AN ANTIVIRAL SUBSTANCE FROM PENICILLIUM FUNICULOSUM : IV. INQUIRY INTO THE MECHANISM BY WHICH HELENINE EXERTS ITS ANTIVIRAL EFFECT

1. Helenine injected intraperitoneally 24 hr prior to a regularly fatal dose of Semliki Forest virus saves most of the mice to which it is administered. 2. Mice saved by helenine develop no viral immunity and regularly succumb when rechallenged 2 wk later with the same dose of virus from which they were originally saved. 3. The time during which helenine is optimally effective in protecting mice from death by Semliki Forest virus covers a period of approximately 36 hr beginning after about 12 hr and extending to 48 hr before virus infection. When periods of less than 12 hr, or more than 48 hr, elapse between the time of helenine administration and virus inoculation, its protective effectiveness diminishes progressively. 4. Repeated injections of helenine at 2- or 3-day intervals, if continued long enough, exhaust the capacity of a host to respond favorably to helenine administered 24 hr before virus inoculation. 5. Helenine injections at intervals of 4, 3, and 2 wk before its administration 24 hr prior to infection do not decrease the effectiveness of this final dose in protecting mice from fatal infection by the virus. The experimental results here reported indicate that, as suggested by the findings of earlier work, helenine does not act directly as an antiviral substance, but instead exerts its effect through some substance that it induces the host to elaborate. The nature of this induced antiviral substance is as yet unknown though, to judge from the failure of spared mice to acquire viral immunity, it appears to act at a stage in viral replication prior to that at which antigenic viral protein is produced. The findings with helenine and those thus far reported for interferon afford no factual basis for judging the relationship of the two, if any.     

Enhanced therapeutic efficacy of poly(ICLC) and ribavirin combinations against Rift Valley fever virus infection in mice.

The therapeutic efficacy of polyriboinosinic-polyribocytidylic acid stabilized with poly-L-lysine and carboxymethyl cellulose [poly(ICLC)] given alone or in combination with ribavirin was evaluated in Swiss Webster mice infected with Rift Valley fever virus. Four or more 20-micrograms doses of poly(ICLC) given at various intervals beginning 24 h after infection protected all mice against death. On the other hand, a treatment regimen consisting of only three doses of poly(ICLC) given 24 h postinfection resulted in a 50% survival rate. When initiated 48 h postinfection, an extended treatment regimen with the same dose was required to yield 40% survivors. Lower doses (5 micrograms) of poly(ICLC) per mouse were only marginally effective even when six injections were given between days 1 and 9 postinfection. The combined administration of ribavirin and poly(ICLC) initiated as late as 48 h postinfection was effective even when treatment consisted of doses that were ineffective when either drug was used alone.     

Potentiation of the hepatotoxic effect of acetaminophen by prior administration of salicylate

The effect of sodium salicylate (SS) pretreatment on acetaminophen (APAP) metabolism and hepatotoxicity in mice was studied. Mice were given a single oral dose of SS (100 mg/kg) 1 hr before graded doses of APAP (150-500 mg/kg). Liver histology, serum hepatic enzymes (serum glutamic-oxaloacetic transaminase, serum glutamic-pyruvic transaminase and isocitric dehydrogenase) and APAP metabolites in urine were examined 24 hr after APAP treatment. Free plasma APAP and liver glutathione were determined over 24 hr after treatment with 400 mg/kg of APAP alone or after SS pretreatment. At 500 mg of APAP per kg, mortality rate was 38% in SS + APAP group; no mortality was seen among animals treated with APAP alone. Centrilobular hepatic hemorrhagic necrosis and/or vacuolation were observed in both treatments. Mitosis of hepatocytes was increased in all APAP-treated mice. Incidence of hepatic necrosis and mean lesion grades at 300- and 500-mg/kg doses increased in mice pretreated with SS. Mice that received SS + APAP had significantly higher levels of serum glutamic-oxaloacetic transaminase, serum glutamic-pyruvic transaminase and isocitric dehydrogenase at all doses compared to mice treated with APAP alone. APAP glucuronide and sulfate conjugates decreased and APAP mercapturate conjugate increased in urine of mice receiving SS + APAP treatment. Free plasma APAP was significantly higher 2 hr after APAP treatment in SS + APAP-treated mice as compared to mice that received APAP alone. Hepatic glutathione levels were similarly decreased over 24 hr in both groups. These data demonstrate that SS pretreatment alters APAP biotransformation profile and potentiates the hepatotoxic effect of APAP in mice.     

