Antibodies against viral nonstructural proteins in response to infection with poliovirus

Immunoreactivity Analysis of the Nonstructural Proteins of Human Enterovirus 71

Human enterovirus 71 (EV-A71) is one of the main etiological agents of hand, foot, and mouth disease (HFMD), which has been prevalent mainly in the Asia-Pacific region in the past several decades. The nonstructural proteins of EV-A71 will be expressed significantly during viral replication in host cells after EV-A71 infection. For the determination of the antibodies response against nonstructural proteins of EV-A71, in this study, the complete 2ABC, 3ABC, and 3D proteins were expressed in Escherichia coli and were then studied for their immunoreactivity by immunoblot assay and indirect enzyme-linked immunosorbent assay (ELISA), respectively. Three His-tagged fusion proteins were expressed effectively in E. coli, which were in agreement with the expected molecular mass. The results from immunoblot assay and indirect ELISA showed that all three purified fusion proteins can react with IgG antibodies from EV-A71-infected patients, but can hardly be recognized by IgG antibodies derived from mice or rabbits immunized by inactivated EV-A71 virus particles. The IgG antibody response against nonstructural proteins of EV-A71 is associated with viral infection or replication, which indicate that these nonstructural proteins could be used as candidate antigen for early diagnosis of EV-A71 infection, or to distinguish the EV-A71-specific antibodies after viral infection from inactivated vaccine immunization.

The 2010 outbreak of poliomyelitis in Tajikistan: epidemiology and lessons learnt

A large outbreak of poliomyelitis, with 463 laboratory-confirmed and 47 polio-compatible cases, took place in 2010 in Tajikistan. Phylogenetic analysis of the viral VP1 gene suggested a single importation of wild poliovirus type 1 from India in late 2009, its further circulation in Tajikistan and expansion into neighbouring countries, namely Kazakhstan, Russia, Turkmenistan and Uzbekistan. Whole-genome sequencing of 14 isolates revealed recombination events with enterovirus C with cross-overs within the P2 region. Viruses with one class of recombinant genomes co-circulated with the parental virus, and representatives of both caused paralytic poliomyelitis. Serological analysis of 327 sera from acute flaccid paralysis cases as well as from patients with other diagnoses and from healthy people demonstrated inadequate immunity against polio in the years preceding the outbreak. Evidence was obtained suggesting that vaccination against poliomyelitis, in rare cases, may not prevent the disease. Factors contributing to the peculiarities of this outbreak are discussed. The outbreak emphasises the necessity of continued vaccination against polio and the need, at least in risk areas, of quality control of this vaccination through well planned serological surveillance.

Systemic and intestinal antibody responses to NSP4 enterotoxin of Wa human rotavirus in a gnotobiotic pig model of human rotavirus disease

