Comparison of non-magnetic and magnetic beads in bead-based assays

Advancing Toxoplasma gondii multiplex serology

Toxoplasma gondii is a highly prevalent pathogen causing zoonotic infections with significant public health implications. Yet, our understanding of long-term consequences, associated risk factors, and the potential role of co-infections is still limited. Seroepidemiological studies are a valuable approach to address open questions and enhance our insights into T. gondii across human populations. Here, we present substantial advancements to our previously developed T. gondii multiplex serology assay, which is based on the immunodominant antigens SAG1 and P22. While our previous bead-based assay quantified antibody levels against multiple targets in a high-throughput fashion requiring only a small sample volume, impaired assay characteristics emerged in sample dilutions beyond 1:100 and when being transferred to magnetic beads. Both are now critical for inclusion in large-scale seroprevalence studies. Using the truncated versions, SAG1D1 and P22trunc, significantly enhanced signal-to-noise ratios were achieved with almost perfect concordance with the gold-standard Sabin-Feldman dye test. In sample dilutions of 1:100, the diagnostic accuracy of SAG1D1 and P22trunc reached sensitivities (true positive rates) of 98% and 94% and specificities (true negative rates) of 93% and 95%, respectively. Importantly, performance metrics were reproducible in a 1:1,000 sample dilution, using both magnetic and nonmagnetic beads. Thresholds for seropositivity were derived from finite mixture models and performed equally well as thresholds by receiver operating characteristic analysis. Our improved multiplex serology assay is therefore able to generate robust and reproducible performance metrics under various assay conditions. Inclusion of T. gondii antibody measurements with other pathogens, in multiplex serology panels will allow for large-scale seroepidemiological research.

IMPORTANCE

Toxoplasma gondii is a pathogen of significant public health concern due to its widespread prevalence and zoonotic potential. However, our understanding of key aspects, such as risk factors for infection and disease, potential outcomes, and their trends, remains limited. Seroepidemiological studies in large cohorts are invaluable for addressing these questions but remain scarce. Our revised multiplex serology assay equips researchers with a powerful tool capable of delivering T. gondii serum antibody measurements with high sensitivity and specificity under diverse assay conditions. This advancement paves the way for the integration of T. gondii antibody measurements into multi-pathogen multiplex serology panels, promising valuable insights into public health and pathogen interactions.

Separation mixed semen of two individuals using magnetic beads coupled ABH blood group antibody

In sexual assault cases, one of the most common samples collected is a mixed semen stain, which is often found on the vagina, female underwear, or bed sheets. However, it is usually difficult to identify the perpetrator based on this sample alone. One technique that has been developed to address this issue is magnetic bead-based separation. This method involves using modified magnetic microspheres to capture and enrich specific target cells, in this case, sperm cells. In this study, we utilized magnetic beads coupled with ABH blood group antibody to isolate sperm cells from an individual of a single ABO blood type. Subsequently, polymerase chain reaction amplification and capillary electrophoresis were employed to perform the genotyping the short tandem repeat (STR) loci. This approach allows for the identification of different individuals in a mixed seminal stain sample from two individuals, by first separating sperm cells based on ABH antigen differences and subsequently utilizing autosomal STR typing on the enriched single blood group cells.

Multiplexed bead-based assay for the simultaneous quantification of human serum IgG antibodies to tetanus, diphtheria, pertussis toxin, filamentous hemagglutinin, and pertactin

Background

Luminex bead-based assays offer multiplexing to test antibodies against multiple antigens simultaneously; however, this requires validation using internationally certified reference standards. Therefore, there is an urgent need to characterize existing reference standards for the standardization of multiplex immunoassays (MIAs). Here, we report the development and validation of an MIA for the simultaneous estimation of levels of human serum immunoglobulin G (IgG) antibodies for pertussis toxin (PT), filamentous hemagglutinin (FHA), pertactin (PRN), diphtheria toxoid (DT), and tetanus toxoid (TT).

Methods

The MIA was assessed using a panel of human serum samples and WHO reference standards. The WHO reference standards were also studied for suitability in the MIA. Purified antigens (PT, FHA, PRN, DT, and TT) were coupled to the spectrally unique magnetic carboxylated microspheres. The method was validated in accordance with the United States Food and Drug Administration (US FDA), European Medicines Agency (EMA), and the International Committee of Harmonization Multidisciplinary (ICH M10) guidelines, and parameters such as precision, accuracy, dilutional linearity, assay range, robustness, and stability were assessed. Method agreements with commercially available IgG enzyme-linked immunosorbent assay (ELISA) assays were also evaluated. In addition, the study assessed the level of correlation between the IgG levels estimated by the MIA and the cell-based neutralizing antibody assays for PT and DT.