The effect of Sendai virus infection on bactericidal and transport mechanisms of the murine lung

Pulmonary virus infections predispose to bacterial infections in the lung. The mechanism of this effect was studied by quantitative comparison of the effects of airborne acute viral infection on pulmonary transport vs. in situ bactericidal mechanisms in mice. Animals infected by aerosol with 10(4) TCID(50) of Sendai virus developed pathologic pulmonary changes of interstitial pneumonitis, bronchial epithelial desquamation, and peribronchial mononuclear cell infiltration 7 days later. At that time, the mice were challenged with an aerosol of viable (32)P-labeled Staphylococcus aureus. Pulmonary bactericidal activity and physical transport by the lung were determined by the determination of viable staphylococcal and (32)P radiotracer counts respectively at 4, 24, 48, and 72 hr after bacterial challenge. Infected mice showed a significant decrease from normal in the rate of reduction of viable bacterial counts in the first 4 hr after challenge followed by a proliferation of the staphylococci. By contrast, radiotracer removal rates at 4 and 24 hr were similar in infected and noninfected mice. There was a small but significant retention of (32)P in the lungs of the infected animals at the later periods. These data demonstrate that bacterial multiplication associated with virus infection of lungs is related to defects in in situ bactericidal (phagocytic) mechanisms rather than transport mechanisms of the lung, despite histologic evidence of extensive destruction of bronchial-ciliated epithelium.     

Efficacy of 1-beta-D-ribofuranosyl-1,2,4-triazole-3-carboxamide against influenza virus infections in mice.

1-beta-d-Ribofuranosyl-1,2,4-triazole-3-carboxamide (ribavirin) was effective against strains of influenza virus types A and F, whereas amantadine hydrochloride was effective only against strains of influenza virus type A. Dose-related protective effects against lethal influenza infections in mice were obtained with single oral doses of 25 to 400 mg of ribavirin per kg administered at the time of virus inoculation or up to 24 h thereafter. Therapeutic indexes (maximum tolerated dose/median effective dose) against various strains of influenza virus ranged from 5 to 35. With multiple-dose treatment initiated immediately after virus inoculation, oral doses as low as 12 to 25 mg/kg twice daily also afforded significant protection. Treatment with ribavirin inhibited the growth of influenza virus in the lungs of mice and delayed by about 24 h the attainment of maximal viral titers, which in nontreated mice were reached within 24 to 48 h. Inhibition of viral growth was correlated with a suppression of lung consolidation. Ribavirin appears to exert its protective effects against influenza infections by inhibiting virus growth, thereby preventing virus titers from reaching levels that result in massive lung tissue destruction and death of the mice.     

Experimental infection of immunocompromised mice with Achromobacter xylosoxidans

The natural resistance of mice to Achromobacter (A.) xylosoxidans was decreased to 1/80 by a single dose of 250 mg of cylophosphamide (CY) per kg intraperitoneally. When mice were infected with 1 X 10(9) A. xylosoxidans, the numbers of organisms in the liver, spleen, kidneys, lungs and heart blood reached to more than 10(6) per g at 6 hr after infection, and then decreased to less than 10(4) at 96 hr after infection. However, in the CY-treated mice, the numbers of organisms in these organs began to increase rapidly at 6 hr after infection and exceeded 10(9) per g at 48 hr when the mice died. Seventeen of 18 immunocompromised mice and 23 of 24 normal mice which were infected with 1 to 2 X 10(9) organisms of A. xylosoxidans, respectively, were still living until 4 weeks after infection when they were killed and examined. Thirteen of the 33 surviving mice which were examined for bacteriological assay were chronically infected with A. xylosoxidans, some in the spleen, others in the kidney, lung, brain and/or heart blood but none were infected in the liver. Most of the infected and surviving mice had produced an antibody against A. xylosoxidans and its titer was higher in the bacteriologically "cured" group than in the chronically infected one. All surviving mice were resistant to the 2nd challenge with a lethal dose of A. xylosoxidans even when they received an effective dose of CY. The surviving mice showed activated cellular immunity and rather depressed humoral immunity as compared with normal mice or the mice which were infected with killed A. xylosoxidans.     

