Enhanced production of biologically active interleukin‐1α and interleukin‐1β by psoriatic epidermal cells ex vivo: evidence of increased cytosolic interleukin‐1β levels and facilitated interleukin‐1 release

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Abstract
The expression of interleukin (IL)-1 is altered in psoriatic lesions. However, little is known about the actual production of IL-1α and IL-1β by psoriatic epidermal cells (EC). We monitored IL-1 in the extracellular, the membrane and the intracellular compartment of freshly isolated EC from untreated lesional psoriatic (PP) and normal healthy (NN) skin during non-stimulated short-term cultures, representing a psoriasis model ex vivo. Cytokines were measured using bioassays combined with neutralizing antibodies and enzyme-linked immunosorbent assay in parallel. PP EC released significantly increased amounts of biologically active IL-1α and IL-1β in a ratio of 3:1, whereas NN EC only released IL-1α. Also, the release of IL-6, but not of TNF-α, by PP EC was significantly increased. Membrane-associated IL-1 activity, analyzed using glutaraldehydefixed EC, was low and not unique to PP EC. The cytosol of PP EC contained significantly increased levels of immunoreactive IL-1β. Furthermore, PP EC displayed loss of membrane integrity, as determined by trypan blue exclusion and release of cytosolic lactate dehydrogenase. This facilitated release of intracellular IL-1. Depletion of CD45+ cells showed that intraepidermal leukocytes did not contribute to the production of IL-1. Our observations show that resident PP EC express enhanced IL-1 production ex vivo, which is due to an increased cytosolic IL-1β content and facilitated IL-1 release. This study provides the first evidence that PP EC can produce bioactive IL-1β.