Development of an immunochromatographic strip for detection of antibodies against porcine reproductive and respiratory syndrome virus

Research Progress on Porcine Reproductive and Respiratory Syndrome Virus NSP7 Protein

Porcine reproductive and respiratory syndrome (PRRS) is a highly contagious and severe infectious disease caused by the PRRS virus (PRRSV). PRRS is characterized by reproductive disorders in sows and respiratory dysfunction in pigs. Non-structural protein 7 (NSP7) is one of the most conserved functional proteins in PRRSV, and it plays an important role in viral replication and humoral immune responses in infected hosts. This review discusses the biological characteristics of NSP7 to provide theoretical support for its application in PRRS diagnosis, novel vaccine design, and therapeutic drug development.

Lateral flow immunoassays for antigens, antibodies and haptens detection

Lateral flow immunoassay (LFIA) is widely used as a rapid point-of-care testing (POCT) technique in food safety, veterinary and clinical detection on account of the accessible, fast and low-cost characteristics. After the outbreak of the coronavirus disease 2019 (COVID-19), different types of LFIAs have attracted considerable interest because of their ability of providing immediate diagnosis directly to users, thereby effectively controlling the outbreak. Based on the introduction of the principles and key components of LFIAs, this review focuses on the major detection formats of LFIAs for antigens, antibodies and haptens. With the rapid innovation of detection technologies, new trends of novel labels, multiplex and digital assays are increasingly integrated with LFIAs. Therefore, this review will also introduce the development of new trends of LFIAs as well as its future perspectives.

A Novel Immunochromatographic Strip Based on Latex Microspheres for the Rapid Detection of North American-Type Porcine Reproductive and Respiratory Syndrome Virus

A latex microsphere-based immunochromatographic strip (ICS) test was successfully developed for the rapid and sensitive detection of porcine reproductive and respiratory syndrome virus (PRRSV). The PRRSV N protein-specific monoclonal antibody (mAb) 1H4 labeled with latex microspheres was dispensed on a conjugate pad for use as the detector. The same mAb and goat anti-mouse antibody were blotted on a nitrocellulose membrane to generate test and control lines, respectively. The limit of virus detection was approximately 5 × 10^2.0 median tissue culture infectious dose (TCID₅₀)/ml, and the limit of N protein detection was approximately 15 ng/ml. Other common porcine viruses were tested to evaluate the specificity of the ICS, and positive results were observed for only North American-type PRRSV. A comparison of the strip with a standard diagnostic test (reverse transcriptase polymerase chain reaction, RT-PCR) was also performed, and the results showed that the ICS test exhibited relatively high specificity and sensitivity (90.32 and 73.91%, respectively) and relatively high positive predictive value (PPV) and negative predictive value (NPV; 85 and 82.35%, respectively). These results suggest that the ICS test can be used to rapidly and accurately detect PRRSV and can be suitable for diagnostic applications in the field.

Development of a p72 trimer-based colloidal gold strip for detection of antibodies against African swine fever virus

Abstract

African swine fever virus (ASFV) causes a highly contagious and often lethal swine viral disease, and leads to tremendous economic losses to the swine industry. Unfortunately, there are no vaccines and effective antiviral agents available to prevent and control ASFV outbreaks. Therefore, it is necessary to develop simple and rapid strategies to monitor ASFV-infected pigs to restrain its spread. In the current study, ASFV capsid protein p72 was expressed along with its chaperone pB602L to form trimers in human embryonic kidney 293 (HEK293) cells. The p72 trimers were subsequently labeled with colloidal gold to develop a immunochromatographic strip. The strip showed high specificity to ASFV-positive serum and no cross-reactivity to other swine virus positive sera. Importantly, the strip showed a higher sensitivity of detecting ASFV antibodies in both positive standard serum and clinical serum samples than a commercial enzyme-linked immunosorbent assay (ELISA) kit. Taken together, these results demonstrate the strip as a reliable diagnostic tool against ASFV infection, which will be appropriate for application in prevention and control of ASFV.

Key points

• ASFV p72 trimers were successfully generated.

