Analysis of the inhibitory effect of peritoneal macrophages on the spread of herpes simplex virus

Neuropeptides (SP and CGRP) augment pro-inflammatory cytokine production in HSV-infected macrophages

Neuropeptides are able to modulate cytokine production by macrophages in response to various stimulators. In this study, the effects of neuropeptides substance P (SP) and calcitonin gene-related peptide (CGRP) on production of pro-inflammatory cytokines TNF and IL-1 beta by macrophages were considered. Mouse peritoneal macrophages were infected with herpes simplex virus type-1 (HSV-1), or remained unstimulated, and cytokine assays were performed after 12 h. IL-1 beta and TNF secretion by unstimulated macrophages have been significantly increased in the presence of SP and CGRP. Each neuropeptide, alone or in coordination with the other, caused significant increase in IL-1 beta and TNF production by HSV-infected mouse peritoneal macrophages. It was concluded that the macrophage-mediated inflammatory response to HSV-1 is enhanced in the presence of these neuropeptides.

Conjunctival macrophage-mediated influence of the local and systemic immune response after corneal herpes simplex virus-1 infection

Recently it has been shown that selective subconjunctival macrophage depletion reduced the incidence and severity of stromal herpes simplex virus (HSV) keratitis in mice. In this study, we examined the effect of conjunctival macrophage depletion on the corneal and systemic T-cell-mediated immune response. BALB/c mice were treated with subconjunctival injections of dichloromethylene diphosphonate (Cl2MDP)-liposomes (Cl2MDP-LIP) or phosphate-buffered saline (PBS) 7 and 2 days before corneal infection with 105 plaque-forming units (PFU) of HSV-1 (KOS strain). Interferon (IFN)-gamma, interleukin (IL)-2, and IL-4 production in the cornea was analysed by enzyme-linked immunosorbent assay (ELISA), and cytokine mRNA levels (IFN-gamma, IL-4) were measured by semiquantitative reverse transcription-polymerase chain reaction (RT-PCR). Cell culture supernatants from submandibular lymph nodes were analysed by ELISA for expression of IFN-gamma, IL-2, and IL-4 and by bioassay for IL-6. The HSV-1-specific proliferative response of lymphocytes from regional lymph nodes and the delayed-type hypersensitivity (DTH) response were tested after corneal infection. Virus-neutralizing antibody titres and HSV-1-specific immunoglobulin G (IgG)2a/IgG1-ratios were measured. Cytokine mRNA expression (IFN-gamma, IL-4) and secretion (IFN-gamma, IL-2, IL-4) in the corneas were decreased after HSV-1 corneal infection in the macrophage-depleted mice. The secretion of IFN-gamma and IL-2 was decreased in the regional lymph nodes from Cl2MDP-LIP-treated animals (P<0.05). Furthermore, Cl2MDP-LIP-treated mice had decreased HSV-1 specific proliferative responses (P<0.05) and DTH response after corneal HSV-1 infection (P<0.05). The virus-neutralizing serum-antibody levels (P<0.05) increased while the HSV-1 specific IgG2a/IgG1-ratio was unaffected after macrophage depletion. Macrophage depletion did not induce a shift between the T helper 1 (Th1) and Th2 response in this HSK model. The data suggest that conjunctival macrophage functions are enhancing the T-cell-mediated immune response after corneal infection. This effect is at least in part responsible for the impaired course of herpetic keratitis after macrophage depletion.

The immune response to ocular herpes simplex virus type 1 infection

Herpes simplex virus type 1 (HSV-1) is a prevalent microbial pathogen infecting 60% to 90% of the adult world population. The co-evolution of the virus with humans is due, in part, to adaptations that the virus has evolved to aid it in escaping immune surveillance, including the establishment of a latent infection in its human host. A latent infection allows the virus to remain in the host without inducing tissue pathology or eliciting an immune response. During the acute infection or reactivation of latent virus, the immune response is significant, which can ultimately result in corneal blindness or fatal sporadic encephalitis. In fact, HSV-1 is one of the leading causes of infectious corneal blindness in the world as a result of chronic episodes of viral reactivation leading to stromal keratitis and scarring. Significant inroads have been made in identifying key immune mediators that control ocular HSV-1 infection and potentially viral reactivation. Likewise, viral mechanisms associated with immune evasion have also been identified and will be discussed. Lastly, novel therapeutic strategies that are currently under development show promise and will be included in this review. Most investigators have taken full advantage of the murine host as a viable working in vivo model of HSV-1 due to the sensitivity and susceptibility to viral infection, ease of manipulation, and a multitude of developed probes to study changes at the cellular and molecular levels. Therefore, comments in this review will primarily be restricted to those observations pertaining to the mouse model and the assumption (however great) that similar events occur in the human condition.

