Optimizing the Binding Affinity of a Carrier Protein

Structural integrity with functional plasticity: what type I IFN receptor polymorphisms reveal

The type I IFNs activate an array of signaling pathways, which are initiated after IFNs bind their cognate receptors, IFNα/β receptor (IFNAR)1 and IFNAR2. These signals contribute to many aspects of human health including defense against pathogens, cancer immunosurveillance, and regulation of inflammation. How these cytokines interact with their receptors influences the quality of these signals. As such, the integrity of receptor structure is pivotal to maintaining human health and the response to immune stimuli. This review brings together genome wide association studies and clinical reports describing the association of nonsynonymous IFNAR1 and IFNAR2 polymorphisms with clinical disease, including altered susceptibility to viral and bacterial pathogens, autoimmune diseases, cancer, and adverse reactions to live-attenuated vaccines. We describe the amino acid substitutions or truncations induced by these polymorphisms and, using the knowledge of IFNAR conformational changes, IFNAR-IFN interfaces and overall structure-function relationship of the signaling complexes, we hypothesize the effect of these polymorphisms on receptor structure. That these predicted changes to IFNAR structure are associated with clinical manifestations of human disease, highlights the importance of IFNAR structural integrity to maintaining functional quality of these receptor-mediated responses. Type I IFNs are pivotal to innate immune responses and ultimately, to human health. Understanding the consequences of altered structure on the actions of these clinically significant cell receptors provides important information on the roles of IFNARs in health and disease.

Antiviral, Immunomodulatory and Antiproliferative Activities of Recombinant Soluble IFNAR2 without IFN-ß Mediation

Soluble receptors of cytokines are able to modify cytokine activities and therefore the immune system, and some have intrinsic biological activities without mediation from their cytokines. The soluble interferon beta (IFN-ß) receptor is generated through alternative splicing of IFNAR2 and has both agonist and antagonist properties for IFN-ß, but its role is unknown. We previously demonstrated that a recombinant human soluble IFN-ß receptor showed intrinsic therapeutic efficacy in a mouse model of multiple sclerosis. Here we evaluate the potential biological activities of recombinant sIFNAR2 without the mediation of IFN-ß in human cells. Recombinant sIFNAR2 down-regulated the production of IL-17 and IFN-ɣ and reduced the cell proliferation rate. Moreover, it showed a strong antiviral activity, fully protecting the cell monolayer after being infected by the virus. Specific inhibitors completely abrogated the antiviral activity of IFN-ß, but not that of the recombinant sIFNAR2, and there was no activation of the JAK-STAT signaling pathway. Consequently, r-sIFNAR2 exerts immunomodulatory, antiproliferative and antiviral activities without IFN-ß mediation, and could be a promising treatment against viral infections and immune-mediated diseases.

Decreased soluble IFN-β receptor (sIFNAR2) in multiple sclerosis patients: A potential serum diagnostic biomarker

Background:

The soluble isoform of the interferon-β (IFN-β) receptor (sIFNAR2) could modulate the activity of both endogenous and systemically administered IFN-β. Previously, we described lower serum sIFNAR2 levels in untreated multiple sclerosis (MS) than in healthy controls (HCs).

Objective:

To assess sIFNAR2 levels in a new cohort of MS patients and HCs, as well as in patients with clinically isolated syndrome (CIS) and with other inflammatory neurological disorders (OIND) and to assess its ability as a diagnostic biomarker.

Methods:

The cross-sectional study included 148 MS (84 treatment naive and 64 treated), 87 CIS, 42 OIND, and 96 HCs. Longitudinal study included 94 MS pretreatment and after 1 year of therapy with IFN-β, glatiramer acetate (GA), or natalizumab. sIFNAR2 serum levels were measured by a quantitative ELISA developed and validated in our laboratory.

Results:

Naive MS and CIS patients showed significantly lower sIFNAR2 levels than HCs and OIND patients. The sensitivity and specificity to discriminate between MS and OIND, for a sIFNAR2 cutoff value of 122.02 ng/mL, were 70.1%, and 79.4%, respectively. sIFNAR2 increased significantly in IFN-β-treated patients during the first year of therapy in contrast to GA- and natalizumab-treated patients who showed non-significant changes.

Conclusion:

The results suggest that sIFNAR2 could be a potential diagnostic biomarker for MS.

