Role of macrophages in hepatitis induced by Herpes simplex virus types 1 and 2 in mice

Possible role of a cell surface carbohydrate in evolution of resistance to viral infections in old world primates

Due to inactivation of the α1,3-galactosyltransferase gene (GGTA1, or the α1,3GT gene) approximately 28 million years ago, the carbohydrate αGal (Galα1,3Galβ1,4GlcNAc) is not expressed on the cells of Old World monkeys and apes (including humans) but is expressed in all other mammals. The proposed selective advantage of this mutation for these primates is the ability to produce anti-Gal antibodies, which may be an effective immune component in neutralizing αGal-expressing pathogens. However, loss of α1,3GT expression may have been advantageous by providing natural resistance against viral pathogens that exploited the α1,3GT pathway or cell surface αGal for infection. Infections of paired cell lines with differential expression of α1,3GT showed that Sindbis viruses (SINV) preferentially replicate in α1,3GT-positive cells, whereas herpes simplex viruses type 1 and type 2 (HSV-1 and HSV-2) preferentially grow in cells lacking α1,3GT. Viral growth and spread correlated with the ability of the different viruses to successfully initiate infection in the presence or absence of α1,3GT expression. GT knockout (KO) suckling mice infected with SINV strains (AR339 and S.A.AR86) experienced significant delay in onset of disease symptoms and mortality compared to wild-type (WT) B6 suckling mice. In contrast, HSV-2-infected GT KO mice had higher viral titers in spleen and liver and exhibited significantly more focal hepatic necrosis than WT B6 mice. This study demonstrates that α1,3GT activity plays a role in the course of infections for certain viruses. Furthermore, this study has implications for the evolution of resistance to viral infections in primates.

Acyclovir delivery systems

Herpes viruses (herpes simplex, varicella zoster, cytomegalovirus) are the main cause of a wide variety of human infections. Although the development of successful antiviral agents against infections caused by herpes viruses had been slow until the last decade, the production of delivery systems for acyclovir are a promising alternative. The present review summarizes the principal advances made in developing carriers for the delivery of acyclovir by different routes of administration.

Macrophages and cytokines in the early defence against herpes simplex virus

Herpes simplex virus (HSV) type 1 and 2 are old viruses, with a history of evolution shared with humans. Thus, it is generally well-adapted viruses, infecting many of us without doing much harm, and with the capacity to hide in our neurons for life. In rare situations, however, the primary infection becomes generalized or involves the brain. Normally, the primary HSV infection is asymptomatic, and a crucial element in the early restriction of virus replication and thus avoidance of symptoms from the infection is the concerted action of different arms of the innate immune response. An early and light struggle inhibiting some HSV replication will spare the host from the real war against huge amounts of virus later in infection. As far as such a war will jeopardize the life of the host, it will be in both interests, including the virus, to settle the conflict amicably. Some important weapons of the unspecific defence and the early strikes and beginning battle during the first days of a HSV infection are discussed in this review. Generally, macrophages are orchestrating a multitude of anti-herpetic actions during the first hours of the attack. In a first wave of responses, cytokines, primarily type I interferons (IFN) and tumour necrosis factor are produced and exert a direct antiviral effect and activate the macrophages themselves. In the next wave, interleukin (IL)-12 together with the above and other cytokines induce production of IFN-gamma in mainly NK cells. Many positive feed-back mechanisms and synergistic interactions intensify these systems and give rise to heavy antiviral weapons such as reactive oxygen species and nitric oxide. This results in the generation of an alliance against the viral enemy. However, these heavy weapons have to be controlled to avoid too much harm to the host. By IL-4 and others, these reactions are hampered, but they are still allowed in foci of HSV replication, thus focusing the activity to only relevant sites. So, no hero does it alone. Rather, an alliance of cytokines, macrophages and other cells seems to play a central role. Implications of this for future treatment modalities are shortly considered.