The role of the UL41 gene of herpes simplex virus type 1 in evasion of non-specific host defence mechanisms during primary infection

The UL41 gene product (vhs) of herpes simplex virus (HSV) is packaged in the virion, and mediates host protein synthesis shutoff at the early stage of the virus replication cycle. In order to clarify the role of vhs in virus replication and virulence, we isolated a completely UL41-deficient mutant (the VRDelta41 strain) and its revertant (the VRDelta41R strain). In the mouse encephalitis model, the replication of strain VRDelta41 was inhibited after 2 days post-infection, resulting in low virulence, by gamma-ray-sensitive cells such as lymphocytes and/or neutrophils. The result suggested that some cytokines, produced in VRDelta41-inoculated brains, activate and induce the migration of gamma-ray-sensitive cells to the infection site. Therefore, cytokines produced by HSV-1-infected human cells were screened, and potent inductions of interleukin (IL)-1beta, IL-8 and macrophage inflammatory protein-1alpha by VRDelta41 infection were observed. Moreover, the VRDelta41 strain showed 20- and 5-fold higher sensitivity to interferon-alpha and -beta compared to the wild-type strain, respectively. These results indicate that one important role of vhs in vivo is evasion from non-specific host defence mechanisms during primary infection through suppression of cytokine production in HSV-infected cells and reduction of the anti-HSV activity of interferon-alpha and -beta.

Nitric oxide and macrophage antiviral extrinsic activity

In this study we evaluated the relationship between nitric oxide (NO) and macrophage antiviral extrinsic activity. Macrophages activated by intraperitoneal injection of herpes simplex virus-2 (HSV-2), showed both extrinsic antiviral activity and high nitrite production in contrast to non-activated, resident macrophages. The extrinsic antiviral activity was observed in cultures of Vero cells infected with HSV-1 and HSV-2. The NO inhibitor N-monomethyl-l-arginine acetate (l-NMA) impaired the antiviral activity of HSV-elicited macrophages. The effect was dose dependent and correlated with a reduction of nitrite in the culture media. The effect of l-NMA was reversed by the addition of l-arginine. These data indicate that NO could be responsible for the described activity. Furthermore, l-NMA treatment resulted in the aggravation of HSV-1-induced keratitis in the mouse model, supporting a defensive role of NO in the pathogenesis of HSV-1 corneal infection.

The pathogenicity of a US3 protein kinase-deficient mutant of herpes simplex virus type 2 in mice

We have investigated the pathogenicity of a US3 protein kinase-deficient mutant (L1 BR1) of herpes simplex virus type 2 (HSV-2) for 4-week-old ICR mice to define the role of the viral protein kinase in virus-host interaction. When mice were intraperitoneally infected with 10(5)PFU of L1 BR1, the virus disappeared from the peritoneal cavity by 2 days postinfection and failed to induce any significant histopathological changes in the liver and spleen although viral antigens were occasionally detected in the epithelial cells of small bile ducts and small vascular wall. The parental virus (HSV-2 186) and a revertant of the mutant (L1 B-11) both caused severe hepatitis, and viral antigens were clearly detected in the hepatocytes and Kupffer cells in the focal necrotic areas. Both of the virulent viruses, unlike L1 BR1, could produce infectious progeny and cytopathic effects in freshly harvested peritoneal macrophages. The growth of L1 BR1 in peritoneal macrophages was restricted at a stage of or prior to viral DNA synthesis but after the induction of viral DNA polymerase. In addition, the production and/or the spread of mutant in mouse embryo fibroblasts (MEF) was found to be much more effectively suppressed by cocultivation of peritoneal macrophages than that of 186. An almost complete inhibition of L1 BR1-plaque formation was observed at a macrophage-to-MEF ratio of 4:1. These results suggest that the attenuation of L1 BR1 following intraperitoneal infection is primarily due to its high sensitivity to intrinsic and extrinsic inhibition of peritoneal macrophages and that the US3 protein kinase may play a role in viral DNA replication in peritoneal macrophages.