Development and validation of an ELISA for quantification of soluble IFN-β receptor: assessment in multiple sclerosis

Aim: The soluble isoform of the IFN-β receptor (sIFNAR2) can bind IFN-β and modulate its activity, although its role in autoimmune diseases remains unknown. Methods: A recombinant human sIFNAR2 protein was cloned, expressed and purified after which we developed and validated an ELISA for its quantification in human serum. Serum sIFNAR2 were assessed in multiple sclerosis (MS) patients and healthy controls. Results: The ELISA has a dynamic range of 3.9–250 ng/ml and a detection limit of 2.44 ng/ml. Serum sIFNAR2 were significantly lower in untreated-MS patients than in healthy controls. Conclusion: The ELISA is suitable for quantification of sIFNAR2 in serum and should facilitate the study of sIFNAR2 in neuroimmunological diseases such as MS.

G-CSF/anti-G-CSF antibody complexes drive the potent recovery and expansion of CD11b+Gr-1+ myeloid cells without compromising CD8+ T cell immune responses

BACKGROUND

Administration of recombinant G-CSF following cytoreductive therapy enhances the recovery of myeloid cells, minimizing the risk of opportunistic infection. Free G-CSF, however, is expensive, exhibits a short half-life, and has poor biological activity in vivo.

METHODS

We evaluated whether the biological activity of G-CSF could be improved by pre-association with anti-G-CSF mAb prior to injection into mice.

RESULTS

We find that the efficacy of G-CSF therapy can be enhanced more than 100-fold by pre-association of G-CSF with an anti-G-CSF monoclonal antibody (mAb). Compared with G-CSF alone, administration of G-CSF/anti-G-CSF mAb complexes induced the potent expansion of CD11b+Gr-1+ myeloid cells in mice with or without concomitant cytoreductive treatment including radiation or chemotherapy. Despite driving the dramatic expansion of myeloid cells, in vivo antigen-specific CD8+ T cell immune responses were not compromised. Furthermore, injection of G-CSF/anti-G-CSF mAb complexes heightened protective immunity to bacterial infection. As a measure of clinical value, we also found that antibody complexes improved G-CSF biological activity much more significantly than pegylation.

CONCLUSIONS

Our findings provide the first evidence that antibody cytokine complexes can effectively expand myeloid cells, and furthermore, that G-CSF/anti-G-CSF mAb complexes may provide an improved method for the administration of recombinant G-CSF.

Structural and dynamic determinants of type I interferon receptor assembly and their functional interpretation

Type I interferons (IFNs) form a network of homologous cytokines that bind to a shared, heterodimeric cell surface receptor and engage signaling pathways that activate innate and adaptive immune responses. The ability of IFNs to mediate differential responses through the same cell surface receptor has been subject of a controversial debate and has important medical implications. During the past decade, a comprehensive insight into the structure, energetics, and dynamics of IFN recognition by its two-receptor subunits, as well as detailed correlations with their functional properties on the level of signal activation, gene expression, and biological responses were obtained. All type I IFNs bind the two-receptor subunits at the same sites and form structurally very similar ternary complexes. Differential IFN activities were found to be determined by different lifetimes and ligand affinities toward the receptor subunits, which dictate assembly and dynamics of the signaling complex in the plasma membrane. We present a simple model, which explains differential IFN activities based on rapid endocytosis of signaling complexes and negative feedback mechanisms interfering with ternary complex assembly. More insight into signaling pathways as well as endosomal signaling and trafficking will be required for a comprehensive understanding, which will eventually lead to therapeutic applications of IFNs with increased efficacy.

IL-28A, IL-28B, and IL-29: promising cytokines with type I interferon-like properties

IL-28A, IL-28B and IL-29 (also designated type III interferons) constitute a new subfamily within the IL-10-interferon family. They are produced by virtually any nucleated cell type, particularly dendritic cells, following viral infection or activation with bacterial components, and mediate their effects via the IL-28R1/IL-10R2 receptor complex. Although IL-28/IL-29 are closer to the IL-10-related cytokines in terms of gene structure, protein structure, and receptor usage, they display type I interferon-like anti-viral and cytostatic activities. Unlike type I interferons, the target cell populations of IL-28/IL-29 are restricted and mainly include epithelial cells and hepatocytes. These properties suggest that IL-28/IL-29 are potential therapeutic alternatives to type I interferons in terms of viral infections and tumors. This review describes the current knowledge about these cytokines.

Cytokine-receptor interactions as drug targets

Cytokines are essential proteins that exert potent control over entire cell populations to fight infections and other pathologies, but can by themselves cause disease. Therefore, cytokine-related drugs act either by stimulating or blocking their activities. Our knowledge of the structures of cytokine-receptor complexes, the biophysical basis of their binding, and their mode of biological activation has substantially increased in recent years. This knowledge has been translated into new drugs and drug candidates. This review summarizes our current understanding of the receptor-mediated activity of cytokines, their relation to health and disease, and the agents in use to activate and block their actions.

