Measles virus-induced changes in leukocyte function antigen 1 expression and leukocyte aggregation: possible role in measles virus pathogenesis

Measles virus (MV) infection of U937 cell or peripheral blood leukocyte cultures was shown to induce changes in the expression of leukocyte function antigen 1 (LFA-1) and cause marked aggregation of these cells. Addition of selected monoclonal antibodies specific for LFA-1 epitopes that did not neutralize MV in standard neutralization assays were found to block both virus-induced leukocyte aggregation and virus dissemination. These data suggest that MV modulation of LFA-1 expression on leukocytes may be an important step in MV pathogenesis.

Parainfluenza virus type 3 (PIV3)-specific and non-virus-specific delayed type hypersensitivity responses in cotton rats given different PIV3 antigen preparations

Virus-specific, T-lymphocyte-mediated delayed type hypersensitivity (DTH) responses were studied in cotton rats using replicating (wild-type parainfluenza virus type 3 (PIV3) and recombinant vaccinia virus expressing PIV3 haemagglutinin-neuraminidase (HN) or fusion (F) glycoproteins), and non-replicating (detergent-solubilized, affinity chromatography purified HN and F glycoproteins or inactivated whole PIV3) virus preparations. Significant virus-specific DTH responses were observed in all test groups 1-2 weeks after a single antigen inoculation or 5 days after two inoculations given 3 weeks apart. Peak swelling of ear pinnas in these animals generally occurred 24 h after elicitation and was marked by a cellular infiltration consisting of mono- and polymorphonuclear leucocytes. A considerable non-virus-specific inflammatory response, presumably due to tissue culture or media components in the priming antigen preparations, was observed 3 weeks after priming. No significant differences in DTH responses were observed in cotton rats primed with any of the PIV3 preparations. The possible roles and significance of both the virus-specific and non-virus-specific DTH responses in paramyxovirus-induced disease in humans and cotton rats are discussed.

Measles virus replication in lungs of hispid cotton rats after intranasal inoculation

Hispid cotton rats were inoculated intranasally with either measles virus (MV) Edmonston, a multipassaged, tissue culture-adapted strain of MV, or with one of three clinical MV isolates that had limited passages (three to five times) in tissue culture cells. MV Edmonston was recovered from the lungs of every (n = 37) hispid cotton rat inoculated with this virus for at least 7 days after virus inoculation. Peak pulmonary titers occurred on Day +4 (3.3-4.4 log10/g lung). Scattered areas of inflammation were observed interstitially in lung sections from infected animals stained with hematoxylin and eosin, and a similar pattern of diffuse fluorescence was seen in cryostat sections stained with an indirect fluorescent antibody procedure specific for virus antigens. Fluorescent antibody and virus isolation studies on lung lavage cells both suggested that lung leukocytes were a primary target of the virus. In contrast to these findings, virus was isolated only sporadically from hispid cotton rats inoculated with any of the clinical measles virus isolates. Despite the restricted growth of MV in these animals, cotton rats may be useful for studying certain aspects of measles virus pathogenesis and for screening potential antiviral compounds in vivo.

Aerosolized liposomal amphotericin B for treatment of pulmonary and systemic Cryptococcus neoformans infections in mice

Cryptococcus infections of the lung and central nervous system have become major problems in immuno-compromised patients, leading to the need for additional treatment protocols. We have utilized a Cryptococcus-mouse model that mimics human cryptococcal disease to evaluate the efficacy of amphotericin B-liposomes (AmpB-Lip) when delivered by small-particle aerosol (SPA). In the model, initial intranasal inoculation leads to a pulmonary infection that spreads after 2 to 3 weeks to distant organs, including the brain. Aerosols of AmpB-Lip that were generated by a Collison nebulizer had mass median aerodynamic diameters of 1.8 microns and contained 10.3 micrograms of AmpB per liter. When AmpB-Lip SPA was begun at 24 h postinoculation, a single 2-h treatment (0.3 mg of AmpB per kg of body weight) was effective in reducing pulmonary Cryptococcus infection. This regimen was more effective than intravenous administration of AmpB-Lip given for 3 continuous days. This single 2-h exposure to AmpB-Lip also was effective in reducing pulmonary Cryptococcus infection when treatment was delayed for 7 or 14 days. At day 21, when organisms had spread to the brain in all animals, the single 2-h aerosol treatment reduced the number of cryptococci in the brain as well as in the lungs. AmpB-Lip SPA administered once for 2 h on days 7, 14, and 21 also was effective in increasing the duration of survival of infected animals. These results demonstrate that aerosolized AmpB-Lip can be effective in treating both local, pulmonary Cryptococcus disease and systemic disease.

