengue disease severity 6, and CR1 variants associate with chr1 Chagas disease susceptibility and cardiomyopathy risk 7. Additionally, CR1 serves as a receptor for Epstein-Barr virus 1.