Detection of parvovirus B19 NS1-specific antibodies by ELISA and western blotting employing recombinant NS1 protein as antigen

The PentaFOLD 3.0 Algorithm for the Selection of Stable Elements of Secondary Structure to be Included in Vaccine Peptides

AIMS

The aim of this study was to create a new version of the PentaFOLD algorithm and to test its performance experimentally in several proteins and peptides.

BACKGROUND

Synthetic vaccines can cause production of neutralizing antibodies only in case if short peptides form the same secondary structure as fragments of full-length proteins. The Penta- FOLD 3.0 algorithm was designed to check stability of alpha helices, beta strands, and random coils using several propensity scales obtained during analysis of 1730 3D structures of proteins.

OBJECTIVE

The algorithm has been tested in the three peptides known to keep the secondary structure of the corresponding fragments of full-length proteins: the NY25 peptide from the Influenza H1N1 hemagglutinin, the SF23 peptide from the diphtheria toxin, the NQ21 peptide from the HIV1 gp120; as well as in the CC36 peptide from the human major prion protein.

METHODS

Affine chromatography for antibodies against peptides accompanied by circular dichroism and fluorescence spectroscopy were used to check the predictions of the algorithm.

RESULTS

Immunological experiments showed that all abovementioned peptides are more or less immunogenic in rabbits. The fact that antibodies against the NY25, the SF23, and the NQ21 form stable complexes with corresponding full-length proteins has been confirmed by affine chromatography. The surface of SARS CoV-2 spike receptor-binding domain interacting with hACE2 has been shown to be unstable according to the results of the PentaFOLD 3.0.

CONCLUSION

The PentaFOLD 3.0 algorithm (http://chemres.bsmu.by/PentaFOLD30.htm) can be used with the aim to design vaccine peptides with stable secondary structure elements.

Human Parvoviruses

Parvovirus B19 (B19V) and human bocavirus 1 (HBoV1), members of the large Parvoviridae family, are human pathogens responsible for a variety of diseases. For B19V in particular, host features determine disease manifestations. These viruses are prevalent worldwide and are culturable in vitro, and serological and molecular assays are available but require careful interpretation of results. Additional human parvoviruses, including HBoV2 to -4, human parvovirus 4 (PARV4), and human bufavirus (BuV) are also reviewed. The full spectrum of parvovirus disease in humans has yet to be established. Candidate recombinant B19V vaccines have been developed but may not be commercially feasible. We review relevant features of the molecular and cellular biology of these viruses, and the human immune response that they elicit, which have allowed a deep understanding of pathophysiology.

Parvovirus B19 Achievements and Challenges

Parvovirus B19 is a widespread human pathogenic virus, member of the Erythrovirus genus in the Parvoviridae family. Infection can be associated with an ample range of pathologies and clinical manifestations, whose characteristics and outcomes depend on the interplay between the pathogenetic potential of the virus, its adaptation to different cellular environments, and the physiological and immune status of the infected individuals. The scope of this review is the advances in knowledge on the biological characteristics of the virus and of virus-host relationships; in particular, the interactions of the virus with different cellular environments in terms of tropism and ability to achieve a productive replicative cycle, or, on the contrary, to establish persistence; the consequences of infection in terms of interference with the cell physiology; the process of recognition of the virus by the innate or adaptive immune system, hence the role of the immune system in controlling the infection or in the development of clinical manifestations. Linked to these issues is the continuous effort to develop better diagnostic algorithms and methods and the need for development of prophylactic and therapeutic options for B19V infections.

Antibodies against structural and nonstructural proteins of human bocavirus in human sera

Immunofluorescence assays (IFAs) for detection of human bocavirus (HBoV) proteins (VP1, VP2, NP-1, and NS1) were developed. The VP1 IFA was the most sensitive for detection of IgG antibody and suitable for screening. IgG antibodies in convalescent-phase sera from HBoV-positive patients were detected by VP1 and VP2 IFAs. Sensitivities of NP-1 and NS1 IFAs were low.

