The novel role of IL-7 ligation to IL-7 receptor in myeloid cells of rheumatoid arthritis and collagen-induced arthritis.

Although the role of IL-7 and IL-7R has been implicated in the pathogenesis of rheumatoid arthritis (RA), the majority of the studies have focused on the effect of IL-7/IL-7R in T cell development and function. Our novel data, however, document that patients with RA and greater disease activity have higher levels of IL-7, IL-7R, and TNF-α in RA monocytes, suggesting a feedback regulation between IL-7/IL-7R and TNF-α cascades in myeloid cells that is linked to chronic disease progression. Investigations into the involved mechanism showed that IL-7 is a novel and potent chemoattractant that attracts IL-7R(+) monocytes through activation of the PI3K/AKT1 and ERK pathways at similar concentrations of IL-7 detected in RA synovial fluid. To determine whether ligation of IL-7 to IL-7R is a potential target for RA treatment and to identify their mechanism of action, collagen-induced arthritis (CIA) was therapeutically treated with anti-IL-7 Ab or IgG control. Anti-IL-7 Ab treatment significantly reduces CIA monocyte recruitment and osteoclast differentiation as well as potent joint monocyte chemoattractants and bone erosion markers, suggesting that both direct and indirect pathways might contribute to the observed effect. We also demonstrate that reduction in joint MIP-2 levels is responsible for suppressed vascularization detected in mice treated with anti-IL-7 Ab compared with the control group. To our knowledge, we show for the first time that expression of IL-7/IL-7R in myeloid cells is strongly correlated with RA disease activity and that ligation of IL-7 to IL-7R contributes to monocyte homing, differentiation of osteoclasts, and vascularization in the CIA effector phase.

Anti-CXCL5 therapy ameliorates IL-17-induced arthritis by decreasing joint vascularization.

IL-17-induced joint inflammation is associated with increased angiogenesis. However, the mechanism by which IL-17 mediates angiogenesis is undefined. Therefore, the pathologic role of CXCL1 and CXCL5 was investigated in arthritis mediated by local expression of IL-17, employing a neutralizing antibody to each chemokine. Next, endothelial chemotaxis was utilized to examine whether endothelial migration was differentially mediated by CXCL1 and CXCL5. Our results demonstrate that IL-17-mediated disease activity was not affected by anti-CXCL1 treatment alone. In contrast, mice receiving anti-CXCL5 demonstrated significantly reduced clinical signs of arthritis, compared to the mice treated with IgG control. Consistently, while inflammation, synovial lining thickness, bone erosion and vascularization were markedly reduced in both the anti-CXCL5 and combination anti-CXCL1 and 5 treatment groups, mice receiving anti-CXCL1 antibody had clinical scores similar to the control group. In contrast to joint FGF2 and VEGF levels, TNF-α was significantly reduced in mice receiving anti-CXCL5 or combination of anti-CXCL1 and 5 therapies compared to the control group. We found that, like IL-17, CXCL1-induced endothelial migration is mediated through activation of PI3K. In contrast, activation of NF-κB pathway was essential for endothelial chemotaxis induced by CXCL5. Although CXCL1 and CXCL5 can differentially mediate endothelial trafficking, blockade of CXCR2 can inhibit endothelial chemotaxis mediated by either of these chemokines. These results suggest that blockade of CXCL5 can modulate IL-17-induced inflammation in part by reducing joint blood vessel formation through a non-overlapping IL-17 mechanism.

Characterization of interleukin-7 and interleukin-7 receptor in the pathogenesis of rheumatoid arthritis.

