CXCL8 and pulmonary arterial hypertension: In a study conducted by Soon et al., serum levels of several interleukins (IL), such as IL-1, IL-2, IL-4, IL-6, IL-8, Il-10, and IL-12p70, and tumor necrosis factor-α (TNFα) were higher in patients with PAH in comparison to a group of healthy controls.