HRP-conjugated-nanobody-based cELISA for rapid and sensitive clinical detection of ASFV antibodies

Abstract

African swine fever (ASF), which is caused by the ASF virus (ASFV), is a highly contagious hemorrhagic disease that causes high mortality to domestic porcine and wild boars and brings huge economic losses to world swine industry. Due to the lack of an effective vaccine, the control of ASF must depend on early, efficient, and cost-effective detection and strict control and elimination strategies. Traditional serological testing methods are generally associated with high testing costs, complex operations, and high technical requirements. As a promising alternative diagnostic tool to traditional antibodies, nanobodies (Nb) have the advantages of simpler and faster generation, good stability and solubility, and high affinity and specificity, although the system is dependent on the immunization of Bactrian camels to obtain the specific VHH library of the target protein. The application of Nbs in the detection of ASFV antibodies has not yet been reported yet. Using a phage display technology, one Nb against the ASFV p54 protein that exhibited high specificity and affinity, Nb8, was successfully screened. A HEK293T cell line stably expressing Nb8-horseradish peroxidase (HRP) fusion protein was established using the lentiviral expression system. Following the optimization of the reaction conditions, the Nb8-HRP fusion protein was successfully used to establish a competitive enzyme-linked immunosorbent assay (cELISA) to detect ASFV-specific antibodies in pig serum, for the first time. There was no cross-reaction with healthy pig serum, porcine pseudorabies virus (PRV), porcine reproductive and respiratory syndrome virus (PRRSV), classical swine fever virus (CSFV), porcine epidemic diarrhea virus (PEDV), and classical swine fever virus (CSFV) positive sera. The optimal cut-off value for the cELISA by ROC analysis was 52.5%. A total of 209 serum samples were tested using the developed cELISA and a commercial ELISA kit. The results showed that the relative specificity of the cELISA was 98.97%, and the relative sensitivity of the cELISA was 93.3%, with the percent agreement between the two ELISA methods being 98.56%. In conclusion, a specific, sensitive, and repeatable cELISA was successfully developed based on the Nb8 as a probe, providing a promising method for the detection of anti-ASFV antibodies in clinical pig serum.

Key points

• We successfully screened a specific, high affinity nanobody against ASFV p54 protein.

• We establish a method for continuous and stable expression of Nb-HRP fusion protein using a lentiviral packaging system.

• We establish a nanobody cELISA detection method that can monitor an ASF infection.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00253-022-11981-4.

Nanoplasmonic multiplex biosensing for COVID-19 vaccines

The ongoing emergence of severe acute respiratory syndrome caused by the new coronavirus (SARS-CoV-2) variants requires swift actions in identifying specific antigens and optimizing vaccine development to maximize the humoral response of the patient. Measuring the specificity and the amount of antibody produced by the host immune system with high throughput and accuracy is critical to develop timely diagnostics and therapeutic strategies. Motivated by finding an easy-to-use and cost-effective alternative to existing serological methodologies for multiplex analysis, we develop a proof-of-concept multiplex nanoplasmonic biosensor to capture the humoral response in serums against multiple antigens. Nanoplasmonic sensing relies on the wavelength shift of the localized surface plasmon resonance (LSPR) peak of gold nanostructures upon binding interactions between the antibodies and the immobilized antigens. Here the antigens are first immobilized on different sensing areas by using a mono-biotinylation system based on the high affinity interaction between biotin and streptavidin. We then validate the multiplex platform by detecting the presence of 3 monoclonal antibodies against 3 antigens (2 different hemagglutinins (HAs) from influenza viruses, and the SARS-CoV-2 Spike RBD (receptor binding domain)). We also measure the humoral response in murine sera collected before and after its immunization with the SARS-CoV-2 Spike protein, in good agreement with the results obtained by the ELISA assay. Our nanoplasmonic assays have successfully demonstrated multiple serum antibody profiling, which can be further integrated with microfluidics as an effective high throughput screening platform in future studies for the ongoing SARS-CoV-2 vaccine development.

The Accuracy of the Serum Antibody Test for Helicobacter pylori Infection among Junior High School Students

OBJECTIVE

Recently, screening for Helicobacter pylori infection has been performed among children in Japan as a prevention strategy for gastric cancer. However, the diagnostic accuracy of the serum antibody test, using the ELISA-kit, for screening in children has not been confirmed, and it is unknown whether the cutoff value used for adults is appropriate for children. The aim of this study was to evaluate the accuracy of the serum antibody test for H. pylori infection for the mass screening of junior high school students in Japan.

