A principal component analysis (PCA) was performed to define associations among serum cytokines (IL-1β, IL-12p70, IL-6, TNF-α, and IL-10), C-reactive protein (CRP), and DAS28 variables in patients with seropositive and seronegative RA and HCs (Fig. 1B). The gene discussed is IL6; the disease is rheumatoid arthritis.