Expression, purification and structural analysis of human IL-18 binding protein: a potent therapeutic molecule for allergy

Interleukin‑18 binding protein: Biological properties and roles in human and animal immune regulation (Review)

IL-18 binding protein (IL-18BP) is a natural regulatory molecule of the proinflammatory cytokine IL-18. It can regulate activity of IL-18 by high affinity binding. The present review aimed to highlight developments, characteristics and functions of IL-18BP. IL-18BP serves biological and anti-pathological roles in treating disease. In humans, it modulates progression of a number of chronic diseases, such as adult-onset Still's disease. The present review summarizes molecular structure, role of IL-18BP in disease and interaction with other proteins in important pathological processes.

Production of recombinant human long-acting IL-18 binding protein: inhibitory effect on ulcerative colitis in mice

Interleukin-18 binding protein (IL-18BP) is a natural IL-18 inhibitor in vivo, which can effectively neutralize IL-18 and inhibit the inflammatory signaling pathway induced by IL-18, thus playing an anti-inflammatory role. Traditional production methods primarily rely on eukaryotic animal cell expression systems, which often entail complex processes, lower yields, and increase production costs. In this study, we present a novel approach for expressing IL-18BP fusion protein using the Escherichia coli (E. coli) system. The N-terminal segment of IL-18BP was fused with the small ubiquitin-related modifier (SUMO) tag, enabling soluble expression, while the C-terminal segment was fused with the human IgG1 Fc fragment to prolong its in vivo lifespan. Through screening, we obtained a high-expression engineering strain from a single colony and developed optimized protocols for fermentation and purification of the recombinant SUMO-IL-18BP-Fc protein. The SUMO tag was subsequently cleaved using SUMO protease, and the purified recombinant human IL-18BP-Fc (rhIL-18BP-Fc) exhibited a purity exceeding 90% with a yield of 1 g per liter of bacterial solution. The biological activities and underlying mechanisms of rhIL-18BP-Fc were evaluated using cell lines and a mouse model. Our results demonstrated that rhIL-18BP-Fc effectively inhibited IL-18-stimulated IFN-γ production in KG-1a cells in vitro and ameliorated DSS-induced ulcerative colitis in mice. In conclusion, we successfully employed the SUMO fusion system to achieve high-level production, soluble expression, and prolonged activity of rhIL-18BP-Fc in E. coli. These findings lay the groundwork for future large-scale industrial production and pharmaceutical development of rhIL-18BP-Fc protein. KEY POINTS: • Effective expression, fermentation, and purification of bioactive rhIL-18BP-Fc protein in E. coli. • The rhIL-18BP-Fc protein has a great potential for the therapy of ulcerative colitis by inhibiting the expression of inflammatory factors.

Interleukin-18 and IL-18BP in inflammatory dermatological diseases

Interleukin (IL)-18, an interferon-γ inducer, belongs to the IL-1 family of pleiotropic pro-inflammatory factors, and IL-18 binding protein (IL-18BP) is a native antagonist of IL-18 in vivo, regulating its activity. Moreover, IL-18 exerts an influential function in host innate and adaptive immunity, and IL-18BP has elevated levels of interferon-γ in diverse cells, suggesting that IL-18BP is a negative feedback inhibitor of IL-18-mediated immunity. Similar to IL-1β, the IL-18 cytokine is produced as an indolent precursor that requires further processing into an active cytokine by caspase-1 and mediating downstream signaling pathways through MyD88. IL-18 has been implicated to play a role in psoriasis, atopic dermatitis, rosacea, and bullous pemphigoid in human inflammatory skin diseases. Currently, IL-18BP is less explored in treating inflammatory skin diseases, while IL-18BP is being tested in clinical trials for other diseases. Thereby, IL-18BP is a prospective therapeutic target.