THE DEMONSTRATION OF LESIONS AND VIRUS IN THE LUNGS OF MICE RECEIVING LARGE INTRA-PERITONEAL INOCULATIONS OF EPIDEMIC INFLUENZA VIRUS

Following the intraperitoneal inoculation of mice with large doses of epidemic influenza virus (50,000 to 1 million intranasal M.L.D.) it can be recovered from the lungs in high concentration, and pulmonary lesions of moderate extent may be observed. The virus reaches its highest titer in the lungs 48 to 72 hours after intraperitoneal injection and may persist for 10 days. Virus may be recovered from the blood in the first 24 hours, but is readily detected in the omentum and peritoneum for 5 to 6 days. Mice which as a result of the intraperitoneal injection of virus show a high concentration of virus in the lungs do not die but become solidly immune to intranasal infection. Moreover, as early as 24 to 48 hours after intraperitoneal inoculation of large amounts of virus the animals may exhibit resistance to infection with fatal doses of virus given intranasally. Influenza virus given intravenously to mice is rapidly removed from the blood but persists in the lungs and induces pulmonary lesions. Virus can also be recovered from the liver for several days. With subcutaneous inoculation of influenza virus, however, the virus does not reach the blood or lungs in detectable amounts although the regional lymph nodes may yield considerable quantities of the agent. A brief consideration is presented of the mechanisms of infection and resistance which may be involved.     

Comparative activity of penciclovir and acyclovir in mice infected intraperitoneally with herpes simplex virus type 1 SC16.

Penciclovir [PCV; 9-(4-hydroxy-3-hydroxymethylbut-1-yl)guanine; BRL 39123] is a potent and selective inhibitor of herpes simplex virus and varicella-zoster virus in human cell culture. We have compared the activities of PCV and acyclovir (ACV) in DBA/2 mice infected intraperitoneally with herpes simplex virus type 1 SC16 by measuring the amount of virus in peritoneal washings. In untreated mice after an eclipse phase, virus titers are maximum at 48 h after infection and decline thereafter. PCV and ACV reduced virus replication to a similar extent when given ad libitum in drinking water, even though ACV had better oral bioavailability and greater potency in murine cells. Thus, PCV was more active than had been predicted. In dose-response experiments, PCV given as a single subcutaneous dose 24 h after infection was active at a 10-fold-lower dose than ACV (P < 0.01). A single subcutaneous dose of PCV at 5 h after infection prevented virus replication for 3 days and was more effective than three doses of ACV given 1, 5, and 20 h after infection (P < 0.05). The superior activity of PCV following discrete dosing is not due to pharmacokinetic differences but is probably a reflection of the known stability of the intracellular triphosphate. In this model, the maintenance of high concentrations in blood is less important for PCV than for ACV and may lead to less-frequent doses in clinical use.     

Acute demyelination in mice inoculated intraspinally with mouse hepatitis virus, JHM strain

After intracerebral or intralumbar inoculation of mouse hepatitis virus, JHM strain, into weanling mice, viral growth and lesions in the central nervous system were comparatively studied for 5 days postinoculation. In the intralumbar group the virus titer of the spinal cord exceeded that of the brain until 24 hr postinoculation, and declined later. In the intracerebral group the brain virus titer was always higher, and the cord titer attained the same level as that of intralumbar group at 72 hr. Demyelinating lesions in the spinal cord appeared 48 hr after intralumbar inoculation, that is, 36 hr earlier than after intracerebral inoculation. Virus-specific fluorescence was detected within glia cells in the cord white matter 48 hr intralumbar inoculation. Electron microscopy revealed a number of virions within oligodendroglia cells, suggesting that the acute phase demyelination might be due to viral growth within this type of cells.     

