Development of a monoclonal antibody-based enzyme-linked immunoabsorbent assay for the binding of gp130 to the IL-6/IL-6R complex and its competitive inhibition

Triptolide Inhibits Expression of Inflammatory Cytokines and Proliferation of Fibroblast-like Synoviocytes Induced by IL-6/sIL-6R-Mediated JAK2/STAT3 Signaling Pathway

Triptolide, a component of the Chinese herb Tripterygium wilfordii Hook F, has been proved to be effective in the treatment of rheumatoid arthritis (RA). However, its underlying mechanisms on RA have not yet been well established. We observed the inhibitory effect of triptolide on the expression of inflammatory cytokines and proliferation of fibroblast-like synoviocytes (FLS) induced by the complex of interleukin-6 (IL-6) and the soluble form of the IL-6 receptor (sIL-6R). Furthermore, to clarify the underlying mechanisms, we treated FLS with the Janus-activated kinase 2 (JAK2) inhibitor/signal transducer and activator of transcription 3 (STAT3) activation blocker AZD1480. In this study, immunohistochemical staining was used to identify vimentin (+) and CD68 (-) in FLS. The FLS proliferation was measured by cell proliferation assay, and the cell cycles were analyzed by flow cytometry. Furthermore, ELISA was used to detect the expression of the inflammatory factors in culture solution. The expression levels of p-JAK2, JAK2, p-STAT3 and STAT3 were investigated through Western blotting analysis. The results showed that IL-6/sIL-6R significantly increased the cell proliferation and expression of inflammatory cytokines, including IL-6, interleukin-1β (IL-1β) and vascular endothelial growth factor (VEGF). Triptolide or AZD1480 inhibited the cell proliferation and inflammatory cytokine expression in IL-6/sIL-6R-stimulated FLS by suppressing JAK2/STAT3. The study suggested that the physiological effects of triptolide on RA were due to its contribution to the inhibition of the inflammatory cytokine expression and FLS proliferation by suppressing the JAK2/STAT3 signaling pathway. It may provide an innovative insight into the effect of triptolide in preventing RA pathogenesis.

The Role of IL-6RA in UHMWPE Promotes Proliferation in Fibro-Like Synovial Cells

UHMWPE granule could induce macrophages and inflammatory responses in interfacial tissues, which eliminated the wear debris of UHMWPE component and further induced dissolution of the surrounding bone, leading aseptic loosening. However, the mechanism of synovial cells, especially fibroblast-like synovial (FLS) cells response to UHMWPE, remains unknown. Herein we choose FLS cells as research object. Vimentin (+) CD68 (-) was identified by flow cytometry and immunofluorescent staining assay, and the cells were identified as FLS cells, which was consistent with the experimental requirements. The inhibitory evaluation showed that UHMWPE could significantly promote the proliferation and inhibit apoptosis of FLS cells in dose- and time-dependent manners and increase the levels of proinflammatory cytokines, including IL-6, IL-1β, TNF-α, PGE2, MMP2, and LOX. UHMWPE also can induce the expression of mIL-6R protein in FLS cells and further investigate the relationship between apoptosis and inflammation. Interestingly enough, when we added the interleukin-6 receptor antagonist (IL-6RA), the expression levels of proapoptosis-related proteins increased; in other words, UHMWPE-induced antiapoptosis diminished by IL-6RA (50 μg/ml). Taken together, these findings clearly demonstrated that UHMWPE promote growth in FLS cells through upregulating inflammatory factors to produce antiapoptotic effect.

Cellular and Oxidative Mechanisms Associated with Interleukin-6 Signaling in the Vasculature

Reactive oxygen species, particularly superoxide, promote endothelial dysfunction and alterations in vascular structure. It is increasingly recognized that inflammatory cytokines, such as interleukin-6 (IL-6), contribute to endothelial dysfunction and vascular hypertrophy and fibrosis. IL-6 is increased in a number of cardiovascular diseases, including hypertension. IL-6 is also associated with a higher incidence of future cardiovascular events and all-cause mortality. Both immune and vascular cells produce IL-6 in response to a number of stimuli, such as angiotensin II. The vasculature is responsive to IL-6 produced from vascular and non-vascular sources via classical IL-6 signaling involving a membrane-bound IL-6 receptor (IL-6R) and membrane-bound gp130 via Jak/STAT as well as SHP2-dependent signaling pathways. IL-6 signaling is unique because it can also occur via a soluble IL-6 receptor (sIL-6R) which allows for IL-6 signaling in tissues that do not normally express IL-6R through a process referred to as IL-6 trans-signaling. IL-6 signaling mediates a vast array of effects in the vascular wall, including endothelial activation, vascular permeability, immune cell recruitment, endothelial dysfunction, as well as vascular hypertrophy and fibrosis. Many of the effects of IL-6 on vascular function and structure are representative of loss or reductions in nitric oxide (NO) bioavailability. IL-6 has direct effects on endothelial nitric oxide synthase activity and expression as well as increasing vascular superoxide, which rapidly inactivates NO thereby limiting NO bioavailability. The goal of this review is to highlight both the cellular and oxidative mechanisms associated with IL-6-signaling in the vascular wall in general, in hypertension, and in response to angiotensin II.

