Virus-specific Antibody Responses Research Articles

Efficacy Evaluation of an Inactivated Duck Tembusu Virus Vaccine.

To evaluate the potential use of an inactivated virus-based vaccine for the control and prevention of the newly emerged duck Tembusu virus infection in China, a duck Tembusu virus isolate, Tembusu-HB, was propagated in 12-day-old duck embryos and inactivated by treatment with formaldehyde. The inactivated viral antigen was emulsified with mineral oil, and five batches of the vaccine were manufactured. The immunogenicity and protection efficacy of the vaccine were evaluated in Beijing ducks and Beijing white geese. Results showed that more than 80% of immunized ducks were protected against virulent virus challenge after two intramuscular or subcutaneous injections of the inactivated vaccine, as evidenced by the negative virus isolation results. The protection is also correlated with a positive virus-specific antibody response as detected by ELISA. In contrast, none of the control ducks and geese had any detectable antibody response. Virus was isolated from all control ducks and geese after virulent virus challenge. Interestingly, a variable level of protection (20%-80%) was observed in Beijing white geese immunized twice with the same batches of vaccine, suggesting a species-specific effect of the vaccine. Overall, the results clearly suggest that the inactivated duck Tembusu virus vaccine is immunogenic and provides protection against virulent virus challenge.

The immunogenicity of tetravalent dengue DNA vaccine in mice pre-exposed to Japanese encephalitis or Dengue virus antigens.

Asian countries are an endemic area for both dengue (DENV) and Japanese encephalitis viruses (JEV). While JEV vaccines have been used extensively in this region, DENV vaccines remains under development. Whether preexisting naturally acquired or vaccination-induced immunity against JEV may affect the immune response to dengue vaccine candidate is unclear. In this study we used mice previously immunized with JEV vaccines to evaluate the impact on dengue-specific neutralizing antibody responses to a tetravalent dengue DNA vaccine candidate (TDNA). A tetravalent cocktail of plasmids encoding pre-membrane and envelope proteins from each dengue serotype was administered into mice which had been previously primed with inactivated or live-attenuated JEV vaccines, or dengue serotype2 virus (DENV-2). Neutralizing antibody response was measured employing a plaque reduction neutralization test at two weeks after the priming and at four weeks after the second dose of the dengue tetravalent plasmids. Inactivated or live-attenuated JEV vaccines, or DENV-2 induced low levels of neutralizing antibodies against the homologous viruses (JE and dengue virus, respectively). DENV-2 injection induced also low levels of cross-reactive antibodies against DENV-1, -3 and -4. JEV vaccines have no effect on the dengue-specific neutralizing antibody responses to the subsequent TDNA immunization. Pre-exposure to DENV-2 infection increased DENV-2 specific response neutralizing antibody to two doses of TDNA plasmids by six folds, but did not affect antibody response to other serotypes. Priming with JEV vaccines did not impact on dengue virus-specific neutralizing antibody response to a dengue TDNA vaccine candidate in mice.

A Potent Virus-Specific Antibody-Secreting Cell Response to Acute Enterovirus 71 Infection in Children.

Enterovirus 71 (EV71) remains a leading pathogen for acute infectious diseases in children, especially in Asia. The cellular basis for establishing a virus-specific antibody response to acute EV71 infections is unclear in children. We studied the magnitude of virus-specific antibody-secreting B cells (ASCs) and its relationship with serological response, clinical parameters, and virological parameters among children with laboratory-confirmed EV71 infection. A potent EV71 genogroup B- and virus-specific ASC response was detected in the first week of illness among genotype B5 EV71-infected children. The cross-reactive EV71-specific ASC response to genogroup C viral antigens composed about 10% of the response. The EV71-specific ASC response in children aged ≥3 years produced immunoglobulin G predominantly, but immunoglobulin M was predominant in younger children. Proliferation marker was expressed by the majority of circulating ASCs in the acute phase of EV71 infection. Virus-specific ASC responses significantly correlated with throat viral load, fever duration, and serological genogroup-specific neutralization titer. The presence of a virus-specific ASC response serves an early cellular marker of an EV71-specific antibody response. Further detailed study of EV71-specific ASCs at the monoclonal level is crucial to delineate the specificity and function of antibody immunity in children.

