IL6 and rheumatoid arthritis: Ashino et al. (2007) also found that serum IL-1β and IL-6 concentrations were significantly higher in pX transgenic mice than those in non-transgenic or non-arthritic pX transgenic mice. Consistent with our arthropathic mice, their serum TNF-α concentrations were low, with no significant differences between the groups (Ashino et al., 2007). IL-6 is a key proinflammatory cytokine that is abundant in the synovium and synovial tissues of patients with rheumatoid arthritis (Okamoto et al., 1997).