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 drug 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) production by flow cytometry, and neutrophil extracellular traps (NETs) production and molecular signature of neutrophils by transcriptome analysis before and after PDE4 inhibition. Results Activation surface markers (CD64, CD66b, CD11b, and CD11c), ROS production, and NETosis were up‐regulated in BD patient neutrophils compared to healthy donor neutrophils. Transcriptome analysis revealed 1,021 significantly dysregulated neutrophil genes between BD patients and healthy donors. Among dysregulated genes, we found a substantial enrichment for pathways linked to innate immunity, intracellular signaling, and chemotaxis in BD. Skin lesions of BD patients showed increased infiltration of neutrophils that colocalized 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 highlight key biologic effects of apremilast on neutrophils in BD.