TNF and osteoarthritis, knee: To further address this issue, the current study (1) investigated serum concentrations of proinflammatory cytokines (IL-6, IL-8, and TNF-α) and an anti-inflammatory cytokine (IL-10) in OA patients (with painful knee osteoarthritis) and healthy controls and (2) correlated these serum levels with pain intensity, functional capacity, and pressure pain thresholds (PPTs).