SUBJECTS AND METHODS

H. pylori infection testing and eradication therapy in junior high schools began in the 2015 fiscal year for students in Yurihonjo and Nikaho cities, located in the Akita prefecture. The data of 410 students who underwent both stool antigen tests (SATs) and serum antibody test, between 2016 and 2018, were used for analysis. Students who had positive results on the SATs test were diagnosed with H. pylori infection.

RESULTS

The rate of H. pylori infection was 3.7% (15/410). The optimal cutoff of serum antibody for children was identified to be 5.4 U/mL, with this cutoff having an area under the curve of 0.94 (95% CI 0.83-1.00), specificity of 99.5% (95% CI 98.2-99.9) and sensitivity of 93.3% (95% CI 68.1-99.8), which was wide because of the small sample size.

CONCLUSION

The accuracy of the serum antibody test may be enough for practical use in children 13-14 years old.

Serum Helicobacter pylori antibody reactivity in seven Asian countries using an automated latex aggregation turbidity assay

BACKGROUND AND AIM

To determine the application range of diagnostic kits utilizing anti-Helicobacter pylori antibody, we tested a newly developed latex aggregation turbidity assay (latex) and a conventional enzyme-linked immunosorbent assay (E-plate), both containing Japanese H. pylori protein lysates as antigens, using sera from seven Asian countries.

METHODS

Serum samples (1797) were obtained, and standard H. pylori infection status and atrophy status were determined by culture and histology (immunohistochemistry) using gastric biopsy samples from the same individuals. The two tests (enzyme-linked immunosorbent assay and latex) were applied, and receiver operating characteristics analysis was performed.

RESULTS

Area under the curve (AUC) from the receiver operating characteristic of E-plate and latex curves were almost the same and the highest in Vietnam. The latex AUC was slightly lower than the E-plate AUC in other countries, and the difference became statistically significant in Myanmar and then Bangladesh as the lowest. To consider past infection cases, atrophy was additionally evaluated. Most of the AUCs decreased using this atrophy-evaluated status; however, the difference between the two kits was not significant in each country, but the latex AUC was better using all samples. Practical cut-off values were 3.0 U/mL in the E-test and 3.5 U/mL in the latex test, to avoid missing gastric cancer patients to the greatest extent possible.

CONCLUSIONS

The kits were applicable in all countries, but new kits using regional H. pylori strains are recommended for Myanmar and Bangladesh. Use of a cut-off value lower than the best cut-off value is essential for screening gastric cancer patients.

Serum Antibody Against NY-ESO-1 and XAGE1 Antigens Potentially Predicts Clinical Responses to Anti-Programmed Cell Death-1 Therapy in NSCLC

INTRODUCTION

Programmed cell death-1 (PD-1) inhibitors effectively treat NSCLC and prolong survival. Robust biomarkers for predicting clinical benefits of good response and long survival with anti-PD-1 therapy have yet to be identified; therefore, predictive biomarkers are needed to select patients with benefits.

METHODS

We conducted a prospective study to explore whether serum antibody against NY-ESO-1 and/or XAGE1 cancer-testis antigens predicted primarily good clinical response and secondarily long survival with anti-PD-1 therapy for NSCLC. The serum antibody was detected by enzyme-linked immunosorbent assay, and tumor immune microenvironment and mutation burden were analyzed by immunohistochemistry and next-generation sequencing.

RESULTS

In the discovery cohort (n = 13), six antibody-positive NSCLC cases responded to anti-PD-1 therapy (two complete and four partial responses), whereas seven antibody-negative NSCLC cases did not. Antibody positivity was associated with good response and survival, regardless of tumor programmed death ligand 1 (PD-L1) expression, mutation burden, and CD8⁺ T-cell infiltration. In the validation cohort (n = 75), 17 antibody-positive NSCLC cases responded well to anti-PD-1 therapy as compared with 58 negative NSCLC cases (objective response rate 65% versus 19%, p = 0.0006) and showed significantly prolonged progression-free survival and overall survival. Antibody titers highly correlated with tumor reduction rates. In the multivariate analysis, response biomarkers were tumor programmed death ligand 1 expression and antibody positivity, and only antibody positivity was a significantly better predictive biomarker of progression-free survival (hazard ratio = 0.4, p = 0.01) and overall survival (hazard ratio = 0.2, p = 0.004).

CONCLUSIONS

Our results suggest that NY-ESO-1 and/or XAGE1 serum antibodies are useful biomarkers for predicting clinical benefits in anti-PD-1 therapy for NSCLC and probably for other cancers.