Mathematical modeling provides kinetic details of the human immune response to vaccination.

With major advances in experimental techniques to track antigen-specific immune responses many basic questions on the kinetics of virus-specific immunity in humans remain unanswered. To gain insights into kinetics of T and B cell responses in human volunteers we combined mathematical models and experimental data from recent studies employing vaccines against yellow fever and smallpox. Yellow fever virus-specific CD8 T cell population expanded slowly with the average doubling time of 2 days peaking 2.5 weeks post immunization. Interestingly, we found that the peak of the yellow fever-specific CD8 T cell response was determined by the rate of T cell proliferation and not by the precursor frequency of antigen-specific cells as has been suggested in several studies in mice. We also found that while the frequency of virus-specific T cells increased slowly, the slow increase could still accurately explain clearance of yellow fever virus in the blood. Our additional mathematical model described well the kinetics of virus-specific antibody-secreting cell and antibody response to vaccinia virus in vaccinated individuals suggesting that most of antibodies in 3 months post immunization were derived from the population of circulating antibody-secreting cells. Taken together, our analysis provided novel insights into mechanisms by which live vaccines induce immunity to viral infections and highlighted challenges of applying methods of mathematical modeling to the current, state-of-the-art yet limited immunological data.

Epstein-Barr Virus Specific Antibody Response in Multiple Sclerosis Patients during 21 Months of Natalizumab Treatment.

Multiple sclerosis (MS) is a chronic inflammatory autoimmune disease of the central nervous system. Natalizumab, a humanized anti-α4 integrin monoclonal antibody, is a highly effective treatment approved for MS. An association between MS and an exposure to Epstein-Barr Virus (EBV) sustained by the levels of antiviral capsid antigen (VCA) and anti-Epstein-Barr nuclear antigen-1 (EBNA-1) IgG has been described. Our goal was to verify the utility of EBV-specific IgG as a marker in Natalizumab treated MS. Twenty patients (17 female and 3 male) in treatment with Natalizumab were enrolled. Serum levels of anti-VCA and anti-EBNA-1 IgG were determined and expressed as arbitrary units (AU) before treatment and every three months for 21 months of therapy. Anti-VCA IgG levels were increased at the 15th month (235410 ± 196712 AU) comparing with the 3rd (98146 ± 47145 AU) and the 6th (109866 ± 52270 AU) months of therapy (p < 0.05). No significant differences were found for serum anti-EBNA-1 IgG levels. Our data indicate that a transient, self-limited, EBV reactivation can occur in MS during Natalizumab therapy but our results do not support the use of serum EBV-specific antibody levels as biomarkers for monitoring therapeutic response to Natalizumab in the course of MS.

Nonhuman primate infants have an impaired respiratory but not systemic IgG antibody response following influenza virus infection

Respiratory infection of young infants results in increased morbidity and mortality compared to infection of adults. In spite of the significance of this health issue, our understanding of the immune response elicited in infants especially in the respiratory tract is highly limited. We developed a nonhuman primate model to probe the virus-specific antibody response in infants following infection with influenza virus. Infection of infants resulted in more pulmonary damage and higher viral loads compared to adults. While the systemic IgG antibody response was similar in infant and adult animals, the response in the upper respiratory tract of the infant was compromised. This lower response was associated with an increased prevalence of Treg cells and low levels of BALT. These data suggest a defect in the ability to produce effective virus-specific antibody responses at the local infection site is a contributor to increased pulmonary damage in the at-risk infant population.

