In addition, serum TNF-α concentrations above 20.1 pg/mL were negatively correlated to treatment response of MTX at 6 months in 42 RA patients [29], while serum IL-1β, IL-6, IL-8, IL-10, and IL-12 level and expression of multidrug resistance protein (encoded by MDR1) in PBMCs did not correlate with response to MTX [29]. This evidence concerns the gene IL1B and rheumatoid arthritis.