Further studies with short duration ribavirin aerosol for the treatment of influenza virus infection in mice and respiratory syncytial virus infection in cotton rats

Ribavirin aerosol administration has been shown to be effective in the treatment of respiratory syncytial virus (RSV) infections in infants and in influenza A and B virus infections in young adults. Long treatment schedules and potential for environmental contamination have stimulated the search for alternative dosing schedules. Thus, we attempted to determine the length of time of ribavirin aerosol necessary for effective treatment of influenza and RSV. In RSV-infected cotton rats, aerosolization for just 30 min with high-dose ribavirin (HDR:60 mg ribavirin/ml in reservoir), 3 times daily, reduced viral lung titers/gm of tissue by 1.1 log10. In influenza virus-infected mice, 15 min of aerosolized HDR, 3 times daily, was effective in reducing both mortality and pulmonary virus titers (1.1 log10 reduction). When the intervals between aerosol administration each day were equally divided (i.e., q.8 h), the treatments were most effective. Treatment for 45 min, once daily, was not as effective as divided doses. Calculations of ribavirin concentrations in respiratory secretions following 15 min treatment in mice with HDR indicated that drug levels dropped below the ED50 for influenza viruses after about 9 h. A daily dosage of ribavirin, estimated to be 8-15 mg/kg, was effective for the treatment of influenza and RSV infections.

Evaluation of the immunogenicity and protective efficacy of a candidate parainfluenza virus type 3 subunit vaccine in cotton rats

A parainfluenza virus type 3 (PIV3) subunit vaccine consisting of detergent-solubilized, affinity-purified haemagglutinin-neuraminidase (HN) and fusion (F) surface glycoproteins was tested in cotton rats for immunogenicity, short-term effects on virus-induced immunopathology and protective efficacy. Groups of animals were immunized twice, 4 weeks apart, with graded doses of vaccine administered either alone or with aluminium phosphate (AlPO4). The minimum immunogenic dose of vaccine was 0.1 microgram HN and F when the vaccine was given alone and 0.01 microgram when the vaccine was administered with AlPO4 adjuvant. Antibody responses in animals immunized with 1 microgram HN and F mixed with adjuvant were similar to those in control animals infected with live PIV3 intranasally. Pulmonary and nasal wash PIV3 titres generally were inversely correlated with serum antibody levels. Virus titres were significantly reduced in all groups of animals immunized with greater than or equal to 0.1 microgram HN and F compared with control animals immunized with vehicle only. Four days after virus challenge, there was no evidence of enhanced histopathology in lung sections from animals immunized with the candidate vaccine.

Aerosol and intraperitoneal administration of ribavirin and ribavirin triacetate: pharmacokinetics and protection of mice against intracerebral infection with influenza A/WSN virus

Ribavirin is active in vitro but not in vivo against a number of viruses capable of causing encephalitis. Ribavirin triacetate (RTA), a lipophilic derivative, has been reported to be more effective than ribavirin in protecting animals from encephalitis. By using an influenza A/WSN virus encephalitis model, we demonstrated that RTA administered by small-particle aerosol was able to decrease the death rate and increase the time of survival. To determine if this beneficial effect was due to increased delivery of drug, the pharmacokinetic properties of ribavirin and RTA when administered as an aerosol or by intraperitoneal injection were examined. Aerosol administration of ribavirin or RTA gave significantly higher concentrations of ribavirin in the lungs and serum of mice than did intraperitoneal injection. There was no difference, however, in ribavirin levels when either ribavirin or RTA was administered by small-particle aerosol. In brain tissue, ribavirin concentrations increased with time and did not appear to decrease as rapidly as in lungs and serum. Mean peak ribavirin concentrations in the brain were higher following aerosol administration of ribavirin than RTA, and both were higher than that following intraperitoneal injection of either drug. Administration of ribavirin or RTA by intraperitoneal injection failed to protect mice from a lethal intracerebral inoculation of influenza A/WSN virus, while aerosolized RTA did protect mice. The pharmacokinetics of ribavirin in brain tissue following aerosol administration of either drug did not explain the advantage of RTA over ribavirin in protecting mice from intracerebral infection with influenza A/WSN virus.