Antiviral instruction of bone marrow leukocytes during respiratory viral infections

Respiratory viral infections trigger a robust inflammatory response in the lung, producing cytokines, chemokines, and growth factors that promote infiltration of effector leukocytes. Whereas the role of chemokines and infiltrating leukocytes in antiviral immunity is well studied, the effect that lung cytokines have on leukocytes in distal hematopoietic and lymphoid tissues and their role in antiviral immunity is unknown. We show that, during infection with influenza or Sendai virus, the lung communicates with the sterile bone marrow, the primary site of hematopoiesis, through type I interferons. While in the bone marrow, leukocytes exposed to type I interferons activate an antiviral transcriptional program and become resistant to infection with different viruses. The protected bone marrow leukocytes are capable of migrating to the infected lung and contribute to virus clearance. These findings show that appropriate instruction of cells during their development in the bone marrow is needed for effective control of infection.

Two interferons alpha influence each other during their interaction with the extracellular domain of human type interferon receptor subunit 2

The interaction between two human interferons alpha (IFN-alphas) and the extracellular (EC) domain of human type I IFN receptor subunit 2 (IFNAR2) was analyzed. Previous experiments using Daudi cells showed that IFN-alpha21b and some IFN-alpha hybrids (made from IFN-alpha2c and 21b) competed poorly for the IFN-alpha2b binding site. This study examined the causes of the poor competition between these IFN-alphas. IFN-alpha2c and the IFN hybrid CM3 {IFN-alpha21b(1-75)(81-95)/IFN-alpha2c(76-80) (96-166), Y86K} were selected for this study based on their cell binding and biological properties. Competitive binding ELISA, native electrophoresis followed by Western blot, electrospray ionization mass spectrometry (ESI-MS), surface plasmon resonance biosensor (SPR) analysis, as well as neutralization of antiproliferative activities on Daudi cells in the presence of soluble IFNAR2-EC show evidence that each of the described IFN-alpha subtypes affected the binding of the other IFN-alpha to IFNAR2-EC by affecting the stability of the complex, i.e., dissociation of the complex. Moreover, native electrophoresis with different IFNAR2-EC mutants showed that IFN-alpha2c and CM3 utilize different amino acids in the binding domain of IFNAR2-EC. In addition to that, analytical ultracentrifugation (AUC) revealed differences in the oligomeric state of the two studied interferons. Our results demonstrated that two individual IFN-alphas interact differentially with IFNAR2-EC and influence each other during this interaction. This study contributes to the understanding of the mutual interaction between multiple IFN-alpha subtypes during the competition for binding to the receptor.

Structures in systems biology

Oil and water do not normally mix, and apparently structural biology and systems biology look like two different universes. It can be argued that structural biology could play a very important role in systems biology. Although at the final stage of understanding a signal transduction pathway, a cell, an organ or a living system, structures could be obviated, we need them to be able to reach that stage. Structures of macromolecules, especially molecular machines, could provide quantitative parameters, help to elucidate functional networks or enable rational designed perturbation experiments for reverse engineering. The role of structural biology in systems biology should be to provide enough understanding so that macromolecules can be translated into dots or even into equations devoid of atoms.

IL-22 induces lipopolysaccharide-binding protein in hepatocytes: a potential systemic role of IL-22 in Crohn's disease

Crohn's disease (CD) is a common, chronic, inflammatory bowel disease characterized by intestinal infiltration of activated immune cells and distortion of the intestinal architecture. In this study, we demonstrate that IL-22, a cytokine that is mainly produced by activated Th1 and Th17 cells, was present in high quantities in the blood of CD patients in contrast to IFN-gamma and IL-17. In a mouse colitis model, IL-22 mRNA expression was elevated predominantly in the inflamed intestine but also in the mesenteric lymph nodes. IL-22BP, the soluble receptor for IL-22, demonstrated an affinity to IL-22 that was at least 4-fold higher than its membrane-bound receptor, and its strong constitutive expression in the intestine and lymph nodes was decreased in the inflamed intestine. To investigate the possible role of systemic IL-22 in CD, we then administered IL-22 to healthy mice and found an up-regulation of LPS-binding protein (LBP) blood levels reaching concentrations known to neutralize LPS. This systemic up-regulation was associated with increased hepatic but not renal or pulmonary LBP mRNA levels. IL-22 also enhanced the secretion of LBP in human primary hepatocytes and HepG2 hepatoma cells in vitro. This increase was mainly transcriptionally regulated and synergistic with that of other LBP inducers. Finally, elevated LBP levels were detected in CD patients and the mouse colitis model. These data suggest that systemic IL-22 may contribute to the prevention of systemic inflammation provoked by LPS present in the blood of CD patients through its induction of hepatic LBP.