Novel G3/DT adjuvant promotes the induction of protective T cells responses after vaccination with a seasonal trivalent inactivated split-virion influenza vaccine

Vaccines used against seasonal influenza are poorly effective against influenza A viruses of novel subtypes that may have pandemic potential. Furthermore, pre(pandemic) influenza vaccines are poorly immunogenic, which can be overcome by the use of adjuvants. A limited number of adjuvants has been approved for use in humans, however there is a need for alternative safe and effective adjuvants that can enhance the immunogenicity of influenza vaccines and that promote the induction of broad-protective T cell responses. Here we evaluated a novel nanoparticle, G3, as an adjuvant for a seasonal trivalent inactivated influenza vaccine in a mouse model. The G3 adjuvant was formulated with or without steviol glycosides (DT, for diterpenoid). The use of both formulations enhanced the virus-specific antibody response to all three vaccine strains considerably. The adjuvants were well tolerated without any signs of discomfort. To assess the protective potential of the vaccine-induced immune responses, an antigenically distinct influenza virus strain, A/Puerto Rico/8/34 (A/PR/8/34), was used for challenge infection. The vaccine-induced antibodies did not cross-react with strain A/PR/8/34 in HI and VN assays. However, mice immunized with the G3/DT-adjuvanted vaccine were partially protected against A/PR/8/34 infection, which correlated with the induction of anamnestic virus-specific CD8+ T cell responses that were not observed with the use of G3 without DT. Both formulations induced maturation of human dendritic cells and promoted antigen presentation to a similar extent. In conclusion, G3/DT is a promising adjuvant formulation that not only potentiates the antibody response induced by influenza vaccines, but also induces T cell immunity which could afford broader protection against antigenically distinct influenza viruses.

Hemozoin as a novel adjuvant for inactivated whole virion influenza vaccine

Because vaccination is an effective means to protect humans from influenza viruses, extensive efforts have been made to develop not only new vaccines, but also for new adjuvants to enhance the efficacy of existing inactivated vaccines. Here, we examined the adjuvanticity of synthetic hemozoin, a synthetic version of the malarial by-product hemozoin, on the vaccine efficacy of inactivated whole influenza viruses in a mouse model. We found that mice immunized twice with hemozoin-adjuvanted inactivated A/California/04/2009 (H1N1pdm09) or A/Vietnam/1203/2004 (H5N1) virus elicited higher virus-specific antibody responses than did mice immunized with non-adjuvanted counterparts. Furthermore, mice immunized with hemozoin-adjuvanted inactivated viruses were better protected from lethal challenge with influenza viruses than were mice immunized with non-adjuvanted inactivated vaccines. Our results show that hemozoin improves the immunogenicity of inactivated influenza viruses, and is thus a promising adjuvant for inactivated whole virion influenza vaccines.

Activation of the aryl hydrocarbon receptor during development leads to an altered CD4+ T cell response to influenza A virus infection (IRC2P.448)

Abstract Epidemiological evidence suggests developmental exposures to certain pollutants correlate with lower antibody responses to childhood immunizations, but the mechanism by which this occurs is unknown. The transcription factor aryl hydrocarbon receptor (AhR) is activated by a variety of chemicals, expressed by immune cells, and has been shown to influence immune function, such as CD4+ T cell subset specification and function. The effect of maternal exposure to AhR ligands on the function of CD4+ T cells has never been directly examined. We report here the consequences of developmental triggering of the AhR on the CD4+ T cell response to influenza virus infection. Mice developmentally exposed to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), the prototypical AhR ligand, have fewer activated, virus-specific CD4+ T cells, Th1, and T follicular helper cells, yet an increase in regulatory T cells in their lung draining lymph nodes. Consistent with this, developmentally exposed mice have a reduction in their class-switched, virus-specific antibody response. By using reciprocal adoptive transfers, we demonstrate that the effects of developmental activation of the AhR on CD4+ T cells occur through both direct and indirect pathways. These findings suggest changes in the functional capacity of CD4+ T cells may be a key contributor to the decreased antibody response to immunizations observed in children of mothers exposed to AhR-binding chemicals.