Unscrambling the role of human parvovirus B19 signaling in systemic autoimmunity

Despite enormous progress in understanding how the immune system works, the pathogenesis of autoimmune diseases still remains unclear. Growing evidence indicates that infectious agents can be potent initial triggers, subverting and exploiting host cell signaling pathways. This role is exemplified by the association of parvovirus B19 (B19) with human autoimmune disease. Infection with this common virus exhibits striking similarities with systemic autoimmune diseases, and can be associated with elevated serum autoantibody titers. The B19 virus produces proline-rich, 11-kDa proteins that have been implicated in modulation of host signaling cascades involved in virulence and pathogenesis. Additionally, B19 produces a non-structural protein (NS1) that functions as a transcription regulator by directly binding the p6 promoter and the Sp1/Sp3 transcription factors. The protein is also involved in DNA replication, cell cycle arrest and initiation of apoptotic damage, particularly in erythroid cells. When transfected to non-permissive cells, NS1 recruits the mitochondria cell death pathway. It is even more remarkable that NS1 functions as a trans-acting transcription activator for the IL6 promoter, up-regulating IL6 expression in host cells. Hence, B19 infection may play a pivotal role in triggering inflammatory disorders. By promoting apoptotic damage and trans-activating pro-inflammatory cytokine promoters, B19 may break the delicate balance between cell survival and apoptosis, and may contribute to immune deregulation. Understanding the mechanisms used by B19 to alter the cell signaling machinery may provide further insight into the mechanism by which autoimmune diseases develop.

Serologic and molecular detection of human Parvovirus B19 infection

Following its identification by Yvonne Cossart in 1975, human Parvovirus B19 has been recognized as the causative agent of a wide range of diseases. In childhood, the most common disease is a typical exanthema called "fifth disease". In adults, viral infection may be responsible for fetal loss and for aplastic anaemia in immuno-compromised patients. Because persistent viral infection may induce an autoimmune response, Parvovirus B19 is emerging as an environmental factor linked to the pathogenesis of autoimmunity. As a result of its expanding disease spectrum, Parvovirus B19 is the subject of intense efforts to clarify the pathogenesis of virus-related disorders as well as improve diagnostic laboratory testing including standardization of serological and nucleic acid-based detection assays. Enzymatic immunoassays based on conformational antigens have proven to be the most important tools for accurate diagnosis in the majority of cases. In other selected clinical cases, the detection of Parvovirus B19 infection can be complemented by PCR and, more recently, by the real-time PCR.

The recombinant nonstructural polyprotein NS1 of porcine parvovirus (PPV) as diagnostic antigen in ELISA to differentiate infected from vaccinated pigs

To differentiate pigs infected with porcine parvovirus (PPV) from those vaccinated with inactivated whole-virus vaccine, an enzyme-linked immunosorbent assay (ELISA) based on detection of a nonstructural polyprotein 1 (NS1) was developed. A threshold of 0.23 optical density units was established and the assay had high specificity (100), sensitivity (88), accuracy (90) and positive predictive value (100) using haemagglutination inhibition as the standard method. A reproducibility test revealed that the coefficients of variation of sera within-plates and between-run were less than 10%. The assay showed no cross-reactivity with antibodies to porcine reproductive respiratory syndrome virus, pseudorabies virus, foot and mouth disease virus, Actinobacillus pleuropneumoniae, Toxoplasma or Chlamydia. Sera obtained from pigs infected with PPV reacted with recombinant NS1 protein in the ELISA. Sera from pigs vaccinated with inactivated whole virus did not recognize this protein in the ELISA. In contrast, antibodies against PPV whole virus were present in both PPV-infected and vaccinated animals. Serum conversion against NS1 was first detected 10 days after infection and NS1-specific antibodies were detectable up to half a year post infection. In conclusion, the PPV-NS1 ELISA can differentiate PPV-infected versus inactivated PPV-vaccinated pigs and could be applied in disease diagnosis and surveillance.

Expression of capsid proteins and non-structural proteins of waterfowl parvoviruses in Escherichia coli and their use in serological assays

While there are a number of methods available for detection of antibodies against waterfowl parvoviruses, none is able to differentiate responses against the capsid and non-structural proteins. To enable this, the capsid and non-structural proteins of goose parvovirus (GPV) and Muscovy duck parvovirus (MDPV) were expressed in Escherichia coli. These proteins were purified and used as antigens in western blotting assays of antibodies against GPV and MDPV. The results showed that 94.7% of the goose and 90.0% of the duck sera collected from the field contained antibodies against GPV or MDPV. Moreover, these sera could be classified into distinct groups based on differences in patterns of western blot reactivity. These different patterns might indicate different stages in infection. Western blotting assays of sera collected from experimentally infected ducks showed that antibodies against the non-structural protein appeared first after infection, followed by antibodies against the capsid protein. It was concluded that the recombinant capsid and non-structural proteins might serve as useful antigens for assays for antibodies against GPV and MDPV. Moreover, because these assays could discriminate between antibodies against the non-structural protein and those against the capsid protein, they may be useful in differentiating vaccinated from infected birds when recombinant capsid protein is used as the vaccine.

