Development and validation of a standardized ELISA for the detection of soluble Fc-epsilon-RI in human serum

Plasma concentrations of thioredoxin, thioredoxin reductase and peroxiredoxin-4 can identify high risk patients and predict outcome in patients with acute coronary syndrome: A clinical observation

BACKGROUND

Oxidative stress is a pathological feature of acute coronary syndrome (ACS), a complex disease with varying clinical outcomes. Surrogate biomarkers of oxidative stress including, peroxiredoxin-2 (PRDX2), PRDX4, thioredoxin (TRX) and thioredoxin reductase (TRXR) were measured in ACS patients at presentation and follow-up, to assess their clinical utility in diagnosis and risk stratification.

METHODS

Plasma from 145 participants (80 ACS and 65 healthy) at diagnosis, 1-3 month (first) and 6-month follow-up (second) was analysed by ELISA. ACS patients were monitored for 12-months.

RESULTS

ACS patients at diagnosis had significantly higher concentrations of TRX (p < 0.05), TRXR (p < 0.01) and PRDX4 (p < 0.01), compared to healthy donors. This was increase was driven by non-ST elevated myocardial infarction for TRX (p < 0.01) and PRDX4 (p < 0.05). For TRXR, ACS females were significantly higher than males (p < 0.05). TRX was also higher in older females (>55 years) at diagnosis (p < 0.05). At first follow-up, TRX had lowered, whereas PRDX4 remained significantly high (p < 0.05). Stratification of ACS patients according to percutaneous coronary intervention (PCI) revealed that TRXR was significantly higher in patients receiving PCI to the right coronary artery (p < 0.05). Whereas both TRXR (p < 0.01) and PRDX4 (p < 0.01) were significantly higher in patients receiving PCI to the left anterior descending (LAD) artery. ACS patients who had plasma TRX >13.40 ng/ml at second follow-up were at high risk of readmission (p < 0.05), as were patients with TRXR of <1000 pg/ml at diagnosis having PCI to the LAD (p < 0.05).

CONCLUSION

This study indicates that TRX, TRXR and PRDX4 may have clinical utility for ACS stratification.

Development of an Enzyme-Linked Immunosorbent Assay (ELISA) as a tool to detect NS1 of dengue virus serotype 2 in female Aedes aegypti eggs for the surveillance of dengue fever transmission

Dengue is a significant disease transmitted by Aedes mosquitoes in the tropics and subtropics worldwide. The disease is caused by four virus (DENV) serotypes and is transmitted to humans by female Aedes aegypti mosquito bites infected with the virus and vertically to their progeny. Current strategies to control dengue transmission focus on the vector. In this study, we describe an indirect Enzyme-Linked Immunosorbent Assay (ELISA), using a monoclonal antibody against the non-structural dengue virus protein 1 (NS1), to detect DENV2 in Ae. aegypti eggs. The assay detects NS1 in eggs homogenates with 87.5% sensitivity and 75.0% specificity and it is proposed as a tool for the routine entomovirological surveillance of DENV 2 in field mosquito populations.

Engineering a versatile and retrievable cell macroencapsulation device for the delivery of therapeutic proteins

Encapsulated cell therapy holds a great potential to deliver sustained levels of highly potent therapeutic proteins to patients and improve chronic disease management. A versatile encapsulation device that is biocompatible, scalable, and easy to administer, retrieve, or replace has yet to be validated for clinical applications. Here, we report on a cargo-agnostic, macroencapsulation device with optimized features for protein delivery. It is compatible with adherent and suspension cells, and can be administered and retrieved without burdensome surgical procedures. We characterized its biocompatibility and showed that different cell lines producing different therapeutic proteins can be combined in the device. We demonstrated the ability of cytokine-secreting cells encapsulated in our device and implanted in human skin to mobilize and activate antigen-presenting cells, which could potentially serve as an effective adjuvant strategy in cancer immunization therapies. We believe that our device may contribute to cell therapies for cancer, metabolic disorders, and protein-deficient diseases.