• A colloidal gold strip was developed based on ASFV p72 trimers.

• The strip is appropriate for detecting ASFV antibodies in the field.

Development of immunochromatographic strip assay for rapid detection of novel goose astrovirus

The novel goose astrovirus (GoAstV) is an emerging pathogenic virus that has resulted in large economic losses to the goose-rearing industry in China since 2016. The novel goose astrovirus cause gout in goslings with a mortality rate of around 50 %. Therefore, an effective diagnostic approach to monitor the spread of GoAstV is necessary. Here, a novel diagnostic immunochromatographic strip (ICS) assay was developed to detect GoAstV. A rapid immunochromatographic assay based on antibody colloidal gold nanoparticles specific to GoAstV was developed for the detection of GoAstV in goose allantoic fluid and supernatant of tissue homogenate. Monoclonal antibodies (Mabs) were prepared using the hybridoma technology, and the polyclonal antibodies (Pabs) were generated by immunizing the rabbits with recombinant ORF2 protein. In addition, the colloidal gold was prepared by reducing gold salt with sodium citrate coupled with Mabs against GoAstV. The optimal concentrations of the coating antibody and the capture antibody were examined as 1.6 mg/mL and 6 μg/mL. The optimal pH of the colloidal gold labeling was pH 8.0. With the visual observation, the lower limit of the ICS was reported to be approximately 1.2 μg/mL. Common diseases of goose were examined to assess the specificity of the ICS, and no cross-reaction was identified. 40 clinical positive samples were simultaneously detected by using the ICS and the PCR with a 92.5% coincidence rate between them. Furthermore, the mentioned samples could be stored at 25 °C and 4 °C for 4 and 6 months, respectively. It was proved that the ICS in this study was highly specific, sensitive, repeatable and more convenient to rapidly detect GoAstV in clinical samples.

Purification of Classical Swine Fever Virus E2 Subunit Vaccines Based on High Affinity Peptide Ligand

BACKGROUND

The purification of expressed proteins is the most critical part of subunit-- vaccine production. Protein-purification methods such as affinity chromatography and ion exchange still have the shortcomings of being time consuming and complicated. With the rapid development of computational molecular-simulation technology, structure-based peptide-ligand design has become feasible. Objection: We aimed to apply molecular docking for a peptide ligand designed for classical swine fever virus (CSFV) E2 purification.

METHODS

Computational-derived peptides were synthesized, and the in vitro binding interaction with E2 was investigated. The effects of purification on E2 were also evaluated.

RESULTS

The best peptide recognizing E2 was P₆, which had a sequence of KKFYWRYWEH. Based on kinetic surface plasmon resonance (SPR) analysis, the apparent affinity constant of P6 was found to be 148 nM. Importantly, P₆ showed suitable binding affinity and specificity for E2 purification from transgenic rice seeds. Evaluation of immune antibodies in mice showed that the antibody- blocking rate on day 42 after inoculation reached 86.18% and 90.68%.

CONCLUSION

The computational-designed peptide in this study has high sensitivity and selectivity and is thus useful for the purification of CSFV E2. The novel method of design provided a broad platform and powerful tool for protein-peptide screening, as well as new insights into CSFV vaccine design.

A rapid and quantitative fluorescent microsphere immunochromatographic strip test for detection of antibodies to porcine reproductive and respiratory syndrome virus

A fluorescent microsphere-based immunochromatographic strip test (FICT) was developed for the rapid, sensitive, and quantitative detection of porcine reproductive and respiratory syndrome virus (PRRSV) antibodies at the pen-side. The assay was based on the formation of a sandwich immune-complex (anti-pig IgG-PRRSV antibodies-NSP7/N), which was validated by a comparison with IDEXX-ELISA using 3325 clinical specimens. The diagnostic specificity, sensitivity, and accuracy of FICT were 97.28, 93.41, and 94.95%, respectively. FICT showed a good correlation with the virus neutralization assay. Overall, a promising pen-side diagnostic tool was developed for the rapid and quantitative detection of PRRSV antibodies within 15 min.