Inhibitory effects of recombinant manganese superoxide dismutase on influenza virus infections in mice.

The oxygen free-radical scavenger recombinant human manganese superoxide dismutase (MnSOD) was studied for its effects on influenza virus infections in mice when used alone and in combination with ribavirin. Mice challenged with influenza A/NWS/33 (H1N1) virus were treated parenterally in doses of 25, 50, and 100 mg/kg of body weight per day every 8 h for 5 days beginning at 48 h post-virus exposure. An increase in mean day to death, lessened decline in arterial oxygen saturation, and reduced lung consolidation and lung virus titers occurred in the treated animals. To determine the influence of viral challenge, experiments were run in which mice were infected with a 100 or 75% lethal dose of virus and were treated intravenously once daily for 5 days beginning 96 h after virus exposure. Weak inhibition of the mortality rate was seen in mice receiving the high viral challenge, whereas significant inhibition occurred in the animals infected with the lower viral challenge, indicating that MnSOD effects are virus dose dependent. To determine if treatment with small-particle aerosol would render an antiviral effect, infected mice were treated by this route for 1 h daily for 5 days beginning 72 h after virus exposure. A dose-responsive disease inhibition was seen. An infection induced by influenza B/Hong Kong/5/72 virus in mice was mildly inhibited by intravenous MnSOD treatment as seen by increased mean day to death, lessened arterial oxygen saturation decline, and lowered lung consolidation. MnSOD was well tolerated in all experiments. A combination of MnSOD and ribavirin, each administered with small-particle aerosol, resulted in a generally mild improvement of the disease induced by the influenza A virus compared with use of either material alone.     

In vitro and in vivo Phlebovirus inhibition by ribavirin.

Ribavirin (1-beta-D-ribofuranosyl-1,2,4-triazole-3-carboxamide) was markedly inhibitory in vitro to Adames and Balliet strains of Punta Toro virus (PTV), a Phlebovirus related to Rift Valley fever and sandfly fever viruses. By using inhibition of viral cytopathic effect in LLC-MK2 cells with both virus strains, the 50% effective dose was 4 to 10 micrograms/ml and the virus rating was 1.3. The Adames strain of PTV infection in mice was established for evaluation of the in vivo antiviral efficacy of ribavirin. The drug was administered subcutaneously (s.c.) twice daily for 5 to 7 days beginning 4 h pre-virus inoculation, 24 h post-virus inoculation, or 36 h post-virus inoculation, with increased survivors, reduced hepatic icterus, reduction of serum glutamic oxalic acid transaminase and serum glutamic pyruvic acid transaminase, and inhibition of infectious virus from sera and livers of infected mice. The minimum effective dose was 4.7 mg/kg per day, with a maximum tolerated dose of 75 mg/kg per day. When the same treatment schedule beginning 4 h pre-virus inoculation, 4 h post-virus inoculation, or 24 h post-virus inoculation was used, orally administered ribavirin was effective at doses as low as 6.3 mg/kg per day. Single s.c. ribavirin treatments at doses of 175 to 700 mg/kg administered from 4 to 48 h post-virus inoculation were also effective. No effect was seen when ribavirin was administered s.c. to mice infected intracerebrally with the PTV strain Balliet, even though treatment was begun 36 h before virus exposure.     

Treatment of murine cytomegalovirus infections in severe combined immunodeficient mice with ganciclovir, (S)-1-[3-hydroxy-2-(phosphonylmethoxy)propyl]cytosine, interferon, and bropirimine.

