Virus Titers In Spleen Research Articles

Neonatal mouse model to study Zika virus pathogenesis: Host immune response determines ZIKV tropism and outcome of disease.

Abstract Zika virus (ZIKV) is a mosquito-borne flavivirus that has spread to more than 70 countries and has infected more than 2 million people worldwide. The recent ZIKV outbreak has resulted in CNS complications including microcephaly, Guillain Barre and polyneuropathy. Current ZIKV infection models use interferon (IFN) deficient mice that develop high viral loads systemically and die within a week. Establishing an Immunocompetent animal model that replicates ZIKV neurotropism is critical to understand ZIKV pathology and testing of immunotherapies. We developed an immunocompetent neonatal mouse model in wild type C57BL/6 mice by challenging 1 day old mice with contemporary ZIKV isolate PRVABC59. Infected mice developed unsteady gait, loss of balance, kinetic tremors, severe ataxia and seizures beginning 13 days post infection (dpi) that resolved by 28 dpi. Following challenge the mice developed a systemic infection with high virus titers in spleen, liver and kidney that was cleared by 10 dpi. In the Central Nervous System (CNS) and the eye, the virus was detected starting 6 dpi, peaked at 9–15 dpi, and then decreased over 6 weeks. Unlike IFN deficient that have a significant increase in mRNA expression of complement (C3), Cox2, Il1a, Il1b, and Il6, the CNS of infected B6 mice showed increased expression of genes associated with T cell responses including CD3, CD4, CD8, MHC-II, CD80, IFNg, perforin and granzyme B., Despite the absence of clinical disease in convalescent B6wt mice, there remain increased expression of inflammatory and T cell associated genes that suggest that the virus could have long-term effects on the CNS. Further investigation including behavioral studies is needed to explore possible long term CNS sequelae of ZIKV infection.

Tissue Factor On The Herpes Simplex Virus Type 1 Surface Enhances Infection In Vivo

Tissue factor (TF) is a multifunctional transmembrane receptor. As the pivotal initiator of the coagulant response to vascular damage, it accelerates factor (F) VIIa-dependent generation of FXa. However, TF also functions in FVIIa/FXa-dependent cell signaling via protease activated receptors (PARs), and has consequently been implicated in a wide variety of physiological and pathological conditions. Our previous work adds to this repertoire by revealing that TF, originating from the host cell membrane, is on the surface of enveloped viruses. Using herpes simplex virus type 1 (HSV1) as a model for enveloped viruses, we recently produced TF +/- HSV1 variants, which showed that viral TF enhances infection of cultured cells through a mechanism involving FXa/FVIIa-mediated activation of PAR-2. In the current project we extended these studies in vivo, hypothesizing that TF on the HSV1 surface would enhance infection by influencing the activation of coagulation proteases and/or their role in cell signaling. As before, HSV1 NS strain (with restored glycoprotein C) was propagated in TF- or genetically engineered TF+ human melanoma A7 cells, then purified and quantified. HSV1 TF+ or HSV1 TF- virus (5 x 105 virus plaque forming units of similar particle number) was injected slowly in 100 µL into the tail vein of female, eight-week old balb/c mice. On the third day, organs and blood were harvested. Live virus and total HSV1 genome were evaluated by plaque assays and rtPCR, respectively. Strikingly, production of live HSV1 TF+ (n=13) in the lung, heart, spinal cord, liver and brain was greater by an order of magnitude compared to HSV1 TF- (n=13), which was not detected in some tissues. The presence of TF on HSV1 furthermore increased virus titers in spleen and blood by several fold. Viral replication in organs was corroborated by rtPCR. The procoagulant and signaling functions of TF can be dissected using epitope-specific monoclonal antibodies (mAbs) selective for human TF. These mAbs only recognize HSV1 surface TF and not the endogenous mouse TF. These mAbs or an irrelevant mAb (TIB115, n=8) were administered by intraperitoneal injection 4 hours pre-inoculation (1 mg/mouse). When TF-dependent coagulation and the related effects on cell signaling due to attenuated protease activation was blocked by a potent combination of three mAbs to non-overlapping epitopes (5G9/6B4/9C3; 0.33 mg/mouse each, n=10), reduced levels of live HSV1 TF+ were seen in lung, heart, liver, brain and blood, with concordantly reduced viral genome levels measured by rtPCR. Similar results were obtained with mAb 5G9 alone (n=6), which selective blocks FXa generation. Interestingly, titers of HSV1 TF+ in blood and spleen were not affected by mAB 10H10 (n=6) that has no effect on coagulation, but is an effective direct inhibitor of TF signaling. Despite normal blood titers, mAb 10H10 (n=6) reduced virus titers in heart and brain, but not in other organs. These data demonstrate that virus surface TF is important for HSV1 infection in vivo and indicate that distinct functions of TF contribute to organ-specific tropism. Disclosures:No relevant conflicts of interest to declare.

