Anti-Nucleocapsid Protein Immune Responses Counteract Pathogenic Effects of Rift Valley Fever Virus Infection in Mice

University of Texas Medical Branch, United States of America
PLoS ONE (Impact Factor: 3.23). 09/2011; 6(9):e25027. DOI: 10.1371/journal.pone.0025027
Source: PubMed


The known virulence factor of Rift Valley fever virus (RVFV), the NSs protein, counteracts the antiviral effects of the type I interferon response. In this study we evaluated the expression of several genes in the liver and spleen involved in innate and adaptive immunity of mice immunized with a RVFV recombinant nucleocapsid protein (recNP) combined with Alhydrogel adjuvant and control animals after challenge with wild type RVFV. Mice immunized with recNP elicited an earlier IFNβ response after challenge compared to non-immunized controls. In the acute phase of liver infection in non-immunized mice there was a massive upregulation of type I and II interferon, accompanied by high viral titers, and the up- and downregulation of several genes involved in the activation of B- and T-cells, indicating that both humoral and cellular immunity is modulated during RVFV infection. Various genes involved in pro-inflammatory responses and with pro-apoptotic effects were strongly upregulated and anti-apoptotic genes were downregulated in liver of non-immunized mice. Expression of many genes involved in B- and T-cell immunity were downregulated in spleen of non-immunized mice but normal in immunized mice. A strong bias towards apoptosis and inflammation in non-immunized mice at an acute stage of liver infection associated with suppression of several genes involved in activation of humoral and cellular immunity in spleen, suggests that RVFV evades the host immune response in more ways than only by inhibition of type I interferon, and that immunopathology of the liver plays a crucial role in RVF disease progression.

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Available from: Petrus Jansen van Vuren
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    • "The RVFV N protein elicits potent IgM and IgG responses that arise early after infection in humans and animals [25]–[28]. Of interest, N-subunit alone vaccines delivered as a recombinant protein [24], [29], [30] or a DNA vaccine [31]–[34] have been shown by independent laboratories to confer protection in the absence of detectable neutralizing antibodies (Abs) [29], [31], [34]. A role for N-specific T cells was implicated by the detection of dose-dependent proliferation of the spleen cells to N [31] and a rapid recall expression of Cd40, Cd40 ligand, Cd8a and Cd8b1 genes in the spleens of immunized mice, consistent with the activation of memory CD8 T cell immunity [30]. "
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    ABSTRACT: There is no licensed human vaccine currently available for Rift Valley Fever Virus (RVFV), a Category A high priority pathogen and a serious zoonotic threat. While neutralizing antibodies targeting the viral glycoproteins are protective, they appear late in the course of infection, and may not be induced in time to prevent a natural or bioterrorism-induced outbreak. Here we examined the immunogenicity of RVFV nucleocapsid (N) protein as a CD8(+) T cell antigen with the potential for inducing rapid protection after vaccination. HLA-A*0201 (A2)-restricted epitopic determinants were identified with N-specific CD8(+) T cells from eight healthy donors that were primed with dendritic cells transduced to express N, and subsequently expanded in vitro by weekly re-stimulations with monocytes pulsed with 59 15mer overlapping peptides (OLPs) across N. Two immunodominant epitopes, VT9 (VLSEWLPVT, N121-129) and IL9 (ILDAHSLYL, N165-173), were defined. VT9- and IL9-specific CD8(+) T cells identified by tetramer staining were cytotoxic and polyfunctional, characteristics deemed important for viral control in vivo. These peptides induced specific CD8(+) T cell responses in A2-transgenic mice, and more importantly, potent N-specific CD8(+) T cell reactivities, including VT9- and IL9-specific ones, were mounted by mice after a booster vaccination with the live attenuated RVF MP-12. Our data suggest that the RVFV N protein is a potent human T cell immunogen capable of eliciting broad, immunodominant CD8(+) T cell responses that are potentially protective. Understanding the immune responses to the nucleocapsid is central to the design of an effective RVFV vaccine irrespective of whether this viral protein is effective as a stand-alone immunogen or only in combination with other RVFV antigens.
    Full-text · Article · Mar 2013 · PLoS ONE
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    ABSTRACT: Rift Valley fever virus (RVFV) is a major human and animal pathogen associated with severe disease including hemorrhagic fever or encephalitis. RVFV is endemic to parts of Africa and the Arabian Peninsula, but there is significant concern regarding its introduction into non-endemic regions and the potentially devastating effect to livestock populations with concurrent infections of humans. To date, there is little detailed data directly comparing the host response to infection with wild-type or vaccine strains of RVFV and correlation with viral pathogenesis. Here we characterized clinical and systemic immune responses to infection with wild-type strain ZH501 or IND vaccine strain MP-12 in the C57BL/6 mouse. Animals infected with live-attenuated MP-12 survived productive viral infection with little evidence of clinical disease and minimal cytokine response in evaluated tissues. In contrast, ZH501 infection was lethal, caused depletion of lymphocytes and platelets and elicited a strong, systemic cytokine response which correlated with high virus titers and significant tissue pathology. Lymphopenia and platelet depletion were indicators of disease onset with indications of lymphocyte recovery correlating with increases in G-CSF production. RVFV is hepatotropic and in these studies significant clinical and histological data supported these findings; however, significant evidence of a pro-inflammatory response in the liver was not apparent. Rather, viral infection resulted in a chemokine response indicating infiltration of immunoreactive cells, such as neutrophils, which was supported by histological data. In brains of ZH501 infected mice, a significant chemokine and pro-inflammatory cytokine response was evident, but with little pathology indicating meningoencephalitis. These data suggest that RVFV pathogenesis in mice is associated with a loss of liver function due to liver necrosis and hepatitis yet the long-term course of disease for those that might survive the initial hepatitis is neurologic in nature which is supported by observations of human disease and the BALB/c mouse model.
    Full-text · Article · Feb 2012 · PLoS Neglected Tropical Diseases
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    ABSTRACT: Currently, there are no worldwide licensed vaccines for Rift Valley fever (RVF) that are both safe and effective. Development and evaluation of vaccines, diagnostics and treatments depend on the availability of appropriate animal models. Animal models are also necessary to understand the basic pathobiology of infection. Here, we report the use of an inbred MBT/Pas mouse model that consistently reproduces RVF disease and serves our purpose for testing the efficacy of vaccine candidates; an attenuated Rift Valley fever virus (RVFV) and a recombinant RVFV-capripoxvirus. We show that this model is relevant for vaccine testing.
    Full-text · Article · Apr 2012 · Journal of General Virology
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