Severe combined immunodeficient (SCID) mice were found to be highly susceptible to murine cytomegalovirus (MCMV) infection. Treatment of infected mice with ganciclovir (12.5, 25, and 50 mg/kg of body weight for 10 days) starting 24 h after virus challenge resulted in delays in death by 2 to 8 days, and no animals survived the infection. (S)-1-[3-Hydroxy-2-(phosphonylmethoxy)propyl]cytosine (HPMPC) was much more potent, with doses of 1, 3.2, and 10 mg/kg/day (for 10 days) increasing the mean survival time by 15 to 30 days. Twenty-day treatments with HPMPC starting 5 days after virus inoculation increased the mean survival time by 24 to 32 days, with once-weekly (50-mg/kg) treatments being equivalent to daily (10-mg/kg) treatments. Delays in the development of liver, lung, and spleen virus titers in ganciclovir- and HPMPC-treated groups correlated with extensions in the mean survival times relative to the survival times of the placebo controls. The two compounds were approximately equally toxic to uninfected BALB/c mice treated for 10 days, causing 80 to 100% mortality after a dose of 150 mg/kg and 0% mortality after a dose of 75 mg/kg. Thus, the relative therapeutic index of HPMPC was 50-fold greater than that of ganciclovir. Recombinant alpha interferon delta 4 alpha 1/alpha 2 (1 x 10(4) and 5 x 10(4) units per mouse per day) and bropirimine (100 and 300 mg/kg/day) provided no protection from the lethal MCMV infection. The severe combined immunodeficient mouse MCMV infection is an important new model that will permit chemotherapy regimens to be studied over several months.     

Activity of 1-(2''-deoxy-2''-fluoro-beta-D-arabinofuranosyl)-5-iodouracil against simian varicella virus infections in African green monkeys.

The fluorinated pyrimidines 1-(2'-deoxy-2'-fluoro-beta-D-arabinofuranosyl)-5-iodouracil (FIAU) and 1-(2'-deoxy-2'-fluoro-beta-D-arabinofuranosyl)-5-methyluracil (FMAU) are highly effective inhibitors of herpesvirus infections in vitro and in vivo. This report is concerned with an evaluation of their activities in African green monkeys (Cercopithecus aethiops) infected with simian varicella virus, a herpesvirus closely related to human varicella-zoster virus. Oral or intravenous administration of FIAU at 50 mg/kg per day as divided doses beginning 48 h after virus inoculation prevented the development of evidences of clinical infection. Oral treatment with FIAU at 30 mg/kg per day deferred as late as 7 days after virus inoculation modified the course of the disease. When treatment was started 48 h after virus inoculation, daily doses of FIAU as small as 1 mg/kg inhibited development of infections; daily doses of 0.2 mg/kg were ineffective. At the latter dose FMAU prevented development of clinical disease, suggesting that it was more active than FIAU. No signs of FIAU toxicity were observed, with the single exception of an early but transitory elevation in aspartate aminotransferase activity in serum.     

A novel mechanism for the enhancement of acetaminophen hepatotoxicity by phenobarbital

Pretreatment of mice with multiple doses of phenobarbital (PB) potentiates N-acetyl-para-aminophenol (APAP) hepatotoxicity through induction of cytochrome P-450, thus increasing the formation of APAP-reactive metabolites. The objective of this report is to investigate the effect of a single oral dose of PB on APAP hepatotoxicity in mice. PB was administered (150 mg/kg) 1 hr before oral administration of APAP (400 mg/kg). Blood, liver and urine were collected from mice at 2, 4, 8, 12 and 24 hr after APAP treatment. Mortality rate and incidence of gross hepatic lesions were significantly higher in mice pretreated with PB than in mice treated with APAP alone. At 8, 12 and 24 hr post-APAP treatment, serum glutamic oxalacetic transaminase activity was significantly higher in mice receiving the combination treatment. Hepatic glutathione levels were significantly lower at 1 and 2 hr in mice pretreated with PB. Urinary excretion of APAP mercapturate, APAP sulfate and free APAP increased, whereas APAP glucuronide decreased, in mice pretreated with PB compared with mice treated with APAP alone. Covalent binding of [3H]APAP to hepatic microsomes was markedly increased after PB pretreatment. PB pretreatment was found to deplete uridine diphosphate glucuronic acid in livers of mice at 1 and 2 hr post-APAP treatment. These results indicate that the biochemical mechanism by which a single dose of PB enhances APAP hepatotoxicity does not involve cytochrome P-450 induction; interference with APAP glucuronidation may occur.     

