CD4, IL-17, and COX-2 Are Associated With Subclinical Inflammation in Malar Melasma.

The pathogenesis of melasma, a common, photo-induced hyperpigmentary disorder, is not clearly understood. Significant factors linked to melasma are ultraviolet radiation exposure and genetic predisposition. Histological analysis has demonstrated that melasma is caused by a network of cellular interactions among melanocytes, keratinocytes, mast cells, fibroblasts, and dermal vasculature exhibits, features similar to chronic sun damage. Dermal inflammation caused by ultraviolet radiation might play an important role in the hyperpigmentation and reactivation of melasma lesions through the production of melanogenic cytokines and growth factors. Because the role of inflammation in this disorder is unknown, we used histochemistry, immunohistochemistry, and quantitative real-time polymerase chain reaction to evaluate melasma lesions from healthy female patients (n = 20) with malar melasma. Lesional skin without specific solar exposure or photoprotection measures within the previous 4 weeks was compared with nonlesional skin. The increased lymphocytic infiltrate in lesional skin was mainly composed of CD4 T cells, mast cells, and macrophages. Levels of the cytokine interleukin (IL)-17 and the proinflammatory mediator cyclooxygenase (COX)-2 were significantly elevated in affected skin compared with healthy skin. In addition, the Melasma Activity and Severity Index score, fraction of solar elastosis, and epidermal melanin were positively associated with COX-2 expression. There was no statistically significant difference in IL-1α, IL-1β, R-IL1, IL-6, IL-8, vascular endothelial growth factor, and tumor necrosis factor alpha expression levels. Together, these data indicated that melasma under unchallenged conditions is characterized by chronic inflammatory cells and mediators, which may explain its recurrent nature.