Advances in the biology, diagnosis and host-pathogen interactions of parvovirus B19

Increased recognition of parvovirus B19 (B19), an erythrovirus, as a significant human pathogen that causes fetal loss and severe disease in immunocompromised patients has resulted in intensive efforts to understand the pathogenesis of B19-related disease, to improve diagnostic strategy that is deployed to detect B19 infection and blood-product contamination and, finally, to elucidate the nature of the cellular immune response that is elicited by the virus in diverse patient cohorts. It is becoming clear that at least three related erythrovirus strains (B19, A6/K71 and V9) are circulating in the general population and that viral entry into target cells is mediated by an expanding range of cellular receptors, including P antigen and beta-integrins. Persistent infection by B19 is emerging as a contributory factor in autoimmune disease, a hypothesis that is constrained by the detection of B19 in the skin of apparently healthy individuals. B19 infection during pregnancy may account for thousands of incidences of fetal loss per annum in Europe, North America and beyond, yet there is currently only minimal screening of pregnant women to assess serological status, and thereby risk of infection, upon becoming pregnant. Whilst major advances in diagnosis of B19 infection have taken place, including standardization of serological and DNA-based detection methodologies, blood donations that are targeted at high-risk groups are only beginning to be screened for B19 IgG and DNA as a means of minimizing exposure of at-risk patients to the virus. It is now firmly established that a Th1-mediated cellular immune response is mounted in immunocompetent individuals, a finding that should contribute to the development of an effective vaccine to prevent B19 infection in selected high-risk groups, including sickle-cell anaemics.

Comparison of three commercially available serologic assays used to detect human parvovirus B19-specific immunoglobulin M (IgM) and IgG antibodies in sera of pregnant women

A split-sample study was conducted to evaluate the performances of three enzyme immunoassays (EIAs) utilizing one or more conformational antigens to detect human parvovirus B19 (B19V)-specific immunoglobulin M (IgM) or IgG in the sera of 198 pregnant women. We compared EIAs available from Biotrin International, Inc. (Dublin, Ireland), Medac Diagnostika (Wedel, Germany), and Mikrogen (Martinsried, Germany). Specimens with discordant results were analyzed further using an immunofluorescence assay (Biotrin). Equivocal data accounted for close to half of all the discrepant results for both IgM and IgG, with 7 of 15 discrepant results from the Medac and Mikrogen kits involving equivocal data and the Biotrin kit giving a single equivocal result. For each specimen, a consensus was established from the four test results if agreement occurred among at least three of four results. Overall, the highest percentage of agreement with the consensus results was seen when Biotrin kits were used; 194 (100%) of 194 and 194 (99.5%) of 195 results for IgM and IgG, respectively, agreed with the consensus results. When Medac kits were used, 189 (97.4%) of 194 and 191 (97.9%) of 195 results for IgM and IgG, respectively, agreed with the consensus, and when Mikrogen kits were used, 179 (92.3%) of 194 and 193 (99%) of 195 results for IgM and IgG, respectively, agreed with the consensus. Given the consensus results, the Medac EIA appeared to generate presumed false-positive results for IgM and the Mikrogen EIA appeared to generate presumed false-positive results for IgG and IgM. In summary, the Biotrin EIAs produced far fewer equivocal results than the other assays and results of the Biotrin EIAs agreed more often with the consensus results than did those of the other commercially available EIAs for detecting B19V-specific IgM and IgG antibodies.

Immunogenicity of gonococcal transferrin binding proteins during natural infections

In this study, we examined the immune response during gonococcal infection to the individual transferrin binding proteins by using a quantitative enzyme-linked immunosorbent assay (ELISA). Recombinant transferrin binding protein A (rTbpA) and rTbpB were purified under nondenaturing conditions for use as ELISA antigens. Sera and secretions from culture-positive individuals were analyzed for antibodies to rTbpA and rTbpB and compared to samples from individuals with no history of gonococcal infection. Although antibodies to both rTbpA and rTbpB were detected in serum, in most cases the antibody levels were not significantly different from those measured in the control population. Also, previous history of gonococcal infection did not increase antibody levels in serum, suggesting the lack of an anamnestic response. Analysis of secretion samples revealed antibody levels that were generally below the limits of detection in our assay. Overall, this study demonstrated a paucity of systemic and local antibody responses to rTbps as a result of natural infection and represents a baseline over which a protective antibody response will have to be generated in order to develop an efficacious gonococcal vaccine.