EXPERIMENTAL TRANSMISSION OF INFLUENZA VIRUS INFECTION IN MICE : I. THE PERIOD OF TRANSMISSIBILITY

An experimental model has been developed for the reproducible transmission of influenza virus infection from experimentally infected mice to uninfected cage mates. Infector mice transmit influenza virus infection most readily during the period 24 to 48 hours after initiation of their infection. This restricted period of transmission is not due to declining titers of infective virus in the nose, trachea, or lungs of infector mice after 48 hours of infection, since peak titers in these tissues are maintained for another 48 hours. A mouse-adapted strain of A2 virus was found to be more readily transmitted than the mouse-adapted CAM strain of influenza A1 virus, although the CAM strain induced higher pulmonary virus titers and more extensive lung lesions.     

Antiretroviral activity and pharmacokinetics in mice of oral bis(pivaloyloxymethyl)-9-(2-phosphonylmethoxyethyl)adenine, the bis(pivaloyloxymethyl) ester prodrug of 9-(2-phosphonylmethoxyethyl)adenine.

Lipophilic ester prodrugs of 9-(2-phosphonylmethoxyethyl)adenine (PMEA), i.e., bis(pivaloyloxymethyl)-PMEA [bis(POM)-PMEA] and diphenyl-PMEA, have been synthesized in an attempt to increase the oral bioavailability of this broad-spectrum antiviral agent. The antiretroviral efficacy was determined in severe combined immune deficiency (SCID) mice infected with Moloney murine sarcoma virus (MSV). They were treated twice daily for 5 days after infection. Oral treatment with bis(POM)-PMEA at a dose equivalent to 100 or 50 mg of PMEA per kg of body weight per day proved markedly effective in delaying MSV-induced tumor formation and death of the mice. Oral bis(POM)-PMEA afforded anti-MSV efficacy equal to that of subcutaneous PMEA given at equimolar doses. Oral treatment with PMEA or diphenyl-PMEA proved less efficient. Similarly, in mice infected with Friend leukemia virus (FLV), oral treatment with bis(POM)-PMEA at a dose equivalent to 100 or 50 mg of PMEA per kg per day effected a marked inhibition of FLV-induced splenomegaly (87 and 48% inhibition, respectively), the efficacy being equal to that of PMEA given subcutaneously at equivalent doses. Pharmacokinetic experiments with mice showed that the oral bioavailabilities of PMEA following oral gavage of bis(POM)-PMEA, diphenyl-PMEA, or PMEA (at a dose equivalent to 50 mg of PMEA per kg) were 53,3, and 16%, respectively. These data were calculated from the levels of free PMEA in plasma. Also, the recoveries of free PMEA in the urine upon oral administration of bis(POM)-PMEA, diphenyl-PMEA, or PMEA (at a dose equivalent to 25 mg of PMEA per kg) were 48, 4, and 7%, respectively. Oral bis(POM)-PMEA was not recovered from plasma, suggesting that it was readily cleaved to free PMEA. In contrast, diphenyl-PMEA was not efficiently cleaved to free PMEA, resulting in a rather low oral bioavailability of PMEA from this prodrug. Bis(POM)-PMEA appears to be an efficient oral prodrug of PMEA that deserves further clinical evaluation in human immunodeficiency virus-infected individuals.     

Behavioral evidence for differential adaptation of the serotonergic system after acute and chronic treatment with (+/- )-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI) or ketanserin.

The 5-hydroxytryptamine (5-HT)2 agonist (+/- )-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI) and antagonist ketanserin were evaluated for acute and chronic effects on the 5-HT2 receptor-mediated head-twitch response (HTR) in mice. A single dose of DOI resulted in tolerance to the DOI-induced HTR at 24 hr but supersensitivity at 48 hr. This apparent supersensitivity persisted up to 144 hr after the first DOI injection. Chronic once daily DOI administration significantly reduced the HTR frequency (days 2-6), which then returned slowly to control levels by treatment day 13. A 48-hr withdrawal from this chronic regimen produced a similar supersensitivity to that observed after a single DOI injection upon a 48-hr challenge. This effect also persisted up to 144 hr after cessation of chronic treatment. Acute pretreatment with a single injection of ketanserin significantly reduced the DOI-induced HTR frequency when tested 24 and 48 hr, but not 120 hr, after injection of the antagonist. After withdrawal from chronic ketanserin treatment, the DOI-induced HTR was significantly reduced at 24 hr but significantly increased at 48 hr. This enhanced effect subsided when mice were tested with DOI 72 hr after cessation of chronic antagonist treatment. These data suggest that the serotonergic system adapts to chronic exposure of either agonists or antagonists in a fashion distinctly different from that exhibited by other monoamine neurotransmitter systems.     

