CXCL8 and systemic sclerosis: In addition, studies have shown that plasma interleukin-1β, interleukin-6, and interleukin-8 levels are significantly increased in SSc-PH patients, but interleukin-5 levels are not statistically different between SSc-PH and SSc patients (Christmann et al., 2011; McMahan et al., 2015).