Hydrogel particles-on-chip (HyPoC): a fluorescence micro-sensor array for IgG immunoassay

Novel microparticles have generated growing interest in diagnostics for potential sensitivity and specificity in biomolecule detection and for the possibility to be integrated in a micro-system array as a lab-on-chip. Indeed, bead-based technologies integrated in microfluidics could speed up incubation steps, reduce reagent consumption and improve accessibility of diagnostic devices to non-expert users. To limit non-specific interactions with interfering molecules and to exploit the whole particle volume for bioconjugation, hydrogel microparticles, particularly polyethylene glycol-based, have emerged as promising materials to develop high-performing biosensors since their network can be functionalized to concentrate the target and improve detection. However, the limitations in positioning, trapping and mainly fine manipulation of a precise number of particles in microfluidics have largely impaired point-of-care applications. Herein, we developed an on-chip sandwich immunoassay for the detection of human immunoglobulin G in biological fluids. The detection system is based on finely engineered cleavable PEG-based microparticles, functionalized with specific monoclonal antibodies. By changing the particle number, we demonstrated tuneable specificity and sensitivity (down to 3 pM) in serum and urine. Therefore, a controlled number of hydrogel particles have been integrated in a microfluidic device for on-chip detection (HyPoC) allowing for their precise positioning and fluid exchange for incubation, washing and target detection. HyPoC dramatically decreases incubation time from 180 minutes to one minute and reduces washing volumes from 3.5 ml to 90 μL, achieving a limit of detection of 0.07 nM (with a dynamic range of 0.07-1 nM). Thus, the developed approach represents a versatile, fast and easy point-of-care testing platform for immunoassays.

Optimization and evaluation of a live virus SARS-CoV-2 neutralization assay

Virus neutralization assays provide a means to quantitate functional antibody responses that block virus infection. These assays are instrumental in defining vaccine and therapeutic antibody potency, immune evasion by viral variants, and post-infection immunity. Here we describe the development, optimization and evaluation of a live virus microneutralization assay specific for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). In this assay, SARS-CoV-2 clinical isolates are pre-incubated with serial diluted antibody and added to Vero E6 cells. Replicating virus is quantitated by enzyme-linked immunosorbent assay (ELISA) targeting the SARS-CoV-2 nucleocapsid protein and the standardized 50% virus inhibition titer calculated. We evaluated critical test parameters that include virus titration, assay linearity, number of cells, viral dose, incubation period post-inoculation, and normalization methods. Virus titration at 96 hours was determined optimal to account for different growth kinetics of clinical isolates. Nucleocapsid protein levels directly correlated with virus inoculum, with the strongest correlation at 24 hours post-inoculation. Variance was minimized by infecting a cell monolayer, rather than a cell suspension. Neutralization titers modestly decreased with increasing numbers of Vero E6 cells and virus amount. Application of two different normalization models effectively reduced the intermediate precision coefficient of variance to <16.5%. The SARS-CoV-2 microneutralization assay described and evaluated here is based on the influenza virus microneutralization assay described by WHO, and are proposed as a standard assay for comparing neutralization investigations.

Activated steady status and distinctive FcεRI-mediated responsiveness in basophils of atopic dermatitis

BACKGROUND

Although basophils are considered to play an important role for maintenance of type 2 inflammation in atopic dermatitis (AD), studies on basophils in AD patients are limited. Some studies have reported the activation status, including CD203c and CD63, of peripheral blood basophils in AD patients.

METHODS

We examined the features of circulating basophils in AD patients, assessed cell surface marker expressions and total serum IgE, and compared basophil responsiveness to stimulation between AD patients and healthy controls (HCs). In addition, the correlations among AD severity, laboratory factors, and features of basophils were examined. Blood samples from 38 AD patients and 21 HCs were analyzed. Basophil response markers CD203c and CD63, and expression of surface-bound IgE and FcεRI on basophils were measured. CD203c and CD63 expressions induced by stimulation with anti-IgE and anti-FcεRI antibodies were measured. Clinical/laboratory factors including total serum IgE were examined for correlations with these basophil parameters.

