IL-33 induces neutrophil migration in rheumatoid arthritis and is a target of anti-TNF therapy.

OBJECTIVES: Interleukin 33 (IL-33) is a new member of the IL-1 family of cytokines which signals via its receptor, ST2 (IL-33R), and has an important role in Th2 and mast cell responses. This study shows that IL-33 orchestrates neutrophil migration in arthritis. METHODS AND RESULTS: Methylated bovine serum albumin (mBSA) challenge in the knee joint of mBSA-immunised mice induced local neutrophil migration accompanied by increased IL-33R and IL-33 mRNA expression. Cell migration was inhibited by systemic and local treatments with soluble (s)IL-33R, an IL-33 decoy receptor, and was not evident in IL-33R-deficient mice. IL-33 injection also induced IL-33R-dependent neutrophil migration. Antigen- and IL-33-induced neutrophil migration in the joint was dependent on CXCL1, CCL3, tumour necrosis factor alpha (TNFalpha) and IL-1beta synthesis. Synovial tissue, macrophages and activated neutrophils expressed IL-33R. IL-33 induces neutrophil migration by activating macrophages to produce chemokines and cytokines and by directly acting on neutrophils. Importantly, neutrophils from patients with rheumatoid arthritis successfully treated with anti-TNFalpha antibody (infliximab) expressed significantly lower levels of IL-33R than patients treated with methotrexate alone. Only neutrophils from patients treated with methotrexate alone or from normal donors stimulated with TNFalpha responded to IL-33 in chemotaxis. CONCLUSIONS: These results suggest that suppression of IL-33R expression in neutrophils, preventing IL-33-induced neutrophil migration, may be an important mechanism of anti-TNFalpha therapy of inflammation.

Prostaglandin mediates IL-23/IL-17-induced neutrophil migration in inflammation by inhibiting IL-12 and IFNgamma production.

IL-23/IL-17-induced neutrophil recruitment plays a pivotal role in rheumatoid arthritis (RA). However, the mechanism of the neutrophil recruitment is obscure. Here we report that prostaglandin enhances the IL-23/IL-17-induced neutrophil migration in a murine model of RA by inhibiting IL-12 and IFN gamma production. Methylated BSA (mBSA) and IL-23-induced neutrophil migration was inhibited by anti-IL-23 and anti-IL-17 antibodies, COX inhibitors, IL-12, or IFNgamma but was enhanced by prostaglandin E(2) (PGE(2)). IL-23-induced IL-17 production was increased by PGE(2) and suppressed by COX-inhibition or IL-12. Furthermore, COX inhibition failed to reduce IL-23-induced neutrophil migration in IL-12- or IFNgamma-deficient mice. IL-17-induced neutrophil migration was not affected by COX inhibitors, IL-12, or IFNgamma but was inhibited by MK886 (a leukotriene synthesis inhibitor), anti-TNFalpha, anti-CXCL1, and anti-CXCL5 antibodies and by repertaxin (a CXCR1/2 antagonist). These treatments all inhibited mBSA- or IL-23-induced neutrophil migration. IL-17 induced neutrophil chemotaxis through a CXC chemokines-dependent pathway. Our results suggest that prostaglandin plays an important role in IL-23-induced neutrophil migration in arthritis by enhancing IL-17 synthesis and by inhibiting IL-12 and IFNgamma production. We thus provide a mechanism for the pathogenic role of the IL-23/IL-17 axis in RA and also suggest an additional mechanism of action for nonsteroidal anti-inflammatory drugs.

CXCR2-specific chemokines mediate leukotriene B4-dependent recruitment of neutrophils to inflamed joints in mice with antigen-induced arthritis.

OBJECTIVE: To investigate the mechanism underlying neutrophil migration into the articular cavity in experimental arthritis and, by extension, human inflammatory synovitis. METHODS: Antigen-induced arthritis (AIA) was generated in mice with methylated bovine serum albumin (mBSA). Migration assays and histologic analysis were used to evaluate neutrophil recruitment to knee joints. Levels of inflammatory mediators were measured by enzyme-linked immunosorbent assay. Antibodies and pharmacologic inhibitors were used in vivo to determine the role of specific disease mediators. Samples of synovial tissue and synovial fluid from rheumatoid arthritis (RA) or osteoarthritis patients were evaluated for CXCL1 and CXCL5 expression. RESULTS: High levels of CXCL1, CXCL5, and leukotriene B4 (LTB4) were expressed in the joints of arthritic mice. Confirming their respective functional roles, repertaxin (a CXCR1/CXCR2 receptor antagonist), anti-CXCL1 antibody, anti-CXCL5 antibody, and MK886 (a leukotriene synthesis inhibitor) reduced mBSA-induced neutrophil migration to knee joints. Repertaxin reduced LTB4 production in joint tissue, and neutrophil recruitment induced by CXCL1 or CXCL5 was inhibited by MK886, suggesting a sequential mechanism. Levels of both CXCL1 and CXCL5 were elevated in synovial fluid and were released in vitro by RA synovial tissues. Moreover, RA synovial fluid neutrophils stimulated with CXCL1 or CXCL5 released significant amounts of LTB4. CONCLUSION: Our data implicate CXCL1, CXCL5, and LTB4, acting sequentially, in neutrophil migration in AIA. Elevated levels of CXCL1 and CXCL5 in the synovial compartment of RA patients provide robust comparative data indicating that this mechanism plays a role in inflammatory joint disease. Together, these results suggest that inhibition of CXCL1, CXCL5, or LTB4 may represent a potential therapeutic strategy in RA.

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-1alpha (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-1alpha, 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-1alpha, TNF-alpha and LTB4. In an antigen-specific inflammation model, ovalbumin (OVA)-induced neutrophil migration was completely inhibited by soluble IL-15Ralpha (sIL-15Ralpha) or anti-MIP-2 antibody. Furthermore, cell migration was absent in IL-18-/-, MIP-1alpha-/-, TNFR1-/-, or 5-LOX-/- mice. OVA challenge induced the release of MIP-2, MIP-1alpha, 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-1alpha, TNF-alpha, LTB4 and neutrophil migration signaling cascade.

IL-18 enhances collagen-induced arthritis by recruiting neutrophils via TNF-alpha and leukotriene B4.

IL-18 expression and functional activity have been associated with a range of autoimmune diseases. However, the precise mechanism by which IL-18 induces such pathology remains unclear. In this study we provide direct evidence that IL-18 activates neutrophils via TNF-alpha induction, which drives the production of leukotriene B(4) (LTB(4)), which in turn leads to neutrophil accumulation and subsequent local inflammation. rIL-18 administered i.p. resulted in the local synthesis of LTB(4) and a rapid influx of neutrophils into the peritoneal cavity, which could be effectively blocked by the LTB(4) synthesis inhibitor MK-886 (MK) or its receptor antagonist CP-105,696. IL-18-induced neutrophils recruitment and LTB(4) production could also be blocked by a neutralizing anti-TNF-alpha Ab. In addition, IL-18 failed to induce neutrophil accumulation in vivo in TNFRp55(-/-) mice. In an IL-18-dependent murine collagen-induced arthritis model, administration of MK significantly inhibited disease severity and reduced articular inflammation and joint destruction. Furthermore, MK-886-treated mice also displayed suppressed proinflammatory cytokine production in response to type II collagen in vitro. Finally, we showed that IL-18-activated human peripheral blood neutrophils produced significant amounts of LTB(4) that were effectively blocked by the MK. Together, these findings provide a novel mechanism whereby IL-18 can promote inflammatory diseases.