Within host RNA virus persistence : mechanisms and consequences

RER is funded by the Wellcome Trust, UK (Grant 101788/Z/13/Z) and DEG by US National Institutes of Health (R01 NS038932).In a prototypical response to an acute viral infection it would be expected that the adaptive immune response would eliminate all virally infected cells within a few weeks of infection. However many (non-retrovirus) RNA viruses can establish “within host” persistent infections that occasionally lead to chronic or reactivated disease. Despite the importance of “within host” persistent RNA virus infections, much has still to be learnt about the molecular mechanisms by which RNA viruses establish persistent infections, why innate and adaptive immune responses fail to rapidly clear these infections, and the epidemiological and potential disease consequences of such infections.Publisher PDFPeer reviewe

SPECIFICITY OF THE INFLAMMATORY RESPONSE IN VIRAL ENCEPHALITIS : I. ADOPTIVE IMMUNIZATION OF IMMUNOSUPPRESSED MICE INFECTED WITH SINDBIS VIRUS

The viral-induced perivascular inflammatory response in Sindbis virus encephalitis of mice was shown to be immunologically specific. Mice were inoculated intracerebrally with Sindbis virus, and 24 hr later a single dose of cyclophosphamide was given which ablated the inflammatory response. 3 days after virus inoculation, cells and/or sera from specifically and nonspecifically sensitized donor mice were given, and the inflammatory reactions, virus content, and antibody response of recipients were examined 5 days later. Reconstitution of the viral inflammatory response required virus-specific sensitized lymph node cells and was enhanced when these lymph node cells were combined with bone marrow cells. Reconstitution was not achieved with Sindbis virus immune serum even when combined with nonspecifically sensitized cells. Combination of immune serum with Sindbis virus-sensitized cells did not produce an accentuation of the reaction. In distinction, reconstitution of the inflammatory reaction surrounding the stab wound was reconstituted with bone marrow cells from mice inoculated with Sindbis virus or control antigens. Reconstitution of the perivascular reaction was associated with a reduction in brain virus content. Although the transfer of Sindbis virus-sensitized lymph node cells and bone marrow cells resulted in the limited production of neutralizing antibody in the immunosuppressed recipient, the reduction in virus was significantly greater with the transfers of Sindbis virus-sensitized lymph node cells than with the passive transfer of immune serum alone

Heparin-binding and patterns of virulence for two recombinant strains of Sindbis virus

AbstractE2 is an important determinant of Sindbis virus neurovirulence. Increased heparan sulfate (HS) binding is associated with rapid clearance of viremia and usually with decreased virulence. However, substitution of histidine for arginine at E2-157 (R157H) or glutamate for lysine at E2-159 (K159E) produces viruses with decreases in heparin-Sepharose binding and increases in viremia but different levels of binding to HS-expressing cells and virulence phenotypes in newborn CD-1 mice (Byrnes, A.P., Griffin, D.E., 2000. Large-plaque mutants of Sindbis virus show reduced binding to heparan sulfate, heightened viremia and slower clearance from the circulation. J. Virol. 74, 644–651). To identify mechanisms of virulence, R157H and K159E were studied in newborn CD-1 and BALB/c mice. Subcutaneous inoculation of R157H caused 100% and K159E 60% mortality in 2-day-old CD-1 mice. R157H caused 25% and K159E no mortality in 2-day-old BALB/c mice. R157H and K159E replicated similarly at the site of inoculation with the same level of viremia, but clearance was slower in CD-1 than BALB/c mice. R157H replicated better than K159E in the central nervous system (CNS) after subcutaneous and intracerebral inoculation and in undifferentiated neurons. These studies show a genetic restriction of replication in newborn BALB/c mice, and that amino acid substitutions affecting binding to proteoglycans may differ in importance for CNS infection and viremia

Class II fusion protein of alphaviruses drives membrane fusion through the same pathway as class I proteins

Viral fusion proteins of classes I and II differ radically in their initial structures but refold toward similar conformations upon activation. Do fusion pathways mediated by alphavirus E1 and influenza virus hemagglutinin (HA) that exemplify classes II and I differ to reflect the difference in their initial conformations, or concur to reflect the similarity in the final conformations? Here, we dissected the pathway of low pH–triggered E1-mediated cell–cell fusion by reducing the numbers of activated E1 proteins and by blocking different fusion stages with specific inhibitors. The discovered progression from transient hemifusion to small, and then expanding, fusion pores upon an increase in the number of activated fusion proteins parallels that established for HA-mediated fusion. We conclude that proteins as different as E1 and HA drive fusion through strikingly similar membrane intermediates, with the most energy-intensive stages following rather than preceding hemifusion. We propose that fusion reactions catalyzed by all proteins of both classes follow a similar pathway

The Conserved Macrodomain Is a Potential Therapeutic Target for Coronaviruses and Alphaviruses

