Complement receptor type 1 (CR1) is a multi-modular membrane receptor composed of 30 homologous complement control protein modules (CCP) organized in four different functional regions called long homologous repeats (LHR A, B, C, and D). CR1 is a receptor for complement-opsonins C3b and C4b and specifically interacts through pairs of CCP modules located in LHR A, B, and C. Human CR1 plays a role in the clearance of complement opsonized molecules and may facilitate the entry of pathogens into host cells. Lower CR1 expression has been associated with susceptibility to systemic lupus erythematosus (SLE). In contrast, subjects displaying lower CR1 expression are protected against severe manifestations of falciparum malaria. The CR1 gene was shown to be involved in Alzheimer's disease (AD).