The effect of lead on chemical- and viral-induced tumor production in mice

Female Swiss mice were exposed to lead in the drinking water at concentrations ranging from 0 to 1000 ppm for 105 or 280 day periods of time. The effect of lead on urethan-induced pulmonary adenoma formation was evaluated in the 105 day study. Urethan-induced sleeping times observed following ip injection of urethan (1.5 mg/g) after 3 weeks of lead exposure were not altered by lead indicating that lead did not affect the rate of urethan elimination. Pulmonary adenoma formation was evaluated 84 days later. Lead exposure did not affect the number of tumors produced, nor did it alter the mean tumor diameter in the lead treatment groups. This suggests that the immunosuppressive activity of lead does not enhance urethan-induced adenoma formation. In the 280 day study, the incidence of spontaneous murine lymphocytic leukemia was evaluated. Leukemia was observed in all treatment groups. Mortality was greater in the lead-exposed mice. Mice exposed to 50 or 1000 ppm lead had 41.6% and 58.3% more deaths associated with the virus. The median survival time was also reduced in the lead-exposed mice. It appears that the immunosuppressive effects of lead allow for increased expression of the murine lymphocytic leukemia virus.

Role of Calomys musculinus peritoneal macrophages in age-related resistance to Junin virus infection

In nature, the cricetid Calomys musculinus is the principal host of Junin virus, the etiological agent of Argentine hemorrhagic fever. In the experimental infection, adult C. musculinus survived whereas newborns died after intraperitoneal inoculation with the XJ.Cl3 strain of Junin virus. The role of peritoneal macrophages in this age-related resistance was studied. Junin virus multiplied in cultivated macrophages from either neonatal or adult animals and, therefore, it was not possible to correlate the susceptibility of peritoneal macrophages to Junin virus infection with the age-dependent resistance. When adult and neonatal animals were treated with silica prior to Junin virus infection, deaths occurred in the adults, while a delay and decrease in the mortality rate were observed in neonatals. These results suggest that in neonatal C. musculinus macrophages could be permissive cells for Junin virus multiplication, whereas in adult cricetids, these cells would act as a barrier against viral infection by means of an extrinsic antiviral activity.

Macrophage response to herpes simplex encephalitis in immune competent and T cell-deficient mice

Corneal inoculation of Nude (athymic) mice and Balb/c mice with herpes simplex virus Type I produces a brainstem encephalitis with demyelination of the trigeminal root entry zone. The extent of CNS demyelination is less in the immune-deficient athymic mice 7 days after infection compared to the immune-competent Balb/c mice. Both groups demonstrate a macrophage response and beginning myelin disruption approximately 3 days after corneal infection when herpes viral particles are first observed within central nervous system cells. Five to seven days after infection when differences in the extent of demyelination between the immune-competent and immune-deficient animals become evident, the Balb/c mice demonstrate T cells and increasing numbers of macrophages at the trigeminal root entry zones. These findings suggest an interaction between macrophages and T cells which leads to an extension of the demyelination in the immune competent Balb/c mice and that lack of T cells is important in limiting demyelination in Nude (athymic) mice.

Genetic aspects of macrophage involvement in natural resistance to virus infections

Macrophages are thought to constitute an important element in the body's natural defense against invasion and dissemination of viruses. Possible antiviral mechanisms of macrophages are defined and referred to as intrinsic, i.e. the ability of macrophages to serve as a nonpermissive barrier between the virus and susceptible cells and extrinsic, i.e. the ability of macrophages to affect the virus or virus replication in surrounding cells. Most studies on the role of macrophages in natural resistance to virus infections have been performed in animal models. An interesting aspect of many viral infections in animals is the finding of a genetically determined variation in natural resistance. Because of the availability of numerous inbred and congenic strains most studies on genetically determined resistance have been performed in mice. The classical examples are resistance to flaviviruses and susceptibility to mouse hepatitis virus, both of which are inherited as dominant, monogenic traits. With these viruses macrophage intrinsic restriction of virus replication has been found to express at the cellular level the genetics of resistance/susceptibility seen in the intact animal. Other examples, where macrophages have been implicated in genetically determined resistance include herpes simplex virus and influenza virus. The involvement of macrophages in natural resistance to these viruses is discussed in relation to other putative resistance determinants like interferon production and sensitivity and natural killer cell activity.

