IL-15 mediates antigen-induced neutrophil migration by triggering IL-18 production

We have investigated the mechanisms underlying IL-15-induced neutrophil migration into inflamed tissues. IL-15 induced neutrophil migration to the peritoneal cavity in mice in a time- and dose-dependent manner. The cell migration was not induced in IL-18(-/-), MIP-1 alpha (CCL3)(-/-), TNFR1(-/-) or 5-LOX-/- mice but was normal in IFN-gamma(-/-) mice. IL-15-induced neutrophil migration was inhibited by anti-MIP-2 (CXCL2) antibody or MK886 (leukotriene synthesis inhibitor). IL-18-induced neutrophil migration was also dependent on TNFR1, MIP-1 alpha, MIP-2 and leukotriene. Consistent with this observation, IL-15 induced IL-18 production, and IL-15 or IL-18 injection induced the production of MIP-2, MIP-1 alpha, TNF-alpha and LTB4. In an antigen-specific inflammation model, ovalbumin (OVA)-induced neutrophil migration was completely inhibited by soluble IL-15R alpha (sIL-15R alpha) or anti-MIP-2 antibody. Furthermore, cell migration was absent in IL-18-/-, MIP-1 alpha(-/-), TNFR1(-/-), or 5-LOX-/- mice. OVA challenge induced the release of MIP-2, MIP-1 alpha, TNF-alpha and LTB4 in the peritoneal cavity in an IL-15- and IL-18-dependent manner. We also found that neutrophils from the peripheral blood and synovial fluid of patients with rheumatoid arthritis produced substantial amounts of IL-18 and LTB4 following activation by IL-15. Together, these results demonstrate that IL-15 plays an important role in antigen-induced neutrophil migration during inflammation, triggering a sequential OVA, IL-15, IL-18, MIP-2, MIP-1 alpha, TNF-alpha, LTB4 and neutrophil migration signaling cascade.