Cytokine secretion profile of human keratinocytes exposed to Malassezia yeasts.

The lipophilic yeast Malassezia is an exacerbating factor in atopic dermatitis (AD). Among organisms of the Malassezia species, Malassezia globosa and Malassezia restricta are particularly dominant on the skin of AD patients. However, the precise role of Malassezia yeasts in the pathophysiology of AD remains uncertain. Keratinocytes play a critical role in cutaneous inflammatory and immune responses by secreting cytokines. In this study, we attempted to determine the cytokine secretion profiles of human keratinocytes that were exposed to Malassezia yeasts. The human keratinocyte cell line PHK16-0b was cocultivated with M. globosa or M. restricta for 24 h, and the resulting cytokine secretion profile was analysed using a cytokine antibody array. The keratinocytes responded to the two Malassezia species with different Th2-type cytokine profiles, i.e. M. globosa induced IL-5, IL-10 and IL-13 secretion from the keratinocytes, whereas M. restricta induced IL-4 secretion. Similar results were obtained with primary normal human epidermal keratinocytes. cDNA microarray analysis confirmed that IL-5, IL-10, and IL-13 mRNAs were induced only by M. globosa, while IL-4 mRNA expression was induced only by M. restricta. These findings suggest that M. globosa and M. restricta play a synergistic role in triggering or exacerbating AD by stimulating the Th2 immune response.