Mathematical modeling of the human immune response to vaccination (VIR1P.969)

Abstract With major advances in experimental techniques to track antigen-specific immune responses many basic questions on the kinetics of virus-specific immunity in humans remain unanswered. To gain insights into kinetics of T and B cell responses in human volunteers we combine mathematical models and experimental data from recent studies employing vaccines against yellow fever and smallpox. We found that the peak of the yellow fever-specific CD8 T cell response is determined by the rate of T cell proliferation and not by the precursor frequency of antigen-specific cells as has been suggested in several studies in mice. We also found that the rise in the virus-specific T cell numbers accurately explains clearance of yellow fever virus in the blood. Our additional mathematical model describes well the kinetics of virus-specific plasma cell and antibody response to vaccinia virus in vaccinated individuals. The model suggests that to explain the data either the rate of antibody production by plasma cells has to increase with time since immunization, or production of the majority of antibodies comes from cells located in tissues and not in the blood. Taken together, our analysis provides novel insights into mechanisms by which live vaccines induce highly efficient immunity to viral infections.

Dual Functions of Lactobacillus acidophilus NCFM as Protection Against Rotavirus Diarrhea

The aim of the study was to examine the dose effects of Lactobacillus acidophilus (LA) NCFM strain on rotavirus-specific antibody and B-cell responses in gnotobiotic pigs vaccinated with an oral attenuated human rotavirus (AttHRV). Pigs were inoculated with AttHRV vaccine in conjunction with high-dose LA (14 doses, total 2.2 × 10(6) colony-forming units [CFU]), intermediate-dose LA (MidLA) (9 doses, total 3.2 × 10(9) CFU), low-dose LA (LoLA) (5 doses, total 2.1 × 10(6) CFU), or without LA feeding. Protection against rotavirus shedding and diarrhea was assessed upon challenge with a virulent HRV. Rotavirus-specific immunoglobulin A (IgA) and IgG antibodies in serum and rotavirus-specific IgA and IgG antibody-secreting cells (ASCs) and memory B cells in ileum, spleen, and blood of the pigs were measured and compared among treatment groups. The MidLA, but not high-dose LA or LoLA, significantly reduced rotavirus diarrhea (MidLA-only group) and significantly improved the protection conferred by AttHRV vaccine (MidLA + AttHRV group). Associated with the increased protection, MidLA significantly enhanced rotavirus-specific antibody, ASCs, and memory B-cell responses to AttHRV vaccine. High-dose LA or LoLA did not enhance virus-specific antibody and ASC responses, and hence did not improve the vaccine efficacy. These findings highlight the importance of dose selection and indicate that certain specific lactobacilli strains at the appropriate dose have the dual function of reducing rotavirus diarrhea and enhancing the immunogenicity and protective efficacy of rotavirus vaccines.

Virus-Specific Antibody Secreting Cell, Memory B-cell, and Sero-Antibody Responses in the Human Influenza Challenge Model

Antibodies play a major role in the protection against influenza virus in human. However, the antibody level is usually short-lived and the cellular mechanisms underlying influenza virus-specific antibody response to acute infection remain unclear. We studied the kinetics and magnitude of influenza virus-specific B-cell and serum antibody responses in relation to virus replication during the course of influenza infection in healthy adult volunteers who were previously seronegative and experimentally infected with seasonal influenza H1N1 A/Brisbane/59/07 virus. Our data demonstrated a robust expansion of the virus-specific antibody-secreting cells (ASCs) and memory B cells in the peripheral blood, which correlated with both the throat viral load and the duration of viral shedding. The ASC response was obviously detected on day 7 post-infection when the virus was completely cleared from nasal samples, and serum hemagglutination-inhibition antibodies were still undetectable. On day 28 postinfection, influenza virus-specific B cells were further identified from the circulating compartment of isotype-switched B cells. Virus-specific ASCs could be the earliest marker of B-cell response to a new flu virus infection, such as H7N9 in humans.