Mannan-binding lectin modulates the response to HSV-2 infection

Viruses have developed numerous strategies to escape recognition by the immune system. However, some viruses such as herpes simplex virus-2 (HSV-2) are recognized by initiators of the complement system, e.g. mannan-binding lectin (MBL). To study the effects of MBL deficiency during viral infection we have chosen a model of generalized HSV-2 infection. We infected MBL-A and MBL-C double knock-out mice (DKO) with HSV-2 via the intraperitoneal (i.p.) route. DKO mice cleared HSV-2 from the liver less efficiently than the comparable wild-type animals. The impairment to effectively neutralize HSV-2 correlated with compromised liver function as measured by increased plasma levels of alanine-amino transferase. No differences in the viral burden were found in other organs such as spleen or brain. Thus, MBL-mediated protection was limited to the effects of preservation of liver homeostasis. Reconstitution with recombinant human MBL before and during the HSV-2 infection dramatically lowered the viral titres in the liver. Taken together, the data show that MBL modulates the response to HSV-2 in mice by affecting neutralization of the virus. To analyse if MBL plays a role in establishment and progression of human HSV-2 infection we analysed MBL levels in the serum samples from asymptomatic (virus-exposed people who have never displayed symptoms of HSV-2 infection) and symptomatic HSV-2 patients (people with recurrent HSV-2 infections). We found that the frequency of the MBL deficiency (<100 ng/ml) was higher in the symptomatic group and significantly different from that in the asymptomatic group (P = 0.0369). This suggests that lack of MBL-mediated complement activation increases susceptibility to viral infection.

Histochemical localization of autometallographically detectable mercury in tissues of the immune system from mice exposed to mercuric chloride

The distribution of mercury in the spleen, liver, lymph nodes, thymus and bone marrow was studied by autometallography in mice exposed to mercuric chloride intraperitoneally. Application of immunofluorescence histochemistry and an autometallographic silver amplification method was employed to the same tissue section. Mercury was not only detected in macrophages marked by the antibody M1/70 but also in macrophage-like cells, which were either autofluorescent or devoid of fluorescent signals. These two cell types were identified as macrophages at the electron microscopical level. Autometallographically stained macrophages were observed in the spleen, lymph nodes, thymus and in Kupffer cells of the liver. Furthermore, mercury was observed in endothelial cells. No obvious pathological disturbances were observed at light and electron microscopical level. At the subcellular level mercury was localized in lysosomes of macrophages and endothelial cells.

Suppression of infectious virus spread to the liver by foscarnet following lethal infection of acyclovir-resistant herpes simplex virus type 2 in mice

Patients with the acquired immune deficiency syndrome (AIDS) occasionally develop hepatitis, pneumonia or esophagitis due to herpes simplex virus type 2 (HSV-2) infection. HSV hepatitis is a rare but serious complication in liver transplantation. Acyclovir-resistant HSV strains may emerge in immunocompromised patients. Following intraperitoneal inoculation, HSV-2 induces necrotizing hepatitis in mice. We studied the virus spread and mortality following intraperitoneal inoculation of HSV-2 RK (an acyclovir-resistant recombinant virus with altered thymidine kinase activity) as compared to its parent virus 8620K. Neither the 50% lethal dose (LD50) nor the average survival time was significantly different between the two strains. Parenteral acyclovir treatment was found to be effective against 8620K but not RK infection. Parenteral foscarnet treatment was effective against both RK and 8620K, and also inhibited the spread of either virus to the liver, spinal cord and brain. Peroral foscarnet administration was found to prevent the virus growth in the liver.

Effect of mercuric chloride on macrophage-mediated resistance mechanisms against infection with herpes simplex virus type 2

Macrophages play an important role in the early, nonspecific resistance to infection with herpes simplex virus. Mercuric chloride (HgCl2) accumulates in macrophages and has in certain concentrations a marked influence on the functional capacity of these cells. Therefore the influence of HgCl2 on resistance to generalized infection with herpes simplex virus type 2 (HSV-2) in mice and its effect on the HSV-2-induced activation of macrophages in vitro was examined. Mice injected intraperitoneally with HgCl2 24 h before infection with HSV-2 had more than 100 times higher virus titres in the liver 4 days after infection than mice not receiving any mercury. HgCl2 exerted a toxic effect on macrophages in vitro, which was especially pronounced during their adherence. Macrophages infected with HSV-2 were activated for an enhanced respiratory burst. This activation was abolished by treatment of the cells for 24 h with relatively low concentrations of HgCl2, resulting in macrophages with a potential to react with a respiratory burst comparable to that of uninfected cells. The HSV-2-induced activation of macrophages is mediated through the production and synergistic interaction of interferon-alpha/beta and tumour necrosis factor-alpha in an autocrine manner. The ability of these cytokines to activate macrophages and to interact synergistically was not affected by mercury. However the production by macrophages of both cytokines during the HSV-2 infection, but especially interferon-alpha/beta, which is essential for the activation, was reduced at low concentrations of HgCl2. Collectively these data indicate that mercury, by interfering with the early macrophage-production of cytokines, disables the early control of virus replication, leading to an enhanced infection.