Development of a rapid immunochromatographic strip test for the detection of porcine epidemic diarrhea virus specific SIgA in colostrum

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A rapid immunochromatographic strip test for the detection of porcine epidemic diarrhea virus specific SIgA in colostrum was established.

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The rapid immunochromatographic strip test is sensitive as compared with ELISA.

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The rapid immunochromatographic strip test can be used to epidemiological surveillance as well as vaccine immunity assessment.

Porcine epidemic diarrhea virus (PEDV) causes very high mortality in newborn piglets. The mucosal immune system in the gut must eliminate potential pathogens while maintaining a mutually beneficial relationship with the commensal microbiota. Antibodies derived from the secretory immunoglobulin A (SIgA) class, act as the first line of antigen-specific immunity in the gut by recognizing both pathogens and commensals. Therefore, the measurement of SIgA levels is an important index in evaluating PEDV infections and immune status. A simple and rapid method for the detection of PEDV-specific SIgA using an immunochromatographic test strip has been developed; incorporating a colloidal gold-labeled anti-SIgA secretory component (SC) mAb probe for the detection of anti-PEDV-specific SIgA in swine. On the strip, a gold-labeled anti-SIgA SC mAb was applied to a conjugate pad; purified PEDV particles and goat anti-mouse antibodies were blotted onto a nitrocellulose membrane to form the test and control lines, respectively. Results showed that the immunochromatographic test strip had high sensitivity and specificity. When compared with enzyme-linked immunosorbent assay, kappa value suggesting that the strip could be used to detect PEDV specific SIgA in colostrum samples. Furthermore, the strip assay is rapid and easy to perform with no requirement for professional-level skills or equipment. We found that the immunochromatographic test strip was a rapid, sensitive, and reliable method for the identification of PEDV specific SIgA, indicating its suitability for epidemiological surveillance as well as vaccine immunity when studying PEDV.

Simultaneous detection of porcine reproductive and respiratory syndrome virus and porcine circovirus 3 by SYBR Green І-based duplex real-time PCR

The SYBR Green І-based duplex real-time PCR assay was developed for simultaneous detection of porcine reproductive and respiratory syndrome virus (PRRSV) and porcine circovirus 3 (PCV-3) genomes. PRRSV and PCV-3 were distinguished in the same sample by their distinctive melting temperature (Tm) which was 84 °C for PRRSV and 81.5 °C for PCV-3, and other non-targeted swine viruses showed no specific melting peaks. The detection limits of this assay were 46.1copies/μL for PRRSV and 49.3copies/μL for PCV-3, respectively. Thirty-three lung samples of porcine with respiratory and reproductive failure symptoms were collected and confirmed by the SYBR Green І-based real-time PCR assay and conventional PCR assay. The real-time PCR detection results showed that the PRRSV positive rate was 45.45%, the PCV-3 positive rate was 63.63%, the PRRSV and PCV-3 co-infection positive rate was 36.36%, which were more sensitive than conventional PCR detection. This duplex real-time PCR assay could be a rapid, sensitive and reliable method for the detection of PRRSV and PCV-3 co-infection.

Fluorescence resonance energy transfer combined with asymmetric PCR for broad and sensitive detection of porcine reproductive and respiratory syndrome virus 2

With its ever-increasing viral genetic diversity, accurate diagnosis of porcine reproductive and respiratory syndrome virus (PRRSV) infection is indispensable for PRRSV control. Here, a sensitive graphene oxide (GO)-based FRET method was developed to detect PRRSV-2 based on the ability of GO to quench fluorophore by fluorescence resonance energy transfer (FRET). Using primers and a fluorophore-labeled ssDNA probe targeting a conserved region between the PRRSV M gene and 3'UTR, asymmetric PCR specifically amplified viral ssDNA that could anneal with probe to generate dsDNA only in the presence of virus. Upon exonuclease III treatment to release the probe fluorophore, which degrades dsDNA with blunt ends or recessed 3´-termini, the ssDNA annealed with other probe to generate enhanced fluorescence. This GO-based FRET assay specifically detected both classical and highly pathogenic PRRSV, with analytical sensitivity approaching 10 copies/μL, similar to that of real-time PCR but greater than that of conventional reverse transcription PCR (RT-PCR). Consistent with real-time RT-PCR detection, the assay developed here exhibited high diagnostic sensitivity for virus detection of sera from experimentally and naturally infected pigs. Thus, this novel GO-based FRET assay combined with asymmetric PCR detection is sensitive and specific and will be valuable for future PRRSV diagnosis.