High dose-short duration ribavirin aerosol treatment--a review

A high-dose, short-duration treatment with ribavirin aerosol consisting of a three-fold increase in concentration of drug (60 mg versus 20 mg of ribavirin per mL in the liquid reservoir of the generator administered for about one-third the time of the standard treatment) was as effective as the standard dosage in the treatment of experimental influenza A and B infections in mice and in the treatment of experimental respiratory syncytial virus infection in cotton rats. Despite some minor pulmonary intolerance, it was considered to be suitable for use in treatment of patients with severe chronic pulmonary disease, and it was well-tolerated and apparently effective in the treatment (by face mask and endotracheal tube) of infants with bronchiolitis principally caused by respiratory syncytial virus infection. Pharmacokinetic studies in mice revealed very high concentrations of drug in the lungs, about triple the level with the standard dose, with similar blood and brain concentrations. Ribavirin concentrations were similarly high in respiratory secretions of infants given the triple dose.

Mutational analysis of regulation of MHC and anti-viral genes

CTL-mediated selection for loss of expression of Mta by H-2-heterozygous SV40-transformed mouse fibroblasts (line 24SV) produced an unusual phenotypic class of maternally transmitted Ag negative mutants defective in both MHC expression and in anti-viral activity. Severely reduced surface expression of class I MHC Ag from multiple loci of both haplotypes correlated with low levels of MHC H chain and beta 2-microglobulin mRNA. Inasmuch as IFN can up-regulate class I expression and some fibroblasts elaborate autocrine IFN-beta, we examined whether IFN could restore wild-type expression of class I MHC Ag. However, IFN could not restore wild-type expression. Moreover, the fold-increases in class I Ag and mRNA expression were significantly reduced in mutant cells compared to wild-type cells. These results suggested that the mutants might have generalized defects in IFN response. Inasmuch as the induction of an anti-viral state is a hallmark of IFN responses, we exposed cells to IFN-alpha, -beta, or -gamma and challenged with virus. 24SV cells, exposed to any of the three IFNs, were completely protected from destruction by vesicular stomatitis, mengovirus or respiratory syncytial viruses. In contrast, MHC and anti-viral defective mutants could not be protected from virus-induced lysis by any IFN. Somatic cell hybridization analyses indicated that both basal MHC and IFN-inducible phenotypes were recessive to wild-type, and that a trans-acting regulatory factor required for basal MHC expression is defectively expressed in the mutants. Such a factor may integrate the organismal response to virus infection, encompassing both immune and nonimmune anti-viral responses.

Mutational analysis of regulation of MHC and anti-viral genes

CTL-mediated selection for loss of expression of Mta by H-2-heterozygous SV40-transformed mouse fibroblasts (line 24SV) produced an unusual phenotypic class of maternally transmitted Ag negative mutants defective in both MHC expression and in anti-viral activity. Severely reduced surface expression of class I MHC Ag from multiple loci of both haplotypes correlated with low levels of MHC H chain and beta 2-microglobulin mRNA. Inasmuch as IFN can up-regulate class I expression and some fibroblasts elaborate autocrine IFN-beta, we examined whether IFN could restore wild-type expression of class I MHC Ag. However, IFN could not restore wild-type expression. Moreover, the fold-increases in class I Ag and mRNA expression were significantly reduced in mutant cells compared to wild-type cells. These results suggested that the mutants might have generalized defects in IFN response. Inasmuch as the induction of an anti-viral state is a hallmark of IFN responses, we exposed cells to IFN-alpha, -beta, or -gamma and challenged with virus. 24SV cells, exposed to any of the three IFNs, were completely protected from destruction by vesicular stomatitis, mengovirus or respiratory syncytial viruses. In contrast, MHC and anti-viral defective mutants could not be protected from virus-induced lysis by any IFN. Somatic cell hybridization analyses indicated that both basal MHC and IFN-inducible phenotypes were recessive to wild-type, and that a trans-acting regulatory factor required for basal MHC expression is defectively expressed in the mutants. Such a factor may integrate the organismal response to virus infection, encompassing both immune and nonimmune anti-viral responses.

