Nicholas Topley

IL-6 and Its Soluble Receptor Orchestrate a Temporal Switch in the Pattern of Leukocyte Recruitment Seen during Acute Inflammation

During acute inflammation, leukocyte recruitment is characterized by an initial infiltration of neutrophils, which are later replaced by a more sustained population of mononuclear cells. Based on both clinical and experimental evidence, we present a role for IL-6 and its soluble receptor (sIL-6R) in controlling this pattern of leukocyte recruitment during peritoneal inflammation. Liberation of sIL-6R from the initial neutrophil infiltrate acts as a regulator of CXC and CC chemokine expression, which contributes to a suppression of neutrophil recruitment and the concurrent attraction of mononuclear leukocytes. Soluble IL-6R-mediated signaling is therefore an important intermediary in the resolution of inflammation and supports transition between the early predominantly neutrophilic stage of an infection and the more sustained mononuclear cell influx.

The soluble interleukin 6 receptor: mechanisms of production and implications in disease

Interleukin 6 (IL‐6) performs a prominent role during disease and has been described as both a pro‐ and anti‐inflammatory cytokine. A key feature in the regulation of IL‐6 responses has been the identification of a soluble interleukin 6 receptor (sIL‐6R), which forms a ligand‐receptor complex with IL‐6 that is capable of stimulating a variety of cellular responses including proliferation, differentiation and activation of inflammatory processes. Elevated sIL‐6R levels have been documented in numerous clinical conditions indicating that its production is coordinated as part of a disease response. Thus, sIL‐6R has the potential to regulate both local and systemic IL‐6‐mediated events. This review will outline the central role of sIL‐6R in the coordination of IL‐6 responses. Details relating to the mechanisms of sIL‐6R production will be provided, while the potential significance of sIL‐6R during the development of clinical conditions will be emphasized. We want to convey, therefore, that when thinking about the inflammatory capability of IL‐6, it is essential to consider not only the action of IL‐6 itself, but also the effect sIL‐6R may have on cellular processes.—Jones, S. A., Horiuchi, S., Topley, M. Yamamoto, N., Fuller, G. M. The soluble interleukin 6 receptor: mechanisms of production and implications in disease. FASEB J. 15, 43–58 (2001)

Differential Regulation of Neutrophil-Activating Chemokines by IL-6 and Its Soluble Receptor Isoforms

Interleukin-6 signaling via its soluble receptor (sIL-6R) differentially regulates inflammatory chemokine expression and leukocyte apoptosis to coordinate transition from neutrophil to mononuclear cell infiltration. sIL-6R activities may, however, be influenced in vivo by the occurrence of two sIL-6R isoforms that are released as a consequence of differential mRNA splicing (DS) or proteolytic cleavage (PC) of the cognate IL-6R (termed DS- and PC-sIL-6R). Using human peritoneal mesothelial cells and a murine model of peritoneal inflammation, studies described in this work have compared the ability of both isoforms to regulate neutrophil recruitment. In this respect, DS- and PC-sIL-6R were comparable in their activities; however, these studies emphasized that IL-6 trans signaling differentially controls neutrophil-activating CXC chemokine expression. In vitro, stimulation of mesothelial cells with IL-6 in combination with either DS-sIL-6R or PC-sIL-6R showed no induction of CXC chemokine ligand (CXCL)1 (GROα) and CXCL8 (IL-8), whereas both isoforms enhanced CXCL5 (ENA-78) and CXCL6 (granulocyte chemotactic protein-2) expression. Moreover, when complexed with IL-6, both isoforms specifically inhibited the IL-1β-induced secretion of CXCL8. These findings were paralleled in vivo, in which induction of peritoneal inflammation in IL-6-deficient (IL-6−/−) mice resulted in enhanced keratinocyte-derived chemokine and macrophage-inflammatory protein-2 (the murine equivalent of CXCL1 and CXCL8) levels, but reduced LPS-induced CXC chemokine (the murine equivalent of CXCL5) expression. Reconstitution of IL-6 signaling in IL-6−/− mice with IL-6 and its soluble receptor isoforms corrected this chemokine imbalance and suppressed overall neutrophil infiltration. These data confirm that sIL-6R-mediated signaling primarily limits neutrophil influx; however, induction of CXCL5 and CXCL6 may regulate other neutrophil responses.

Differential regulation of chemokine production in human peritoneal mesothelial cells: IFN-gamma controls neutrophil migration across the mesothelium in vitro and in vivo.