Antibody responses to the Wa human rotavirus (HRV) nonstructural protein NSP4, a viral enterotoxin, were evaluated in neonatal gnotobiotic (Gn) pigs. Gn pigs were inoculated orally with one dose of 10(5) fluorescent focus units (FFU) of virulent Wa HRV (HRV-V), to mimic natural infection, or with three doses of 5 x 10(7) FFU attenuated Wa HRV (HRV-A) at 10-day intervals, to mimic oral attenuated rotavirus vaccines, or they were mock inoculated (mock). Subsets of pigs were challenged with 10(6) FFU of virulent Wa HRV at post-inoculation day 28 (PID 28). Post-challenge, the HRV-V pigs were completely protected against diarrhea and virus shedding, whereas the HRV-A pigs had a 50% protection rate against diarrhea and a 67% protection rate against virus shedding. All mock-inoculated pigs shed virus and had diarrhea post-challenge. Isotype antibody titers to NSP4 were compared in serum and intestinal contents, at post-inoculation day (PID) 28 and at post-challenge day 7 (PCD 7/PID 35) by indirect ELISA, using purified recombinant NH2-6xHis-tagged NSP4 of virulent Wa HRV. Pre-challenge, both the HRV-V and HRV-A-inoculated pigs had similar moderate titers of serum IgG antibodies to NSP4. However, only the HRV-V-inoculated pigs developed detectable serum and intestinal IgA antibody titers to NSP4 pre-challenge, compared with the HRV-A-inoculated pigs. The mock-inoculated pigs had no IgM, IgA, or IgG antibodies to NSP4 pre-challenge. All Wa HRV-inoculated pigs developed low to moderate titers of serum IgM, IgG, and IgA antibodies to NSP4 post-challenge, but the mock-inoculated pigs had only IgM antibodies post-challenge. Both Wa HRV-inoculated groups developed low titers of IgA antibody to NSP4 in the small intestinal contents post-challenge, but titers were 5.8-fold higher in the HRV-V pigs. Our results concur with findings that both rotavirus vaccinated and naturally infected children seroconvert with modest IgG antibodies to NSP4 [Johansen et al. (1999) J Med Virol 59:369-367]. These data suggest that Gn pigs could be a useful model to evaluate serum and intestinal IgA antibodies to NSP4 and their role in protection against HRV infection. Further experiments may clarify whether (1) the NSP4 antibodies detected pre-challenge in the HRV-V pigs contribute to the higher protection rates observed, or (2) the reduced or delayed NSP4 antibody responses of the HRV-A pigs are associated with the lower protection rates in these pigs.

Combined cell culture enzyme-linked immunosorbent assay for quantification of poliovirus neutralization- relevant antibodies

A combined cell culture enzyme-linked immunosorbent assay (CCC-ELISA) was developed for measuring the neutralizing antipoliovirus antibodies in human sera. The binding of different concentrations of each of the three poliovirus types to BGM cells in the presence and absence of a constant dilution from each test and reference serum was measured in the CCC-ELISA. The titers of the viruses neutralized by each serum were measured with the titration curves and used for interpretation of neutralizing titers to the three poliovirus types. Analysis of human sera revealed that the sensitivity and specificity of the CCC-ELISA and the microneutralization assay were comparable. The CCC-ELISA is nonsubjective, rapid, and highly reproducible. Furthermore, the CCC-ELISA could potentially be used as a seroepidemiologic tool for assessment of the humoral response to the cell culture infectious viruses.

Rubella virus nonstructural protein 2 is a minor immunogen

The full-length nonstructural protein P90 of rubella virus (RV) was expressed as recombinant protein in Escherichia coli bacteria, as well as in Vero cells. Monoclonal antibodies raised against the protein specifically reacted with the protein in both P90-transfected and RV infected Vero cells. Ninety human sera obtained from reconvalescents, vaccinees and patients with acute RV infection were tested for reactivity against the P90 protein. A weak immune reaction was detected only in a small minority (8%), indicating that P90 is minor immunogen for RV and is not suitable for diagnostic purposes.

Immunological reactivity of baculovirus-expressed enterovirus proteins

In order to study immunological reactivity of individual enterovirus polypeptides and evaluate their usefulness for enterovirus diagnosis, the genes coding for viral structural and nonstructural proteins were expressed using recombinant baculoviruses. A histidine-tailed coxsackievirus B3 (CBV3) VP1 capsid protein was expressed and purified by immobilized metal ion affinity chromatography for EIAs. To elucidate the usefulness of the other CBV3 capsid proteins for immunoassays, recombinant baculovirus expressing the whole CBV3 capsid polyprotein region was constructed. For the detection of a potentially broader spectrum of enteroviruses, the conserved nonstructural P3 region was expressed. The P3 region encodes four nonstructural proteins including a cysteine protease (3C) and an RNA-dependent RNA-polymerase (3D). The 3C polypeptide was shown to be proteolytically active indicating that the baculovirus system is capable of expressing biologically functional enterovirus proteins. Immunoblot analysis detected antibodies against the VP1, 3C and 3D proteins in human serum samples. When the baculovirus-expressed antigens were compared with lysates of enterovirus-infected cells and a synthetic peptide in EIA highly similar results were obtained with recombinant VP1 and the lysate antigens. Although reactive in immunoblots, the P3 encoded proteins were not satisfactory for EIA.

