RA patients with RF presence were characterized by significantly lower serum levels of IL-17F (p = 0.02), IL-17 (p = 0.04), IL-10 (p = 0.04), IL-22 (p = 0.02), and IL-21 (p < 0.001) than RA patients without RF (Figure 5). Here, IL17F is linked to rheumatoid arthritis.