Antigen of 49.6-kDa subunitpili protein of Helicobacter pylori as a potential biomarker for early and rapid detection of the infection

Background and Aim:

Helicobacter pylori infection has been identified as a major cause of peptic ulcer diseases, including gastric and duodenal ulcers, gastritis, chronic and gastric carcinoma, and even gastric lymphoma. In vitro studies using Western blotting analysis, hemagglutination test, adherence inhibition assays, and immunocytochemical staining revealed that the 49.6-kDa subunit pili protein of H. pylori was considered an immunogenic protein. This study aimed to develop a serological diagnostic test using 49.6 kDa for detecting antibodies against H. pylori proteins in an early phase of the infection.

Materials and Methods:

An in-house immunochromatographic test (ICT) kit was developed and used to test a panel of sera sample obtained from a randomly selected symptomatic patient, in which 40 sera were H. pylori positive and 40 sera were H. pylori negative.

Results:

The results showed that ICT with 49.6 kDa as an antigen was highly sensitive and specific for detecting anti-H. pylori immunoglobulin G antibodies in human serum, with a high negative predictive value.

Conclusion:

The developed test could be used to exclude H. pylori infection in symptomatic patients.

Development of luciferase-linked antibody capture assay based on luciferase immunoprecipitation systems for antibody detection of porcine reproductive and respiratory syndrome virus

BACKGROUND

Early detection of porcine reproductive and respiratory syndrome virus (PRRSV) infection of swine is necessary to control this devastating disease. By monitoring host serum antibodies to viral antigens, early virus detection within herds is feasible. In this study, recombinant antigens were generated using recombinant DNA techniques to fuse PRRSV structural protein (N) or nonstructural protein 1α (nsp1α) with the Rellina luciferase gene. Next, fused genes were cloned into plasmids and transfected into HEK-293 T cells for transient expression. Upon co-incubation of lysates with pig sera, antigen-antibody complexes formed that bound to Protein-G coated onto microplates. By further measurement of luminance value, a modified form of Luciferase Immunoprecipitation Systems, namely luciferase-linked antibody capture assay (LACA) was developed for detection of PRRSV-specific antibodies.

RESULTS

Known anti-PRRSV antibody-positive or -negative serum samples (125 and 122 samples, respectively) were used to validate the LACA and compared it with IDEXX PRRS ×3 ELISA. Based on the result, N-Rluc and nsp1α-Rluc LACA results were 95.3 and 94.4% in agreement with IDEXX ELISA, suggested a similar specificity of LACA to IDEXX ELISA. Moreover, when both LACA and IDEXX ELISA were used to evaluate sequential serum samples obtained from PRRSV experimentally infected pigs, the PRRSV-specific antibody response was detectable as early as 3 days post-inoculation (dpi) using N-Rluc LACA, but undetectable until 7 dpi using IDEXX ELISA, suggesting an improved sensitivity of LACA. Meanwhile, antibodies specific for nsp1α were detected at higher levels overall, but were undetectable until 10 dpi. Furthermore,. Notably, one IDEXX ELISA positive result was not confirmed by LACA or IFA and was thus considered a false-positive result.

CONCLUSION

The LACA exhibited similar specificity but improved sensitivity to that of the commercial IDEXX PRRS ×3 ELISA kit for detection of PRRSV-specific antibodies in pig serum. Importantly, LACA could be adapted for detecting antibodies against other PRRSV targets, such as nsp1α, to achieve earlier detection of PRRSV infection.