Immunization with nonstructural proteins promotes functional recovery of alphavirus-infected neurons

The encephalitic alphaviruses are useful models for understanding virus-neuron interactions. A neurovirulent strain of Sindbis virus (NSV) causes fatal paralysis in mice by infecting motor neurons and inducing apoptosis of these nonrenewable cells. Antibodies to the surface glycoproteins suppress virus replication, but other recovery-promoting components of the immune response have not been recognized. We assessed the effect on the outcome of NSV-induced encephalomyelitis of immunization of mice with nonstructural proteins (nsPs) by using recombinant vaccinia viruses. Mice immunized with vaccinia virus expressing nsPs and challenged with NSV initially developed paralysis similar to unimmunized mice but then recovered neurologic function. Mice preimmunized with vaccinia virus expressing structural proteins were completely protected from paralysis. Mice immunized with vaccinia virus alone showed paralysis with little evidence of recovery. Vaccinia virus expressing only nsP2 was as effective as vaccinia virus expressing all the nsPs. Protection provided by immunity to nsPs was not associated with a reduction in virus replication or with improved antibody responses to structural proteins. Protection could not be passively transferred with nsP immune serum. The depletion of T cells at the time of NSV infection decreased protection. The data show that antiviral immune responses can improve the ability of neurons to survive infection and to recover function without altering virus replication.

Long-term humoral immunity against viruses: revisiting the issue of plasma cell longevity

Despite extensive documentation of prolonged antibody responses following vaccination or acute viral infection, the mechanisms behind long-term antibody production are not fully understood. We propose the hypothesis that long-lived plasma cells are an important, yet largely overlooked, component of long-term humoral immunity.

Mengo virus 3C proteinase: recombinant expression, intergenus substrate cleavage and localization in vivo

Mengo virus 3C proteinase was cloned and expressed to high levels in a bacterial vector system. The protein was solubilized from inclusion bodies then purified to homogeneity (> 95%) by ion exchange chromatography. The recombinant enzyme was proteolytically active in cell-free processing assays with a Mengo capsid precursor substrate, L-P1-2A, correctly and proficiently cleaving it into L, 1AB, 1C, 1D and 2A protein products. Further analyses with synthetic peptide substrates encompassing the Mengo or rhinovirus-14 2C/3A cleavage sequences, showed the Mengo 3C could recognize and process specific glutamine-glycine sites within these peptides. The reactivity with the rhinovirus peptide was unexpected, because cross-reactivity between a picornavirus 3C enzyme and a protein substrate from different genus of this family has otherwise never been observed. In reciprocal reactions, a rhinovirus-14 3C preparation was unable to cleave the Mengo-derived synthetic peptide substrate. The recombinant Mengo 3C reactions were also characterized with regard to substrate Km, optimum pH and temperature. The protein was additionally used to raise monoclonal antibodies (mAbs) in mice, which in turn localized natural 3C, 3ABC, 3CD and P3 in immunoblots, immunoprecipitations and indirect immunofluorescence assays of Mengo-infected HeLa cells. The monoclonals showed cross-reactivity with 3C and 3C-containing precursors from encephalomyocarditis virus (EMCV), but did not react with 3C proteins from rhinovirus-14 or poliovirus-1M.

Epitope mapping of monoclonal antibodies raised to recombinant Mengo 3D polymerase

The cDNA coding sequence of the RNA-dependent RNA polymerase (3Dpol) of Mengovirus was cloned and expressed in a bacterial system. Eleven monoclonal antibodies were raised against the recombinant Mengo 3Dpol (rM3D). All of them recognized the recombinant and the viral-induced form of the protein. The panel of monoclonals belonged to the IgG1 and IgG2a isotypes and were mapped to four different epitopes in the 3D molecule by competition assays. All monoclonals recognized Mengo 3Dpol in western blots and cross-reacted with the homologous polymerases of seven other cardioviruses but failed to react with 3Dpol from poliovirus type 1 and 3 or rhinovirus type 14 and 16.