Postinfection therapy of arbovirus infections in mice

Antiviral Therapy of Haemorrhagic Fevers and Arbovirus Infections

RNA viruses of the families Arena-, Bunya-, Filo-, Flavi-and Togaviridae cause illness in humans ranging from mild, non-specific febrile syndromes to fulminant, lethal haemorrhagic fever. They are transmitted from animals to humans and from human to human by arthropods, aerosols or contact with body fluids. Antiviral compounds, convalescent plasma and interferon inhibit many of these agents in vitro and in virus-infected animals. Drug or plasma treatment is now in use for several human diseases, and would probably be beneficial for a number of others for which there is only limited treatment experience. Success is linked to early diagnosis and initiation of therapy. Ribavirin is used to treat Lassa fever and haemorrhagic fever with renal syndrome, and would probably be effective for Crimean-Congo haemorrhagic fever and for all New World arenavirus diseases. The value of ribavirin in the early treatment of hantavirus pulmonary syndrome is under evaluation. Convalescent plasma is the therapy of choice for Argentine haemorrhagic fever, and would also probably be effective for other New World arenaviruses and some other infections if a safe supply of plasma could be maintained. Ribavirin and interferon-α have both shown protective efficacy in non-human primates infected with Rift Valley fever virus. No effective therapy has yet been identified for filovirus infections, but results in animal models are encouraging. More clinical research is urgently needed. Even if placebo-controlled drug trials cannot be performed, conscientious reports of the results of therapy in limited numbers of patients can still provide evidence of antiviral drug effects.

Capsid-deficient alphaviruses generate propagative infectious microvesicles at the plasma membrane

Alphavirus budding is driven by interactions between nucleocapsids assembled in the cytoplasm and envelope proteins present at the plasma membrane. So far, the expression of capsid and envelope proteins in infected cells has been considered an absolute requirement for alphavirus budding and propagation. In the present study, we show that Semliki Forest virus and Sindbis virus lacking the capsid gene can propagate in mammalian and insect cells. This propagation is mediated by the release of infectious microvesicles (iMVs), which are pleomorphic and have a larger size and density than wild-type virus. iMVs, which contain viral RNA inside and viral envelope proteins on their surface, are released at the plasma membrane and infect cells using the endocytic pathway in a similar way to wild-type virus. iMVs are not pathogenic in immunocompetent mice when injected intravenously, but can infect different organs like lungs and heart. Finally, we also show that alphavirus genomes without capsid can mediate the propagation of heterologous genes, making these vectors potentially interesting for gene therapy or vaccination studies. The minimalist infectious system described in this study shows that a self-replicating RNA able to express membrane proteins with binding and fusion properties is able to propagate, providing some insights into virus evolution.

Effects of Elm Bark (Ulmus davidianavar.japonica) Extracts on the Modulation of Immunocompetence in Mice

The immunomodulative effects of elm bark extract were studied in vitro by the proliferation of splenocytes and the production capacity of three kinds of cytokines [interleukin (IL)-1beta, IL-6, and tumor necrosis factor (TNF)-alpha] by mouse peritoneal macrophages cultured with various fractions (methanol, hexane, chloroform, ethyl acetate, butanol, and water) of elm bark extract. Splenocyte proliferation and cell viability of peritoneal macrophages were increased with concentrations of polar fractions, such as butanol and water, in the range of 1-500 microg/mL. Significantly higher levels of the production of all three cytokines were detected with supplementation of methanol extract compared with other fractions. In order to elucidate its effect in vivo, elm bark water extract was orally administrated every other day for 2 weeks. Proliferation of splenocytes and the production capacity of cytokines (IL-1beta, IL-6, and TNF-alpha) by mouse peritoneal macrophages were used as indices for immune activity. Splenocyte proliferation induced by elm bark with lipopolysaccharide or concanavalin A stimulation was enhanced at 500 mg/kg of body weight concentrations compared to that of the control group. In the case of cytokines, the highest production of IL-6 and TNF was detected at 500 mg/kg of body weight concentrations. In conclusion, this study suggests through in vitro and in vivo experiments that Ulmus davidiana var. japonica (elm bark) extracts may enhance the immunocompetent properties such as splenocyte proliferation and cytokine production capacity by activated macrophages and have a protective effect in mice.

