Interleukin 8 (IL8 or chemokine (C-X-C motif) ligand 9, CXCL8) is a chemokine produced by macrophages and other cell types such as epithelial cells, airway smooth muscle cells and endothelial cells. In humans, the interleukin-8 protein is encoded by the IL8 gene. IL-8 is initially produced as a precursor peptide of 99 amino acids long which then undergoes cleavage to create several active IL-8 isoforms.

Interleukin-8 is a key mediator associated with inflammation where it plays a key role in neutrophil recruitment and neutrophil degranulation. As an example, it has been cited as a proinflammatory mediator in gingivitis and psoriasis. IL-8 has also been implied to have a role in colorectal cancer by acting as an autocrine growth factor for colon carcinoma cell lines or the promotion of division and possible migration by cleaving metalloproteinase molecules.