Mannan-binding protein and bovine conglutinin mediate enhancement of herpes simplex virus type 2 infection in mice

A broad range of plant lectins have recently been shown to inhibit the infectivity of herpes simplex virus type 1 (HSV-1) in vitro. We decided to investigate the role of mammalian lectins in infection with herpes simplex virus. Two lectins, conglutinin and mannan-binding protein (also called mannose-binding protein, MBP), belonging to the collectin family of lectins, were examined. Four week-old BALB/c mice were injected subcutaneously with 100 micrograms bovine conglutinin or 50 micrograms human MBP 1 day before intravenous infection with 5 x 10(4) PFU of herpes simplex virus type 2 (HSV-2). A three-fold increase in virus titre of the liver was observed on day 3 of the infection in the mice pretreated with conglutinin or MBP, whereas no effect was seen on days 1 and 5. In a standard plaque assay using Vero cells we were not able to demonstrate reproducibly either infection inhibition or infection enhancement, when virus was pre-incubated with differing concentrations of the collectins. The concentrations used were similar to those used by us in vivo, and by others in in vitro experiments showing inhibition of the infectivity of HSV-1 with plant lectins. In an ELISA with HSV-2 antigens captured on anti-HSV-2 antibodies, calcium-dependent and carbohydrate inhibitable binding of the collectins was observed. Our results indicate that the effect of endogenous mammalian collectins in vivo may not be neutralization as suggested by the data using plant lectins. Instead, the previously described opsonizing activity of the mammalian collectins may provide the virions with an alternative port of entry into cells leading to infection enhancement.

Construction of a US3 lacZ insertion mutant of herpes simplex virus type 2 and characterization of its phenotype in vitro and in vivo

We have constructed and characterized a mutant of herpes simplex virus type 2 (HSV-2) which was inserted a modified lacZ gene, placed under the control of HSV-1 beta 8 promotor, into the US3 protein kinase gene. The mutant, L1BR1, could not induce the virus-encoded protein kinase activity, but could replicate in Vero cells as efficiently as the parental virus. When the biological properties of L1BR1 were examined in mice by using four routes (footpad, intraperitoneal, corneal, and intracerebral) of infection, the mutant displayed the route-dependent reduction of virulence; after inoculation by footpad and intraperitoneal routes, the mutant was more than 10,000-fold less virulent than the parental virus, but it exhibited only about a 10-fold decrease in virulence following the corneal and intracerebral infection. In the intraperitoneal inoculation into adult mice, the replication of L1BR1 in the liver and spleen was severely restricted, but in newborn mice the mutant could grow as well as the parental virus in these organs. The adoptive transfer of peritoneal macrophages from adult mice resulted in a marked inhibition in the replication of L1BR1 in the liver and spleen of newborn mice, while the transfer exhibited little or no effect on the production of the wild-type virus in these organs. We also found that the mutant, unlike the parental virus, could not replicate in precultured peritoneal macrophages from adult mice. Taking these observations together, it seems likely that L1BR1 lost the ability to overcome the mononuclear-phagocytic defense system and thereby lost its pathogenicity by intraperitoneal and footpad routes. Furthermore, the mutant was shown to be rescued by a 4.8-kb HindIII/Xbal fragment containing the entire US3 open reading frame. However, we could not rule out the possibility that some of the phenotypes of L1BR1 are due to mutations in the US3-neighboring genes, US2 and US4.

Herpes simplex virus type 1 latency-associated transcription unit promotes anatomical site-dependent establishment and reactivation from latency

Defined herpes simplex virus type 1 (HSV-1) mutants KOS/1 and KOS/62 (positive and negative, respectively, for latency-associated transcripts [LATs]) express the Escherichia coli beta-galactosidase (beta-Gal) gene during latency. These mutants were employed to assess the functions of the latency-associated transcription unit on establishment and maintenance of and reactivation from the latent state. It was found that in the trigeminal ganglia, the frequencies of hyperthermia-induced reactivation of KOS/62 and an additional LATs- mutant (KOS/29) were reduced by at least 80%. Quantification of latently infected neurons expressing the beta-Gal gene revealed that the LATs- mutant KOS/62 established approximately 80% fewer latent infections in the trigeminal ganglia than did KOS/1 (LATs+). This reduction in establishment which is evident in the trigeminal ganglia could account for the reduced frequency of reactivation from this site. In striking contrast, both LATs- mutants reactivated with wild-type frequencies from lumbosacral ganglia. Quantification of beta-Gal-positive neurons at this site revealed that KOS/62 established as many as or more latent infections than the LATs+ virus, KOS/1. Colocalization of HSV antigen and beta-Gal suggested that the decreased establishment by LATs- mutants in trigeminal ganglia was the result of inefficient viral shutoff. Thus, one function of the HSV-1 LATs transcription unit is to promote the establishment of latency in trigeminal but not lumbosacral ganglia. Such a function may be relevant to understanding the distinct clinical recurrent disease patterns of HSV-1 and HSV-2.