Insight into the structures of Interleukin-18 systems

Structure-based molecular designs play a critical role in the context of next generation drug development. Besides their fundamental scientific aspects, the findings established in this approach have significant implications in the expansions of target-based therapies and vaccines. Interleukin-18 (IL-18), also known as interferon gamma (IFN-γ) inducing factor, is a pro-inflammatory cytokine. The IL-18 binds first to the IL-18α receptor and forms a lower affinity complex. Upon binding with IL-18β a hetero-trimeric complex with higher affinity is formed that initiates the signal transduction process. The present study, including structural and molecular dynamics simulations, takes a close look at the structural stabilities of IL-18 and IL-18 receptor-bound ligand structures as functions of time. The results help to identify the conformational changes of the ligand due to receptor binding, as well as the structural orders of the apo and holo IL-18 protein complexes.

Cloning and characterization of giant panda (Ailuropoda melanoleuca) IL-18 binding protein

The giant panda (Ailuropoda melanoleuca) is an endangered species. Interleukin-18 (IL-18) plays an important role in the innate and adaptive immune responses by inducing IFN-γ. IL-18 has been implicated in the pathogenesis of various diseases. IL-18 binding protein (IL-18BP) is an intrinsic inhibitor of IL-18 that possesses higher affinity to IL-18. In this study, we cloned and characterized IL-18BP in giant panda (AmIL-18BP) from the spleen. The amino acid sequence of giant panda IL-18BP ORF shared about 65% identities with other species. To evaluate the effects of AmIL-18BP on the immune responses, we expressed the recombinant AmIL-18BP in Escherichia coli BL21 (DE3).The fusing protein PET-AmIL-18BP was purified by nickel affinity column chromatography. The biological function of purified PET-AmIL-18BP was determined on mice splenocyte by qRT-PCR. The results showed that AmIL-18BP was functional and could significantly reduce IFN-γ production in murine splenocytes. These results will facilitate the study of protecting giant panda on etiology and immunology.

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We cloned and characterized IL-18BP in giant panda (AmIL-18BP) from the spleen.

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We expressed and purified the recombinant AmIL-18BP in E. coli BL21 (DE3).

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AmIL-18BP could significantly reduce IFN-γ production in murine splenocytes.

Interleukin 18--binding protein ameliorates liver ischemia--reperfusion injury

BACKGROUND

The aim of this study was to investigate the possible protective effect of interleukin 18-binding protein (IL-18BP) on ischemia-reperfusion (I/R)-induced liver injury in experimental rat models. Liver is one of the most affected organs from I/R process. IL-18 is an important proinflammatory cytokine, which may induce some events such as production of reactive oxygen substances and release of various cytokines. IL-18BP acts as an inhibitor of IL-18. The relationship between IL-18 and IL-18BP has an important place in inflammatory process.

MATERIALS AND METHODS

Rats were equally divided into three groups as follows: sham: Hepatic pedicle dissection was done, but hepatic pedicle clamping was not used. I/R: Sixty minutes of ischemia and 2 h of reperfusion were applied. IR + IL-18BP: Recombinant human IL-18BP (100 μg/kg) was administered 30 min before the surgery. Hepatic pedicle was clamped during 60 min of ischemia and 2 h of reperfusion was achieved.

RESULTS

Liver enzyme levels were significantly lower in the IR + IL-18BP group, when compared with the I/R group. Serum and tissue levels of tumor necrosis factor-α, IL-6, and IL-18 were considerably lower in the IR + IL-18BP group, when compared with the I/R group, but hepatic interferon-γ and IL1β levels were not significant. Serum oxidative stress index level was significantly higher in the I/R group, when compared with the IR + IL-18BP group. In immunostaining, it was observed that pathologic changes were lower in IR + IL-18BP group than the I/R group.

CONCLUSIONS

IL-18BP exhibited anti-inflammatory, antioxidant, and protective effects in I/R-mediated hepatic injury via regulating some liver enzyme activities and cytokine levels. Additionally, these effects have been verified by histomorphologic examination and oxidative stress markers.

