There were significant differences found between RA and SpA in serum levels of β-defensin 2, IFN-γ, IL-22, IL-23, IL-17F, GM-CSF, CCL20/MIP3a, IL-15, IL-1β, IL-17A, and IL-6 (S1 Table). The gene discussed is IL15; the disease is rheumatoid arthritis.