Persistence of viral RNA in mouse brains after recovery from acute alphavirus encephalitis

Abstract

Little is known about the relationship between recovery from acute viral encephalitis and the clearance of viral genetic material from the central nervous system. In a mouse model of Sindbis virus encephalitis, we have previously shown that clearance of infectious virus is mediated by antibody-induced restriction of viral gene expression rather than by cytotoxic destruction of virally infected cells. To explore whether Sindbis virus genomes persist in mouse brain after the clearance of infectious virus, we used reverse transcriptasepolymerase chain reaction amplification methods to detect Sindbis virus RNA in brain samples from immunocompetent BALB/c and antibody-treated immunodeficient scid/CB17 mice. RNA sequences from both the nonstructural region (NSP1 gene) and structural regions (E2 gene) of Sindbis virus were detected in the brains of all BALB/c and antibody-treated scid mice examined at 1, 2, and 3 months after infection. Additional BALB/c mouse brains were also positive at 8, 12, and 17 months after infection. To determine whether persistent RNA was capable of resuming unrestricted replication in the absence of the continuous presence of antiviral antibodies, viral titers were measured in the brains ofscid mice at 1, 2, 3, and 6 months after antibody treatment. Viral reactivation was seen in scid mice treated with hyperimmune serum or a low dose of monoclonal antibody to the E2 envelope glycoprotein, but not in mice treated with a high dose of monoclonal antibody to E2. Replication of infectious virus isolated from scid mouse brain could be restricted by repeat treatment with immune serum, indicating that viral reactivation is not due to antibody-escape mutations. These results demonstrate that Sindbis virus can persist long term in a nonproductive form in mouse brain and suggest that the humoral immune response plays an important role in preventing viral reactivation.

Alpha-beta T cells provide protection against lethal encephalitis in the murine model of VEEV infection

“…Infectious virus persisted in the brain, despite a moderate level of inflammation and cellular infiltration at the site of infection, which was observed in histopathological evaluation of brain tissues. The persistence of infectious VEEV has not heretofore been described, although viral RNA has been detected in the brains of mice that survived acute Sindbis virus infection (Levine and Griffin, 1992). The nature of persistence of VEEV in these γδ T cell deficient mice, which occurs in the absence of clinical disease, is an interesting finding that warrants further molecular pathogenesis studies.…”

Clearance of virus infection from the CNS

“…In immunologically normal mice, viral RNA levels gradually decrease over several weeks after infectious virus has been cleared ( Figure 1). In SCID mice that have cleared virus in response to passively transferred antibody, virus replication is renewed in the brains of most mice once antibody levels have decayed [39]. Thus, viral RNA persists and the RNA that remains is capable of renewing virus production if there is a secondary failure of immune control.…”

Immune Responses to Viruses in the CNS

“…Antibody that mediates virus clearance from neurons is often directed against viral structural proteins on the infected cell surface and has been most completely analyzed for cells infected with SINV (Hooper et al, 2009;Levine et al, 1991). In addition to neutralizing free virus, antibody to the SINV E2 glycoprotein can bind to the surface of infected cells and may direct intracellular signaling to control virus replication (Després et al, 1995b;Levine and Griffin, 1992). The antiviral effect of this antibody does not require complement or phagocytic cells, but is dependent on bivalent antibody, implying that cross-linking of viral proteins at the cell surface results in intracellular inhibition of virus production (Ubol et al, 1995;Levine et al, 1991).…”

“…Although control of the acute phase of MHV infection by the adaptive response is independent of antibody, long-term production of antibody is necessary to prevent reactivation of infection Lin et al, 1999). As the BBB does not allow antibody to efficiently enter the CNS from the periphery, ASCs must either be continuously recruited to the CNS or maintained in the brain parenchyma to produce antibody locally (Metcalf et al, 2013;Stewart et al, 2011;Hooper et al, 2009;Diamond, 2003;Diamond et al, 2003;Ramakrishna et al, 2002;Tyor et al, 1992;Levine and Griffin, 1992;Parsons, 1989). Antibody controls persistent infection in the CNS through a multifaceted defense strategy that preserves neuronal function following infection.…”

“…Antibody controls persistent infection in the CNS through a multifaceted defense strategy that preserves neuronal function following infection. The need for continued antibody production in the CNS is highlighted in studies where passive transfer of antibody blocked recrudescence only during the time of treatment Levine and Griffin, 1992;Levine et al, 1991).…”