Prophylactic treatment with recombinant Eimeria protein, alone or in combination with an agonist cocktail, protects mice from Banzi virus infection

A recombinant Eimeria protozoan protein antigen (rEA) has been shown to have antitumor and antiviral activity. The purpose of this study was to determine the effect of rEA treatment alone or in combination with an agonist cocktail consisting of granulocyte macrophage colony stimulating factor (GM-CSF), interferon gamma (IFN-gamma), interleukin 4 (IL-4), and anti CD-40 antibody, in the treatment of Banzi virus (BV) disease in BALB/c mice. Treatment with rEA resulted in a significant increase in survival, weight gain, and mean day to death in BV-infected mice and resulted in a significant decrease in brain virus titer. Treatment with rEA, in combination with a 4-agonist cocktail, improved disease parameters to a greater degree than rEA treatment alone. The effect of treatment with a reduced concentration of agonist cocktail or fewer components of the agonist cocktail, in combination with rEA, on disease outcome in BV-infected mice was also investigated. Treatment with rEA, alone or in combination with agonist cocktail, 24h after virus challenge did not improve disease. Treatment with rEA, alone or in combination with an agonist cocktail, is efficacious for the prophylaxis of BV infection in mice.

Oligonucleotides and polyribonucleotides: a review of antiviral activity

Current antiviral therapies are insufficient for treating emerging, re-emerging and established viral diseases. In an effort to find new therapeutics, oligo- and polyribonucleotides are being studied for their antiviral capabilities. Studies have shown that uniquely modified single- and double-stranded nucleic acid constructs are effective in inhibiting viral proliferation by various mechanisms. This review gives a brief history and highlights the development of oligo- and polyribonucleotides as antiviral agents primarily in the fields of interferon induction, mRNA complementation and reverse transcriptase inhibition.

Effect of interferon-alpha and interferon-inducers on West Nile virus in mouse and hamster animal models

The recent West Nile virus (WNV) outbreak in the United States has increased the need to identify effective therapies. Studies were conducted in cell culture and in rodent animal models to determine the efficacy of interferon-alpha (IFN-alpha), interferon (IFN) inducers and ribavirin, alone or in combination with IFN, in treating WNV. Intraperitoneal injection of IFN-alpha B/D (qd for 7 days), polyI-polyC(12)U [Ampligen (every other day for 7 days)] and topically applied imiquimod (qd for 7 days), administered from 1 day before viral challenge, were effective in protecting, respectively, 100%, 100% and 70% of BALB/c mice from mortality induced by subcutaneous injection of WNV. When IFN-alpha B/D or Ampligen treatments were delayed to 4-6 h before viral challenge in mice, efficacy was greatly diminished. Infected Syrian golden hamsters treated with interferon alphacon-1 (Infergen) and Ampligen 4-6 h before viral challenge gained more weight and had a greater survival than saline-treated animals. A combination study of subcutaneously administered Infergen (5 to 0.05 microg/kg/day) and ribavirin (75 to 7.5 mg/kg/day) in >7 week old hamsters demonstrated that Infergen was slightly efficacious in reducing mortality and disease signs; however, it was not synergistic in its antiviral effects when combined with ribavirin. Ribavirin treatment alone increased mortality of infected hamsters. The reduced mortality correlated with reduced plasma viraemia. Since WNV-infected patients have already been treated with IFN and ribavirin and future clinical trials have been suggested, this first report of IFN alone or in combination with ribavirin in WNV-infected animal models might provide useful information for subsequent treatment of patients.

Poly I:CLC induction of the interferon system in mice: an initial study of four detection methods

