Tohru Akahoshi

Essential involvement of interleukin-8 (IL-8) in acute inflammation.

Neutrophil infiltration into inflammatory sites is one of the hallmarks of acute inflammation. Locally produced chemotactic factors are presumed to mediate the sequence of events leading to the infiltration at inflammatory sites. Interleukin‐8 (IL‐8), a novel leukocyte chemotactic activating cytokine (chemokine), is produced by various types of cells upon stimulation with inflammatory stimuli and exerts a variety of functions on leukocytes, particularly, neutrophils in vitro. However, no definitive evidence has been presented on its role in recruiting and activating neutrophils in the lesions of various types of inflammatory reactions. We administered a highly specific neutralizing antibody against IL‐8 in several types of acute inflammatory reactions, including lipopolysaccharide (LPS)‐induced dermatitis, LPS/IL‐1‐induced arthritis, lung reperfusion injury, and acute immune complex‐type glomerulonephritis. Anti‐IL‐8 treatment prevented neutrophil‐dependent tissue damage as well as neutrophil infiltration in these conditions. These results suggest that IL‐8 plays a causative role in acute inflammation by recruiting and activating neutrophils. J. Leukoc. Biol. 56: 559–564; 1994.

Expression of the chemokine superfamily in rheumatoid arthritis.

The infiltration of leucocytes into the Joint of rheumatoid arthritis (RA) is believed to be mediated by chemotactic factors released by activated cells. In this study, examination was made of the gene expression and production of the chemokine superfamily in RA patients by reverse transcriptase‐polymerase chain reaction (RT‐PCR) and immunoprecipitation. Cultured synovial fibroblasts were found capable of expressing and producing IL‐8, GRO, monocyte chemotactie and activating factor (MCAF), macrophage inflammatory protein‐la (MIP‐1α), MIP‐1β and RANTES in response to IL‐1α, The expression of IL‐8, GRO. MCAF, MIP‐1α, and MIP‐1β was clearly shown to increase in freshly isolated synovial fluid mononuclear cells (SFMC) of RA patients, in contrast to peripheral blood mononuclear cells (PBMC) of RA patients and normal subjects. The gene expression of RANTES appeared to be the same for RA SFMC. RA PBMC, and normal PBMC. Thus, the over‐expression of various chemokines may promote the recruitment of inflammatory cells into rheumatoid inflamed joints.

Selective recruitment of CCR6-expressing cells by increased production of MIP-3α in rheumatoid arthritis

Infiltration of various types of leucocytes has been shown to play a crucial role in the pathogenesis of rheumatoid arthritis (RA). Macrophage inflammatory protein‐3α (MIP‐3α) is a recently identified chemokine which is a selective chemoattractant for leucocytes such as memory T cells, naïve B cells and immature dendritic cells. In this study, we investigated the expression of MIP‐3α and its specific receptor CCR6 in the inflamed joints of patients with RA. Increased amounts of MIP‐3α were found by ELISA in synovial fluids (SF) of patients with RA. MIP‐3α was apparently detected in all synovial tissue specimens of RA patients (n = 6), but it could not be detected in that of osteoarthritis (OA) patients (n = 4). Expression of MIP‐3α was detected especially in the sublining layer, and infiltrating mononuclear cells in RA synovial tissue. Gene expression of MIP‐3α was also found in six out of 11 RA‐synovial fluid cells by RT‐PCR. Cultured synovial fibroblasts derived from either RA or OA patients were capable of producing MIP‐3α in response to IL‐1β and TNFα in vitro. Furthermore, expression of CCR6 was found in infiltrating mononuclear cells in the cellular clusters and around the vessels of RA synovial tissue. These findings indicate that increased production of MIP‐3α may contribute to the selective recruitment of CCR6‐expressing cells in RA.

Attenuation of monosodium urate crystal‐induced arthritis in rabbits by a neutralizing antibody against interleukin‐8

Accumulating evidence implicates interleukin‐8 (IL‐8) as an essential mediator in neutrophil‐mediated acute inflammation. Neutrophils have also been shown to have a crucial role in the pathogenesis of acute gouty arthritis. Thus, we investigate the pathophysiological role of IL‐8 in an experimental model of acute gout, monosodium urate (MSU) crystal‐induced arthritis in rabbits. The injection of MSU crystals into knee joints caused a marked swelling of joints. Concomitantly, the infiltration of leukocytes, mostly neutrophils, was observed in synovial membrane and synovial fluids. The injection of MSU crystals also induced an elevation in synovial fluid IL‐8 levels preceding neutrophil infiltration into synovial fluids, without an accompanying increase in plasma IL‐8 levels. Immunoreactive IL‐8 protein was detected in synovial lining cells at 12–24 h after the injection. IL‐8 protein was also observed in infiltrated leukocytes in synovium as early as 3–24 h after the injection. Finally, the intraarticular injection of a neutralizing anti‐IL‐8 antibody significantly attenuated the crystal‐induced joint swelling that occurred at 12 h, and neutrophil infiltration into arthritic joints at 12 and 24 h after the induction. These results provide evidence on the pathogenic roles of locally produced IL‐8 in MSU crystal‐induced gouty arthritis. J. Leukoc. Biol. 62: 444–449; 1997.