Intrinsic resistance of feline peritoneal macrophages to coronavirus infection correlates with in vivo virulence

Cats infected with virulent feline coronavirus strains develop feline infectious peritonitis, an invariably fatal, immunologically mediated disease; avirulent strains cause either clinically inapparent infection or mild enteritis. Four virulent coronavirus isolates and five avirulent isolates were assessed by immunofluorescence and virus titration for their ability to infect and replicate in feline peritoneal macrophages in vitro. The avirulent coronaviruses infected fewer macrophages, produced lower virus titers, were less able to sustain viral replication, and spread less efficiently to other susceptible macrophages than the virulent coronaviruses. Thus, the intrinsic resistance of feline macrophages may play a pivotal role in the outcome of coronavirus infection in vivo.

HSV hepatitis in the mouse: a light and electron microscopic study with immunohistology and in situ hybridization

In order to characterize better the morphology and immune response in acute necrotizing HSV infection, murine HSV hepatitis was examined. BALB/c mice were inoculated intraperitoneally with 10(6) plaque-forming units (PFU) of HSV-1 (Lenette) and HSV-2 (D316). In both groups half the animals were pretreated with silica particles to block macrophage function. Up to 6 days after infection four mice from each group were sacrificed at daily intervals and the livers were examined by light and electron microscopy, immunohistology, in situ hybridization, combined immunohistology/in situ hybridization and titration of viral PFU. HSV-2 infected mice developed severe necrotizing hepatitis with persistence of HSV in the liver tissue until the end of the study. HSV-1 infected mice rapidly eliminated the virus and revealed only small necrotic foci. Early phase alterations and necrotic phase lesions were distinguished and characterized and morphologic evidence of a direct cytopathic effect of HSV was detected. A specific immune reaction in late stages appeared to be mediated by T4-positive T-lymphocytes. In situ hybridization and immunohistochemistry showed a close correlation with virus titration and were valuable in characterizing early phases and in the assessment of prognosis and differential diagnosis.

Protective effect of passive immunization on herpetic retinitis of newborn rabbits

We studied the protective effects of passive immunization with virus specific antibody in newborn rabbits inoculated subcutaneously with type 2 herpes simplex virus (HSV-2). Newborn rabbits given anti-HSV-2 antibody intraperitoneally (IP) on days 0, 2 and 4 post infection had smaller herpetic skin lesions and reduced mortality when compared to controls. In addition, the IP treatment using this schedule reduced virus growth in the skin lesions and virus dissemination, so that it decreased the frequency of herpetic retinitis. When the IP antibody administration was started at 24 hours post virus inoculation, according to the schedule days 1, 3 and 5, there was less protection; larger skin lesions, higher mortality, and greater evidence of virus dissemination. Also HSV-infected mononuclear cells (MNCs) treated with anti-HSV serum resulted in a significant reduction in the number of infected MNCs. The results of these studies suggest that anti-HSV-2 antibody contributes to protection against HSV-2 infection of skin as well as eyes, probably by inactivation of the virus locally at the skin inoculation site, and by combating the hematogenous spread of HSV-infected MNCs as well as free virus to various organs including the eye.

The potential use of liposome-mediated antiviral therapy

The natural targeting of liposomes to cells of the reticuloendothelial system should be exploited to examine whether selective delivery of antiviral or immunomodulatory agents could be beneficial for the treatment of virus diseases. In this review we discuss the potential use of liposomes in the treatment of virus diseases, the targeting of liposome-encapsulated immunomodulators to macrophages in order to render these cells cytolytic for virus-infected cells, and the targeting of liposome-encapsulated antiviral drugs to macrophages to achieve direct suppression of virus replication with in these cells.

Infection of murine hepatocyte cultures by herpes simplex virus (HSV) 1 and 2

A study was undertaken of the interaction between liver cells and Herpes Simplex Virus (HSV) in vitro. Hepatocytes were obtained from HSV-resistant (C57/B16) and from HSV-susceptible (BALB/c, A/J, C3H) mouse strains and cultured according to standard methods. Each culture was infected with several strains of HSV-type 1 or of HSV-type 2, respectively. The multiplicity of infection was 5. The cytopathic effect was evaluated by light- and electron-microscopy. The number of infectious particles was determined using rabbit kidney or Vero cell cultures. All evaluations were made at different time intervals after infection. No difference concerning the replication rate of HSV-1 and 2 in isolated hepatocytes from resistant and susceptible mouse strains was detected. However, a marked difference was observed with respect to the production of infectious particles: HSV-1 exhibited a good multiplication rate, whereas no production of virus particles was observed with HSV-2. The data show that mice hepatocytes fail to bear the genotype for resistance to HSV infections.