Induction of a large number of the components of the interferon (IFN) system (IFN genes, their mRNAs, IFN proteins, IFN receptors, IFN signaling molecules, the IFN response genes, and their effector proteins) has been studied. Less well studied is the comparative induction of these components in vivo. Induction of IFN by double-stranded RNA (dsRNA) treatment mimics certain aspects of viral infection and induces the components of the IFN system. To determine the comparative sensitivity of detection of induction in mice, we initially studied the limiting concentrations of polyribinosinic-polyribocytidylic acid, polylysine complex (poly I:CLC, a synthetic dsRNA preparation), for induction of four representative components of the IFN system: (1) IFN in serum, (2) the IFN response gene mRNA ISG54 in spleen and liver, (3) the IFN-beta mRNA in spleen, and (4) resistance of mice to Banzi viral infection. The results of this initial study showed that resistance to infection was 7-fold more sensitive for detection of the IFN response than was ISG54 mRNA and 70-fold more sensitive than either IFN-beta mRNA or IFN production in serum. In comparison, mouse cells in vitro treated with poly I:CLC were 3-10-fold less sensitive to its antiviral action than is the mouse. The results demonstrate that in the four tests in mice, the most sensitive indicator of poly I:CLC induction of the IFN system was protection against Banzi viral infection, followed by ISG54 mRNA levels, IFN-beta mRNA, and IFN protein levels. It is hypothesized that the highest sensitivity of mouse protection may be due to priming by the initial poly I:CLC-induced IFN of the subsequent Banzi virus-induced IFN, resulting in rapid and high concentrations of IFN at the local site of viral replication. Future studies are needed to study other molecular components of the IFN system to identify those that cause the unanticipated high sensitivity of mice to protection against Banzi virus.

Innate antiviral defenses in body fluids and tissues

Innate, non-specific, resistance mechanisms are important barriers to pathogens, particularly delaying virus multiplication at the onset of infections. These innate defense mechanisms include a series of mechanical barriers, pre-existing inhibitory molecules, and cellular responses with antimicrobial activity. The antiviral activities of these innate inhibitors reside in a variety of partly characterized substances. This review presents the innate antiviral inhibitors in cell cultures, urine, serum, the gastrointestinal tract, the nervous system, tissues of crustaceans, and saliva. Medical adaptation of the innate antiviral defense mechanisms may be useful for prevention and treatment of viral infections.

The role of antibody in recovery from alphavirus encephalitis

Alphaviruses infect neurons in the brain and spinal cord and cause acute encephalomyelitis in a variety of mammals. The outcome of infection is determined by whether the neurons survive infection and this, in turn, is determined by the virulence of the virus and the age of the host at the time of infection. We have been studying Sindbis virus (SV) infection of mice as a model system for alphavirus-induced encephalomyelitis. Investigation of intracerebral infection of weanling mice with two different strains of SV has allowed us to analyze the role of the immune response in protection from fatal disease (virulent NSV strain) and in clearance of virus from the nervous system during non-fatal disease (less virulent SV AR339 strain). Neutralizing and non-neutralizing antibodies to the E1 and E2 surface glycoproteins can protect mice from fatal NSV infection when given before or after infection, while T cells are not protective. The mechanism of antibody-mediated protection is not known, but it is likely that more than one mechanism is involved and that different mechanisms are involved in pre-infection and post-infection treatment protection. Clearance of infectious virus from the nervous system of mice during recovery from non-fatal disease is accomplished by antibodies to the E2 glycoprotein. The process does not involve damage to the infected neurons and is independent of complement and mononuclear cells. Bivalent antibody is required and binds to the surface of the infected cell. Initially, release of virus by budding from the cell surface is prevented and, subsequently, intracellular virus replication is inhibited possibly through antiviral mechanisms induced in co-operation with interferon. This non-lytic mechanism for control of virus infection results in the prolonged presence of viral RNA in tissue and the need for prolonged intrathecal synthesis of antiviral antibody by B cells within the central nervous system.

Antiviral activity of alpha interferon in Sindbis virus-infected cells is restored by anti-E2 monoclonal antibody treatment

Pretreatment of AT3 rat prostatic carcinoma cells expressing the inhibitor of apoptosis bcl-2 (AT3-bcl-2 cells) with alpha interferon (IFN-alpha) affected replication of a virulent strain of Sindbis virus (SV) but did not protect against virus-induced cell death. Treatment of cells with IFN-alpha late during infection affected ongoing SV replication very little. Previous studies have shown that cross-linking of the viral glycoprotein E2 with antibody delays the inhibition of K+ influx by improving the function of Na+K+ATPase and the Na(+)-K(+)-2Cl-cotransport system in SV-infected cells (P. Després, J. W. Griffin, and D. E. Griffin, J. Virol. 69:7006-7014, 1995). In these studies, we have shown that treatment of infected cells with anti-E2 monoclonal antibody also restored the ability of IFN-alpha to induce antiviral activity in infected cells late during infection. The very low rate of virus release in SV-infected cells treated simultaneously with anti-E2 monoclonal antibody and IFN-alpha was postulated to be linked to inhibition of virus maturation. Synergistic effects of antibody and IFN-alpha are likely to be important for control of SV replication in vivo.

