Emerging roles and therapeutic implications of HDAC2 and IL-17A in steroid-resistant asthma.

Steroid resistance represents a major clinical problem in the treatment of severe asthma, and therefore a better understanding of its pathogenesis is warranted. Recent studies indicated that histone deacetylase 2 (HDAC2) and interleukin 17A (IL-17A) play important roles in severe asthma. HDAC2 activity is reduced in patients with severe asthma and smoking-induced asthma, perhaps accounting for the amplified expression of inflammatory genes, which is associated with increased acetylation of glucocorticoid receptors. Neutrophilic inflammation contributes to severe asthma and may be related to T helper (Th) 17 rather than Th2 cytokines. IL-17A levels are elevated in severe asthma and correlate with the presence of neutrophils. Restoring the activity of HDAC2 or targeting the Th17 signaling pathway is a potential therapeutic approach to reverse steroid insensitivity.