Evaluation of the Replication, Pathogenicity, and Immunogenicity of Avian Paramyxovirus (APMV) Serotypes 2, 3, 4, 5, 7, and 9 in Rhesus Macaques

Avian paramyxoviruses (APMV) serotypes 1–9 are frequently isolated from domestic and wild birds worldwide. APMV-1 (also called Newcastle disease virus, NDV) is attenuated in non-human primates and is being developed as a candidate human vaccine vector. The vector potential of the other serotypes was unknown. In the present study, we evaluated nine different biologically- or recombinantly-derived APMV strains for the ability to replicate and cause disease in rhesus macaque model. Five of the viruses were: biologically-derived wild type (wt) APMV-2, -3, -5, -7 and -9. Another virus was a recombinant (r) version of wt APMV-4. The remaining three viruses were versions of wt rAPMV-2, -4 and -7 in which the F cleavage site had been modified to be multi-basic. Rhesus macaques were inoculated intranasally and intratracheally and monitored for clinical disease, virus shedding from the upper and lower respiratory tract, and seroconversion. Virus shedding was not detected for wt APMV-5. Very limited shedding was detected for wt rAPMV-4 and modified rAPMV-4, and only in a subset of animals. Shedding by the other viruses was detected in every infected animal, and usually from both the upper and lower respiratory tract. In particular, shedding over a number of days in every animal was observed for modified rAPMV-2, wt APMV-7, and modified rAPMV-7. Modification of the F protein cleavage site appeared to increase shedding by wt rAPMV-2 and marginally by wt rAPMV-4. All APMVs except wt APMV-5 induced a virus-specific serum antibody response in all infected animals. None of the animals exhibited any clinical disease signs. These results indicate that APMVs 2, 3, 4, 7, and 9 are competent to infect non-human primates, but are moderately-to-highly restricted, depending on the serotype. This suggests that they are not likely to significantly infect primates in nature, and represent promising attenuated candidates for vector development.

The adaptive immune response does not influence hantavirus disease or persistence in the Syrian hamster

Pathogenic New World hantaviruses cause severe disease in humans characterized by a vascular leak syndrome, leading to pulmonary oedema and respiratory distress with case fatality rates approaching 40%. Hantaviruses infect microvascular endothelial cells without conspicuous cytopathic effects, indicating that destruction of the endothelium is not a mechanism of disease. In humans, high levels of inflammatory cytokines are present in the lungs of patients that succumb to infection. This, along with other observations, suggests that disease has an immunopathogenic component. Currently the only animal model available to study hantavirus disease is the Syrian hamster, where infection with Andes virus (ANDV), the primary agent of disease in South America, results in disease that closely mimics that seen in humans. Conversely, inoculation of hamsters with a passaged Sin Nombre virus (SNV), the virus responsible for most cases of disease in North America, results in persistent infection with high levels of viral replication. We found that ANDV elicited a stronger innate immune response, whereas SNV elicited a more robust adaptive response in the lung. Additionally, ANDV infection resulted in significant changes in the blood lymphocyte populations. To determine whether the adaptive immune response influences infection outcome, we depleted hamsters of CD4(+) and CD8(+) T cells before infection with hantaviruses. Depletion resulted in inhibition of virus-specific antibody responses, although the pathogenesis and replication of these viruses were unaltered. These data show that neither hantavirus replication, nor pathogenesis caused by these viruses, is influenced by the adaptive immune response in the Syrian hamster.

Chicken astrovirus capsid proteins produced by recombinant baculoviruses: potential use for diagnosis and vaccination

