CXCL1 and systemic inflammatory response syndrome: In the aforementioned study, analysis of serum inflammatory cytokine expression of opioid-exposed animals compared to saline-exposed controls demonstrated elevated levels of interleukin 1β (IL-1β), tumor necrosis factor α (TNF-α), IL-6, and C-X-C motif chemokine ligand 1 (CXCL1), indicating systemic inflammatory response syndrome induced by opioid exposure.