Interleukin-18 is elevated in the horny layer in patients with atopic dermatitis and is associated with Staphylococcus aureus colonization.

ABSTRACT

BACKGROUND: An increase in interleukin (IL)-18 production from epidermal cells has been reported in an atopic dermatitis (AD) mouse model, and subsequent topical application of Staphylococcus aureus results in severe dermatitis. OBJECTIVES: To reveal the relationship between S. aureus colonization of skin lesions and keratinocyte IL-18 production, particularly in AD with relatively low serum IgE levels. We also aimed to establish a simple and noninvasive method of assaying IL-18 produced by epidermal keratinocytes to evaluate local skin inflammation and therapeutic effects in patients with AD. METHODS: IL-18 in the horny layer of the skin was collected via a tape-stripping method and measured in 95 patients with AD and 40 healthy controls by enzyme-linked immunosorbent assay (ELISA). Clinical severity, blood data and S. aureus skin colonization were evaluated before and after treatment. RESULTS: IL-18 levels in the horny layer were significantly higher in the skin lesions of patients with AD than in healthy controls and correlated with SCORAD, levels of serum IL-18, IgE, lactate dehydrogenase, thymus and activation-regulated chemokine, blood eosinophils and transepidermal water loss. In the AD group with serum IgE < 1500 IU mL(-1) , significantly higher IL-18 levels were observed in the horny layer of patients colonized with S. aureus compared with those who were not. CONCLUSIONS: Epidermal IL-18 production was associated with the severity of AD. Staphylococcus aureus colonization seems to contribute to this IL-18 production, especially in the AD group with relatively low IgE production. Tape stripping provides an easy and noninvasive method to assess epidermal IL-18 production by ELISA.