Effects of Nasal or Pulmonary Delivered Treatments with an Adenovirus Vectored Interferon (mDEF201) on Respiratory and Systemic Infections in Mice Caused by Cowpox and Vaccinia Viruses

An adenovirus 5 vector encoding for mouse interferon alpha, subtype 5 (mDEF201) was evaluated for efficacy against lethal cowpox (Brighton strain) and vaccinia (WR strain) virus respiratory and systemic infections in mice. Two routes of mDEF201 administration were used, nasal sinus (5-µl) and pulmonary (50-µl), to compare differences in efficacy, since the preferred treatment of humans would be in a relatively small volume delivered intranasally. Lower respiratory infections (LRI), upper respiratory infections (URI), and systemic infections were induced by 50-µl intranasal, 10-µl intranasal, and 100-µl intraperitoneal virus challenges, respectively. mDEF201 treatments were given prophylactically either 24 h (short term) or 56d (long-term) prior to virus challenge. Single nasal sinus treatments of 106 and 107 PFU/mouse of mDEF201 protected all mice from vaccinia-induced LRI mortality (comparable to published studies with pulmonary delivered mDEF201). Systemic vaccinia infections responded significantly better to nasal sinus delivered mDEF201 than to pulmonary treatments. Cowpox LRI infections responded to 107 mDEF201 treatments, but a 106 dose was only weakly protective. Cowpox URI infections were equally treatable by nasal sinus and pulmonary delivered mDEF201 at 107 PFU/mouse. Dose-responsive prophylaxis with mDEF201, given one time only 56 d prior to initiating a vaccinia virus LRI infection, was 100% protective from 105 to 107 PFU/mouse. Improvements in lung hemorrhage score and lung weight were evident, as were decreases in liver, lung, and spleen virus titers. Thus, mDEF201 was able to treat different vaccinia and cowpox virus infections using both nasal sinus and pulmonary treatment regimens, supporting its development for humans.

Therapy and Long-Term Prophylaxis of Vaccinia Virus Respiratory Infections in Mice with an Adenovirus-Vectored Interferon Alpha (mDEF201)

An adenovirus 5 vector encoding for mouse interferon alpha, subtype 5 (mDEF201) was evaluated for efficacy against lethal vaccinia virus (WR strain) respiratory infections in mice. mDEF201 was administered as a single intranasal treatment either prophylactically or therapeutically at doses of 106 to 108 plaque forming units/mouse. When the prophylactic treatment was given at 56 days prior to infection, it protected 90% of animals from death (100% protection for treatments given between 1–49 days pre-infection), with minimal weight loss occurring during infection. Surviving animals re-challenged with virus 22 days after the primary infection were protected from death, indicating that mDEF201 did not compromise the immune response against the initial infection. Post-exposure therapy was given between 6–24 h after vaccinia virus exposure and protection was afforded by a 108 dose of mDEF201 given at 24 h, whereas a 107 dose was effective up to 12 h. Comparisons were made of the ability of mDEF201, given either 28 or 1 day prior to infection, to inhibit tissue virus titers and lung infection parameters. Lung, liver, and spleen virus titers were inhibited to nearly the same extent by either treatment, as were lung weights and lung hemorrhage scores (indicators of pneumonitis). Lung virus titers were significantly (>100-fold) lower than in the placebo group, and the other infection parameters in mDEF201 treated mice were nearly at baseline. In contrast, viral titers and lung infection parameters were high in the placebo group on day 5 of the infection. These results demonstrate the long-acting prophylactic and treatment capacity of mDEF201 to combat vaccinia virus infections.