Experimental infection of inbred mice with herpes simplex virus. VI. Effect of interferon on in vitro virus replication in macrophages

Peritoneal exudate cells (PEC) of DBA/2 mice, after 7 days of in vitro preculture and consisting of virtually 100 per cent macrophages, were able to support the replication of Herpes Simplex Virus type 1 strain WAL (HSV). Using a standard medium based on Dulbecco's Modified Eagle Medium (D-MEM), no virus replication was observed in freshly isolated PEC. However a medium based on RPMI 1640 consistently yielded higher virus titres in precultured PEC than the D-MEM medium, and also allowed virus replication in freshly isolated PEC. Macrophages derived from the spleens or the bone marrow, and precultured in the same way as PEC represented a highly pure population and were permissive for infection with HSV. Titres of about 10(6) PFU HSV were observed in PEC 48 hours after infection with 10(3) or 10(6) PFU. However, whereas a complete destruction of the cell monolayer was observed 24 hours after infection with 10(6) PFU, complete cytopathogenicity in PEC infected with 10(3) PFU required at least twice this time. In the latter situation, plaque formation was observed 24 hours after infection. PEC of different strains of mice were compared. Of these, PEC of all mice that are susceptible to HSV infection in vivo replicated HSV to the same degree as PEC of DBA/2 mice, whereas PEC of resistant C57BL/6 and C3H/HeJ mice produced 1000 fold lower titres of viral progeny. Whereas the number of infectious centres were equal in PEC of DBA/2 and C57BL/6 mice, the plaques observed after infection of confluent PEC with a low MOI were considerable smaller in cells from C57BL/6 mice. Furthermore, significantly higher titres of interferon were measured in the supernatants of HSV-infected C57BL/6 macrophages than in those of DBA/2 macrophages, and the former were made fully susceptible by the in vitro addition of an anti-interferon serum.

Protection of mice against infection with mouse hepatitis virus type 3 by injection of silica

Injection of silica did not brake the resistance against MHV3 conferred to C57BL/6 mice by injection of C. parvum. However, silica itself had a marked protective effect against MHV3 infection that was maximal when injecting 1 mg 2 hrs before virus infection. The protective effect of silica was observed in a number of inbred mouse strains that differ in their relative resistance to MHV3 infection. No viral titers were observed in the spleen and liver of mice which had received MHV3 plus silica, whereas high titers were observed in the virus-infected controls. Injection of silica caused a marked decrease in the number of esterase-positive macrophages in the peritoneal wash-out population, that may be compatible with the possibility that the cause of the protection is the depletion of target cells for the viral infection. This latter effect, however, was short-lived and 24-48 hrs after injection of silica, high numbers of esterase-positive cells were again observed. This may explain why only little protection was observed when silica was administered 2 days before virus infection.

Mechanisms of enhanced resistance of Mycobacterium bovis BCG-treated mice to ectromelia virus infection

The mechanism of enhanced resistance of Mycobacterium bovis BCG-treated mice to ectromelia virus infection was investigated by determining the effect of splenectomy, antithymocyte serum, and antimacrophage serum on resistance. It was greatly reduced by these treatments, not only in normal mice, but also in mice treated with live or heat-inactivated BCG. Production of circulating interferon by ectromelia virus and Newcastle disease virus was augmented in BCG-treated mice and was markedly depressed by splenectomy and antithymocyte and antimacrophage serum treatments in both BCG-treated and normal mice. Carbon clearance activity was activated in BCG-treated mice, but splenectomy did not influence phagocytic activity. These results suggest that augmented interferon production in the spleens of BCG-treated mice plays a major role in enhanced resistance. Other possible mechanisms are discussed.

