The Ki67 staining of the different Treg/Tresp cell subsets revealed a significant age-independent reduction in CD31+ and CD31− memory Treg proliferation, suggesting a predominant differentiation via CD31+ memory Tregs in SLE patients, which most probably is strongly restrained by the immunosuppressive drugs, even below the normal level of healthy volunteers. Here, PECAM1 is linked to systemic lupus erythematosus.