Cutoff Pepsinogen Level for Predicting Unintendedly Eradicated Cases of Helicobacter pylori Infection in Subjects with Seemingly Normal Pepsinogen Levels

BACKGROUNDS/AIMS

In the ABC method, which is a method for risk stratification of gastric cancer using serum anti-Helicobacter pylori antibody and pepsinogen (PG) test, subjects with normal PG and seronegative for H. pylori are named as "Group A" and are regarded as having a low risk of gastric cancer. These "Group A" subjects include unintentionally eradicated cases at relatively high risk, and this study aimed to identify these subjects.

METHODS

Of the 109 subjects, 76 were classified as uninfected Group A subjects with negative histologic H. pylori infection and no histologic and endoscopic atrophy, and 33 subjects were classified serologically as Group A after successful eradication, which are serologically equal to the unintendedly eradicated cases in Group A. The usefulness of measuring PG levels to detect post-eradication cases was validated by using a receiver operating characteristic (ROC) curve analysis.

RESULTS

The area under the ROC curve for PGI level was 0.736 ± 0.06 (p < 0.01; cutoff value, 37.0 ng/mL; sensitivity, 77.6%; specificity, 72.7%), and that for the PGI/II ratio was 0.660 ± 0.06 (p < 0.01; cutoff value, 5.1; sensitivity, 84.2%; specificity, 43.4%).

CONCLUSION

PGI levels of ≤37 ng/mL and PGI/II ratios of ≤5.1 effectively identified unintendedly eradicated cases in Group A.

Development of an antigen specific colloidal gold immunochromatographic assay for detection of antibody to M. wenyonii in bovine sera

The goal of this research was to develop a colloidal gold immunochromatographic strip test for detection of antibody to Mycoplasma wenyonii (M. wenyonii) in bovine using specific antigen. M. wenyonii was isolated from blood samples from the spontaneously infected cattle in Hebei province, China. Suspensions of the M. wenyonii antigenic proteins were prepared by freeze-thaw cycles and ultrasonication. Candidate antigens were screened with sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) and Western blotting. The specific bands of the most antigenic proteins were excised from the gel and were purified by using a gel extraction kit. A colloidal gold immunochromatographic assay using the purified specific proteins as the coating antigen (sp-GICA) was developed for detection of antibody to M. wenyonii. Blood samples from cows in the field were tested for antibody to M. wenyonii by the sp-GICA strip and enzyme-linked immunosorbent assay (ELISA) simultaneously to compare the specificity, sensitivity and accuracy. The results showed that the specific proteins bands with sufficient immunoreactivity have been identified. The apparent molecular weights of the proteins were 115 kDa and 60 kDa, respectively. The stability and reproducibility were quite excellent after the storage of the strip at room temperature for 5 months. This sp-GICA showed 95.48% (148/155), 92.86% (39/42) and 94.92% (187/197) in terms of specificity, sensitivity and accuracy compared to ELISA. The sp-GICA described here shows excellent agreement with ELISA and it is shown to be a simple, convenient, specific and highly sensitive assay for detection of serum antibodies to M. wenyonii.

A Luciferase Immunoprecipitation System (LIPS) assay for profiling human norovirus antibodies

A luciferase immunoprecipitation systems (LIPS) assay was developed to define the antigenic specificity and titer of antibodies directed against human norovirus (HuNoV). Recombinant proteins, expressed by plasmid constructs encoding Renilla luciferase (Ruc) fused to the full-length HuNoV major capsid protein (VP1) (Ruc-antigen), were generated for ten HuNoV strains. In addition, subdomain constructs Ruc-Shell (S) and Ruc-Protruding (P) were engineered for a representative GII.4 norovirus (strain GII.4/2006b). The LIPS assay measured antibody levels in a well-defined panel of HuNoV-specific sera, and the results were compared to an ELISA standard. In hyperimmune sera, the LIPS produced titers similar to or higher than those measured by the ELISA of HuNoV-specific antibodies. The specificity of antibodies in various sera was profiled by LIPS with a panel of diverse Ruc-antigens containing full-length HuNoV VP1 proteins or VP1 subdomains, and the assay detected both specific and cross-reactive antibodies. Competition assays, in which antibodies were pre-incubated with one or more intact VLPs representing different genotypes, proved useful in further assessment of the antibody specificity detected by LIPS in complex polyclonal sera. The profiling of HuNoV-specific antibodies in the high-throughput LIPS format may prove useful in defining the strength or specificity of the adaptive immune response following natural infection or vaccination.