Converting IL-15 to a superagonist by binding to soluble IL-15R{alpha}

IL-15 is normally presented in vivo as a cell-associated cytokine bound to IL-15Ralpha. We show here that the biological activity of soluble IL-15 is much improved after interaction with recombinant soluble IL-15Ralpha; after injection, soluble IL-15/IL-15Ralpha complexes rapidly induce strong and selective expansion of memory-phenotype CD8(+) cells and natural killer cells. These findings imply that binding of IL-15Ralpha to IL-15 may create a conformational change that potentiates IL-15 recognition by the betagamma(c) receptor on T cells. The enhancing effect of IL-15Ralpha binding may explain why IL-15 normally functions as a cell-associated cytokine. Significantly, the results with IL-2, a soluble cytokine, are quite different; thus, IL-2 function is markedly inhibited by binding to soluble IL-2Ralpha.

Theileria orientalis: cloning a cDNA encoding a protein similar to thiol protease with haemoglobin-binding activity

A gene encoding a protein (Tocp1) from Theileria orientalis was isolated from a cDNA library and the deduced amino acid sequence of Tocp1 has 476 amino acids. The primary structure of Tocp1 is similar to eukaryotic thiol proteases (EC 3.4.22.-), but no enzymatic activity was observed with the substitution of essential cysteine at the cysteine active site for glycine. Southern blot analysis showed that multiple genes similar to Tocp1 were present in the parasite genome. Sequence analysis of the genome of the parasite showed that there are at least five different genes similar to Tocp1. Tocp1 transcripts were detected in the T. orientalis piroplasma by Northern blot analysis. Western blot analysis showed that Tocp1 was expressed in the piroplasm of T. orientalis. To address the role of Tocp1 in the life cycle of T. orientalis, Tocp1 was expressed using pET32 expression system. Binding affinity to haemoglobin was demonstrated by enzyme-linked immunosorbent assay.

Survey of the year 2004 commercial optical biosensor literature

The year 2004 represents a milestone for the biosensor research community: in this year, over 1000 articles were published describing experiments performed using commercially available systems. The 1038 papers we found represent an approximately 10% increase over the past year and demonstrate that the implementation of biosensors continues to expand at a healthy pace. We evaluated the data presented in each paper and compiled a 'top 10' list. These 10 articles, which we recommend every biosensor user reads, describe well-performed kinetic, equilibrium and qualitative/screening studies, provide comparisons between binding parameters obtained from different biosensor users, as well as from biosensor- and solution-based interaction analyses, and summarize the cutting-edge applications of the technology. We also re-iterate some of the experimental pitfalls that lead to sub-optimal data and over-interpreted results. We are hopeful that the biosensor community, by applying the hints we outline, will obtain data on a par with that presented in the 10 spotlighted articles. This will ensure that the scientific community at large can be confident in the data we report from optical biosensors.

Reversible PEGylation: A Novel Technology To Release Native Interferon α2 over a Prolonged Time Period

Many peptide and protein drugs have a short circulatory half-life in vivo. The covalent attachment of polyethylene glycol (PEG) chains (PEGylation) can overcome this deficiency, but pegylated peptides and proteins are often inactive. In this study, we present a novel PEG-IFNalpha2 conjugate, PEG(40)-FMS-IFNalpha2, capable of regenerating native interferon alpha2 (IFNalpha2) at a slow rate under physiological conditions. A 2-sulfo-9-fluorenylmethoxycarbonyl (FMS) containing bifunctional reagent, MAL-FMS-NHS, has been synthesized, enabling the linkage of a 40 kDa PEG-SH to IFNalpha2 through a slowly hydrolyzable bond. By use of a BIAcore binding assay, the in vitro rate of regeneration of native interferon was estimated to have a half-life of 65 h. Following subcutaneous administration to rats and monitoring circulating antiviral activity, active IFNalpha2 levels peaked at 50 h, with substantial levels still being detected 200 h after administration. This value contrasts with a half-life of about 1 h measured for unmodified interferon. The concentration of active IFNalpha2 scaled linearly with the quantity injected. Comparing subcutaneous to intravenous administration of PEG(40)-FMS-IFNalpha2, we found that the long circulatory lifetime of IFNalpha2 was affected both by the slow rate of absorption of the PEGylated protein from the subcutaneous volume and by the slow rate of discharge from the PEG in circulation. A numerical simulation of the results was in good agreement with the results observed in vivo. The pharmacokinetic profile of this novel IFNalpha2 conjugate combines a prolonged maintenance in vivo with the regeneration of active-native IFNalpha2, ensuring ready access to peripheral tissues and thus an overall advantage over currently used formulations.