Leukocyte recruitment into the infected peritoneal cavity consists of an early, predominant polymorphonuclear leukocyte (PMN) influx and subsequent, prolonged mononuclear cell migration phase. Although chemokine secretion by resident peritoneal cells plays a primary role in mediating this migration, the mechanisms involved in controlling the switch in phenotype of cell infiltrate remain unclear. The present study investigates a potential role for the Th1-type cytokine IFN-γ in the process of leukocyte recruitment into the peritoneal cavity. Stimulation of cultured human peritoneal mesothelial cells with IFN-γ (1–100 U/ml) alone or in combination with IL-1β (100 pg/ml) or TNF-α (1000 pg/ml) resulted in significant up-regulation of monocyte chemoattractant protein-1 and RANTES protein secretion. In contrast, IFN-γ inhibited basal and IL-1β-, and TNF-α-induced production of IL-8. The modulating effects of IFN-γ on chemokine production occurred at the level of gene expression, and the degree of regulation observed was dependent on the doses of IL-1β and TNF-α used. Analysis of the functional effects of IFN-γ on IL-1β-induced transmesothelial PMN migration with an in vitro human transmigration system and an in vivo murine model of peritoneal inflammation demonstrated that IFN-γ was able to down-regulate PMN migration induced by optimal doses of IL-1β. These effects were mediated in vivo via down-regulation of CXC chemokine synthesis. These findings suggest that IFN-γ may play a role in controlling the phenotype of infiltrating leukocyte during the course of an inflammatory response, in part via regulation of resident cell chemokine synthesis.

Secretion of Oncostatin M by Infiltrating Neutrophils: Regulation of IL-6 and Chemokine Expression in Human Mesothelial Cells

Recently, we identified that regulation of leukocyte recruitment by IL-6 requires shedding of the IL-6R from infiltrating neutrophils. In this study, experiments have examined whether other IL-6-related cytokines possess similar properties. Levels of oncostatin M (OSM) and leukemia inhibitory factor were analyzed in patients with overt bacterial peritonitis during the first 5 days of infection. Although no change in leukemia inhibitory factor was observed throughout the duration of infection, OSM was significantly elevated on day 1 and rapidly returned to baseline by days 2–3. The source of OSM was identified as the infiltrating neutrophils, and OSM levels correlated both with leukocyte numbers and i.p. soluble IL-6R (sIL-6R) levels. FACS analysis revealed that OSM receptor β expression was restricted to human peritoneal mesothelial cells. Stimulation of human peritoneal mesothelial cells with OSM induced phosphorylation of gp130 and OSM receptor β, which was accompanied by activation of STAT3 and secretion of CC chemokine ligand 2/monocyte chemoattractant protein-1 and IL-6. Although OSM itself did not modulate CXC chemokine ligand 8/IL-8 release, it effectively suppressed IL-1β-mediated expression of this neutrophil-activating CXC chemokine. Moreover, OSM synergistically blocked IL-1β-induced CXC chemokine ligand 8 secretion in combination with the IL-6/sIL-6R complex. Thus suggesting that OSM and sIL-6R release from infiltrating neutrophils may contribute to the temporal switch between neutrophil influx and mononuclear cell recruitment seen during acute inflammation.

Biocompatibility of peritoneal dialysis fluids.

The various studies cited here clearly demonstrate that peritoneal dialysis solutions reduce the viability of leukocytes and mesothelial cells, and compromise their capacity for phagocytosis, bacterial killing, and production of cytokines. The inhibitory capacity of the CAPD fluids appears to be related to their low pH, high osmolality, and high glucose concentrations. In some of the experimental settings, lactate was also identified as suppressive factor, but only at low pH. In clinical CAPD, the pH is rapidly buffered following the dialysate instillation, and the high glucose concentrations and osmolality are also partially equilibrated. Nevertheless, for a certain period of time following the dialysate exchange, peritoneal host defense systems are exposed to an unphysiological environment known to compromise important immune-cell functions. Moreover, certain leukocyte properties, such as the production of cytokines, are impaired even following longer i.p. dwell periods. Thus conventional CAPD solutions induce an at least transitory impairment of peritoneal host defense, reflecting a bioincompatibility of the commercial CAPD fluids and underscoring the need for developing fluids with a more physiological formulation.

Inhibition of Cytokine Synthesis by Peritoneal Dialysate Persists throughout the CAPD Cycle

The current study focused on the effect of continuous ambulatory peritoneal dialysis (CAPD) dialysate obtained following different intraperitoneal dwell periods on the release of interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF alpha) from mononuclear leukocytes (PBMC). Aliquots of 5 x 10(6)/ml healthy peripheral PBMC were exposed to fresh or spent CAPD dialysate (10-240 min of intra-peritoneal dwell) and stimulated with Escherichia coli endotoxin (10 micrograms/ml, 2h). IL-6 and TNF alpha in cell supernatants were determined by specific enzyme immunoassays. Control PBMC in physiological buffer released 361 +/- 70 pg/ml IL-6 and 717 +/- 147 pg/ml TNF alpha (mean +/- SEM, n = 8), whereas exposure to fresh dialysis fluids severely suppressed cytokine release from PBMC (less than 30 pg/ml IL-6 and less than 15 pg/ml TNF alpha). A significant inhibition of IL-6 and TNF alpha release was also observed in PBMC exposed to spent dialysate. The inhibitory capacity of the spent fluids was pronounced with increasing intra-peritoneal dwell time (10 min: 183 +/- 45 pg/ml IL-6 and 538 +/- 109 pg/ml TNF alpha; 240 min: 26 +/- 5 pg/ml IL-6 and 105 +/- 30 pg/ml TNF alpha; mean +/- SEM, n = 16). These data indicate that the impairment of cell responsiveness following exposure of PBMC to peritoneal dialysate is not restricted to the unused fluids, but is also observed following intra-peritoneal equilibration. Moreover, our findings suggest the presence of cytokine inhibitory factors in the peritoneal dialysate of CAPD patients which appear to accumulate in the peritoneal effluent during the CAPD cycle.