Efficacy of Coxiella burnetii and its chloroform-methanol residue (CMR) fraction against Rift Valley fever virus infection in mice

Strains of Coxiella burnetii phase I and II whole cells (WC-I and WC-II) or whole cell fractions were assessed for their potential to induce long-lasting protection in endotoxin-non-responder C3H/HeJ or CD-1 mice against Rift Valley fever (RVF) virus challenge. Among the whole cell fractions, only the chloroform-methanol residue (CMR), administered as a single dose (100 micrograms per mouse) 24 h before viral challenge, effectively protected 100% of the mice from RVF virus; the CMR of the Ohio strain of C. burnetii was not protective. Most of the RVF virus-infected mice treated with other C. burnetii cell fractions died, although their times to death varied. Lipopolysaccharide (LPS) associated with CMR preparations used in these studies, did not protect against RVF virus challenge. A single dose of 100 micrograms of CMR given 24 h before viral challenge completely eradicated 4-5 logs of RVF virus in the serum, liver, spleen, and central nervous system. Compared to several other immunomodulators, CMR was an equally effective antiviral agent. Efficacy of CMR of both Henzerling and Ohio strains disappeared or was marginal when treatment was initiated 2-3 days before RVF viral challenge, even when a second or a third dose of CMR was administered after challenge. A single dose of liposome-encapsulated CMR to RVF virus-infected mice extended the range of therapeutic efficacy of this biologically active component of C. burnetii to 4 days before infection.

The mechanism of poly I:C-induced antiviral activity in peritoneal macrophage

Macrophages play an important role in defense against virus infection by intrinsic resistance and by extrinsic resistance. Since interferon-induced enzymes which are 2'-5' oligoadenylate synthetase and P1/eIF-2 protein kinase have been shown to be involved in the inhibition of viral replication, I examined the mechanism by which poly I:C, an interferon inducer, exerts its antiviral effects in inflammatory macrophages infected with herpes simplex virus type 1 (HSV-1). The data presented here demonstrate that poly I:C-induced antiviral activity is partially due to the activation of 2'-5' oligoadenylate synthetase. The activation of 2'-5' oligoadenylate A synthetase by poly I:C is also at least partly mediated via the production of interferon-beta. Taken together, these data indicate that interferon-beta produced in response to poly I:C acts in an autocrine manner to activate the 2'-5' oligoadenylate synthetase and to induce resistance to HSV-1.

Poly I:C-induced antiviral and cytotoxic activities are mediated by different mechanisms

Macrophages play an important role in host defenses against tumors and virus infections by killing tumor or virus infected cells (extrinsic cytotoxicity) and by limiting virus replication within themselves (intrinsic antiviral activity). Since common macrophage products may be involved in both extrinsic cytotoxicity and intrinsic antiviral activity, we decided to investigate the mechanisms by which Poly I:C-activated macrophages resist infection with HSV-1 and inhibit the growth of tumor cells. The ability of macrophages to resist infection with HSV-1 or to inhibit growth of tumor cells was assessed following treatment with Poly I:C in the presence of antibodies to various cytokines or in the presence of inhibitors/scavengers of toxic macrophage products. Only antibodies to IFN-beta were able to abrogate the protective effects of Poly I:C in macrophages infected with HSV-1, suggesting that the antiviral activity induced by this immunomodulator was mediated by the production of IFN-beta, which acted in an autocrine manner. In contrast, anti-TNF-alpha, anti-IFN-alpha/beta anti-IFN-beta antibodies and inhibitors of nitric oxide and C1q production were all able to partially abrogate Poly I:C-induced cytostatic activity, suggesting that multiple mechanisms are involved in macrophage cytostasis. Our results indicate the Poly I:C-induced intrinsic antiviral and extrinsic cytotoxic activities are mediated by different mechanisms.