Synergistic effects of romurtide and cefmenoxime against experimental Klebsiella pneumonia in mice.

We investigated the synergistic effects of romurtide (MDP-Lys [L18]) and cefmenoxime (CMX) in the treatment of experimental Klebsiella pneumonia in mice. Mice were infected with 1 x 10(4) CFU of Klebsiella pneumoniae by inhalation of aerosol bacterial suspension. About 90% of untreated animals died within a week; however, the mortality rate of animals treated with CMX alone at a dose of 40 mg/kg/day was 60% at 7 days after the infection. When one or two doses of L18 were administered before or after the infection concomitantly with CMX, a remarkable improvement in the survival rate was observed. There was no significant improvement in the survival rate of animals treated with L18 alone before or after infection. Histopathological sections of the lungs of mice treated with CMX and L18 showed slower progression of infection than those of mice treated with CMX alone. Significant differences were also found in quantitative cultures of viable bacteria in the lungs 1 to 4 days after the infection. Although viable bacterial counts in the lungs of the control and CMX-treated groups showed a rapid increase 24 to 48 h after the infection, they remained lower than the initial counts (x 10(4)) in the lungs of mice treated with combination regimens. From these results, it can be concluded that L18 is a useful biological response modifier in the treatment of acute pulmonary bacterial infections.     

SUPPRESSION OF CELL-MEDIATED IMMUNITY TO INFECTION BY AN ANTIMITOTIC DRUG : FURTHER EVIDENCE THAT MIGRANT MACROPHAGES EXPRESS IMMUNITY

The development of acquired cell-mediated immunity to infection with Listeria monocytogenes can be blocked by a 15 hr pulse of the antimitotic drug, vinblastine (Vb). The drug has no effect on the host-parasite relationship after 72 hr of infection when a high level of immunity is being expressed, i.e., when infective foci are populated by activated macrophages. Infective foci in mice treated early during infection with Vb do not acquire migrant macrophages, but they become acellular after 48 hr of infection. The results indicate that Vb destroys the dividing precursors of migrant macrophages. The possibility that Vb prevents the activation of these cells by destroying dividing lymphoid cells engaged in the specific immunological phase of the host response is also considered.     

Morphine pellet-induced immunomodulation in mice: temporal relationships

Morphine, an alkaloid known for its potent analgetic action, also affects a variety of immunologic functions. In the experiments reported here, the time course for the effect of 75-mg morphine pellet implants on spleen and thymus size and cellularity and in vitro proliferative responses of lymphocytes from male C3H/HeN mice is described. T lymphocyte proliferation in response to concanavalin A (Con A) was not significantly affected at 6 or 24 hr after morphine pellet implantation but was reduced at 48 and 72 hr. B lymphocyte proliferation in response to lipopolysaccharide was more sensitive to morphinization, as the response was reduced at the 24, 48 and 72 hr intervals after implantation of the morphine pellet. No differences in Con A- or lipopolysaccharide-induced proliferation were observed 96 hr after pellet implantation. Interestingly, a slight elevation of Con A-induced proliferation was observed 120 hr after morphine pellet implantation. By contrast with Con A proliferative data, lipopolysaccharide-induced proliferation of lymphocytes from morphine-treated mice was not different from placebo-pelleted mice at 120 hr. A marked atrophy of the spleen and thymus accompanied the reduced splenocyte proliferative responses of morphine-treated mice and was greatest at the 48 to 72 hr postimplantation interval. The attenuation of mitogen-induced proliferative responses and atrophy of immune organs was accompanied by hypothermia and a marked tolerance to the antinociceptive effect of morphine in morphine-pelleted mice at all of the time points that were monitored.(ABSTRACT TRUNCATED AT 250 WORDS)