Pimecrolimus reduces eosinophil activation associated with calcium mobilization.

BACKGROUND Pimecrolimus is a calcineurin inhibitor that inhibits T cell and mast cell activation and effectively treats atopic dermatitis. However, its effects on eosinophils, a cell type implicated in allergic disease pathology, are unknown. Therefore, we examined the effects of pimecrolimus on eosinophil superoxide anion production, degranulation and survival. METHODS Purified eosinophils from normal or atopic donors were incubated with serial dilutions of pimecrolimus (microM to nM) and then stimulated with platelet activating factor (PAF), interleukin 5 (IL5), secretory immunoglobulin A (sIgA) or Alternaria alternata (Alt) fungus extract. Eosinophil activation was monitored by cytochrome c reduction resulting from superoxide anion production and by a 2-site immunoassay for eosinophil-derived neurotoxin (EDN) in cellular supernatants, as a marker of degranulation. Eosinophil survival was measured by propidium iodide exclusion using flow cytometry after 4 days in culture. RESULTS Normal and atopic eosinophil superoxide anion production induced by PAF, and associated with increased intracellular calcium, was inhibited up to 37% with 1 microM pimecrolimus. However, superoxide anion production induced by IL5 and sIgA was not consistently inhibited. EDN release, which ultimately depends on calcium, was inhibited about 30% with PAF, IL5 and sIgA stimulation for normal and atopic donor eosinophils. Furthermore, calcium-dependent Alt-induced EDN release was inhibited up to 49% with nanomolar pimecrolimus. Finally, increased eosinophil survival promoted by IL5 and sIgA was not influenced by pimecrolimus. CONCLUSION Pimecrolimus moderately inhibits eosinophil superoxide anion production and EDN release associated with calcium mobilization, which may contribute to its efficacy in treating atopic dermatitis.