Comment on “Premature Terminal Exhaustion of Friend Virus-Specific Effector CD8+ T Cells by Rapid Induction of Multiple Inhibitory Receptors”

While there is extensive evidence that Friend virus (FV)-specific CD8+ T cells from chronically infected mice are dysfunctional (1, 2), Takamura et al. (3) put forward the new idea, based on marker staining and in vitro assays, that these cells are already dysfunctional during the acute phase of infection. However, studies using the same virus stock that was provided for the Takamura study have produced extensive in vivo and direct ex vivo data demonstrating that FV-specific CD8+ T cells are highly functional and effective in acute FV infections. The efficacy of CD8+ T cells during acute FV infection is well demonstrated by the fact that mice depleted of CD8+ T cells have 100 fold higher spleen virus titers at two weeks post-infection than CD8+ T cell-replete mice (4). During acute FV infection, FV-specific CD8+ T cells are highly cytotoxic as demonstrated by in vivo CTL assays showing rapid killing of splenocytes loaded with the DbGagL peptide (5). In addition, when analyzed directly ex vivo, CD8+ T cells highly express CD107a, indicating recent cytolytic activity (5). It appears from the Materials and Methods section that direct ex vivo CD107a expression was subtracted as “background” in the Takamura study. Like Takamura et al., we also found that FV-specific CD8+ T cells produce high levels of granzyme B (5). However, this is normally interpreted as evidence of functionality rather than excessive activation. Thus the preponderance of evidence indicates that the acute FV-specific CD8+ T cell response is highly effective and not prematurely exhausted.

The Effects of NS Gene Exchange on the Pathogenicity of H5N1 HPAI Viruses in Ducks

Until 2002, H5N1 highly pathogenic avian influenza (HPAI) viruses caused only mild respiratory infections in ducks. Since then, new viruses have emerged that cause systemic disease and high mortality in ducks and other waterfowl. Studies on HPAI virus pathogenicity in ducks have been limited, and there is no clear explanation of why the pathogenicity of some H5N1 HPAI viruses has increased. The nonstructural protein 1 (NS1 protein) is known to suppress immune responses in influenza virus-infected hosts affecting virus pathogenesis. In order to determine if the NS1 protein contributes to increased virulence in ducks, single-gene reassortant viruses were generated. Exchanging the NS genes from A/Ck/HK/220/97 (a virus that produces mild disease in ducks) and A/Dk/VN/201/05 (a very virulent virus for ducks) in the rEgret/02 background (a recombinant virus derived from A/Egret/HK/757.2/02, a highly pathogenic virus in ducks) resulted in decreased mean death times compared to infection with the rEgret/02 virus in ducks, but the change was not statistically significant. Infection with the reassortant viruses affected the expression of immune-related genes in spleens and lungs when compared to controls, but when compared among them, the expression of the duck genes was similar. Furthermore, virus titers in spleen, lung, and brain as well as antigen distribution in various tissues were similar in ducks infected with the reassortant viruses. All together these data show that, under these experimental conditions, exchanging the NS gene had minimal effect on the virus pathogenicity, and it suggests that other viral genes, or combination of genes, are most likely contributing to the increased virulence of H5N1 HPAI viruses in ducks.

Induction of Natural Killer Cell Responses by Ectromelia Virus Controls Infection

Natural killer (NK) cells play a pivotal role in the innate immune response to viral infections, particularly murine cytomegalovirus (MCMV) and human herpesviruses. In poxvirus infections, the role of NK cells is less clear. We examined disease progression in C57BL/6 mice after the removal of NK cells by both antibody depletion and genetic means. We found that NK cells were crucial for survival and the early control of virus replication in spleen and to a lesser extent in liver in C57BL/6 mice. Studies of various knockout mice suggested that gammadelta T cells and NKT cells are not important in the C57BL/6 mousepox model and CD4+ and CD8+ T cells do not exhibit antiviral activity at 6 days postinfection, when the absence of NK cells has a profound effect on virus titers in spleen and liver. NK cell cytotoxicity and/or gamma interferon (IFN-gamma) secretion likely mediated the antiviral effect needed to control virus infectivity in target organs. Studies of the effects of ectromelia virus (ECTV) infection on NK cells demonstrated that NK cells proliferate within target tissues (spleen and liver) and become activated following a low-dose footpad infection, although the mechanism of activation appears distinct from the ligand-dependent activation observed with MCMV. NK cell IFN-gamma secretion was detected by intracellular cytokine staining transiently at 32 to 72 h postinfection in the lymph node, suggesting a role in establishing a Th1 response. These results confirm a crucial role for NK cells in controlling an ECTV infection.