Restricted replication of herpes simplex virus in human monocyte cultures: role of interferon

Exposure of fresh human monocytes in culture to high or moderate concentrations of herpes simplex virus (HSV) resulted in an abortive infection or in a highly restricted replication of the virus. Infectious progeny virus yields were obtained either by diluting the inoculum virus to multiplicities of 0.1-0.0001 PFU/cell, or by cultivation of the cells for a few days before exposure to the virus. Interferon was synthesized and released into the medium of monocyte cultures infected with the higher multiplicities, while the lower productive multiplicities or inoculations of HSV into mature macrophage cultures resulted in a production of only small amounts, if any, of interferon. Inhibition of the morphological differentiation of monocytes was seen in cultures infected with the higher multiplicities of HSV (m.o.i. 1.0-0.1 PFU/cell) and was not unlike that caused by exogenous interferon added into uninfected monocyte cultures. Antisera against the leukocyte interferon were able to enhance the production of infectious HSV in monocyte-macrophage cultures. These results suggest that interferon induced in monocytes by high multiplicities of HSV can prevent the productive replication of HSV. Apart from its possible direct antiviral effect interferon may cause this restriction of HSV replication by inhibiting the differentiation of host monocytes.

Kinetics and genetics of herpes simplex virus-induced antibody formation in mice

The kinetics of antibody synthesis was investigated after intraperitoneal, subcutaneous, and footpad infection of various strains of mice with herpes simplex virus. Immunoglobulin M antibodies appeared 5 days after and immunoglobulin G antibodies appeared 10 to 12 days after intraperitoneal infection with herpes simplex virus type 1. The major histocompatibility complex and the background genome of inbred mice were not found to have a systematical influence on antibody synthesis. Female mice, however, consistently produced more antibodies than did male if the infection was done intraperitoneally, but not if it was done subcutaneously or into footpads. Castration considerably increased the amount of antibodies produced by male mice. The difference in antibody formation between females and males could be abolished by injection of silica; moreover, antibody titers were enhanced by this treatment. This has also been found by immunization with a Formalin-inactivated herpes simplex virus vaccine. The effect of silica in enhancing antibody formation could be observed up to 12 days after infection. Infectious virus could be detected up to 2 days after infection, and herpes simplex virus type 1 antibody-stimulating antigens could be detected up to 4 days in ultrasonicates of macrophages. The assumption is made that androgen-sensitive cell populations, including macrophages and their soluble products, are involved in antibody-depressing mechanisms.

Early interactions of herpes simplex virus with mouse peritoneal macrophages

Adsorption of herpes simplex virus type 1 (HSV-1) and type 2 (HSV-2) to resident peritoneal macrophages (PM) of 4-week-old Swiss albino (SA) and GR/AFib mice was studied. A significantly (P less than 0.05) higher HSV-2 adsorption rate was found with PM of SA mice than with PM of GR/AFib mice. Of added HSV-2 65% bound to the cells of SA mice over a 120-min period versus 15% to PM of GR/AFib mice. Only 15 to 20% of added HSV-1 bound to PM regardless of the mouse strain. These patterns of adsorption were found with all four HSV-1 and four HSV-2 strains tested. Pretreatment of PM with an HSV-2 mutant blocked the adsorption of added HSV-2. Thus, the receptors for HSV attachment seemed to be virus type selective. To avoid masking of adsorption by phagocytotic activity, the adsorption studies had to be performed at 4 degrees C. Transport of attached HSV-1 and HSV-2 to the nuclei of SA PM was studied with purified virus labeled with 32Pi and [3H]thymidine. In double-isotope experiments, only transport of HSV-2 was detected. The possible importance of differences in density or avidity of virus-binding receptors on the plasma membrane of PM is discussed in relation to macrophage-dependent focal liver necrosis, which was only demonstrable after intraperitoneal inoculation of HSV-2, not HSV-1, only in SA, not GR/AFib, mice.

Recovery of mice from herpes simplex virus type 2 hepatitis: adoptive transfer of recovery with immune spleen cells

Young BALB/c mice inoculated intraperitoneally with herpes simplex virus type 2 develop focal necrotizing hepatitis. After infection, the livers of these mice show increasing virus titers, which reach a maximum on day 3 after infection; this is followed by a dramatic decrease in the amount of virus recovered on days 4 and 5. This decrease in virus content is accompanied by a progressive infiltration of the lesions with mononuclear leukocytes and an apparent resolution of the lesions. Adoptive transfer of immune spleen cells from mice infected 6 days earlier accelerated this process. When 50 x 10(6) to 100 x 10(6) immune spleen cells were transferred 24 h after infection, the inflammatory response and the clearance of virus from the livers were advanced by almost 2 days. As few as 12 x 10(6) immune spleen cells accelerated the healing process, whereas fewer immune cells, disrupted immune cells, or normal spleen cells did not have an effect. The protection conferred by herpes simplex virus type 2-sensitized immune spleen cells was specific since mouse cytomegalovirus- or vaccinia virus-sensitized immune spleen cells had no effect on the course of infection with herpes simplex virus type 2, whereas some cross-reactivity was observed between herpes simplex virus types 1 and 2. This model seems to be suitable for examining the immunological mechanisms that are active during recovery from visceral herpes simplex virus infections.