RESULTS

Baseline CD203c and CD63 expression on basophils were significantly higher in AD patients compared with HCs. The CD203c/CD63 response ratio to anti-FcεRI stimulation was higher than that to anti-IgE stimulation in AD patients, but not HCs. FcεRI expression on basophils was higher in AD patients than in HCs, although surface-bound IgE on basophils was equivalent. Total serum IgE had negative correlations with surface-bound IgE and CD63 responsiveness to anti-IgE stimulation.

CONCLUSIONS

Basophils were spontaneously activated under steady-state conditions in AD patients and responsiveness to anti-IgE stimulation was lower than in HCs. Despite high serum IgE and high basophil FcεRI expression, surface-bound IgE on basophils remained relatively low. Basophils might be suppressed or exhausted regarding FcεRI signaling via IgE in severe AD.

The relationship between released soluble FceRI-alpha and its cell surface density on human basophils

Background

The IgE-mediated activation of mast cells and basophils results in the secretion of many substances, including the release of FceRI-alpha subunit. This released alpha subunit can bind IgE and it may act as a down-regulator of subsequent IgE-dependent reactions. However, previous studies do not observe loss of the mass of FceRI-alpha associated with the cells, at least not for human basophils. This study was designed to understand the basis for the discordant observations.

Methods

Purified human basophils were stimulated with multiple activating secretagogues and supernatants were examined for histamine and released FceRI-alpha. In addition, cell surface IgE densities (occupied and unoccupied) were measured by flow cytometry and total cellular content of mature and immature FceRI-alpha determined with Western blots.

Results

Released FceRI-alpha, on average, represented 7% of the total surface FceRI before the reaction. The molecular weight of the soluble FceRI-alpha was approximately 54 kD, larger than immature subunit and somewhat smaller than surface subunit. In addition, 1) release ceased long before internalized FceRI-alpha was processed, 2) release was insensitive to Bafilomycin A, 3) release was independent of the starting density of FceRI and 4) release occurred more effectively with non-IgE-dependent stimuli, FMLP or C5a.

Conclusions

There appears to be relatively constant amount of nearly mature FceRI-alpha that is susceptible to secretion events induced by any form of stimulation. The amount, on average, represents about 7% of the mature form of FceRI-alpha.

The soluble isoform of human FcɛRI is an endogenous inhibitor of IgE-mediated mast cell responses

BACKGROUND

The soluble isoform of FcɛRI, the high-affinity IgE receptor (sFcεRI), is a protein of the IgE network with poorly defined functions.

OBJECTIVE

To define cellular sources and signals that result in the production of human sFcεRI and study its in vivo functions.

METHODS

FcεRI-transfected human cell lines (MelJuso), human monocyte-derived dendritic cells (moDCs), and murine bone marrow-derived mast cells (MC) were stimulated by FcεRI cross-linking and release of sFcεRI was analyzed (ELISA, Western Blot). Lysosomal-associated membrane protein 1 degranulation assays and human basophil activation tests (BATs) were used to study IgE-dependent activation. Recombinant sFcεRI (rsFcεRI) was used to assess its role in murine models of anaphylaxis with WT (wild-type) and IgE^-/- (IgE-deficient) mice.

RESULTS

Antigen-specific cross-linking of IgE-loaded FcɛRI on MelJuso cells that express the trimeric or tetrameric receptor isoform induced the production of sFcεRI. Using MCs and moDCs, we confirmed that IgE/FcɛRI activation induces sFcɛRI release. We demonstrated that generation of sFcɛRI requires Src phosphorylation and endo/lysosomal acidification. In experimental mouse models, sFcɛRI diminishes the severity of IgE-mediated anaphylaxis. BATs confirmed that, comparable to the anti-IgE monoclonal antibody omalizumab, sFcɛRI is an inhibitor of the human innate IgE effector axis, implying that sFcɛRI and omalizumab potentially inhibit each other in vivo.

