IL-15 expression of Fibroblast-like cells from the synovium of RA patients (RASFib) exerts a dual action on the equilibrium between CD4+CD25+ Treg and CD4+CD25− responder T cells (Tresp) by potentiating the suppressive effect of Treg while augmenting the proinflammatory action of Tresp; the result is a shift of the Treg/Tresp balance toward a proinflammatory state [140]. The gene discussed is CD4; the disease is rheumatoid arthritis.