Results

We identified that an equimix of WHO international standards (i.e., 06/142, 10/262, and TE-3) afforded the best dynamic range for all the antigens in the MIA. For all five antigens, we observed that the back-fitted recoveries using the four-parameter logistic (4-PL) regression fits ranged between 80% and 120% for all calibration levels, and the percentage coefficient of variation (% CV) was < 20%. In addition, the difference in mean fluorescence intensity (MFI) between the monoplex and multiplex format was < 10% for each antigen, indicating no crosstalk among the beads. The MIA also showed good agreement with conventional and commercially available assays, and a positive correlation (> 0.75) with toxin neutralization assays for PT and DT was observed.

Conclusion

The MIA that was calibrated in accordance with WHO reference standards demonstrated increased sensitivity, reproducibility, and high throughput capabilities, allowing for the design of robust studies that evaluate both natural and vaccine-induced immunity.

Magnetic bead-based separation of sperm cells from semen-vaginal fluid mixed stains using an anti-ACRBP antibody

Forensic DNA analysis of semen-vaginal fluid mixed stains is essential and necessary in sexual assault cases. Here, we used a magnetic bead conjugated acrosin binding protein (ACRBP) antibody to separate and enrich sperm cells from mixed stains. Previously, western blotting indicated that ACRBP was specifically expressed in sperm cells, but not in female blood and epithelial cells, while immunofluorescence data showed ACRBP was localized to the acrosome in sperm cells. In our study, sperm were separated from mixed samples at three sperm cell/female buccal epithelial cell ratios (10³:10³; 10³:10⁴; and 10³:10⁵) using a magnetic bead conjugated ACRBP antibody. Subsequently, 23 autosomal short tandem repeat (STR) loci were amplified using the Huaxia™ Platinum PCR Amplification System and genotyped using capillary electrophoresis. The genotyping success rate for STR loci was 90% when the sperm to female buccal epithelial cell ratio was > 1:100 in mixed samples. Our results suggest that the magnetic bead conjugated ACRBP antibody is effective for isolating sperm cells in sexual assault cases.

Alterations in metabolic biomarkers and their potential role in amyotrophic lateral sclerosis

Background

Metabolic dysfunction has been suggested to be involved in the pathophysiology of amyotrophic lateral sclerosis (ALS). This study aimed to investigate the potential role of metabolic biomarkers in the progression of ALS and understand the possible metabolic mechanisms.

Methods

Fifty‐two patients with ALS and 24 normal controls were included, and blood samples were collected for analysis of metabolic biomarkers. Basal anthropometric measures, including body composition and clinical features, were measured in ALS patients. The disease progression rate was calculated using the revised ALS functional rating scale (ALSFRS‐R) during the 6‐month follow‐up.

Results

ALS patients had higher levels of adipokines (adiponectin, adipsin, resistin, and visfatin) and other metabolic biomarkers [C‐peptide, glucagon, glucagon‐like peptide 1 (GLP‐1), gastric inhibitory peptide, and plasminogen activator inhibitor type 1] than controls. Leptin levels in serum were positively correlated with body mass index, body fat, and visceral fat index (VFI). Adiponectin was positively correlated with the VFI and showed a positive correlation with the ALSFRS‐R and a negative correlation with baseline disease progression. Patients with lower body fat, VFI, and fat in limbs showed faster disease progression during follow‐ups. Lower leptin and adiponectin levels were correlated with faster disease progression. After adjusting for confounders, lower adiponectin levels and higher visfatin levels were independently correlated with faster disease progression.

Interpretation

The current study found altered levels of metabolic biomarkers in ALS patients, which may play a role in ALS pathogenesis. Adiponectin and visfatin represent potential biomarkers for prediction of disease progression in ALS.