Production of hybrid cell lines secreting antibodies to herpes simplex virus type 2

Following different immunization schedules we have produced 102 myeloma--spleen cell hybrid lines (30.8% of the total) secreting antibodies to HSV-2 infected cells. The highest yield of hybrids was derived from fusion of myeloma cells with spleen cells from mice sensitized by footpad injection of formalin-inactivated virus and boosted intravenously with the same antigen. To date, twelve of the antibody-producing hybrids have been cloned by limiting dilutions to generate over 100 monoclonal lines reacting specifically with HSV-infected but not with mock-infected cells. Several hybrid lines have also been injected into mice to generate tumors and high titers of anti-HSV-specific antibodies have been detected in ascitic fluids. All of the hybrids so far tested have retained the capacity to secrete anti-HSV antibodies after long-term in culture or repeated passages through mice. Antibodies reacting with cytoplasmic or nuclear antigens in infected cells as well as type-specific and type common antibodies have been detected.

Different susceptibilities of skin to type 1 and type 2 herpes simplex viruses in newborn rabbits

Skin infections with type 1 herpes simplex virus (HSV-1) were compared with skin infections with type 2 virus (HSV-2). Five strains each of HSV-1 and HSV-2 were tested by injecting 10(3) 50% tissue culture infective doses of each strain subcutaneously into 1-day-old New Zealand white rabbits. All five strains of HSV- 2 produced severe skin lesions that resulted in wide dissemination of the infection to many organs, paralysis of the hind legs, and finally death. The virus could be isolated frequently from skin lesions, from various organs (liver, lungs, adrenal glands, brain, and eyes), and from circulating leukocytes and plasma. In contrast, all five strains of HSV-1 failed to produce significant skin lesions or dissemination of virus, only half of the skin lesions yielded HSV, and no virus could be isolated from the blood. These results indicate that HSV-1 dose not grow well in the skin of newborn rabbits and fails to disseminate, whereas HSV-2 is dermatotropic and disseminates readily to many organs by hematogenous routes.

Comparative neurovirulence and latency of HSV1 and HSV2 following footpad inoculation in mice

The effect of virus dose and animal age on the appearance of acute and latent neurologic infection by HSV1 and HSV2 was studied in Balb/c and ICR mice inoculated in the footpad. At low viral doses HSV2 was found to be 1,500 times more neurovirulent than HSV1. At high doses there was no difference in neurovirulence. Age-acquired resistance to disease was shown to be less complete with HSV2 than with HSV1. Neurovirulence was shown to be associated with spread of infection to the spinal ganglia. The data indicate that the factor(s) responsible for the differential neurovirulence of these two viruses is related to events at the level of the footpad and/or sciatic nerve.

Role of macrophages in natural resistance to virus infections

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Properties of coxsackievirus B3 variants which are amyocarditic or myocarditic for mice

Inoculation of adolescent CD-1 mice with one variant of coxsackievirus B3 (CVB3m) results in induction of readily observable myocardial lesions, whereas inoculation of siblings with a second variant (CVB3o) results in little or no myocarditis. These variants could not be distinquished from each other on the basis of replication properties in HeLa cells or cardiac tissues in vivo, sensitivity to human interferon in HeLa cells, induction of interferon in the mouse, generation of detectable levels of defective-interfering particles in HeLa cells or in cardiac tissue in vivo, stimulation of serum-neutralizing antibody titers, nor in their rate of clearance by the spleen. Infectivity of CVB3o was slightly more heat labile at 34 degrees C than CVB3m. Little if any replication of either CVB3o or CVB3m occurred in either adherent or nonadherent populations of normal murine lymphoid cells. Cardiac tissues from mice inoculated with CVB3m but not CVBo contain new antigens that can inhibit migration of sensitized lymphocytes from CVB3m-immunized mice in an in vitro cell-migration-inhibition assay. However, the CVB3o variant was shown to have the genetic capability of inducing myocarditis if the mice were treated with cyclophosphamide prior to virus inoculation. These results suggest, in agreement with our previously published work, that induction of myocarditis by CVB3 requires destruction of myocytes by virus and subsequent stimulation of cell-mediated responses to new antigens produced in the myocardium during virus replication.