Molecular immune response of channel catfish immunized with live theronts of Ichthyophthirius multifiliis

The parasite Ichthyophthirius multifiliis (Ich) has been reported in various freshwater fishes worldwide and results in severe losses to both food and aquarium fish production. The fish surviving natural infections or immunized with live theronts develop strong specific and non-specific immune responses. Little is known about how these immune genes are induced or how they interact and lead to specific immunity against Ichthyophthirius multifiliis in channel catfish Ictalurus punctatus. This study evaluated the differential expression of immune-related genes, including immunoglobulin, immune cell receptor, cytokine, complement factor and toll-like receptors in head kidney from channel catfish at different time points after immunization with live theronts of I. multifiliis. The immunized fish showed significantly higher anti-Ich antibody expressed as immobilization titer and ELISA titer than those of control fish. The vast majority of immunized fish (95%) survived theront challenge. Expression of IgM and IgD heavy chain genes exhibited a rapid increase from 4 hour (h4) to 2 days (d2) post immunization. Expression of immune cell receptor genes (CD4, CD8-α, MHC I, MHC II β, TcR-α, and TcR-β) showed up-regulation from h4 to d6 post immunization, indicating that different immune cells were actively involved in cellular immune response. Cytokine gene expression (IL-1βa, IL-1βb, IFN-γ and TNF-α) increased rapidly at h4 post immunization and were at an up-regulated level until d2 compared to the bovine serum albumin control. Expression of complement factor and toll-like receptor genes exhibited a rapid increase from h4 to d2 post immunization. Results of this study demonstrated differential expression of genes involved in the specific or non-specific immune response post immunization and that the vaccination against Ich resulted in protection against infection by I. multifiliis.

T7 Phage Display Library a Promising Strategy to Detect Tuberculosis Specific Biomarkers

One-third of the world's population is infected with tuberculosis, only 10% will develop active disease and the remaining 90% is considered to have latent TB (LTB). While active TB is contagious and can be lethal, the LTB can evolve to active TB. The diagnosis of TB can be challenging, especially in the early stages, due to the variability in presentation and nonspecific signs and symptoms. Currently, we have limited tools available to diagnose active TB, predict treatment efficacy and cure of active tuberculosis, the reactivation of latent tuberculosis infection, and the induction of protective immune responses through vaccination. Therefore, the identification of robust and accurate tuberculosis-specific biomarkers is crucial for the successful eradication of TB. In this commentary, we summarized the available methods for diagnosis and differentiation of active TB from LTB and their limitations. Additionally, we present a novel peptide microarray platform as promising strategy to identify TB biomarkers.

Serum Helicobacter pylori KatA and AhpC antibodies as novel biomarkers for gastric cancer

AIM: To investigate catalase (KatA) and alkyl hydroperoxide reductase (AhpC) antibodies of Helicobacter pylori as biomarkers for gastric cancer (GC).

METHODS: This study included 232 cases and 264 controls. Recombinant KatA and AhpC proteins were constructed and the levels of antibodies were tested by indirect enzyme-linked immunosorbent assay (ELISA). Logistic regression was applied to analyze the relationships between KatA, AhpC and GC. The χ² trend test was used to evaluate the dose-response relationships between serum KatA and AhpC antibody levels and GC. Receiver operating characteristic (ROC) curve was used to evaluate the screening accuracy of KatA and AhpC as biomarkers. Combined analysis was used to observe screening accuracy of predictors for GC.

RESULTS: In all subjects, the association between KatA and AhpC and GC risk was significant (P < 0.001) with odds ratio (OR) = 12.84 (95%CI: 7.79-21.15) and OR = 2.4 (95%CI: 1.55-3.73), respectively. KatA and AhpC antibody levels were strongly related to GC risk with a dose-dependent effect (P for trend < 0.001). The area under the ROC (AUC) for KatA was 0.806, providing a sensitivity of 66.81% and specificity of 86.36%; and the AUC for AhpC was 0.615, with a sensitivity of 75.65% and specificity of 45.49%. The AUC was 0.906 for KatA and flagella protein A (FlaA) combined analysis.

CONCLUSION: Serum KatA and AhpC antibodies are associated with GC risk and KatA may serve as a biomarker for GC. KatA/FlaA combined analysis improved screening accuracy.