Structural biology of the IL-1 superfamily: key cytokines in the regulation of immune and inflammatory responses

Interleukin-1 superfamily of cytokines (IL-1, IL-18, IL-33) play key roles in inflammation and regulating immunity. The mechanisms of agonism and antagonism in the IL-1 superfamily have been pursued by structural biologists for nearly 20 years. New insights into these mechanisms were recently provided by the crystal structures of the ternary complexes of IL-1β and its receptors. We will review here the structural biology related to receptor recognition by IL-1 superfamily cytokines and the regulation of its cytokine activities by antagonists.

IL-18 provided in dying bacterial-infected macrophages induces IFN-γ production in functional T-cell hybridoma B6HO3 through cell conjugates

We have previously reported that the co-culture of functional T-cell hybridoma B6HO3 with dying J774 macrophage cells infected with Listeria monocytogenes (LM) results in the production of IFN-γ by B6HO3 cells. Here, we explore the mechanism underlying this phenomenon. We found that IFN-γ production was dependent on IL-18, but that the dying LM-infected macrophages produced no more than 100 pg/ml of IL-18, much less than the amount of IL-18 required for stimulating B6HO3 cells to produce IFN-γ. Furthermore, IL-18 binding protein added to the co-culture was unable to easily gain access to IL-18 for neutralisation. B6HO3 cells formed cell conjugates with J774 macrophages, and IFN-γ-producing B6HO3 cells were spatially and temporally associated with LM-infected macrophage cell death that exhibited neither pyroptosis nor pyronecrosis. These results suggest that the IL-18 produced by dying LM-infected macrophages is released to the interface of the cell conjugates, thereby inducing B6HO3 cells to produce IFN-γ. Based on the present and also previous findings, we propose that IL-18 released from macrophages because of cell death caused by bacteria may be the primary cytokine that triggers the innate IFN-γ production that is required for activating the bactericidal functions of macrophages at early stages of bacterial infection.

Subversion of cytokine networks by virally encoded decoy receptors

During the course of evolution, viruses have captured or created a diverse array of open reading frames, which encode for proteins that serve to evade and sabotage the host innate and adaptive immune responses that would otherwise lead to their elimination. These viral genomes are some of the best textbooks of immunology ever written. The established arsenal of immunomodulatory proteins encoded by viruses is large and growing, and includes specificities for virtually all known inflammatory pathways and targets. The focus of this review is on herpes and poxvirus-encoded cytokine and chemokine-binding proteins that serve to undermine the coordination of host immune surveillance. Structural and mechanistic studies of these decoy receptors have provided a wealth of information, not only about viral pathogenesis but also about the inner workings of cytokine signaling networks.

A unique bivalent binding and inhibition mechanism by the yatapoxvirus interleukin 18 binding protein

Interleukin 18 (IL18) is a cytokine that plays an important role in inflammation as well as host defense against microbes. Mammals encode a soluble inhibitor of IL18 termed IL18 binding protein (IL18BP) that modulates IL18 activity through a negative feedback mechanism. Many poxviruses encode homologous IL18BPs, which contribute to virulence. Previous structural and functional studies on IL18 and IL18BPs revealed an essential binding hot spot involving a lysine on IL18 and two aromatic residues on IL18BPs. The aromatic residues are conserved among the very diverse mammalian and poxviruses IL18BPs with the notable exception of yatapoxvirus IL18BPs, which lack a critical phenylalanine residue. To understand the mechanism by which yatapoxvirus IL18BPs neutralize IL18, we solved the crystal structure of the Yaba-Like Disease Virus (YLDV) IL18BP and IL18 complex at 1.75 Å resolution. YLDV-IL18BP forms a disulfide bonded homo-dimer engaging IL18 in a 2∶2 stoichiometry, in contrast to the 1∶1 complex of ectromelia virus (ECTV) IL18BP and IL18. Disruption of the dimer interface resulted in a functional monomer, however with a 3-fold decrease in binding affinity. The overall architecture of the YLDV-IL18BP:IL18 complex is similar to that observed in the ECTV-IL18BP:IL18 complex, despite lacking the critical lysine-phenylalanine interaction. Through structural and mutagenesis studies, contact residues that are unique to the YLDV-IL18BP:IL18 binding interface were identified, including Q67, P116 of YLDV-IL18BP and Y1, S105 and D110 of IL18. Overall, our studies show that YLDV-IL18BP is unique among the diverse family of mammalian and poxvirus IL-18BPs in that it uses a bivalent binding mode and a unique set of interacting residues for binding IL18. However, despite this extensive divergence, YLDV-IL18BP binds to the same surface of IL18 used by other IL18BPs, suggesting that all IL18BPs use a conserved inhibitory mechanism by blocking a putative receptor-binding site on IL18.