Interleukin 1 stimulates its own receptor expression on human fibroblasts through the endogenous production of prostaglandin(s).

The regulation of interleukin 1 receptor (IL 1R) expression on human dermal fibroblasts was investigated. On exposure to IL 1 for 3 h at 37 degrees C, the capacity of fibroblasts to bind 125I-labeled human recombinant IL 1 alpha (125I-IL 1 alpha) was reduced by 75%. The IL 1 binding capability of the fibroblasts was restored to control levels by 16 h after removal of unbound IL 1, and then increased to about twofold over that of control cells by 48 h. This later enhancement of IL 1 receptor expression after IL 1 treatment was abolished by indomethacin. Addition of exogenous (PGE1 and PGE2, also analogues of AMP, or forskolin increased the specific binding of 125I-IL 1 alpha to fibroblasts. Scatchard analysis indicated that PGE2 increased the number of IL 1R from approximately 1.6 X 10(3) to 5.4 X 10(3) per cell without change in the binding affinity. These data suggest that the later IL 1-induced up-regulation of IL 1R is mediated by IL 1 stimulation of endogenous prostaglandin production. The combination of PGE2 and prednisolone increased the number of IL 1R on fibroblasts in an additive manner.

Intervention of an inflammation amplifier, triggering receptor expressed on myeloid cells 1, for treatment of autoimmune arthritis

OBJECTIVE Triggering receptor expressed on myeloid cells 1 (TREM-1) is inducible on monocyte/macrophages and neutrophils and accelerates tissue destruction by propagating inflammatory responses in disease related to bacterial infections. Its blockade rescues the hosts in murine models of sepsis, to clear the bacteria without impairing the host defense. The aim of this study was to investigate the involvement of TREM-1 in an autoimmune, noninfectious disease. METHODS Synovial tissue specimens from the joints of patients with rheumatoid arthritis (RA) and the joints of mice with collagen-induced arthritis (CIA) were examined for TREM-1 expression, using flow cytometric analysis. Expression of TREM-1 on macrophages was induced by lipopolysaccharide, with or without a cyclooxygenase inhibitor. Rheumatoid synovial cells were stimulated with agonistic anti-TREM-1 antibodies. Recombinant adenovirus encoding the extracellular domain of TREM-1 fused with IgG-Fc (AxCATREM-1 Ig) or synthetic TREM-1 antagonistic peptides were injected to treat CIA, and the clinical manifestations of the antigen-specific T cell and B cell responses were evaluated. RESULTS TREM-1 was expressed on CD14+ cells in rheumatoid synovial tissue and synovial macrophages from mice with CIA. Unlike murine macrophages, human monocyte/macrophages did not depend on prostaglandin E2 for up-regulation of TREM-1. Agonistic anti-TREM-1 antibodies promoted tumor necrosis factor alpha production from rheumatoid synovial cells. Blockade of TREM-1 using AxCATREM-1 Ig and antagonistic peptides ameliorated CIA without affecting the serum levels of anti-type II collagen antibodies or the proliferative responses of splenocytes to type II collagen. CONCLUSION TREM-1 ligation contributes to the pathology of autoimmune arthritis. The results of this study implied that blockade of TREM-1 could be a new approach to rheumatic diseases that is safer than the presently available immunosuppressive treatments.

Experimental arthritis induced by continuous infusion of IL-8 into rabbit knee joints.

To determine the roles of IL‐8 in inflammatory synovitis. examination was made of the results of continuously injecting human recombinant IL‐8 into the knee joints of New Zealand white rabbits. Recombinant human lL‐8 was infused continuously into the joint cavity at 75 ng/h for 14 days by a polypropylene catheter connected to a mini‐osmotic pump implanted in each rabbit. Infiltration of inflammatory cells into joint cavity and histopathological changes in synovial tissue were examined at 7 and 14 days following the start of infusion. The continuous infusion of IL‐8 for 14days led to severe arthritis characterized by apparent erythema and joint pain, the accumulation of leucocytes, infiltration of mononuclear cells in synovial tissue, and marked hypervascularization in the synovial lining layer. IL‐8 may be a factor which can contribute to the inflammatory process of chronic arthritis by mediating leucocyte recruitment and hypervascularization in inflamed joints.

Recent advances in crystal-induced acute inflammation.