Protective effect of black seed oil from Nigella sativa against murine cytomegalovirus infection

In this study, antiviral effect of black seed oil (BSO) from Nigella sativa was investigated using murine cytomegalovirus (MCMV) as a model. The viral load and innate immunity mediated by NK cells and Mφ during early stage of the infection were analyzed. Intraperitoneal (i.p.) administration of BSO to BALB/c mice, a susceptible strain of MCMV infection, strikingly inhibited the virus titers in spleen and liver on day 3 of infection with 1×10 5 PFU MCMV. This effect coincided with an increase in serum level of IFN-γ. Although BSO treatment decreased both number and cytolytic function of NK cells on day 3 of infection, it increased numbers of Mφ and CD4 + T cells. On day 10 of infection, the virus titer was undetectable in spleen and liver of BSO-treated mice, while it was detectable in control mice. Although spleen of both control and BSO-treated mice showed similar CTL activities on day 10 after infection, serum level of IFN-γ in BSO-treated mice was higher. Furthermore, BSO treatment upregulated suppressor function of Mφ in spleen. These results show that BSO exhibited a striking antiviral effect against MCMV infection which may be mediated by increasing of Mφ number and function, and IFN-γ production.

Modulation by gamma interferon of antiviral cell-mediated immune responses in vivo

Mice were infected with lymphocytic choriomeningitis virus and injected once 24 h later with a monoclonal antibody directed against gamma interferon. In comparison with controls, the increase of numbers of CD8+ T cells and the generation of virus-specific cytotoxic T lymphocytes in spleens and virus clearance from organs were diminished, as was the ability of spleen cells to transmit adoptive immunity to infected recipients. The same treatment slightly but consistently lessened rather than augmented the virus titers early in infection, which was also observed in thymusless nu/nu mice. Injection into infected mice of the lymphokine itself in quantities probably higher than are produced endogenously resulted in lower virus titers in spleens but higher titers in livers. The adoptive immunity in infected mice achieved by infusion of immune spleen cells was not altered by treating the recipients with gamma interferon monoclonal antibody. Such treatment did not measurably affect the production of antiviral serum antibodies. We conclude that in lymphocytic choriomeningitis virus-infected mice, gamma interferon is needed for the generation of antivirally active CD8+ T lymphocytes, and furthermore that in this experimental model, direct antiviral effects of the lymphokine elude detection.

Antiviral activities of tragacanthin polysaccharides on Punta Toro virus infections in mice.

Tragacanthin polysaccharides from Astragalus brachycentrus (AV208) and Astragalus echidnaeformis (AV212) plants, which are devoid of in vitro antiviral activity, were evaluated in a mouse model of Punta Toro virus (PTV) infection. The PTV (a phlebovirus member of the Bunyaviridae family of viruses) is a model for studying the treatment of Rift Valley fever and hantavirus infections. Single intraperitoneal treatments with 12.5-200 mg/kg/day doses of AV212 given 24 h before or 4 and 24 h after virus inoculation protected the majority of mice from mortality. Single treatments with AV208 were ineffective when given 24 h before the virus challenge; however, protection was afforded when treatments were administered at 4 and 24 h following virus inoculation. In a follow-up study, AV208 treatments of 1.6-50 mg/kg/day given 24 h subsequent to virus exposure caused reductions in mortality, liver infection scores, liver and spleen virus titers, and serum transaminases. The polysaccharides did not activate lymphocytes or natural killer cells, nor was interferon induced in treated mice. However, mice pretreated with fumed silica (a macrophage poison) and infected with the PTV were not protected by subsequent administration of AV208 or AV212 at 50 mg/kg, providing evidence that activation of peritoneal macrophages by the polysaccharides affords protection to infected animals. These compounds should be considered for the potential treatment of significant human infections induced by bunyaviruses and hantaviruses.

