Receptor for complement C3d and for HNRNPU. Participates in B lymphocytes activation. Interacts (via Sushi domain 1 and 2) with C3. Interacts with CD19. Part of a complex composed of CD19, CR2/CD21, CD81 and IFITM1/CD225 in the membrane of mature B-cells. B-lymphocytes. Belongs to the receptors of complement activation (RCA) family.