Ontogeny of macrophage resistance to mouse hepatitis in vivo and in vitro

Simple assays for measuring innate interactions with fungi

In recent decades, there has been a steady rise in immunocompromised populations and consequently a dramatic increase in the clinical relevance of normally non-pathogenic and commensal fungi such as Aspergillus fumigatus and Candida albicans. Understanding how these fungi interact with the host immune system is important for the development of immunotherapeutic approaches. Here, we describe a number of methods which have been developed to investigate the interactions of fungi with host leukocytes in vitro, including measuring fungal binding and induction of cytokines, phagocytosis, the respiratory burst, and fungal killing.

129X1/SvJ mouse strain has a novel defect in inflammatory cell recruitment

Vitamin D-binding protein (DBP) has been reported to contribute to innate immunity. To verify prior in vitro and cell-based observations supporting this role, we assessed the ability of a recently developed DBP-null mouse line to recruit neutrophils and macrophages to a site of chemical inflammation. The interrupted DBP allele had been generated by homologous recombination in 129X1/SvJ embryonic stem cells and these cells were subsequently used to generate a line of DBP(-/-) (null) mice. Initial studies revealed a marked defect in the ability of these DBP(-/-) mice to recruit cells to the peritoneum after localized thioglycolate injection. However, progressive outcrossing of the DBP(-/-) mice to the C57BL/6J strain, conducted to provide a uniform genetic background for comparison of DBP-null and control mice, resulted in a progressive increase in cell recruitment by the DBP(-/-) mice and a loss in their apparent recruitment defect when compared with the DPB wild-type controls. These data suggested that the observed recruitment phenotype initially attributed to the absence of DBP was not linked to the DBP locus, but instead reflected the underlying genetic composition of the 129X1/SvJ ES cells used for the initial DBP gene disruption. A profound cell recruitment defect was confirmed in the 129X1/SvJ mice by direct analysis. Each of three commonly used inbred lines was discovered to have a distinct level of cell recruitment to a uniform stimulus (C57BL/6J > BALB/c > CD1 > 129X1/SvJ). Thus, this study failed to support a unique role for DBP in cellular recruitment during a model inflammatory response. Instead, the data revealed a novel and profound defect of cell recruitment in 129X1/SvJ mice, the strain most commonly used for gene deletion studies.

Pattern of disease after murine hepatitis virus strain 3 infection correlates with macrophage activation and not viral replication

Murine hepatitis virus strain (MHV-3) produces a strain-dependent pattern of disease which has been used as a model for fulminant viral hepatitis. This study was undertaken to examine whether there was a correlation between macrophage activation and susceptibility or resistance to MHV-3 infection. Peritoneal macrophages were isolated from resistant A/J and susceptible BALB/cJ mice and, following stimulation with MHV-3 or lipopolysaccharide (LPS), analyzed for transcription of mRNA and production of interleukin-1 (IL-1), tumor necrosis factor alpha (TNF-alpha), transforming growth factor beta (TGF-beta), mouse fibrinogen-like protein (musfiblp), tissue factor (TF), leukotriene B4, and prostaglandin E2 (PGE2). Macrophages from BALB/cJ mice produced greater amounts of IL-1, TNF-alpha, TGF-beta, leukotriene B4, and musfiblp following MHV-3 infection than macrophages from resistant A/J mice, whereas in response to LPS, equivalent amounts of IL-1, TNF-alpha, TGF-beta, and TF were produced by macrophages from both strains of mice. Levels of mRNA of IL-1, TNF-alpha, and musfiblp were greater and more persistent in BALB/cJ than in A/J macrophages, whereas the levels and kinetics of IL-1, TNF-alpha, and TF mRNA following LPS stimulation were identical in macrophages from both strains of mice. Levels of production of PGE2 by MHV-3-stimulated macrophages from resistant and susceptible mice were equivalent; however, the time course for induction of PGE2, differed, but the total quantity of PGE2 produced was insufficient to inhibit induction of musfiblp, a procoagulant known to correlate with development of fulminant hepatic necrosis in susceptible mice. These results demonstrate marked differences in production of inflammatory mediators to MHV-3 infection in macrophages from resistant A/J and susceptible BALB/cJ mice, which may explain the marked hepatic necrosis and fibrin deposition and account for the lethality of MHV-3 in susceptible mice.