Emerging and re-emerging viral diseases pose continuous public health threats, and effective control requires a combination of non-pharmacologic interventions, treatment with antivirals, and prevention with vaccines. The COVID-19 pandemic has demonstrated that the world was least prepared to provide effective treatments. This lack of preparedness has been due, in large part, to a lack of investment in developing a diverse portfolio of antiviral agents, particularly those ready to combat viruses of pandemic potential. Here, we focus on a drug target called macrodomain that is critical for the replication and pathogenesis of alphaviruses and coronaviruses. Some mutations in alphavirus and coronaviral macrodomains are not tolerated for virus replication. In addition, the coronavirus macrodomain suppresses host interferon responses. Therefore, macrodomain inhibitors have the potential to block virus replication and restore the host’s protective interferon response. Viral macrodomains offer an attractive antiviral target for developing direct acting antivirals because they are highly conserved and have a structurally well-defined (druggable) binding pocket. Given that this target is distinct from the existing RNA polymerase and protease targets, a macrodomain inhibitor may complement current approaches, pre-empt the threat of resistance and offer opportunities to develop combination therapies for combating COVID-19 and future viral threats

Evolution of T Cell Responses during Measles Virus Infection and RNA Clearance

Measles is an acute viral disease associated both with immune suppression and development of life-long immunity. Clearance of measles virus (MeV) involves rapid elimination of infectious virus during the rash followed by slow elimination of viral RNA. To characterize cellular immune responses during recovery, we analyzed the appearance, specificity and function of MeV-specific T cells for 6 months after respiratory infection of rhesus macaques with wild type MeV. IFN-γ and IL-17-producing cells specific for the hemagglutinin and nucleocapsid proteins appeared in circulation in multiple waves approximately 2-3, 8 and 18-24 weeks after infection. IFN-γ-secreting cells were most abundant early and IL-17-secreting cells late. Both CD4 and CD8 T cells were sources of IFN-γ and IL-17, and IL-17-producing cells expressed RORγt. Therefore, the cellular immune response evolves during MeV clearance to produce functionally distinct subsets of MeV-specific CD4 and CD8 T cells at different times after infection

Suppression of human immunodeficiency virus replication during acute measles.

To determine the effect of measles virus coinfection on plasma human immunodeficiency virus (HIV) RNA levels, a prospective study of hospitalized children with measles was conducted between January 1998 and October 2000 in Lusaka, Zambia. Plasma HIV RNA levels were measured during acute measles and 1 month after hospital discharge. The median plasma HIV RNA level in 33 children with measles who were followed longitudinally was 5339 copies/mL at study entry, 60,121 copies/mL at hospital discharge, and 387,148 copies/mL at 1-month follow-up. The median plasma HIV RNA level in children without acute illness was 228,454 copies/mL. Plasma levels of immune activation markers were elevated during the period of reduced plasma HIV RNA. Plasma levels of several potential HIV suppressive factors also were elevated during acute measles. HIV replication is transiently suppressed during acute measles at a time of intense immune activation

Comparison of the Immune Responses Induced by Chimeric Alphavirus-Vectored and Formalin-Inactivated Alum-Precipitated Measles Vaccines in Mice

A variety of vaccine platforms are under study for development of new vaccines for measles. Problems with past measles vaccines are incompletely understood and underscore the need to understand the types of immune responses induced by different types of vaccines. Detailed immune response evaluation is most easily performed in mice. Although mice are not susceptible to infection with wild type or vaccine strains of measles virus, they can be used for comparative evaluation of the immune responses to measles vaccines of other types. In this study we compared the immune responses in mice to a new protective alphavirus replicon particle vaccine expressing the measles virus hemagglutinin (VEE/SIN-H) with a non-protective formalin-inactivated, alum-precipitated measles vaccine (FI-MV). MV-specific IgG levels were similar, but VEE/SIN-H antibody was high avidity IgG2a with neutralizing activity while FI-MV antibody was low-avidity IgG1 without neutralizing activity. FI-MV antibody was primarily against the nucleoprotein with no priming to H. Germinal centers appeared, peaked and resolved later for FI-MV. Lymph node MV antibody-secreting cells were more numerous after FI-MV than VEE/SIN-H, but were similar in the bone marrow. VEE/SIN-H-induced T cells produced IFN-γ and IL-4 both spontaneously ex vivo and after stimulation, while FI-MV-induced T cells produced IL-4 only after stimulation. In summary, VEE/SIN-H induced a balanced T cell response and high avidity neutralizing IgG2a while FI-MV induced a type 2 T cell response, abundant plasmablasts, late germinal centers and low avidity non-neutralizing IgG1 against the nucleoprotein

Vaccination of Rhesus Macaques with a Recombinant Measles Virus Expressing Interleukin-12 Alters Humoral and Cellular Immune Responses

Lack of a vaccine for infants and immunosuppression after infection are problems associated with measles virus (MV). Because interleukin (IL)-12 has been used successfully as a vaccine adjuvant and because inhibition of IL-12 expression has been associated with immunosuppression during measles, the addition of IL-12 may enhance the immune response to MV. To determine the effect of IL-12 supplementation, rhesus macaques were vaccinated with a recombinant MV expressing IL-12; these macaques had increased interferon-γ production by CD4+ T cells, decreased production of IL-4, and lower levels of MV-specific immunoglobulin G4 and neutralizing antibody. Lymphoproliferative responses to mitogen were not improved. IL-12 supplementation altered the T helper type 2 bias of the immune response after MV vaccination, had a detrimental effect on the protective neutralizing antibody response, and did not improve other manifestations of immunosuppression. Reduced IL-12 levels are not the sole factor in MV-induced immunosuppressio