Murine peritoneal macrophages support murine cytomegalovirus replication

Because there have been different conclusions regarding the susceptibility of murine macrophages to murine cytomegalovirus (MCMV) infection and replication, we have undertaken a detailed comparison of MCMV infection of macrophages with that of a permissive cell line, mouse embryo cells. Although both cell lines undergo productive infections with MCMV, there are marked differences in certain aspects of the viral replication which may account for some of the different conclusions regarding the MCMV cycle in macrophages. Although both cell lines produce MCMV after infection, the time course of the infection differed markedly between the cell types. Similarly, the proportion of infected macrophages that are releasing infection virions is much smaller than the proportion of a comparably infected mouse embryo cell culture. Tissue culture passage of MCMV first enhanced (after one passage) and then reduced the infectivity of the virus for macrophages in vitro. The delayed time course and lesser production at early intervals after infection of macrophage cultures could not be attributed to demonstrable inhibitors or to replication in contaminating fibroblasts in the macrophage cultures.

Sequelae of maternally derived cytomegalovirus infections in premature infants

Eighteen of 106 (17%) infants of seropositive mothers, with birth weights less than 1500 gm, acquired cytomegalovirus from a maternal source. Neutropenia, lymphocytosis, thrombocytopenia, and hepatosplenomegaly developed in some infants concomitant with the onset of CMV excretion. Infected infants who excreted CMV at less than 7 weeks of age had longer oxygen requirements than infants who did not excrete CMV until they were older. Passively derived maternal antibody to CMV fell more rapidly over the first few months of life in sick premature infants than would be expected in term infants. Among six infected premature infants, five had undetectable antibody titers when CMV excretion began. Loss of passively acquired antibody and early excretion of virus appear to be associated with symptomatic CMV infections in premature infants of seropositive mothers.

Endocytosis by the mononuclear phagocyte system and autoimmune disease

The mononuclear phagocyte system, formerly called the reticuloendothelial system, is an important element in basic immunology, cell biology, and clinical disease. Secretory products participate in inflammation and immunoregulation. Endocytosis mediated by specific receptors for immunoglobulin and complement or by other opsonins is important in removal of damaged self or foreign particles. The ability to assess receptor-specific endocytosis has led to the recognition of Fc-receptor dysfunction in certain autoimmune diseases. This defect in membrane receptor function, whether inherited or acquired, may be important in the pathogenesis of these diseases.

Inhibition of herpes simplex virus multiplication by activated macrophages: a role for arginase?

Proteose-peptone-activated mouse macrophages can prevent productive infection by herpes simplex virus in neighboring cells in vitro whether or not those cells belong to the same animal species. The effect does not require contact between the macrophages and the infected cells, may be prevented by adding extra arginine to the medium, and may be reversed when extra arginine is added 24 h after the macrophages. Arginase activity was found both intracellularly and released from the macrophages. The extracellular enzyme is quite stable; 64% activity was found after 48 h of incubation at 37 degrees C in tissue culture medium. No evidence was found that the inefficiency of virus replication in macrophages was due to self-starvation by arginase. As might be predicted macrophages can, by the same mechanism, limit productive infection by vaccinia virus.

Preparation of stable target cells for anti-herpes simplex virus cytotoxic T lymphocytes

Using an avirulent strain of herpes simplex virus (HSV), SKa, and a methylcholanthrene induced sarcoma cell line, Meth A cells, we have developed a reliable target cell system for detection of cell-mediated cytotoxicity directed against HSV-infected cells. SKa-infection in Meth A produced no progeny virus but induced HSV-specific surface antigens as revealed by radioimmunoassay using 125I-labeled HSV antibody. Spontaneous release of 51Cr from the SKa-infected Meth A cells was no more than that from uninfected control cells but a strong spontaneous 51Cr release was produced in Meth A cells infected with KOS, a virulent strain which produced a progeny virus in Meth A and was lytic for the cells. When used as a target, SKa-infected Meth A cells could detect HSV-specific cytotoxicity by spleen and lymph node lymphocytes of mice immunized with SKa and KOS. This system also detected effector cytotoxic lymphocytes stimulated in vitro by mixed cultures of immune spleen cells and KOS-infected Meth A cells. Thus, the system should be valuable in studies of cell-mediated cytotoxicity directed against HSV-infected cells.

Ontogeny of murine cellular cytotoxicity to herpes simplex virus-infected cells

Mice infected with herpes simplex virus either orally or intraperitoneally had a markedly age-related mortality. All animals under 3 weeks of age died, whereas all those over 3 weeks of age survived. The ability of murine peritoneal cells to kill herpes simplex virus-infected target cells in the absence (natural killer cytotoxicity) or presence (antibody-dependent cellular cytotoxicity) of antiviral antibody was similarly correlated with age and survival. This correlation is further support for the relevance of these antiviral defense mechanisms, and it may help explain the profound susceptibility of neonatal mice to herpes simplex virus infection.