This peripheral checkpoint breach in SLE may be responsible for high 9G4+ serum autoantibody titers (Isenberg et al., 1993; van Vollenhoven et al., 1999) as well as IgG+9G4+ cells and 9G4+CD138+ plasma cells in SLE peripheral blood, which are otherwise rare in healthy controls (Cappione et al., 2005). The gene discussed is SDC1; the disease is systemic lupus erythematosus.