Evaluation of the toxicity and antiviral activity of carbocyclic 3-deazaadenosine against respiratory syncytial and parainfluenza type 3 viruses in tissue culture and in cotton rats

The toxicity and antiviral efficacy of carbocyclic 3-deazaadenosine (Cc3Ado) against respiratory syncytial (RSV) and parainfluenza type 3 (PIV3) virus infections were tested in tissue culture and in cotton rats. The mean median efficacious dose (ED50) of Cc3Ado in HEp2 cells against RSV and PIV3 was 9 and 14 micrograms/ml, respectively. These values were 85- and 55-fold less than the median inhibitory (toxic) dose (ID50) of Cc3Ado in this cell line (750 micrograms/ml), and similar to values obtained for ribavirin. Cc3Ado exhibited no significant antiviral activity against influenza A, influenza B, adeno type 5 or adeno type 7 viruses (all ED50 were greater than 1000 micrograms/ml). In cotton rats, animals given greater than or equal to 1 mg/kg/day Cc3Ado intraperitoneally on days 1, 2 and 3 after experimental challenge with virus, consistently had significant reductions in pulmonary RSV and PIV3 titers compared to pulmonary virus titers in comparably treated control animals. The minimum efficacious dose of ribavirin given under the same conditions was 30 mg/kg/day. Cc3Ado was also efficacious in cotton rats when given orally by gavage, or when different administration schedules were used. The median efficacious dose of Cc3Ado when given orally was 10 mg/kg/day. No significant toxic effects were noted in cotton rats, even in animals given 20 mg/kg daily for eight consecutive days.

Toxicity and antiviral activity of LY253963 against respiratory syncytial and parainfluenza type 3 viruses in tissue culture and in cotton rats

LY253963, the sodium salt of 1,3,4-thiadiazol-2-ylcyanamide, was evaluated in tissue culture and in cotton rats for toxicity and antiviral efficacy against respiratory syncytial (RSV) and parainfluenza type 3 (PIV3) viruses. The selective index (ratio of the median toxic dose: median efficacious dose) of LY253963 in HEp2 tissue culture cells was greater than 100 against both RSV and PIV3. When given intraperitoneally to cotton rats, the minimum protective dose of LY253963 against both of these viruses was between 1 and 3 mg/kg/day. In contrast, doses of LY253963 as high as 30 mg/kg/day, administered orally after experimental inoculation of virus, did not significantly reduce pulmonary virus titers in treated animals compared to control animals given placebo. No toxic effects were noted in cotton rats, even in those given 20 mg/kg/day for eight consecutive days.

Enhancement of the protective efficacy of inactivated influenza A virus vaccine in aged mice by IL-2 liposomes

A dose-dependent, vaccine-induced protection of aged and young Balb/c mice against lethal influenza A virus challenge has been demonstrated. Low dose formalin-inactivated influenza A virus vaccine was protective in young mice, but not in aged mice, while a higher dose was protective in both. Administration of low dose vaccine with IL-2 liposomes conferred protection comparable to the high dose in aged mice. Serum neutralizing antibody responses were stimulated by vaccine in a dose-dependent manner while IL-2 liposomes significantly enhanced responses in the low dose paralleled protection in young but not in aged mice. Lung interferon levels paralleled lung virus titres in young but not in aged mice. CTL responses in infected mice were generally higher in young than aged mice. These results demonstrate efficacy of IL-2 liposomes as an adjuvant for influenza virus vaccines in the aged.

Influenza virus infection and bacterial clearance in young adult and aged mice

The effects of influenza A/Hong Kong/68 (H3N2) virus infection on clearance of bacteria (Staphylococcus aureus or Serratia marcescens) from lungs of young adult (8-week-old) and aged (2-year-old) CBA/2N mice were studied. No consistent differences in pulmonary bacterial clearance were observed in uninfected animals of either age group. However, both young and aged virus-infected mice consistently exhibited significantly reduced ability to clear challenge bacteria from their lungs compared to age-matched nonvirus-infected controls; this deficit was markedly more pronounced in virus-infected aged mice. The extra deficit seen in virus-infected aged animals did not correlate with pulmonary virus or interferon titers, or with severity of pulmonary histopathology. Moreover, the phagocytic and bactericidal activities of pulmonary macrophages and polymorphonuclear neutrophiles from virus-infected young and aged mice were comparable.

