Antimicrobial human neutrophil peptides (HNPs) play a pivotal role in innate host defense against a broad spectrum of prokaryotic pathogens. In addition, HNPs modulate cellular immune responses by producing the chemokine interleukin-8 (IL-8) in myeloid and epithelial cells and by exerting chemotaxis to T cells, immature dendritic cells, and monocytes. However, the mechanisms by which HNPs modulate the immune responses in the eukaryotic cells remain unclear. We demonstrated that, as with adenosine triphosphate (ATP) and uridine diphosphate (UDP), HNP stimulation of human lung epithelial cells selectively induced IL-8 production in 10 pro- and anti-inflammatory cytokines examined. HNP-induced IL-8 release was inhibited by treatment with the nucleotide receptor antagonists suramin and reactive blue. Transfection of lung epithelial cells with antisense oligonucleotides targeting specific purinergic P2Y receptors revealed that the P2Y₆ (ligand of UDP) signaling pathway plays a predominant role in mediating HNP-induced IL-8 production.