CONCLUSION

sFcɛRI is produced after antigen-specific IgE/FcɛRI-mediated activation signals and functions as an endogenous inhibitor of IgE loading to FcɛRI and IgE-mediated activation. Our results imply, therefore, that sFcɛRI contributes to a negative regulatory feedback loop that aims at preventing overshooting responses after IgE-mediated immune activation.

Establishment of a novel quantum dots-encoded microbead-based flow cytometric method for quantification of soluble FcεRIα in serum

The soluble form of the transmembrane glycoprotein, FcεRIα which corresponds to the high-affinity receptor for IgE, is found in serum. Growing evidence suggests the pathogenic role of IgE and FcεRI in systemic lupus erythematosus (SLE). The goal of this study is to develop a sensitive and standardized cytometric assay for quantification of sFcεRIα. A membrane emulsification technique was utilized to incorporate CuInS₂ /ZnS quantum dots and Fe₃ O₄ nanoparticles into poly (styrene-co-maleic anhydride) microbeads. The beads were then carboxylated and coated with capture antibody monoclonal anti-human FcεRIα. This antibody binds to FcεRIα but does not block the binding of FcεRIα to IgE. After incubation with standards or serum samples, the microbeads were incubated with excessive native human IgE, followed by incubation with Phycoerythrin (PE) conjugated anti-human IgE. The resulting quantum dot microbeads were gated, and sFcεRIα quantification was analyzed based on PE fluorescence intensity. The method exhibited good linearity (R²  > 0.99), and the limit of detection was established at 0.29 ng/mL with the dynamic range of up to 200 ng/mL. The precision of the assay validated by intra- and inter-assay variability met the acceptance criteria with the mean recovery falling within 80-110% of the theoretical concentration and a corresponding CV < 20%. We tested 149 serum samples which 89 were from SLE patients and 60 were from healthy volunteers. For the first time, we detected an increased sFcεRIα level in the serum of SLE patients, which was confirmed by a commercial ELISA kit. Compared to ELISA, this novel method is more sensitive and efficient. It allows for the simple comparative analysis of sFcεRIα levels in health and disease. © 2017 International Society for Advancement of Cytometry.

Elevated levels of leukotriene C4 synthase mRNA distinguish a subpopulation of eosinophilic oesophagitis patients

BACKGROUND

Cysteinyl leukotrienes contribute to Th2-type inflammatory immune responses. Their levels in oesophageal tissue, however, do not distinguish patients with eosinophilic oesophagitis (EoE) from controls.

OBJECTIVE

We asked whether mRNA levels of leukotriene C4 synthase (LTC4 S), a key regulator of leukotriene production, could serve as a marker for EoE.

METHODS

Digital mRNA expression profiling (nCounter(®) Technology) was performed on proximal and distal oesophageal biopsies of 30 paediatric EoE patients and 40 non-EoE controls. Expression data were confirmed with RT-qPCR. LTC4 S mRNA levels were quantified in whole blood samples. Leukotriene E4 was measured in urine.

RESULTS

LTC4 S mRNA levels were elevated in proximal (2.6-fold, P < 0.001) and distal (2.9-fold, P < 0.001) oesophageal biopsies from EoE patients. Importantly, increased LTC4 S mRNA transcripts identified a subpopulation of EoE patients (28%). This patient subgroup had higher serum IgE levels (669 U/mL vs. 106 U/mL, P = 0.01), higher mRNA transcript numbers of thymic stromal lymphopoietin (TSLP) (1.6-fold, P = 0.009) and CD4 (1.4-fold, P = 0.04) but lower IL-23 mRNA levels (0.5-fold, P = 0.04). In contrast, elevated levels of IL-23 mRNA were found in oesophageal biopsies of patients with reflux oesophagitis. LTC4 S mRNA transcripts in whole blood and urinary excretion of leukotriene E4 were similar in EoE patient subgroups and non-EoE patients.