Comparison of the anti-respiratory syncytial virus activity and toxicity of papaverine hydrochloride and pyrazofurin in vitro and in vivo

Based on reports describing their broad antiviral activity, the toxicity and antiviral efficacy of papaverine hydrochloride and pyrazofurin against respiratory syncytial virus (RSV) infection were tested in vitro in tissue culture cells and in vivo in cotton rats. Papaverine inhibited RSV replication in vitro; however, the median minimal toxic dose-median minimal inhibitory concentration ratios (MTD50:MIC50) in vitro and in vivo for papaverine were less than 4. Further work with this compound was discontinued. In contrast, pyrazofurin inhibited RSV replication in vitro (a mean MIC50 of 0.04 microgram/ml was obtained) and in vivo (RSV pulmonary titers were significantly reduced consistently in cotton rats given daily 10 mg/kg doses compared to untreated control animals). However, some toxic effects were observed in both the in vitro and in vivo tests of this compound. The remaining potential of pyrazofurin as an anti-RSV compound is discussed.

Cytotoxic and helper T-lymphocyte responses to antibody recognition regions on influenza virus hemagglutinin

We have previously localized and synthesized twelve antibody recognition sites on influenza virus hemagglutinin (HA). These peptides correspond to exposed surface areas in the 3-D structure of HA. Using intact X31 virus as the immunogen, we have determined the recognition of these synthetic peptides by proliferative T-helper lymphocytes (ThL), delayed type hypersensitivity (DTH), and cytotoxic T-lymphocytes (CTL) responses. The responses to the individual determinants in each of these immune compartments were under separate Ir gene control. Conversely, using the peptides as immunogens, we have determined the ability of various peptide-specific antibodies (in outbred mice) and ThLs (in H-2k, H-2d, H-2s and H-2b mice) to recognize intact virus. Whereas most of the peptides primed the mice for an anti-peptide proliferative ThL response, only very few of these cross-reacted with the virus. The identity of the peptide(s) eliciting virus cross-reactive ThLs varied with the strain. The importance of antibody, ThL, CTL and DTH responses in protection against viral infection and in vaccine design is discussed.

Cytotoxic T lymphocyte recognition sites on influenza virus hemagglutinin

When influenza virus infection occurs, part of the cytotoxic T lymphocyte responses induced are directed to the major surface molecule of the virus, the hemagglutinin. However, despite their potential use as a peptide vaccine, little information is available concerning the submolecular areas in the hemagglutinin that are responsible for its immunologic recognition by cytotoxic T lymphocytes. The primary goal of this study is to determine whether submolecular areas recognized by antibodies and helper T cells are also important in the virus-specific, T lymphocyte-mediated cytotoxic responses generated towards virus-infected cells. A panel of synthetic peptides representing areas of the hemagglutinin, homologous to those in influenza AX-31 virus which have previously been shown to bind anti-influenza virus antibodies and provoke proliferation of virus-primed T-helper lymphocytes, was tested in two different cytotoxicity assays. In the experiments presented here, it was found that when selected peptides were incubated with appropriate L929 target cells, lysis by virus-specific cytotoxic T cells was observed. In addition, AX-31-primed lymphocytes preincubated with these synthetic peptides (both individually and as an equimolar mixture) exhibited enhanced lysis of virus-infected syngeneic targets. The cytotoxic responses showed dose-response characteristics in all cases, and in each of the two assays used the same patterns of cytotoxic induction were observed. The recognition of peptides was MHC-restricted since virus-specific cytotoxic T cells from C3H/He mice (H-2k) lysed L929 (H-2k) target cells after incubation with peptides or viruses, but did not lyse P815 (H-2d) targets under the same conditions.

Small particle aerosols of enviroxime-containing liposomes

Enviroxime inhibits the replication of all rhinoviruses tested in vitro at very low concentrations (10-100 ng/ml), but evaluations in humans have not consistently shown efficacy. Lack of an appropriate method for administering this water-insoluble drug may have contributed to the latter result. The present report describes the characteristics and utilization of small particle aerosols to continuously deliver enviroxime-containing liposomes (LE) throughout the respiratory tract. The enviroxime content of liposomes and biological fluids of exposed individuals was quantified by high performance liquid chromatography using C18 resin, a mobile phase of 60:40 acetonitrile:water, and monitoring at 215 nm. Small particle aerosols of LE generated by Puritan-Bennett nebulizers had mass median diameters ranging from 2.4 to 3.1 microns. The concentration of enviroxime in aerosol particles was proportional to the reservoir concentration; during the first hour of operation, the mean concentration was 20 micrograms of enviroxime/l of aerosol. Liposome particles in the reservoir, although initially heterogeneous in size (less than 0.1 to greater than 1 micron), were processed by passage through the nebulizer to smaller, more homogeneous particles; the majority were less than 0.2 micron. In a preliminary study to evaluate short term tolerance and toxicity, five volunteers were exposed to small particle aerosol of LE for 1 h. At 1 h post-treatment, large amounts of enviroxime were still present in the nasal wash as determined both by HPLC and biological assay. Enviroxime was not detected in any urine sample and was detected in only 1 of 5 serum samples. No side effects were noted. This data suggest that liposome aerosols offer a method for the delivery of hydrophobic compounds for the treatment of respiratory diseases.