Response of genetically susceptible and resistant mice to intranasal inoculation with mouse hepatitis virus JHM

Mouse hepatitis virus (MHV)-JHM infection was studied in genetically susceptible (BALB/cByJ) and resistant (SJL/J) mice following intranasal inoculation at 1, 3, 6 or 12 wk of age. Markers of infection included histology, immunohistochemistry, virus quantification and virus serology. All BALB mice developed severe disseminated disease with high mortality due to encephalitis and hepatitis. Peak MHV titers appeared in brain, liver, spleen and intestine on days 3 or 5. Age at inoculation did not influence virus titers in brain, spleen or intestine, but virus titers in liver were inversely proportional to age at inoculation. In 6-wk-old BALB mice, virus was cleared from spleen, intestine and liver by day 30 and from brain by day 60. In intestine, MHV was localized to lymphoid tissue, without fecal excretion. SJL mice of all ages developed remarkably milder disease with low mortality occurring only among mice inoculated at 1 wk of age. SJL mice inoculated at 1 wk had disseminated infection at day 3, but lesions and antigen were cleared from most organs by day 5. Mice inoculated at 3 and 6 wk of age had minimal or no involvement of peripheral organs, and mice inoculated at 12 wk of age had infections restricted to the nose. At day 5, MHV titers in brain, liver, spleen and intestine were significantly lower or undetectable in SJL mice of all ages compared to age-matched BALB mice. In 6-wk-old mice, MHV was cleared from all organs by day 10. Serum antibody titers to MHV were many-fold higher in BALB mice, compared to SJL mice, which mounted only a modest response.

Differential susceptibility and resistance of immunocompetent and immunodeficient mice to fatal Hantaan virus infection

Susceptibility and resistance to fatal Hantaan virus meningoencephalitis were studied in immunocompetent (nu/+) and congenitally T-cell deficient (nu/nu) CD-1 mice of different ages. Susceptibility of nu/+ mice to fatal infection was age-dependent, as evidenced by 100 percent mortality in mice inoculated intracerebrally with Hantaan virus (strain 76-118) during the first week of life, 60 percent mortality in mice inoculated at 9 days of age, and no disease or death in mice inoculated at 14 to 42 days of age. Deaths occurred significantly earlier in nu/+ mice inoculated at 5 and 7 days of age than in nu/+ mice less than 24 hours old. Nu/nu littermates of the same age did not exhibit a similar inverse relationship between age and survival times. Moreover, nu/nu mice 14 days or older remained susceptible, albeit with delayed onset of illness and time of death. Virus titers in brain tissues of nu/+ mice inoculated at 7 days and of nu/nu mice inoculated at 7, 9 and 14 days of age were nearly identical. In older nu/+ mice, peak virus titers were comparatively lower, but they did not seem to be influenced by the magnitude of the neutralizing antibody response. The more rapidly fatal course in nu/+ mice inoculated at a week of age than at birth, and the differential resistance between weanling nu/+ and nu/nu mice to Hantaan virus meningoencephalitis suggest that cell-mediated immunity may be responsible for both enhancement of disease and recovery from infection.

Selective vulnerability of neural cells and age-related susceptibility to OC43 virus in mice

Suckling CD 1 mice infected intracerebrally or extraneurally with OC43 virus developed a lethal neurotropic infection with high titres of virus in the brain. Examination of infected brain by routine H & E staining revealed no necrosis even in extensively infected tissue. Resistance to infection developed with increasing age, and by 20 days of age mice were completely insusceptible to i.c. inoculation. Virus replication was also demonstrable by FA staining, in spinal cord, dorsal root ganglia and retina. All other tissues were insusceptible and in particular, macrophages from both susceptible and resistant mice were found to be resistant to infection both in vivo and in vitro. Immunosuppression rendered 15 day old mice more susceptible to infection but adult mice remained insusceptible. The transfer of immune or non immune spleen cells from resistant mice did not confer resistance to newborn mice. Treatment of resistant mice with anti interferon globulin (AIG) did not render them more susceptible. These results indicate that the immune response is partially responsible for the development of resistance to OC43 infection but that it is only partially protective and other factors must also be required. The basis for the unique susceptibility of neural tissues in suckling mice is being investigated.

Analysis of age-dependent resistance to murine coronavirus JHM infection in mice

Resistance to intraperitoneal murine coronavirus JHM infection in mice develops with age. C3H mice were found to be fully susceptible up to the age of 20 days and resistant after 23 days of age. Protection of susceptible animals from death due to infection could be achieved by maternal antibodies or by transfer of spleen cells from immunized, but not from nonimmunized, donor mice. Lack of protection by transfer of unprimed adult spleen cells was not related to immunosuppression by the host. Moreover, resistance of adult mice could not be abrogated by application of lymphocytes from suckling mice, although immune suppression by other means did affect the resistance of adult animals. On the other hand, spleen cells from nonimmunized mice could be primed with inactivated JHM virus in suckling mice and protected these mice from death due to a subsequent virus infection. Thus, the outcome of infection with JHM virus in suckling and adult mice can be influenced by immunological events, but is not exclusively due to the different stages of immune competence.