Chicken astroviruses (CAstVs) have been characterized recently. Due to their relatively poor growth in cell culture, virus-specific antigens are not readily available for the development of diagnostic reagents and vaccines. For this purpose two capsid protein antigens, specified by the 11672 isolate of CAstV, were produced in insect cells following infection with recombinant baculoviruses. The GST-11672 capsid protein, a fusion protein comprising the capsid protein and glutathione-S-transferase (GST) as an N-terminal affinity tag, and the 11672 capsid protein alone were detected by western blotting as proteins of ~100 and 70 kDa, respectively. Immunization with the affinity-purified GST-11672 capsid protein produced a polyclonal rabbit antiserum, which reacted by indirect immunofluorescence with Group B CAstVs but which showed no reactivity with the Group A CAstV isolate, 612. When used as part of an immunoperoxidase-based immunohistochemical procedure, this rabbit antiserum facilitated the detection of CAstV antigen in formalin-fixed, paraffin-embedded kidney tissue at the sites of histopathology characteristic of nephritis. Although further evaluation with sera from commercial chickens is required, a prototype indirect antibody-detecting enzyme-linked immunosorbent assay (ELISA) based on affinity-purified GST-11672 capsid protein as coating antigen demonstrated considerable potential with low ELISA absorbance values being generated with sera from specific pathogen free (SPF) chickens, and high absorbance values being generated with serum samples from experimentally infected chickens. Immunization experiments of SPF chickens showed that, when administered as mixtures with oil adjuvant, crude cell lysates containing the GST-11672 capsid protein or the 11672 capsid protein elicited virus-specific antibody responses that were detectable by indirect immunofluorescence and by virus neutralization assays.

Varicella-Zoster Virus–Specific Antibody Responses in 50–59-Year-Old Recipients of Zoster Vaccine

Prevaccination and 6-week postvaccination samples from the immunogenicity substudy (n = 2269) of the zoster vaccine (ZV) efficacy trial (N = 22 439) in 50-59-year-old subjects were examined for varicella-zoster virus-specific antibody responses to vaccination. The varicella-zoster virus geometric mean titer (GMT) and geometric mean fold rise were higher in ZV recipients than in placebo recipients (GMT, 660.0 vs 293.1 glycoprotein enzyme-linked immunosorbent assay units/mL [P < .001], respectively; geometric mean fold rise, 2.31 vs 1.00 [P < .025]). In each group there was a strong inverse correlation between postvaccination GMT and risk of subsequent herpes zoster. Although these data provide strong evidence that relates ZV-induced antibody and the risk of herpes zoster, a protective threshold was not determined. Clinical Trials Registration. NCT00534248.

Evaluation of the Humoral and Cellular Immune Responses Elicited by the Live Attenuated and Inactivated Influenza Vaccines and Their Roles in Heterologous Protection in Ferrets

The humoral and cellular immune responses elicited by the trivalent live attenuated influenza vaccine (LAIV) and the trivalent inactivated influenza vaccine (TIV) were evaluated in the ferret model, using newly developed ferret immunological reagents and assays. In contrast to the TIV, which only induced immune responses in primed animals, LAIV induced strong influenza virus-specific serum antibody and T-cell responses in both naive and influenza-seropositive animals. The LAIV offered significant protection against a heterologous H1N1 virus challenge infection in the upper respiratory tract. Influenza virus-specific immunoglobulin A (IgA) and immunoglobulin G (IgG) antibody-secreting cells (ASCs) and influenza virus-specific CD4(+) and CD8(+) T cells were detected in the circulation and local paratracheal draining lymph nodes. The frequency of the influenza-specific ASCs in the local lymph nodes appeared to correlate with the degree of protection in the upper respiratory tract. The protection conferred by the LAIV could be attributed not only to the antibody response but also to the cell-mediated and local mucosal immune responses, particularly in naive ferrets. These findings may explain why the LAIV is immunologically superior and offers immediate protection after a single dose in children.

Pathogenesis of emerging severe fever with thrombocytopenia syndrome virus in a non-human primate model (P3021)