Activity against rhinoviruses, toxicity, and delivery in aerosol of enviroxime in liposomes

Enviroxime has been shown to inhibit the replication of rhinoviruses and other enteroviruses in concentrations as low as nanograms per milliliter in in vitro assays but is markedly less effective in clinical trials. The marked hydrophobicity and water insolubility of this compound may be a factor for this disparity. To overcome this handicap, we incorporated enviroxime into liposomes and then tested the antirhinovirus activity and toxicity of the liposome-incorporated enviroxime (LE) in cell culture and studied its administration by small-particle aerosol. Free enviroxime and LE were found to have equivalent efficacies against rhinovirus strains 1A and 13 in in vitro assays; however, preparations of LE were 10- to greater than or equal to 50-fold less toxic to tissue culture cells than was free enviroxime. In contrast to free enviroxime, which could not be delivered by small-particle aerosol because of its water insolubility, LE (4 mg/ml) was readily and successfully delivered by small-particle aerosol to the upper and lower respiratory tracts of mice; after just 20 min, significant levels of enviroxime were detected in the lungs and noses of exposed mice. Moreover, mice exposed to aerosols of liposomes containing both enviroxime and fluorescein isothiophosphatidylethanolamine showed accumulations of the fluorescent marker in the lungs, particularly in or around the tall columnar epithelial cells lining the bronchi and bronchioles.

Immunogenicity and efficacy of orally administered inactivated influenza virus vaccine in mice

The immunogenicity and protective efficacy of formalin-inactivated whole influenza A/Bangkok/79 virus vaccine given to unprimed Swiss mice orally in capsules, in their drinking water, or by direct injection into the duodenum were studied. Virus-specific IgG and IgA antibody responses to all these methods were dose-dependent and varied according to immunization conditions. Following intranasal challenge with live A/Bangkok influenza virus, mice given greater than or equal to 66 micrograms haemagglutinin (HA) of vaccine in drinking water or capsules, and mice injected into the duodenum with greater than or equal to 0.66 microgram HA, had significantly lower virus titres in their noses and lungs than control mice comparably inoculated.

Pharmacokinetics of ribavirin aerosol in mice

The pharmacokinetics of ribavirin administered in single or multiple treatments to mice by small-particle aerosol were monitored in lung, serum, and brain tissues. ribavirin aerosol was administered with a standard drug concentration (20 mg/ml) in the reservoir for 12 h or a high dose (60 mg/ml) for 2 or 4 h. After single or 3-day treatments, ribavirin rapidly accumulated in the lungs at concentrations sufficient to inhibit influenza virus or respiratory syncytial virus (1 to 5 mM). While peak levels of ribavirin in the lungs after the high-dose administration were about three times those found with the standard dose, ribavirin was rapidly cleared from the lungs. There was no accumulation of drug in the lungs after multiple treatments. Ribavirin cleared from the lungs was detected in the blood within 15 min. Concentrations in the serum were similar (20 to 30 microM) for standard- and high-dose treatments with either single or multiple treatments. Ribavirin clearance from the serum after treatment was similar for each regimen. Ribavirin also rapidly accumulated in the brain to a similar level (ca. 6 nmol per brain) after standard- or high-dose treatment for 3 days. In contrast to ribavirin in the serum, ribavirin in the brain appeared to be slowly cleared, allowing levels to remain relatively constant during and after treatment. With the interest in viral encephalopathies, further evaluation of the possible advantages of this method of drug administration is warranted.

