Lithium and psoriasis: cytokine modulation of cultured lymphocytes and psoriatic keratinocytes by lithium.

The predominant cutaneous side effect of lithium is the exacerbation or aggravation of psoriasis, but the pathogenesis is still unclear. The hyperproliferation of keratinocytes and a dense lesional infiltrate of mononuclear cells are the hallmarks of psoriatic skin lesions. Interactions between keratinocytes and T cells are thought to be one reason for an increased secretion of proinflammatory cytokines and growth factors. To investigate whether lithium influences cytokines of the "psoriatic cytokine network', we established a coculture model with keratinocytes from psoriatic patients and from healthy controls cultured with HUT 78 lymphocytes and measured the cytokine levels of Il-2, Il-6, Il-8, IFN gamma and TGF alpha in the culture supernatants after treatment with lithium. Il-6 levels were slightly elevated in the supernatants obtained from psoriatic and control keratinocyte cultures after lithium treatment, but IFN gamma and Il-2 levels were elevated only in the lithium-treated cocultures with psoriatic keratinocytes. In contrast, these two cytokines were not affected by lithium in HUT 78 monocultures or in cocultures with normal epidermal cells. We also found slightly elevated TGF alpha levels in lithium-treated psoriatic cocultures but not in control cultures. We therefore demonstrated that lithium influences the cell communication of psoriatic keratinocytes with HUT 78 lymphocytes by triggering the secretion of TGF alpha, Il-2 and, massively, IFN gamma. It seems possible that lithium also influences similar parts of the psoriatic cytokine network in vivo.