A comparison of non-magnetic and magnetic beads for measuring IgG antibodies against Plasmodium vivax antigens in a multiplexed bead-based assay using Luminex technology (Bio-Plex 200 or MAGPIX)

Multiplexed bead-based assays that use Luminex® xMAP® technology have become popular for measuring antibodies against proteins of interest in many fields, including malaria and more recently SARS-CoV-2/COVID-19. There are currently two formats that are widely used: non-magnetic beads or magnetic beads. Data are lacking regarding the comparability of results obtained using these two types of beads, and for assays run on different instruments. Whilst non-magnetic beads can only be run on flow-based instruments (such as the Luminex® 100/200™ or Bio-Plex® 200), magnetic beads can be run on both these and the newer MAGPIX® instruments. In this study we utilized a panel of purified recombinant Plasmodium vivax proteins and samples from malaria-endemic areas to measure P. vivax-specific IgG responses using different combinations of beads and instruments. We directly compared: i) non-magnetic versus magnetic beads run on a Bio-Plex® 200, ii) magnetic beads run on the Bio-Plex® 200 versus MAGPIX® and iii) non-magnetic beads run on a Bio-Plex® 200 versus magnetic beads run on the MAGPIX®. We also performed an external comparison of our optimized assay. We observed that IgG antibody responses, measured against our panel of P. vivax proteins, were moderately-strongly correlated in all three of our comparisons (pearson r>0.5 for 18/19 proteins), however higher amounts of protein were required for coupling to magnetic beads. Our external comparison indicated that results generated in different laboratories using the same coupled beads are also highly comparable (pearson r>0.7), particularly if a reference standard curve is used.

During the Early Stages of Staphylococcus aureus Biofilm Formation, Induced Neutrophil Extracellular Traps Are Degraded by Autologous Thermonuclease

Staphylococcus aureus extracellular DNA (eDNA) plays a crucial role in the structural stability of biofilms during bacterial colonization; on the contrary, host immune responses can be induced by bacterial eDNA. Previously, we observed production of S. aureus thermonuclease during the early stages of biofilm formation in a mammalian cell culture medium. Using a fluorescence resonance energy transfer (FRET)-based assay, we detected thermonuclease activity of S. aureus biofilms grown in Iscove's modified Dulbecco's medium (IMDM) earlier than that of widely studied biofilms grown in tryptic soy broth (TSB). The thermonuclease found was Nuc1, confirmed by mass spectrometry and competitive Luminex assay. These results indicate that biofilm development in IMDM may not rely on eDNA for structural stability. A bacterial viability assay in combination with wheat germ agglutinin (WGA) staining confirmed the accumulation of dead cells and eDNA in biofilms grown in TSB. However, in biofilms grown in IMDM, minimal amounts of eDNA were found; instead, polysaccharide intercellular adhesin (PIA) was detected. To investigate if this early production of thermonuclease plays a role in immune modulation by biofilm, we studied the effect of thermonuclease on human neutrophil extracellular trap (NET) formation using a nuc knockout and complemented strain. We confirmed that thermonuclease produced by early-stage biofilms grown in IMDM degraded biofilm-induced NETs. Additionally, neither the presence of biofilms nor thermonuclease stimulated an increase in reactive oxygen species (ROS) production by neutrophils. Our findings indicated that S. aureus, during the early stages of biofilm formation, actively evades the host immune responses by producing thermonuclease.

New Platform for the Direct Profiling of microRNAs in Biofluids

Circulating microRNAs have been identified as potential biomarkers for early detection, prognosis, and prediction of several diseases. Their use in clinical diagnostics has been limited by the lack of suitable detection techniques. Most of the current technologies suffer from requiring complex protocols, not yet able to deliver robust and cost-effective assays in the field of clinical diagnostics. In this work, we report the development of a breakthrough platform for profiling circulating microRNAs. The platform comprises a novel silicon photomultiplier-based reader in conjunction with a chemical-based method for nucleic acid detection. Accurate microRNAs profiling without extraction, pre-amplification, or pre-labeling of the target is now achievable. We designed and synthesized a set of reagents that combined the chemical-based method with a chemiluminescent reaction. The signals generated were read out using a novel, compact silicon photomultiplier-based reader. The platform sensitivity was determined by measuring known concentrations of hsa-miR-21-5p spike-ins. The limit of detection was calculated as 4.7 pmol/L. The platform was also successfully used to directly detect hsa-miR-21-5p in eight non-small cell lung cancer plasma samples. Levels of plasma hsa-miR-21-5p expression were also measured via TaqMan RT-qPCR. The successful integration of the unique chemical-based method for nucleic acid detection with the novel silicon photomultiplier-based reader created an innovative product (ODG platform) with diagnostic utility, for the direct qualitative and quantitative analysis of microRNA biomarkers in biological fluids.