Response of plasma IL-6 and its soluble receptors during submaximal exercise to fatigue in sedentary middle-aged men

The pleiotropic cytokine interleukin-6 (IL-6) has been demonstrated to increase during exercise. Little is known regarding the response of the soluble IL-6 receptors (sIL-6R and sgp130) during such exercise. The aim of the current study was to investigate the response of plasma IL-6, sIL-6R and sgp130 during fatiguing submaximal exercise in humans. Twelve participants underwent an incremental exercise test to exhaustion and one week later performed a submaximal exercise bout (96 +/- 6% lactate threshold) to volitional exhaustion. Blood samples taken at rest and immediately post exercise were analyzed for IL-6, sIL-6R and sgp130. IL-6 increased (P < 0.01) by 8.4 +/- 8.9 pg ml(-1) (75.7%) during the exercise period. sIL-6R and sgp130 also increased (P < 0.05) by 2.7 +/- 3.9 ng ml(-1) (9.6%) and 37.7 +/- 55.6 ng ml(-1) (9.6%), respectively. The current study is the first investigation to demonstrate that alongside IL-6, acute exercise stress results in an increase in both sIL-6R and sgp130.

The IL-6/sIL-6R complex as a novel target for therapeutic approaches

IL-6 plays a pivotal role in immune responses and certain oncologic conditions. The intense investigation of its biological activity and function led to the discovery of two different IL-6-driven signalling pathways. Binding to the membrane-bound IL-6 receptor (mIL-6R, CD126) causes the recruitment of two gp130 co-receptor molecules (CD130) and the activation of intracellular signalling cascades via gp130. Although this classical pathway is mainly limited to hepatocytes, neutrophils, monocytes/macrophages and certain other leukocyte populations, which express IL-6R on their surface, an alternative mechanism has also been described. Proteolytic cleavage of the mIL-6R protein or translation from alternatively spliced mRNA leads to the generation of a soluble form of the IL-6R (sIL-6R), which is likewise able to bind to IL-6. The resulting IL-6/sIL-6R complex is also capable of binding to gp130 and inducing intracellular signalling. Through this so-called 'trans-signalling' mechanism, IL-6 is able to stimulate cells that lack an endogenous mIL-6R. High levels of IL-6 and sIL-6R have been reported in several chronic inflammatory and autoimmune diseases as well as in cancer. Preclinical animal disease models have provided strong evidence that specific blockade of IL-6-regulated signalling pathways represents a promising approach for the therapy of these diseases. An optimised variant of the recently described fusion protein sgp30Fc is now heading towards its clinical evaluation.

Abrogation of viral interleukin-6 (vIL-6)-induced signaling by intracellular retention and neutralization of vIL-6 with an anti-vIL-6 single-chain antibody selected by phage display

Human herpesvirus 8 (HHV-8) encodes several putative oncogenes, which are homologues to cellular host genes known to function in cell cycle regulation, control of apoptosis, and cytokine signaling. Viral interleukin (vIL-6) is believed to play an important role in the pathogenesis of Kaposi's sarcoma as well as primary effusion lymphoma and multicentric Castleman's disease. Therefore, vIL-6 is a promising target for novel therapies directed against HHV-8-associated diseases. By phage display screening of human synthetic antibody libraries, we have selected a specific recombinant antibody, called monoclonal anti-vIL-6 (MAV), binding to vIL-6. The epitope recognized by MAV was localized on the top of the D helix of the vIL-6 protein, which is a part of receptor binding site III. Consequently, MAV specifically inhibits vIL-6-mediated growth of the primary effusion lymphoma-derived cell line BCBL-1 and blocks STAT3 phosphorylation in the human hepatoma cell line HepG2. Since it was previously found that vIL-6 can also induce signals from within the cell, presumably within the endoplasmic reticulum, we fused the recombinant antibody MAV with the endoplasmic retention sequence KDEL (MAV-KDEL). As a result, COS-7 cells expressing MAV-KDEL and synthesizing vIL-6 ceased to secrete the cytokine. Moreover, we observed that vIL-6 that was bound to MAV-KDEL and retained in the endoplasmic reticulum did not induce STAT3 phosphorylation in HepG2 cells. We conclude that the activity of the intracellularly retained vIL-6 protein is neutralized by MAV-KDEL. Our results might represent a novel therapeutic strategy to neutralize virally encoded growth factors or oncogenes.