Purpose of reviewThe aim of this article is to highlight recent advances suggesting essential involvement of the innate immune system in crystal-induced acute inflammation. Recent findingsGout is a disease caused by the deposition of monosodium urate monohydrate crystals. Precise mechanisms underlying the initiation of monosodium urate monohydrate crystal-induced acute inflammation, however, are not known. Recent investigations provided novel evidence in the pathology of acute gout. Immunological study indicated that monosodium urate monohydrate crystals can act as a ‘danger signal’ that resembles exogenous adjuvants. Two laboratories have documented interesting findings that Toll-like receptor-mediated pathways or MyD88-dependent pathways are involved in monosodium urate monohydrate crystal-induced acute inflammation. Upregulation of the triggering receptor expressed on myeloid cells 1 (TREM-1) in phagocytes by the stimulation with monosodium urate monohydrate crystals has been demonstrated. Furthermore, pathological significance of NALP 3 inflammasome in gout has been shown. These findings provide a new concept that the innate immune system may play a crucial role on the triggering of crystal-induced acute inflammation. Spontaneous resolution is a characteristic feature of acute gout. Involvement of nuclear hormone receptors, peroxisome proliferator-activated receptor γ and liver X receptor α, during the termination of acute gout has been also shown. SummaryThese studies provided a new insight into the mechanisms underlying the initiation and the termination of monosodium urate monohydrate crystal-induced acute inflammation.

Lipopolysaccharide-Induced Up-Regulation of Triggering Receptor Expressed on Myeloid Cells-1 Expression on Macrophages Is Regulated by Endogenous Prostaglandin E2

Triggering receptor expressed on myeloid cells-1 (TREM-1) is a recently identified cell surface molecule that is expressed by neutrophils and monocytes. TREM-1 expression is modulated by various ligands for TLRs in vitro and in vivo. However, the influence of PGE2, a potential mediator of inflammation, on TREM-1 expression has not been elucidated. In this study, we examined the effects of PGE2 on LPS-induced TREM-1 expression by resident murine peritoneal macrophages (RPM) and human PBMC. PGE2 significantly induced murine TREM-1 (mTREM-1) expression by RPM. Up-regulation of TREM-1 expression was specific to PGE2 among arachidonic acid metabolites, while ligands for chemoattractant receptor-homologous molecule expressed on Th2 cells and the thomboxane-like prostanoid receptor failed to induce mTREM-1 expression. PGE2 also increased expression of the soluble form of TREM-1 by PBMC. LPS-induced TREM-1 expression was regulated by endogenous PGE2 especially in late phase (>2 h after stimulation), because cyclooxygenase-1 and -2 inhibitors abolished this effect at that points. A synthetic EP4 agonist and 8-Br-cAMP also enhanced mTREM-1 expression by RPM. Furthermore, protein kinase A, PI3K, and p38 MAPK inhibitors prevented PGE2-induced mTREM-1 expression by RPM. Activation of TREM-1 expressed on PGE2-pretreated PBMC by an agonistic TREM-1 mAb significantly enhanced the production of IL-8 and TNF-α. These findings indicate that LPS-induced TREM-1 expression on macrophages is mediated, at least partly, by endogenous PGE2 followed by EP4 and cAMP, protein kinase A, p38 MAPK, and PI3K-mediated signaling. Regulation of TREM-1 and the soluble form of TREM-1 expression by PGE2 may modulate the inflammatory response to microbial pathogens.

17β-Estradiol Induces IL-1α Gene Expression in Rheumatoid Fibroblast-Like Synovial Cells through Estrogen Receptor α (ERα) and Augmentation of Transcriptional Activity of Sp1 by Dissociating Histone Deacetylase 2 from ERα

Rheumatoid arthritis (RA) occurs four times more frequently in women than in men, although the mechanistic basis of the gender difference is unknown. RA is characterized by the overproliferation of synoviocytes producing proinflammatory cytokines such as IL-1, implicated in the pathogenesis of the disease. In this study we examined whether 17β-estradiol (E2) induced IL-1α mRNA expression in the rheumatoid fibroblast-like cell line MH7A, as well as in primary synovial cells from RA patients, and investigated the underlying molecular mechanisms. E2 induced IL-1α mRNA expression in both cell types in an estrogen receptor-dependent manner. In MH7A cells ERα but not ERβ mediated the effects of E2. Deletion and mutation analysis revealed that a GC-rich region within the IL-1α gene promoter was responsible for the response to E2. EMSAs showed that Sp1 and Sp3 bound to the GC-rich region and that the transcriptional activity of Sp1 was up-regulated by the treatment with E2. Sp1 and ERα interacted physically regardless of the presence of E2. Physical interaction was also observed between ERα and histone deacetylase 2 (HDAC2), and E2 induced the dissociation of HDAC2 from ERα. These results suggest that E2 induces the dissociation of corepressor HDAC2 from ERα, which leads to the augmentation of Sp1 transcriptional activity through the GC-rich region within the IL-1α gene promoter.