EDN1 and freckles: As for the biological mechanisms leading to the activation of EDN and SCF signaling cascades [9], our in vitro studies suggest an interesting contrast that while the upregulation of IL-1α is mainly responsible for stimulating EDN1 and SCF production in UVB-melanosis, the upregulation of TNFα is mainly associated with the stimulated production of those same two cytokines in SLs.