Innate resistance to lethal mousepox is genetically linked to the NK gene complex on chromosome 6 and correlates with early restriction of virus replication by cells with an NK phenotype

Most inbred strains of mice, including DBA/2 (D2), are highly susceptible to the lethal effects of ectromelia virus, but C57BL/6 (B6) mice are innately resistant. Resistance is controlled by multiple, unlinked, autosomal dominant genes. Of 101 male (B6 x D2)F1 x D2 backcrossed (N2) mice, 18 died after ectromelia virus challenge and all were homozygous for the D2 allele at the proline-rich protein (Prp) locus on distal chromosome 6 (P < 0.001). This association was suggested by the patterns of susceptibility to lethal mousepox in recombinant inbred strains derived from B6 and D2 mice (D. G. Brownstein, P. N. Bhatt, L. Gras, and R. O. Jacoby, J. Virol. 65:1946-1951, 1991). The association between the Prp locus and susceptibility to lethal mousepox also held for N2 male mice that were castrated as neonates, which increased the percentage that were susceptible to 40. Spleen virus titers were significantly augmented in B6 (NK1.1+) mice depleted of asialo GM1+ or NK1.1+ cells, whereas spleen virus titers were unaffected in D2 (NK1.1-) mice depleted of asialo GM1+ cells. These results suggest that a gene or genes within the natural killer gene complex, adjacent to the Prp locus, determine strain variations in resistance to lethal ectromelia virus infection.

Murine cytomegalovirus-inhibitory effects of ImuVert

ImuVert, a sterile preparation composed primarily of Serratia marcescens membrane vesicles and ribosomes, was significantly inhibitory to murine cytomegalovirus (MCMV) infections in BALB/c mice. Antiviral activity was manifested as increased survivor number and decreased recoverable virus titers in spleens, lungs and salivary glands. Treatments were intraperitoneal (i.p.) beginning 24 h pre, 4 h post- or 24 h post-virus inoculation and then repeated 4 days later. Doses of 5, 16 or 50 μg/mouse were effective; 160 μg/mouse, which caused host weight loss in toxicity controls, was not inhibitory to the infection. A single i.p. treatment of mice substantially augmented natural killer (NK) cell activity and increased total B-cells, while reducing total T- and T-helper cells. A late (48 h) decline in T-cell function and transient increases in B-cell function were observed in the treated animals. Serum interferon was not induced. Mice pretreated with anti-asialo GMl antibody to reduce their NK cell populations, then infected with MCMV and treated with ImuVert were protected to the same degree as normal animals. Severe combined immunodeficient mice infected with MCMV and treated with ImuVert were not protected from the infection. These data suggest ImuVert to act by a mechanism other than NK cell activation in preventing MCMV infections.

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.

Evidence that NK cells and interferon are required for genetic resistance to lethal infection with ectromelia virus

C 57 BL/6 mice developed resistance to lethal intravenous challenge with virulent (Moscow strain) ectromelia virus between 2 and 3 weeks of age. The fraction of C57 BL/6 mice in which virus was detected in spleen was significantly lower than for DBA/2 mice by day 3. Thereafter, C 57 BL/6 mice had significantly reduced virus titers in spleen compared with those of DBA/2 mice. Resistance was abrogated by treatment with anti-asialo GM1 gammaglobulin, which blocks NK cell activity, or with anti-interferon (IFN) alpha, beta. C 57 BL/6 mice carrying the bg/bg mutation, associated with a deficiency of NK cells, were highly susceptible to lethal infection as were athymic mice derived from a resistant genetic background. Virus titers in spleens of C 57 BL/6 mice treated with anti-asialo GM1 or anti-IFN alpha, beta were significantly higher 4 days after virus challenge than were titers in C 57 BL/6 mice treated with normal rabbit serum. The results strongly suggest that genetic resistance to lethal ectromelia virus infection requires non-specific host defenses such as NK cells and IFN alpha, beta that are activated during the first 3 to 4 days of infection.

Mechanism of recovery from acute virus infection. IV. Questionable role of mononuclear phagocytes in the clearance of lymphocytic choriomeningitis virus from spleens of mice.

