Analysis of IFN- κ Expression in Pathologic Skin Conditions: Downregulation in Psoriasis and Atopic Dermatitis

Interferon-κ (IFN-κ) is a type I IFN expressed by keratinocytes, monocytes and dendritic cells (DCs). In human keratinocytes, it is produced in response to double-stranded RNA (dsRNA) and other IFNs and protects from viral infections. In monocytes and DCs, IFN-κ induces tumor necrosis factor-α (TNF-α) and interleukin-10 (IL-10) and inhibits lipopolysaccharide (LPS)-induced IL-12. In this study, we evaluated IFN-κ expression in skin lesions of patients with common immune-mediated inflammatory disorders using immunohistochemical techniques. IFN-κ was not detectable in healthy skin but was strongly expressed in allergic contact dermatitis and lichen planus-affected skin. IFN-κ was localized mainly in basal and suprabasal keratinocytes and in some leukocytes infiltrating the dermis. In contrast, IFN-κ expression in psoriatic or atopic dermatitis (AD) pidermis was weak and detectable in only 2 of 5 patients examined. Consistently, cultured keratinocytes and monocytes obtained from psoriatic and AD patients expressed null or low levels of IFN-κ in response to IFN-γ, which strongly upregulates IFN-κ in normal keratinocytes. IFN-κ accumulated in keratinocyte cytoplasm and plasma membrane, and only limited amounts were released extracellularly. Soluble IFN-κ did not influence keratinocyte proliferation or chemokine and membrane molecule expression, and only its membrane-associated form activated IFN-stimulated response element (ISRE) signaling. Given the difference in IFN-κ expression levels in the skin disorders examined, IFN-κ presence or deficiency might have different pathogenetic consequences depending also on other disease-specific intrinsic alterations.