The suggestion that complement receptor type 2 (CR2) expression levels might be important in autoimmune disease arose from two studies that noted a marked down regulation of CR2 expression levels on B lymphocytes isolated from patients with systemic lupus erythematosus (SLE) (Marquart et al., 1995; Wilson et al., 1986). This evidence concerns the gene CR2 and systemic lupus erythematosus.