Influence of the immune system on the course of infection with murine coronavirus JHM in suckling mice

The course of infection with murine corona virus JHM in C3H mice depends on the age of the animals. Mice up to 20 days of age are fully susceptible while mice older than 23 days resist the infection. Protection of suckling mice from death of infection can be provided by intraperitoneal administration of immune spleen cells but not by non-immune spleen cells from adult mice. The immune spleen cells can be generated by priming adult mice, or by priming non-immune spleen cells from adult mice in baby mice with inactivated JHM virus. Thus the immune system might well be involved in the different outcome of infection with JHM-virus in suckling and adult mice, but it does not seem to be the exclusive factor responsible for the achievement of natural resistance.

Mouse hepatitis virus strain 3 infection of C57, A/Sn and A/J strain mice and their macrophages. Brief report

Mouse hepatitis virus strain 3 replicated in C57, A/Sn and A/J strain mouse macrophages with the production of a clear cytopathic effect, although only C57 and A/Sn strains of mice were killed with similar MHV3 dilutions. We could not confirm a previous report showing that in vitro cultured macrophages from A/J strain mice were resistant to MHV3 infection.

Factors involved in the age-dependent resistance of mice infected with low-virulence mouse hepatitis virus

Four-week-old weanling mice survived, whereas 1-week-old suckling mice died, after intraperitoneal inoculation of mouse hepatitis virus, MHV-S strain. The factors involved in this difference in susceptibility were studied. After virus inoculation, differences in virus growth in the liver and spleen were observed, which correlated with the susceptibility of animals to the virus. Interferon, detected at an early stage of infection, was considerably lower in suckling mice than in weanling mice. Titers of MHV-S in peritoneal cells from infected animals were at least 100 times greater in suckling than in weanling mice, and a similar, but less prominent difference in virus growth was also found in the corresponding cultured macrophages. After transfer of peritoneal cells from weanling to suckling mice, a decrease in mortality of infected suckling mice was observed. These results suggest that both interferon and macrophages may be important in the age-dependent resistance of mice to MHV-S infection.

Role of macrophages in natural resistance to virus infections

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Genetics of resistance of animals to viruses: I. Introduction and studies in mice

Inherited resistance to animal viruses may be conveniently classified into three types: monogenetic, following simple mendelian ratios; polygenetic; and cytoplasmic. A virus is a unique cellular parasite, dependent upon the host for reproduction and nourishment in a variety of different ways. Since, as with the other types of parasites, the host and the parasite have necessarily evolved together. It is a distortion to consider the resistance of the host, without considering the evolutionary steps in the development of this extreme form of parasitism; therefore, this chapter reviews some of the ideas put forward about host-agent interactions in plants as well as in animals. The importance of genes in regulating the resistance to disease, including parasites and parasitoids, is apparent if the disease is considered to be an important evolutionary force. The selective effects of viruses have not yet been adequately studied. Continued attempts to find a correlation between the different blood groups and differing severity of smallpox infection clearly searched for selective forces, but the results were inconclusive. Most of the knowledge of genetic resistance to virus disease rests on the study of resistance to selected agents in various inbred strains of mice and chickens, rather than on any knowledge of the effects of genetic resistance in a natural heterozygous population. The increasing frequency, however, with which genetic resistance is found, is in itself an evidence that these genes are important in natural outbred populations. In addition, there are increasing numbers of virus diseases, in which the viral agent seems to be inherited in a mendelian fashion.

Interactions between vaccinia virus and sensitized macrophages in vitro

The action of peritoneal exudate cells (PEC) from normal and vaccinia virus infected mice on infectious vaccinia virus particles was investigated in vitro. PEC from immune mice showed a significantly higher infectivity titre reduction (virus clearance, VC) than normal cells. This effect could be clearly attributed to the macrophage. Vaccinia virus multiplied in PEC from normal animals while there was no virus propagation in cells from immunized mice. The release of adsorbed or engulfed virus was reduced significantly in PEC from immunized animals. Anti-vaccinia-antibodies seem to activate normal macrophages to increased virus clearance. This stimulating effect was demonstrable only in the IgG fraction of the antiserum. The activity of macrophages from mice injected three times over a period of 14 days with vaccinia virus could be entirely blocked with anti-mouse-IgG, while PEC from mice injected one time six days previously were not inhibited.