Effect of Mycobacterium tuberculosis BCG infection on the resistance of mice to ectromelia virus infection: participation of interferon in enhanced resistance

Mice infected with Mycobacterium tuberculosis BCG were more resistant than normal mice to ectromelia virus infection. It is suggested that enhanced interferon production in peritoneal exudate cells and spleen cells of BCG-infected mice plays an important role in this resistance.

Role of activated macrophages in resistance of congenitally athymic nude mice to hepatitis induced by herpes simplex virus type 2

Congenitally athymic nude (nu/nu) mice of a BALB/c genetic background were found considerably more resistant to the induction of focal necrotic hepatitis by herpes simplex virus type 2 (HSV-2) tha, were phenotypically normal littermates (nu/+) or BALB/c mice. The augmented resistance was age dependent, as it was only manifested in mice from 4 to 5 weeks of age. Studies of the course of infection showed that nude mice were able to restrain virus multiplication in the liver far better than normal mice in the early phase of infection. However, they seemed inferior to normal mice in eliminating the infectious process. In vitro investigation of peritoneal macrophages revealed that macrophages from 6-week-old nude mice exhibited accelerated spreading and were three times as restrictive in the replication of HSV-2 as macrophages from normal mice. However, no difference was found in the efficiency of adsorption/phagocytosis between macrophages from nude and normal mice. The increased resistance of nude mice could be abolished by blockade of the microphage function of the mice by silica. Nude mice reconstituted at birth with thymus cells were just as susceptible to infection as normal mice. These data suggest that the increased resistance of nude mice to HSV-2 hepatitis is due to the presence of nonspecifically activated macrophages before infection.

Macrophages and age-dependent resistance to hepatitis induced by herpes simplex virus type 2 im mice

An age-dependent increase in the resistance of BALB/c mice to induction of focal necrotic hepatitis by herpes simplex virus type 2 was demonstrated. In 3-week-old mice inoculated intraperitoneally with virus, numerous necrotic foci developed in the liver. As the mice matured, the number of lesions declined until the age of 8 weeks, when no further increase in resistance appeared. Corresponding to this, the virus titers of livers and spleens of 3-week-old mice were higher than in 8-week-old animals throughout the infection, and the infection was apparently terminated in these organs of the adult mice by day 5. In vitro infection of peritoneal macrophages from 3-week-old and 8-week-old mice showed that this age-related resistance was concomitant with an increased restriction of virus replication in peritoneal macrophages from adult mice. Since, furthermore, the resistance of adult mice could be abolished by intravenous inoculation of the macrophage-toxic agent silica before infection, and since adoptive transfer of 2 X 10(6) syngeneic macrophages from adult mice to young ones conferred to the latter a resistance comparable to that of the adult mice, it is concluded that macrophage maturation is responsible for the age-dependent resistance seen in this infection.

Genetics of macrophage-controlled resistance to hepatitis induced by herpes simplex virus type 2 in mice

The genetics of innate resistance of mice to hepatitis induced by herpes simplex virus type 2 (HSV-2) was analyzed by crossing resistant male GR to susceptible female BALB/c mice and backcrossing females of this F1 generation to susceptible male BALB/c mice. By scoring of macroscopic liver lesions and virus isolation studies from the liver 4 days after intraperitoneal inoculation of HSV-2, it appeared that the resistance was governed by one X-linked dominant gene or closely linked gene complex, as F1 female mice were resistant and F1 male mice were susceptible and the trait segregated in a ratio close to 1:1 in the backcross mating. A cellular expression in vitro of virus resistance was found in the macrophage population of the mice as measured by differences in the restriction of HSV-2 replication in macrophage cultures prepared from individual mice. In contrast to what was seen in macrophage cultures, virus replicated equally well in embryonic fibroblast cultures from susceptible and resistant strains of mice.

Effect of silica on the pathogenic distinction between herpes simplex virus type 1 and 2 hepatitis in mice

The role of macrophages in the difference in liver pathogenicity between herpes simplex virus type 1 (HSV-1) and type 2 (HSV-2) in mice was investigated by selectively blocking the macrophage function of the mice by silica. Intravenous administration of 3 mg of silica 2 h before virus inoculation partially abolished the difference between the two virus types, as judged by macroscopic and microscopic examination of the livers and by virus isolation studies. Intraperitoneal inoculation of 50 mg of silical before virus seemed more effective in suppressing the macrophage function, since this treatment almost completely eliminated the difference in hepatotropism between HSV-1 and HSV-2 as assessed by the number and size of the lesions appearing in the liver. The final outcome of the infection, death from encephalitis, was, however, not influenced by macrophage blockade.