Reduction of Neutrophil Activation by Phosphodiesterase 4 Blockade in Behçet's Disease

Objective: Behçet's disease (BD) is a systemic vasculitis with inflammatory lesions mediated by cytotoxic T cells and neutrophils. Apremilast, an orally available small-molecule that selectively inhibits phosphodiesterase 4 (PDE4), has been recently approved for the treatment of BD. We aimed to investigate the effect of PDE4 inhibition on neutrophil activation in BD. Methods: We studied surface markers and reactive oxygen species (ROS) by flow cytometry, neutrophils extra cellular traps (NETs) and molecular signature of neutrophils by transcriptomic before and after PDE4 inhibition. Results: Activation surface markers (CD64, CD66b, CD11b and CD11c), ROS production and NETosis were up-regulated in BD as compared to Healthy Donors (HD) neutrophils. Transcriptome analysis showed 1021 significantly dysregulated neutrophils genes between BD and HD. Among dysregulated genes, we highlighted a great enrichment for pathways linked to innate immunity, intracellular signaling and chemotaxis in BD. Skin lesions of BD showed increased infiltration of neutrophils that co-localized with PDE4. Inhibition of PDE4 by apremilast strongly inhibited neutrophil surface activation markers as well as ROS production, NETosis, and genes and pathways related to innate immunity, intracellular signaling and chemotaxis. Conclusion: We pointed out key biological effects of apremilast on neutrophils in BD. We performed microarray assay on neutrophils extracted from 5 healthy donors (HD, P1 to P5) and 4 patients with Behçet's disease (BD, P1 to P4), either untreated or treated with Apremilast (a PDE4 inhibitor).