Viral replication and interferon production in fetal and adult ovine leukocytes and spleen cells

Peripheral blood leukocyte and spleen cell cultures derived from adult sheep and from third-trimester (107 to 145 days of gestation) and second-trimester (70 to 98 days of gestation) fetal lambs were examined for their ability to support viral replication and to produce interferon. Bluetongue virus, Herpesvirus hominis type 2, and Chikungunya virus failed to replicate in either leukocyte or spleen cell cultures derived from adult ewes or in cultures from second- or third-trimester fetal lambs. Similarly, peripheral blood leukocytes from adult sheep or third-trimester fetal lambs did not support the replication of Semliki Forest virus, vesicular stomatitis virus, Newcastle disease virus, or vaccinia virus. No major differences were observed in the ability of fetal and adult leukocytes to produce interferon in response to viral infection. In contrast, mean interferon titers induced by bluetongue virus, H. hominis type 2, and Chikungunya virus in spleen cells from second-trimester fetuses were 4- to 10-fold greater than those induced in spleen cells from adult ewes. Variations in interferon levels induced on separate occasions with cells from the same donor age group were observed. The antiviral substance induced in both the fetal and adult cell cultures fulfilled the usual criteria for characterization as interferon.

Studies on thymus function. 3. Duration of thymic function

The immune functions of neonatally thymectomized C3Hf mice exposed only temporarily to thymus function show a progressive decay with time in the absence of the thymus. The immune responses studied at different ages in the range of 100-600 days were: first-set rejection of H-2-compatible and incompatible skin allografts, second-set rejection of skin allografts, capacity of spleen cells to produce graft-versus-host reactions in F(1) hybrids, resistance to infection with mouse hepatitis virus, and response of spleen cells to phytohemagglutinin in vitro. These long-term studies had the purpose of determining the duration of the restoration induced by thymus function when the mice were exposed only temporarily to it. Different models were used but the two basic ones were: (a) mice grafted intraperitoneally at 15 days of age with a syngeneic thymus that was removed surgically at 10, 20, or 30 days after grafting, and (b) mice grafted at 15 days of age with allogeneic strain A thymoma or C57BL thymus, these representing situations in which there is spontaneous rejection of the restoring graft. In all the experimental models used, the animals were restored when tested at 100 days of age, but progressively became immunologically incapacitated at 200-300 days of age. From the more controlled experiments in which the restoring thymus graft was removed surgically, the following conclusions can be drawn. (a) A short exposure to a thymus graft can produce restoration of immune functions in neonatally thymectomized mice, but this restoration is not self-sustaining in the absence of the thymus and declines progressively with age. The decline usually starts at 200-300 days of age. (b) This was especially clear in experiments in which the same animal was tested twice in its lifetime for capacity to produce graft-versus-host reactions; these animals were competent at 100 days and became incompetent at 400 days of age. (c) The shortest period of thymic exposure studied was 10 days; if vascularization of the graft is taken into account, 2-3 days of thymic function are sufficient to produce restoration. (d) The immune decay observed in the thymectomized animals exposed temporarily to thymus was more profound than the physiological decay of immunity observed in control animals of similar age. (e) Of all the tests studied, the response of spleen cells to phytohemagglutinin was to be preserved the longest in animals exposed only temporarily to thymic function. The present results were interpreted in accordance with our previous findings indicating that a population of postthymic cells can be developed by temporary exposure of neonatally thymectomized animals to thymic function, but that this population is not self-sustaining in the absence of thymus and progressively decays by physiological attrition.

In vitro interaction of mouse hepatitis virus and macrophages from genetically resistant mice. II. Biological characterization of a variant virus MHV (C3H) isolated from stocks of MHV(PRI)

A variant mouse hepatitis virus MHV(C(3)H) to which cultured peritoneal macrophages from both PRI and C(3)H mice were susceptible was isolated from stocks of the MHV(PRI) strain of mouse hepatitis virus. It was cloned on C(3)H macrophage monolayers and killed both adult PRI and C(3)H mice when injected intraperitoneally. This new variant was antigenically indistinguishable from the wild type virus. While the emergence of the variant virus was delayed in the course of infecting C(3)H macrophages with large inocula of MHV(PRI), the second passage grew to a high titer in both cell types without delay. Thus, adaptation to the new host was immediate. Interference, apparently not interferon-mediated, between the two variant viruses may have been the cause for the delay in the emergence of the variant virus. The delayed destruction of C(3)H-cultured macrophages by large inocula of MHV(PRI) uniformly resulted in the emergence of MHV(C(3)H). Whether the new variant emerged as a result of a selection of a pre-existing stable mutant or was conditioned by "growth" in the resistant host was not determined.

Mouse hepatitis virus (MHV3) infection in chronic murine schistosomiasis mansoni

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