CONCLUSION & CLINICAL RELEVANCE

Elevated oesophageal expression of LTC4 S mRNA is found in a subgroup of EoE patients, concomitant with higher serum IgE levels and an oesophageal transcriptome indicative of a more-pronounced allergic phenotype. Together with TSLP and IL-23 mRNA levels, oesophageal LTC4 S mRNA may facilitate diagnosis of an EoE subpopulation for personalized therapy.

Development of an ELISA for the quantification of the C-terminal decapeptide prothymosin α(100-109) in sera of mice infected with bacteria

Apoptosis is characterized by a series of discrete biochemical events, among which is the truncation of the nuclear polypeptide prothymosin alpha (proTα) by activated caspase-3. This early apoptotic event results in the generation of a carboxy-terminal fragment of proTα, the immunoactive decapeptide proTα(100-109). We hypothesized that the detection of increased levels of proTα(100-109) in serum can be directly correlated with the induction of massive cell apoptosis, resulting from a severe bacterial infection. Thus, using high-affinity-purified polyclonal antibodies (Abs), raised in rabbits and a prototype antibody-capture system, we developed a highly sensitive and specific competitive ELISA for proTα(100-109). The sensitivity of the ELISA (0.1ng/mL to 10μg/mL) is acceptable for the quantification of the decapeptide in serum samples. To assess our initial hypothesis, we determined the concentration of proTα(100-109) in the sera of mice infected with the bacterium Streptococcus pyogenes over the course of the infection. We show that serum concentration of proTα(100-109) was marginal to undetectable before infection, increased over time and peaked at 72h postinfection. In silico analysis suggests that the Abs generated are unlikely to cross-react with any other unrelated mouse or bacterial protein. Further validation of our ELISA using serum samples from humans, infected with bacteria, may provide a useful tool to differentiate the causative agent of a potentially lethal septic infection.

Microarray-to-microarray transfer of reagents by snapping of two chips for cross-reactivity-free multiplex immunoassays

Whereas microarray and microfluidic technologies have progressed on many fronts, servicing microchips with minute amounts of reagents still constitutes an important challenge for many applications. Recently, chip-to-chip reagent transfer methods were introduced that simplify the delivery of reagents but required manual, visual alignment, custom-built microwells, and only showed the reaction of a single sample with multiple chemicals. Here, we present the snap chip, which uses common glass slides for transfer, back-side alignment for achieving precise alignment in spite of mirroring, and a snap-apparatus for facile transfer of arrays of chemicals at once by snapping the two slides together. We recently established that cross-reactivity was a significant problem in multiplex assays both theoretically and experimentally and found that it can be eliminated by avoiding mixing, but which necessitates delivering each detection antibody to a single spot with the cognate capture antibody. Using the snap chip, multiplexed sandwich immunoassays without mixing were performed: a slide with multiple arrays of 10 different capture antibodies was incubated with a sample, and then all detection antibodies transferred at once by snapping, each to the single cognate spot. All binding curves were established and limits of detection in the pg/mL range were obtained. Snap chips were stored up to 3 months prior to usage. The snap chip, by dissociating microarray production, which requires expensive equipment, from assay execution, which can be achieved using a hand-held alignment apparatus, will allow for multiplex reactions to be performed using a user-friendly kit. This new liquid handling format can be easily adapted to other applications that require transfer of minute amounts of different reagents in parallel.

Opportunities for sensitive plasma proteome analysis

Despite great interest, investments, and efforts, the ongoing search for plasma protein biomarkers for disease so far has come up surprisingly empty-handed. Although discovery programs have revealed large numbers of biomarker candidates, the clinical utility has been validated for only a very small number of these. While this disappointing state of affairs may suggest that plasma protein biomarkers have little more to offer for diagnostics, we take the perspective that experimental conditions might not have been optimal and that analyses will be required that offer far greater sensitivity than currently available, in terms of numbers of molecules needed for unambiguous detection. Accordingly, techniques are needed to search deep and wide for protein biomarker candidates. The requirements and feasibility of such assays will be discussed.