The human hyaluronan synthase genes: genomic structures, proximal promoters and polymorphic microsatellite markers.

The glycosaminoglycan (GAG) hyaluronan (HA) is a key component of the vertebrate extracellular matrix (ECM) and is synthesised by the HA synthase (HAS) enzymes HAS1, HAS2 and HAS3 at the plasma membrane. Accumulating evidence emphasises the relevance of HA metabolism in an increasing number of processes of clinical interest including renal fibrosis and peritoneal mesothelial wound healing. In the present study, the genomic sequences and organisation of the genes encoding the human HAS isoforms were deduced, in silico, from reference cDNA and genomic sequence data. These data were confirmed in vitro by sequencing of PCR-amplified HAS exons and flanking genomic sequences, comparison with sequence data for the corresponding murine Has orthologues, rapid amplification of 5 cDNA ends analysis and luciferase reporter assays on putative proximal promoter sequences. The HAS1 gene comprised five exons, with the translation start site situated 9bp from the 3 end of exon 1. In contrast, the genomic structures for HAS2 and both HAS3 variants spanned four exons, exon 1 forming a discrete 5-untranslated region (5-UTR) and the translation start site lying at nucleotide 1 of exon 2. Dinucleotide microsatellite loci were identified in intron 1 of HAS1 and HAS2, and immediately upstream of the HAS3 gene and their utility as linkage markers demonstrated in genomic DNA (gDNA) studies. We thus present a comprehensive resource for mutation detection screening of all HAS exons and/or linkage analysis of each HAS gene in a variety of disorders for which they are attractive candidates.

The suppression of rat collagen-induced arthritis and inhibition of macrophage derived mediator release by liposomal methotrexate formulations

Abstract.Objective and Design: This study was designed to determine whether liposomes are suitable vehicles for the delivery of methotrexate (MTX-γ-DMPE) for arthritis therapy.¶Material or Subjects: Liposomal formulations containing either egg lecithin (EPC), cholesterol (CHOL) and phosphatidic acid (PA) (MTX-EPC) or distearoylphosphatidylcholine (DSPC), CHOL and distearoylphosphatidylethanolamine conjugated to polyethyleneglycol (PEG) (MTX-PEG) were employed. Rat peritoneal macrophages (rPMφ) were used to test the mechanism of action of these liposomes in vitro, whilst, the rat collagen-induced arthritis (CIA) model was used to evaluate the in vivo efficacy of MTX-EPC and MTX-PEG.¶Treatment: In vitro, rPMφ were incubated with liposomal MTX concentrations ranging from 0 to 15 μg/well. In vivo, rats were given 4 daily intravenous injections of liposomal MTX (2.5 mg/Kg).¶Methods: IL-1β and prostaglandin-E2 (PGE2) release from rPMφ were quantified by immunoradiometric assay. Arthritis progression, in vivo, was measured by serial clinical score and hind paw diameter measurements.¶Results: MTX-EPC and MTX-PEG respectively (15 μg of MTX and 0.15 mg of lipid) were powerful inhibitors of both IL-1β (77 ± 2.3%; 79 ± 4.0%) and PGE2 (75.5 ± 4.9%; 68.5 ± 2.3%) release (mean ± SEM % inhibition) from lipopolysaccaride stimulated rPMφ. In vivo, only MTX-EPC exerted an anti-inflammatory effect, clinical score (p < 0.001) and paw diameter (p < 0.001) measurements being significantly lower than in control rats, after 2 days treatment.¶Conclusions: MTX-EPC and MTX-PEG are potent inhibitors of pro-inflammatory mediators in vitro, but liposomes with long circulation times do not appear to have therapeutic potential for treating arthritis in vivo.

Prostaglandin and tumor necrosis factor secretion by peritoneal macrophages isolated from normal and arthritic rats treated with liposomal methotrexate

The effect of a novel liposomal preparation containing a phospholipid conjugate of methotrexate (MTX-LIPO) upon macrophage mediator release was investigated in normal and arthritic rats ex vivo. Peritoneal macrophages isolated from MTX-LIPO-treated arthritic rats and stimulated with lipopolysaccharide produced significantly less tumor necrosis factor (TNF) and prostaglandin (PGE2) than did macrophages isolated from saline-treated controls. In the same experimental system, free methotrexate only inhibited prostaglandin release, but it was more potent than MTX-LIPO in this respect. Additional studies are presently underway to investigate the effect of MTX-LIPO and MTX treatment upon the lipopolysaccharide-induced rise in plasma levels of various proinflammatory mediators in vivo. Haematopoietic toxicity was demonstrated in blood isolated from rats treated with free MTX, and this was as characterized by a significant reduction in reticulocyte count compared with MTX-LIPO and saline-treated rats.