Imbalance of interleukin-18 and interleukin-18 binding protein in children with Henoch-Schönlein purpura

The balance between interleukin-18 (IL-18) and its endogenous antagonist, IL-18 binding protein (IL-18BP), was evaluated in children with Henoch-Schönlein purpura (HSP). Plasma IL-18 and IL-18BP levels and peripheral blood mononuclear cell IL-18 mRNA expression were significantly higher in patients with active HSP (n = 30) than in healthy controls (n = 20); IL-18BP mRNA expression was similar in active HSP and controls. Plasma levels and mRNA expression of IL-18 and IL-18BP in patients in remission (n = 19) were similar to those in controls. The ratios of IL-18 / IL-18BP plasma levels and IL-18 / IL-18BP mRNA levels in active HSP were significantly higher than in patients in remission and healthy controls. Thus, adequate IL-18BP to block the proinflammatory activity of IL-18 may not be present in active HSP and regulation of the IL-18 / IL-18BP balance might provide a potential therapeutic strategy.

Cytokines profiling by multiplex analysis in experimental arthritis: which pathophysiological relevance for articular versus systemic mediators?

INTRODUCTION

We have taken advantage of the large screening capacity of a multiplex immunoassay to better define the respective contribution of articular versus systemic cytokines in experimental arthritis.

METHODS

We performed a follow up (from 7 hours to 14 days) multiplex analysis of 24 cytokines in synovial fluid and sera of rats developing Antigen-Induced Arthritis (AIA) and confronted their protein level changes with molecular, biochemical, histological and clinical events occurring in the course of the disease.

RESULTS

The time-scheduled findings in arthritic joints correlated with time-dependent changes of cytokine amounts in joint effusions but not with their blood levels. From seven hours after sensitization, high levels of chemokines (MCP-1, MIP1α, GRO/KC, RANTES, eotaxin) were found in synovial fluid of arthritic knees whereas perivascular infiltration occurred in the synovium; local release of inflammatory cytokines (IFNγ, IL-1β, IL-6) preceded the spreading of inflammation and resulted in progressive degradation of cartilage and bone. Finally a local overexpression of several cytokines/adipocytokines poorly described in arthritis (IL-13, IL-18, leptin) was observed.

CONCLUSIONS

Distinct panels of cytokines were found in arthritic fluid during AIA, and the expected effect of mediators correlated well with changes occurring in joint tissues. Moreover, multiplex analysis could be helpful to identify new pathogenic mediators and to elucidate the mechanisms supporting the efficacy of putative targeted therapies.

