1617 Impact of type 2 cytokines on the keratinocytes-s. aureus interaction

Type 2-mediated inflammation, skin barrier disruption, and dysbiosis of the cutaneous microbiota are hallmarks of the chronic inflammatory skin disease atopic dermatitis (AD). Staphylococcus aureus (SA) is highly abundant in AD skin and correlates with disease severity. Little is known about the interplay of the type 2 cytokines IL-13 and IL-4 with SA in the context of AD. Therefore, human AD-derived keratinocytes from hair follicles were stimulated with culture supernatants of AD-derived SA in the presence of IL-4, IL-13 and in combination (IL-4/IL-13). SA supernatants alone upregulated gene expression levels of AD-relevant markers and decreased expression of keratinocyte differentiation markers. Some AD-relevant factors (e.g. TSLP) were further upregulated in the presence of IL-4/IL-13. Moreover, the expression of differentiation markers (keratin 10, filaggrin) was further reduced in cells treated with SA together with IL-4/IL-13. These data suggest that type 2 cytokines amplify SA-induced inflammation and barrier disruption of the skin. To evaluate the impact of type 2 cytokines on the capacity of keratinocytes to control the growth of SA we stimulated keratinocytes for 48 h with IL-4 and IL-13 and subsequently treated them for 2 h with AD-derived SA. Viable SA were counted by plating on agar plates. This revealed a significant outgrowth of the total number of SA (extracellular, attached, intracellular) by lL-13 alone or IL-4/IL-13. Interestingly, free extracellular and loosely attached bacteria were increased by IL-4/IL-13 treatment whereas strongly attached bacteria were decreased. Only few bacteria were present intracellularly and their presence decreased by IL-4/IL-13. Overall, our data indicate that IL-4 and IL-13 stimulate the growth of extracellular SA. This supports the hypothesis that type 2 cytokines negatively affect cutaneous defense against SA, which may be of relevance in AD.