CD4 and systemic lupus erythematosus: However, when Tregs were defined as “FOXP3-positive” cells, the proportions of such cells did not differ between SLE patients and controls because the definitions of Tregs were complicated by the addition of CD25 status, giving “CD25-negative and FOXP3-positive” and “CD25 and FOXP3 double positive.” This phenomenon may be explained by the findings of other studies indicating that the CD4+CD25−FOXP3+ T cells of SLE were dysfunctional Tregs [21, 22] and may even be previously activated conventional T cells [23].