A Novel Diagnostic Method to Detect Duck Tembusu Virus: A Colloidal Gold-Based Immunochromatographic Assay

Duck Tembusu virus (DTMUV) is an emerging pathogenic flavivirus that has resulted in large economic losses to the duck-rearing industry in China since 2010. Therefore, an effective diagnostic approach to monitor the spread of DTMUV is necessary. Here, a novel diagnostic immunochromatographic strip (ICS) assay was developed to detect DTMUV. The assay was carried out using colloidal gold coated with purified monoclonal antibody A12D3 against envelope E protein. Purified polyclonal C12D1 antibodies from BALB/c mice against the envelope E protein were used as the capture antibody. Goat anti-mouse IgG was used to detect DTMUV, which was also assembled on the ICS. Results showed that the ICS could specifically detect DTMUV within 10 min. It also could be stored 25 and 4°C for 4 and 6 months, respectively. The sensitivity of the ICS indicated that the dilution multiples of positive allantoic fluid of DTMUV (LD50: 10^4.33/0.2 ml) was up to 200. Its specificity and sensibility showed no significant change under the above storage situations. Fifty clinical samples were simultaneously detected by ICS and reverse-transcription polymerase chain reaction with a 93.9% coincidence rate between them. It proved that the ICS in the present study was highly specific, sensitive, repeatable, and more convenient to rapidly detect DTMUV in clinical samples.

The Nucleocapsid Protein and Nonstructural Protein 10 of Highly Pathogenic Porcine Reproductive and Respiratory Syndrome Virus Enhance CD83 Production via NF-κB and Sp1 Signaling Pathways

Porcine reproductive and respiratory syndrome, caused by porcine reproductive and respiratory syndrome virus (PRRSV), is a panzootic disease that is one of the most economically costly diseases to the swine industry. A key aspect of PRRSV virulence is that the virus suppresses the innate immune response and induces persistent infection, although the underlying mechanisms are not well understood. The dendritic cell (DC) marker CD83 belongs to the immunoglobulin superfamily and is associated with DC activation and immunosuppression of T cell proliferation when expressed as soluble CD83 (sCD83). In this study, we show that PRRSV infection strongly stimulates CD83 expression in porcine monocyte-derived DCs (MoDCs) and that the nucleocapsid (N) protein and nonstructural protein 10 (nsp10) of PRRSV enhance CD83 promoter activity via the NF-κB and Sp1 signaling pathways. R43A and K44A amino acid substitution mutants of the N protein suppress the N protein-mediated increase of CD83 promoter activity. Similarly, P192-5A and G214-3A mutants of nsp10 (with 5 and 3 alanine substitutions beginning at residues P192 and G214, respectively) abolish the nsp10-mediated induction of the CD83 promoter. Using reverse genetics, four mutant viruses (rR43A, rK44A, rP192-5A, and rG214-3A) and four revertants [rR43A(R), rK44A(R), rP192-5A(R), and rG214-3A(R)] were generated. Decreased induction of CD83 in MoDCs was observed after infection by mutants rR43A, rK44A, rP192-5A, and rG214-3A, in contrast to the results obtained using rR43A(R), rK44A(R), rP192-5A(R), and rG214-3A(R). These findings suggest that PRRSV N and nsp10 play important roles in modulating CD83 signaling and shed light on the mechanism by which PRRSV modulates host immunity.IMPORTANCE Porcine reproductive and respiratory syndrome virus (PRRSV) is one of the most economically costly pathogens affecting the swine industry. It is unclear how PRRSV inhibits the host's immune response and induces persistent infection. The dendritic cell (DC) marker CD83 belongs to the immunoglobulin superfamily and has previously been associated with DC activation and immunosuppression of T cell proliferation and differentiation when expressed as soluble CD83 (sCD83). In this study, we found that PRRSV infection induces sCD83 expression in porcine MoDCs via the NF-κB and Sp1 signaling pathways. The viral nucleocapsid protein, nonstructural protein 1 (nsp1), and nsp10 were shown to enhance CD83 promoter activity. Amino acids R43 and K44 of the N protein, as well as residues 192 to 196 (P192-5) and 214 to 216 (G214-3) of nsp10, play important roles in CD83 promoter activation. These findings provide new insights into the molecular mechanism of immune suppression by PRRSV.