CR2 and systemic lupus erythematosus: In this study, we mapped such interactions between genes in the RCA gene cluster at the molecular level using high-resolution chromatin interaction maps and have successfully identified direct chromatin interactions between CTCF sites in CD55, CR2 and CR1. Binding of CTCF at intron 1 of CR2 was modulated by an SLE-associated SNP (rs1876453) and shown to influence the expression of its neighbouring gene, CR1, in B cells (29).