Some soluble factors produced and secreted by fibroblasts have been observed to possess inhibitory activity on pigmentation; for instance, Dickkopf 1 (DKK1), highly expressed in physiologically hypo-pigmented skin areas (i.e., palmoplantar), and IL-6, an inflammatory cytokine found elevated in vitiligo with an inhibitory effect on tyrosinase activity [66]. Here, TYR is linked to vitiligo.