Development and validation of magnetic bead pentaplex immunoassay for simultaneous quantification of murine serum IgG antibodies to acellular pertussis, diphtheria and tetanus antigens used in combination vaccines

We describe here a magnetic bead-based multiplex (pentaplex) immunoassay (MIA) platform developed as an alternative to enzyme-linked immunosorbent assays (ELISA) used in immunogenicity testing of DTaP/TdaP vaccine in animals. MIA simultaneously measures the concentration of serum (IgG) antibodies against B. Pertussis antigens; pertussis toxin, filamentous hemagglutinin (FHA), pertactin (PRN) and tetanus (T) and diphtheria (D) toxoid in the Tdap vaccine immunized animals. Assay validation experiments were done using a panel of serum samples. The results are expressed in IU/ml using WHO reference mice serum. The standard curve was linear with 4PL logistic fit over an eight 2-fold dilution range with LOQ of 0.003, 0.022, 0.005 IU/ml for PT, FHA and PRN and 0.016 U/ml for T and D antigens indicating sensitivity. No interference was observed in monoplex versus multiplex measurements. Specificity was demonstrated by ≥90% homologous and ≤15% heterologous inhibition for all the antigens. The assay was reproducible, with a mean coefficient of variation (CV) of ≤10% for intra-assay duplicates and ≤25% for interassays using different lots of beads and analyst. Accuracy was demonstrated wherein the ratio of observed vs. assigned unitages were within 80-120%. The study suggests that the Pentaplex (MIA) platform meets all the criteria for the serological assay combination vaccines with additional advantages of high throughput, reduced sample volumes, faster analysis with reduced manpower in contrast to conventional monoplex ELISA.

Phage-based assay for rapid detection of bacterial pathogens in blood by Raman spectroscopy

Sepsis is a systemic inflammatory response ensuing from presence and persistence of microorganisms in the bloodstream. The possibility to identify them at low concentrations may improve the problem of human health and therapeutic outcomes. So, sensitive and rapid diagnostic systems are essential to evaluate bacterial infections during the time, also reducing the cost. In this study, from random M13 phage display libraries, we selected phage clones that specifically bind surface of Staphyloccocus aureus, Pseudomonas aeruginosa and Escherichia coli. Then, commercial magnetic beads were functionalized with phage clones through covalent bond and used as capture and concentrating of pathogens from blood. We found that phage-magnetic beads complex represents a network which enables a cheap, high sensitive and specific detection of the bacteria involved in sepsis by micro-Raman spectroscopy. The enter process required 6 h and has the limit of detection of 10 Colony Forming Units on 7 ml of blood (CFU/7 ml).

Production of Staphylococcal Complement Inhibitor (SCIN) and Other Immune Modulators during the Early Stages of Staphylococcus aureus Biofilm Formation in a Mammalian Cell Culture Medium

Immune modulators are known to be produced by matured biofilms and during different stages of planktonic growth of Staphylococcus aureus Little is known about immune modulator production during the early stages of biofilm formation, thus raising the following question: how does S. aureus protect itself from the innate immune responses at these stages? Therefore, we determined the production of the following immune modulators: chemotaxis inhibitory protein of staphylococci (CHIPS); staphylococcal complement inhibitor (SCIN); formyl peptide receptor-like 1 inhibitor; gamma-hemolysin component B; leukocidins D, E, and S; staphylococcal superantigen-like proteins 1, 3, 5, and 9; and staphylococcal enterotoxin A. Production was determined during in vitro biofilm formation in Iscove's modified Dulbecco's medium at different time points using a competitive Luminex assay and mass spectrometry. Both methods demonstrated the production of the immune modulators SCIN and CHIPS during the early stages of biofilm formation. The green fluorescence protein promoter fusion technology confirmed scn (SCIN) and, to a lesser extent, chp (CHIPS) transcription during the early stages of biofilm formation. Furthermore, we found that SCIN could inhibit human complement activation induced by early biofilms, indicating that S. aureus is able to modulate the innate immune system already during the early stages of biofilm formation in vitro These results form a stepping stone toward elucidating the role of immune modulators in the establishment of biofilms in vivo and present opportunities to develop preventive strategies.