Development of a blocking latex agglutination test for the detection of antibodies to chicken anemia virus

A blocking latex agglutination test (b-LAT) developed in this study was evaluated for the detection of antibodies against chicken anemia virus (CAV) in chickens. Polystyrene latex beads were coupled with a neutralizing monoclonal antibody (mAb) to CAV (mAb-beads). When mAb-beads were mixed with antigens prepared from the lysate of MDCC-MSB1 cells infected with CAV, agglutination occurred. A short pre-incubation of CAV antigens with CAV-specific antiserum inhibited the agglutination of mAb-beads. The test results were obtained within 5min. The specificity of b-LAT was evaluated using sera from specific pathogen-free chickens and sera containing antibodies to avian influenza virus, Newcastle disease virus, infectious bursal disease virus, and Marek's disease virus; nonspecific agglutination and cross-reactivity with antibodies to unrelated viruses were not observed. The examination of 94 serum samples collected from commercial breeder chickens of various ages (17-63 weeks) revealed good agreement (93.6%, Kappa value=0.82) between b-LAT and a virus neutralization test, known to be most sensitive and specific in the detection of antibodies to CAV. These results indicate that b-LAT, a simple and rapid test, is a useful and reliable tool in CAV serology.

Development of serum antibodies during early infancy in rhesus macaques: implications for humoral immune responses to vaccination at birth

BACKGROUND

A better understanding of immune responses in human infants could lead to more effective immunization and vaccination strategies in early life.

METHODS

Since antibodies are key components of protective vaccine responses, we examined developmental changes in serum levels of immunoglobulins (IgG, IgA, IgM) in infant rhesus macaques from birth through 6 months of age.

RESULTS

As in human infants, macaques are born with high levels of IgG in sera, with rapid increases in serum IgM, yet very slow increases in levels of IgA from birth. We also examined levels of anti-tetanus antibodies in infants born to vaccinated dams to distinguish and track maternal and infant antibodies. These data suggest essentially all serum IgG in newborn infants is derived from the dams, which gradually wanes over a few weeks. In contrast, levels of IgM and IgA appear to all be infant-derived, as evidenced by their low to undetectable levels at birth. In addition, abnormally high levels of serum IgM and IgA were detected in a few infants, which correlated with specific, yet clinically silent disease processes.

CONCLUSIONS

Our data indicate that newborn macaques have competent immune systems, and are able to produce their own antibodies in response to exposure to environmental antigens immediately upon birth.

Development of a simplified and convenient assay for cell-mediated immunity to the mumps virus

Because methods for measuring cell-mediated immunity (CMI) to the mumps virus are expensive, time-consuming, and technically demanding, the role of CMI in mumps virus infection remains unclear. To address this issue, we report here the development of a simplified method for measuring mumps virus-specific CMI that is suitable for use in diverse laboratory and clinical settings. A mumps vaccine was cultured with whole blood, and interferon (IFN)-γ released into the culture supernatant was measured using an enzyme-linked immunosorbent assay. IFN-γ production in blood from vaccinated subjects markedly increased in response to the vaccine and decreased before the antibody titer decreased in some cases, suggesting that this assay may be used as a simple surrogate method for measuring CMI specific for the mumps virus.

Immune responses to pneumococcal pilus RrgA and RrgB antigens and their relationship with pneumococcal carriage in humans

OBJECTIVES

Pneumococcal pilus antigens are shown to be important in pneumococcal pathogenesis and induce protective immunity in animal studies, but data in humans are limited. We aimed to investigate serum and mucosal immune responses to pilus-1 proteins (RrgA and RrgB) and their relationship with pneumococcal carriage in humans.

METHODS

Serum and salivary antibodies to RrgA and RrgB in children and adults were analysed by ELISA and immunoblotting. Induction of B cell antibody responses to RrgA and RrgB in nasopharynx-associated lymphoid tissue was studied by ELISpot assay following stimulation with pneumococcal culture supernatants containing pilus proteins.

RESULTS

Significant levels of serum anti-RrgA and -RrgB antibodies were observed, and anti-RrgA antibody appeared to develop earlier in childhood. Importantly, anti-RrgA IgG titres in both serum and saliva were shown to be higher in culture-negative children than in those who were culture-positive for Streptococcus pneumoniae. Stimulation of adenotonsillar cells with pneumococcal culture supernatant induced significant RrgA- and RrgB-specific antibody secreting cells and antibody production.

CONCLUSIONS

Pneumococcal pilus antigens, particularly RrgA, seem to induce significant serum and mucosal antibody responses that may contribute to natural immunity against pneumococcal carriage in children.