Abstract Severe Fever with Thrombocytopenia Syndrome (SFTS) emerged as an infectious disease in 2010 in rural China, and its causative agent SFTS virus (SFTSV) is a new member of the family Bunyaviridae, genus phlebovirus, most closely related to the heartland virus recently discovered in Missouri, the US. To develop effective vaccines and therapeutics against this emerging pathogen, animal disease models are urgently needed. Here, we report the first findings of measurable clinical disease in non-human primates infected with SFTSV. In the primate model, the abrupt fever, thrombocytopenia, and leukocytopenia were duplicated. Substantially enhanced aspartate aminotransferase, creatinine, and lactate dehydrogenase in serum was observed, indicating pathological lesions in organs. Viremia peaked around 3 to 5 days after the inoculation of SFTSV. Viral RNA was detected in the spleen, lymph node, liver, kidney, and intestine. Virus-specific IgM and IgG antibody responses were induced, and cytokines IFN-γ and eotaxin were significantly enhanced in the acute phase. Scattered necrosis and degeneration of hepatocytes in liver, as well as glomerular hypercellularity, mesangial thickening, and congestion in Bowman’s space in kidney were observed after 4 weeks of SFTSV infection. Thus, we established a non-human primate model which resembles major clinical features of the human SFTS disease, and further studied virus-specific immune responses and histopathological changes in this primate model.

Development and partial validation of a recombinant E2-based indirect ELISA for detection of specific IgM antibody responses against classical swine fever virus

Detecting classical swine fever virus specific antibody responses is critical for prevention and control of CSF. In this study, a ΔE2-based indirect ELISA was developed to detect specific IgM antibodies against CSFV. The optimized conditions that were determined experimentally are: a ΔE2 antigen concentration of 0.5μg/ml, a serum sample dilution of 1/100 incubated at 37°C for 1.5h, and a HRP conjugated rabbit anti-pig IgM dilution of 1/50,000 incubated at 37°C for 1h. Three hundred clinical sera were tested with ΔE2-IgM-ELISA and IDEXX ELISA and the positive rates were 77.3% (232/300) and 71.7% (215/300), respectively. Concordance rate between them was 80.3% (241/300). The 59 inconsistent sera were tested further: among the 21 IDEXX ELISA +/ΔE2-IgM-ELISA − and 38 IDEXX ELISA +/ΔE2-IgM-ELISA − samples, 17 and 24 were determined positive by virus neutralization test; 15 and 25 were tested positive by ΔE2-IgG-ELISA, respectively. In addition, the E2-specific IgM antibody response in 15 vaccinated piglets could be detected 2 weeks post-vaccination and earlier than specific IgG antibody. It increased regularly and reached high levels by 6 weeks post-vaccination. The ΔE2-IgM-ELISA could be used for clinical detection and for exploring the kinetics of IgM antibody response.

Novel Marmoset (Callithrix jacchus) Model of Human Herpesvirus 6A and 6B Infections: Immunologic, Virologic and Radiologic Characterization

Human Herpesvirus 6 (HHV-6) is a ubiquitous virus with an estimated seroprevalence of 95% in the adult population. HHV-6 is associated with several neurologic disorders, including multiple sclerosis, an inflammatory demyelinating disease affecting the CNS. Animal models of HHV-6 infection would help clarify its role in human disease but have been slow to develop because rodents lack CD46, the receptor for cellular entry. Therefore, we investigated the effects of HHV-6 infections in a non-human primate, the common marmoset Callithrix jacchus. We inoculated a total of 12 marmosets with HHV-6A and HHV-6B intravenously and HHV-6A intranasally. Animals were monitored for 25 weeks post-inoculation clinically, immunologically and by MRI. Marmosets inoculated with HHV-6A intravenously exhibited neurologic symptoms and generated virus-specific antibody responses, while those inoculated intravenously with HHV-6B were asymptomatic and generated comparatively lower antibody responses. Viral DNA was detected at a low frequency in paraffin-embedded CNS tissue of a subset of marmosets inoculated with HHV-6A and HHV-6B intravenously. When different routes of HHV-6A inoculation were compared, intravenous inoculation resulted in virus-specific antibody responses and infrequent detection of viral DNA in the periphery, while intranasal inoculation resulted in negligible virus-specific antibody responses and frequent detection of viral DNA in the periphery. Moreover, marmosets inoculated with HHV-6A intravenously exhibited neurologic symptoms, while marmosets inoculated with HHV-6A intranasally were asymptomatic. We demonstrate that a marmoset model of HHV-6 infection can serve to further define the contribution of this ubiquitous virus to human neurologic disorders.