OBJECTIVE: To characterize the expression of interleukin-7 (IL-7) and IL-7 receptor (IL-7R) in rheumatoid arthritis (RA) synovial tissue and to examine their regulation and pathogenic role in macrophages, endothelial cells, and synovial tissue fibroblasts in RA. METHODS: Expression of IL-7 and IL-7R in RA and normal synovial tissue was demonstrated by immunohistochemistry. Expression and regulation of IL-7 and IL-7R in RA peripheral blood in vitro-differentiated macrophages, RA synovial tissue fibroblasts, and human microvascular endothelial cells (HMVECs) were determined by real-time reverse transcription-polymerase chain reaction and/or flow cytometry. Enzyme-linked immunosorbent assay was used to examine production of proangiogenic factors by IL-7-activated macrophages, RA fibroblasts, and endothelial cells. RESULTS: IL-7 and IL-7R were coexpressed on RA synovial tissue lining and sublining macrophages and endothelial cells. Expression of IL-7 and its receptor was significantly elevated in RA synovial fluid and peripheral blood macrophages as well as RA fibroblasts, compared to normal cells. Toll-like receptor 4 ligation (with lipopolysaccharide) and tumor necrosis factor α (TNFα) stimulation modulated expression of IL-7 and IL-7R on RA macrophages and HMVECs. However, in RA fibroblasts, lipopolysaccharide and TNFα activation increased expression of IL-7R only. IL-7 also mediated RA pathogenesis by inducing production of potent proangiogenic factors from macrophages and endothelial cells. CONCLUSION: We have identified, for the first time, regulators of IL-7 and IL-7R expression in RA fibroblasts, RA peripheral blood in vitro-differentiated macrophages, and endothelial cells. Our results document a novel role of IL-7 in RA angiogenesis.

Local expression of interleukin-27 ameliorates collagen-induced arthritis.

OBJECTIVE: To determine the mechanism of action of interleukin-27 (IL-27) against rheumatoid arthritis (RA). METHODS: Adenovirus containing IL-27 transcript was constructed and was locally delivered into the ankles of mice with collagen-induced arthritis (CIA). Progression of arthritis was determined in treated and untreated mice by measuring ankle circumference and through histologic analysis. IL-17 and its downstream targets as well as cytokines promoting Th17 cell differentiation were quantified by enzyme-linked immunosorbent assay in CIA mouse ankles locally expressing adenoviral IL-27 as well as in control-treated mouse ankles. Ankles from both treatment groups were immunostained for neutrophil and monocyte migration (macrophages in the tissue). Finally, vascularization was quantified by histology and by determining ankle hemoglobin levels. RESULTS: Ectopic expression of IL-27 in CIA mice ameliorated inflammation, lining hypertrophy, and bone erosion as compared with control-treated CIA mice. Serum and joint levels of IL-17 were significantly reduced in the IL-27-treated group compared with the control-treated group. Two of the main cytokines that induce Th17 cell differentiation and IL-17 downstream target molecules were greatly down-regulated in CIA mouse ankles receiving forced expression of IL-27. The control mice had higher levels of vascularization and monocyte trafficking than did mice ectopically expressing IL-27. CONCLUSION: Our results suggest that increased levels of IL-27 relieve arthritis in CIA mouse ankles. This amelioration of arthritis involves a reduction in CIA mouse serum and joint levels of IL-17 and results in decreased IL-17-mediated monocyte recruitment and angiogenesis. Hence, the use of IL-27 may be a strategy for treatment of patients with RA.

Characterization of CCL19 and CCL21 in rheumatoid arthritis.

OBJECTIVE: To characterize the expression of CCL19 and CCL21 in rheumatoid arthritis (RA) synovial tissue (ST) and to examine their regulation and pathogenetic role in macrophages and RA ST fibroblasts. METHODS: Expression of CCL19 and CCL21 in RA and normal ST was demonstrated by immunohistochemistry analysis. CCL19 and CCL21 levels in synovial fluid (SF) from patients with osteoarthritis (OA), juvenile idiopathic arthritis, psoriatic arthritis (PsA), and RA were quantified by enzyme-linked immunosorbent assay (ELISA). Regulation of CCL19 and CCL21 expression in in vitro-differentiated RA peripheral blood macrophages as well as RA ST fibroblasts was determined by real-time reverse transcription-polymerase chain reaction. Proangiogenic factor production in CCL19- and CCL21-activated in vitro-differentiated peripheral blood macrophages and RA ST fibroblasts was examined by ELISA. RESULTS: CCL19 and CCL21 were elevated in RA ST compared to tissue from normal controls. Levels of CCL19 and CCL21 were greatly increased in RA and PsA SF versus OA SF. In RA macrophages and fibroblasts, expression of CCL19 was increased by stimulation with lipopolysaccharide, tumor necrosis factor α (TNFα), and interleukin-1ß (IL-1ß). However, CCL21 expression was modulated only by IL-1ß in RA fibroblasts, and by TNFα and RA SF in RA macrophages. CCL19 and CCL21 activation induced vascular endothelial growth factor and angiotensin I (Ang I) production in RA ST fibroblasts and secretion of IL-8 and Ang I from macrophages. CONCLUSION: The findings of the present study identify, for the first time, regulators of CCL19 and CCL21 in RA fibroblasts and in vitro-differentiated RA peripheral blood macrophages and demonstrate a novel role of CCL19/CCL21 in angiogenesis in RA.