Efficacy of high dose-short duration ribavirin aerosol in the treatment of respiratory syncytial virus infected cotton rats and influenza B virus infected mice

Fifteen to 20 mg/ml ribavirin administered as a small particle aerosol for 10-18 h per day is currently the regimen generally used to treat experimental or naturally-occurring respiratory syncytial (RS) or influenza virus infections in humans. To determine if such prolonged treatment schedules could be reduced, cotton rats and mice were inoculated with RS or influenza B virus, respectively, and then treated with different concentrations of ribavirin small particle aerosols. Aerosols generated from reservoirs containing 60 mg/ml ribavirin given 2 h twice daily, protected cotton rats from RS virus and mice from influenza B virus as well as aerosols generated from reservoirs containing 20 mg/ml ribavirin given 11 h daily. Aerosols generated from reservoirs containing 40 or 20 mg/ml given 2 h daily were less efficacious. There was no evidence of intolerance or pulmonary histopathology in infected or uninfected animals exposed to any of the doses of ribavirin tested. These studies indicate that use of aerosols containing higher concentrations of ribavirin than generally used to treat respiratory virus diseases may permit significantly shorter treatment schedules without loss of efficacy or increase in toxicity.

Immunoglobulin administration and ribavirin therapy: efficacy in respiratory syncytial virus infection of the cotton rat

We studied the effects of combined administration of human immunoglobulin (IVIG) and ribavirin aerosol on respiratory syncytial virus (RSV) infection in cotton rats (Sigmodon hispidus). Cotton rats assigned to receive combined therapy were administered Gamimune, a preparation of purified IVIG with a high titer of anti-RSV neutralizing activity, intraperitoneally 24 h prior to intranasal RSV challenge and then treated with ribavirin aerosol 3 days after challenge. Lung viral titers from these cotton rats (geometric mean titers [GMT] log10 = 0.15 +/- 0.5) were lower than titers from untreated animals (GMT, log10 = 3.7 +/- 0.6) and animals treated with either IVIG alone (GMT, log10 = 1.8 +/- 0.9) or ribavirin alone (GMT, log10 = 1.9 +/- 1.1). Only one of 12 cotton rats treated with both IVIG and ribavirin had a demonstrable titer of virus after RSV challenge. When IVIG administration was delayed until day 3 after virus challenge, lung viral titers were still lowest in animals receiving both IVIG and ribavirin. In comparison, there was no additive antiviral effect between IVIG and ribavirin against RSV infections of HEp-2 cells in vitro. Pathologic changes on histologic examination of pulmonary tissues from animals challenged with RSV were least prominent in animals treated with both IVIG and ribavirin. Despite the apparent absence of in vitro additive antiviral effect, combined use of IVIG and ribavirin was more efficacious against RSV infection in the cotton rat than use of either agent alone.

Protection of mice from lethal influenza virus infection with high dose-short duration ribavirin aerosol

An aerosol generated from a reservoir containing 60 mg of ribavirin per ml given for 2 h twice daily for 4 days afforded the same high level of protection against lethal influenza virus infection of mice as a longer, conventional treatment schedule (20 mg/ml given for 11 h daily for 4 days). Incremental decreases in ribavirin concentration made while maintaining the 2-h intermittent schedule provided progressively less protection of mice. Mice exposed to the 60-mg/ml doses had significantly increased pulmonary and serum drug levels when compared with mice given 20 mg of drug per ml, these increases were transient, and no evidence of pulmonary intolerance was detected. These studies suggest that protective effects of ribavirin against influenza virus infection can be achieved without untoward effects if higher doses and shorter periods of administration are used.

Limited efficacy of aerosolized recombinant alpha interferon against virulent influenza A/HK infection in mice

Hybrid recombinant human alpha interferon A/D (rIFN A/D) is unusual in that it has equivalent antiviral activity in in vitro assays using mouse or human tissue cells. This interferon was delivered to outbred Swiss mice in small particle aerosols before and/or after these mice were inoculated with virulent influenza A/HK/68 virus. Although rIFN A/D was effective in inhibiting influenza virus replication in vitro in primary mouse embryo cells, it had only a limited degree of effectiveness in the in vivo tests; only animals exposed to rIFN A/D for 4 hr and inoculated with influenza virus 4 hr later exhibited a significant decrease in mortality (approximately 25% reduction in deaths; P less than 0.025) compared with that of the untreated control animals. The limited effectiveness of rIFN A/D seen in these studies indicated that the use of this or similar recombinant alpha interferons alone to prevent or treat influenza virus infection in humans is not promising.