After intravenous infection of mice with 10(3) infectious units (IU) the WE strain lymphocytic choriomeningitis (LCM) virus multiplied in the spleens (as in all other major organs), reaching more than 10(8) IU/g of tissue on days 4 to 5. Subsequently, the virus was quickly eliminated, being below detectability usually by day 10. During the time of virus clearance, the mononuclear phagocytes (MNP) of the spleen were activated as revealed by suppression of growth of Listeria monocytogenes and increase of cell-associated hydrolytic enzymes. In athymic nude mice, in whom the MNP system is assumed to be permanently activated, the virus replicated slightly but reproducibly less than in their euthymic counterparts. However, when the MNP were activated by Corynebacterium parvum, virus in spleens attained higher concentrations than in mice not so treated, and the rate of elimination was not altered. In mice whose MNP had been damaged by injection of dextran sulfate 500, the spleen virus titers were also increased, but the subsequent immune elimination was slightly delayed. Activation of spleen MNP was not evident at the time virus was rapidly cleared as a result of transfusion of LCM-immune T lymphocytes. Adoptive immunization was as successful in mice that had been pretreated with gamma-rays or cyclophosphamide, suggesting that replicating cells or their descendants, in particular monocytes, did not participate measurably in the process of elimination. Pretreatments of recipients with dextran sulfate 500 reduced the efficacy of transfused LCM-immune T lymphocytes, but this compound probably directly affected the cells. We interpret these findings to mean that the LCM virus in the mouse's spleen is controlled by a mechanism in which MNP do not play an essential role.

Treatment of experimental cytomegalovirus infections with acyclovir.

Subcutaneous (s.c.) administration of Acyclovir (ACV) (100 mg/1 kg bodyweight) resulted in an ACV blood level of 80 microM at 2 h post infection. Thereafter the level declined rapidly reaching undetectable levels at 12 h post infection. Administration of pro-ACV (100 mg/kg body weight) by s.c. or intravenous (i.v.) route resulted in ACV levels of 75 microM and 160 microM respectively after 30 min. But here again the blood level of ACV declined rapidly and was completely disappeared after 12 h. Continuous administration of pro-ACV in daily doses of 100, 250 and 350 mg/kg body weight resulted in ACV blood levels of 15 microM, 19 microM and 39 microM, respectively. The effect of ACV and pro-ACV on the replication of CMV was measured in immunesuppressed rats. In rats inoculated with RCMV the daily administration of 25 to 50 mg ACV per kg body weight by s.c. injections twice daily, did not result in a reduction of virus titers in spleen and liver, but when the RCMV-infected rats were treated by 100 mg pro-ACV per kg body weight virus titers in the spleen and liver were significantly reduced as compared with those in sham-treated animals.

Antiviral Effects of Amino Acid Derivatives With the Fluorene Substituent on Murine Leukemia Viruses

Two new amino acid derivatives with the fluorene substituent, when administered ip to female inbred ICR-CD1 mice inoculated with Friend murine leukemia virus, significantly inhibited virus-induced splenomegaly, reduced viable virus titers in spleen and plasma, and significantly prolonged survival time. These compounds also inhibited multiplication of the strains of the Friend and Moloney murine leukemia viruses in a cell culture system. The action of these compounds on murine leukemia virus was presumely different from that of tilorone.

Role of specific cytotoxic lymphocytes in cellular immunity against murine cytomegalovirus.

Cytotoxic lymphocytes were generated in vitro against murine cytomegalovirus (MCMV)-infected cells by incubation with ultraviolet light-irradiated, infected fibroblasts. When passively transferred, they reduced virus titers in spleens of mice 1 day after infection with MCMV. Protection was abrogated by anti-theta serum and complement. Spleen cells from mice infected for 6 to 14 days protected mice better than cells from mice after infection for 1, 3, or 30 days. Protection by in vitro- and in vivo-generated cells was H-2K or H-2D restricted. Specific cytotoxic T lymphocytes are therefore present and operative during acute MCMV infection. However, MCMV infection inhibited the development of primary cytotoxic response against ectromelia virus. It also suppressed the ability of lymphocytes from mice with established memory for ectromelia to develop secondary cytotoxic cells in vitro, and it inhibited the development of memory cells for the cytotoxic response to ectromelia virus. In view of these data and the inability of animals recovering from MCMV infection to eliminate all infected cells, the cytotoxic response to MCMV may be qualitatively or quantitatively deficient.

Antiviral Effect of N-Phenylacetoaminomethylene-dl-p-nitrophenylalanine (A-101) on Murine Leukemia Viruses2

N-Phenylacetoaminomethylene-DL-p-nitrophenylalanine (A-101), when administered ip to male DDY mice infected with Friend leukemia virus, significantly inhibited virus-induced splenomegaly, reduced viable virus titers in spleen and plasma, and significantly prolonged survival time. A-101 also inhibited multiplication of the Friend and Moloney viruses in tissue culture systems.