IL-17-mediated monocyte migration occurs partially through CC chemokine ligand 2/monocyte chemoattractant protein-1 induction.

Rheumatoid arthritis (RA) is a chronic inflammatory disease that is mediated, in part, by proinflammatory factors produced by RA synovial tissue (ST) fibroblasts and macrophages, resulting in monocyte migration from the blood to the ST. To characterize the potential role of IL-17 in monocyte migration, RA synovial fibroblasts and macrophages were activated with IL-17 and examined for the expression of monocyte chemokines. The two potentially important monocyte chemoattractants identified were CCL20/MIP-3alpha and CCL2/MCP-1, which were significantly induced in RA synovial fibroblasts and macrophages. However, in vivo, only CCL2/MCP-1 was detectable following adenovirus IL-17 injection. We found that IL-17 induction of CCL2/MCP-1 was mediated by the PI3K, ERK, and JNK pathways in RA ST fibroblasts and by the PI3K and ERK pathways in macrophages. Further, we show that neutralization of CCL2/MCP-1 significantly reduced IL-17-mediated monocyte recruitment into the peritoneal cavity. We demonstrate that local expression of IL-17 in ankle joints was associated with significantly increased monocyte migration and CCL2/MCP-1 levels. Interestingly, we show that RA synovial fluids immunoneutralized for IL-17 and CCL2/MCP-1 have similar monocyte chemotaxis activity as those immunoneutralized for each factor alone. In short, CCL2/MCP-1 produced from cell types present in the RA joint, as well as in experimental arthritis, may be responsible, in part, for IL-17-induced monocyte migration; hence, these results suggest that CCL2/MCP-1 is a downstream target of IL-17 that may be important in RA.

IL-17 contributes to angiogenesis in rheumatoid arthritis.

Angiogenesis is an early and a critical event in the pathogenesis of rheumatoid arthritis (RA). Neovascularization is dependent on endothelial cell activation, migration and proliferation, and inhibition of angiogenesis may provide a novel therapeutic approach in RA. In this study, we document a novel role of IL-17 in mediating angiogenesis. Local expression of IL-17 in mouse ankles increases vascularity. We further demonstrate that IL-17 is angiogenic by showing its ability to promote blood vessel growth in Matrigel plugs in vivo. Additionally, IL-17, in concentrations present in the RA joint, induces human lung microvascular endothelial cell (HMVEC) migration mediated through the PI3K/AKT1 pathway. Furthermore, suppression of the PI3K pathway markedly reduces IL-17-induced tube formation. We also show that both IL-17-induced HMVEC chemotaxis and tube formation are mediated primarily through IL-17 receptor C. Neutralization of either IL-17 in RA synovial fluids or IL-17 receptor C on HMVECs significantly reduces the induction of HMVEC migration by RA synovial fluid. Finally, RA synovial fluid immunoneutralized with anti-IL-17 and antivascular endothelial growth factor does not reduce HMVEC migration beyond the effect detected by immunodepleting each factor alone. These observations identify a novel function for IL-17 as an angiogenic mediator in RA, supporting IL-17 as a therapeutic target in RA.