Serum IL-18 and IL-18BP levels in patients with Chikungunya virus infection

Chikungunya virus infection has recently emerged in several countries. The inflammatory response is suggested to be involved in the pathology observed in this infectious disease. Interleukin-18 (IL-18) is an inducer of interferon-gamma (IFN-gamma) production and has been shown to play a role in several inflammatory diseases. IL-18 binding protein (IL-18BP) is a natural regulator of IL-18. In this study, we determined the levels of IL-18 and IL-18BP in patients with Chikungunya virus infection. Acute and convalescent sera were collected from each patient. The levels of both IL-18 and IL-18BP were measured by ELISA assays. IL-18 and IL-18BP levels were higher in patients than in controls. In addition, the level of IL-18 was higher in convalescent than in acute sera. However, the level of IL-18BP was lower in convalescent than in acute sera. These data suggest that production of both IL-18 and IL-18BP was induced following Chikungunya virus infection. IL-18BP was increased to regulate the activity of IL-18. The ratio of IL-18 to IL-18BP was higher in convalescent than in acute sera. The lower level of IL-18BP in convalescent sera was probably due to loss following IL-18 neutralization. Our data suggest that Chikungunya virus infection promotes the T helper-1 (Th-1) response by inducing IL-18 production. Manipulation of IL-18 and IL-18BP levels could be a promising therapeutic approach to alleviate symptoms in patients with Chikungunya virus infection.

Grading the commercial optical biosensor literature-Class of 2008: 'The Mighty Binders'

Optical biosensor technology continues to be the method of choice for label-free, real-time interaction analysis. But when it comes to improving the quality of the biosensor literature, education should be fundamental. Of the 1413 articles published in 2008, less than 30% would pass the requirements for high-school chemistry. To teach by example, we spotlight 10 papers that illustrate how to implement the technology properly. Then we grade every paper published in 2008 on a scale from A to F and outline what features make a biosensor article fabulous, middling or abysmal. To help improve the quality of published data, we focus on a few experimental, analysis and presentation mistakes that are alarmingly common. With the literature as a guide, we want to ensure that no user is left behind.

Short neuroprotective peptides, ADNF9 and NAP, are structurally disordered and monomeric in PBS

Activity-dependent neurotrophic factor 9 (ADNF9) and NAP are nine and eight amino acid peptides, which exhibit neuroprotective activity at femtomolar concentrations against cell toxic agents. We have here characterized their structures and interactions with dodecylphosphocholine (DPC) in phosphate-buffered saline (PBS). Circular dichroism analysis showed that ADNF9 and NAP are structurally disordered in PBS independent of peptide concentration and temperature, but appear to assume different secondary structure at increasing temperature. Sedimentation equilibrium analysis showed that both ADNF9 and NAP are monomeric at 37 degrees C, suggesting no self-association under physiological conditions. No secondary structure changes were observed in the presence of DPC, suggesting that ADNF9 and NAP do not interact with lipids.

Structural basis for antagonism of human interleukin 18 by poxvirus interleukin 18-binding protein

Human interleukin-18 (hIL-18) is a cytokine that plays an important role in inflammation and host defense against microbes. Its activity is regulated in vivo by a naturally occurring antagonist, the human IL-18-binding protein (IL-18BP). Functional homologs of human IL-18BP are encoded by all orthopoxviruses, including variola virus, the causative agent of smallpox. They contribute to virulence by suppressing IL-18-mediated immune responses. Here, we describe the 2.0-A resolution crystal structure of an orthopoxvirus IL-18BP, ectromelia virus IL-18BP (ectvIL-18BP), in complex with hIL-18. The hIL-18 structure in the complex shows significant conformational change at the binding interface compared with the structure of ligand-free hIL-18, indicating that the binding is mediated by an induced-fit mechanism. EctvIL-18BP adopts a canonical Ig fold and interacts via one edge of its beta-sandwich with 3 cavities on the hIL-18 surface through extensive hydrophobic and hydrogen bonding interactions. Most of the ectvIL-18BP residues that participate in these interactions are conserved in both human and viral homologs, explaining their functional equivalence despite limited sequence homology. EctvIL-18BP blocks a putative receptor-binding site on IL-18, thus preventing IL-18 from engaging its receptor. Our structure provides insights into how IL-18BPs modulate hIL-18 activity. The revealed binding interface provides the basis for rational design of inhibitors against orthopoxvirus IL-18BP (for treating orthopoxvirus infection) or hIL-18 (for treating certain inflammatory and autoimmune diseases).