Altered splenic T cell function of BALB/cByJ mice infected with mouse hepatitis virus or Sendai virus

Mouse hepatitis virus and Sendai virus are among the most common viruses naturally infecting laboratory mice. Concanavalin A-stimulated in vitro proliferative responses of splenocytes were examined after infection of BALB/cByJ mice with the JHM strain of mouse hepatitis virus (MHV-JHM) or Sendai virus. Mice were exposed to these viruses by presumed natural routes (per os or intranasally). Immunodepression was marked but transient among BALB/cByJ mice exposed to MHV-JHM. Among mice exposed to Sendai virus and examined over a 21-day period, spleen cells from only one mouse, sacrificed 10 days postinoculation, exhibited a severely impaired ability to respond to concanavalin A. Lymphokine production by spleen cells from control and infected mice was then assessed. IL 2 was either absent or present at very low levels in culture supernates of concanavalin A-unresponsive spleen cells from MHV-JHM-infected mice. Spleen cells from the single Sendai virus-infected mouse also produced very low levels of IL 2. In contrast, IL 1 was detected in supernatants of all spleen cell cultures derived from control, MHV-JHM-infected, or Sendai virus-infected mice. There was not a clear correlation between concanavalin A responsiveness and the ability of spleen cells to produce interferon-gamma. These results stress the importance of using laboratory mice of known microbiological status for immunologic experiments.     

Characterization of accessory cell function during acute infection of BALB/cByJ mice with mouse hepatitis virus (MHV), strain JHM.

Earlier studies revealed defective concanavalin A-stimulated proliferation and cytokine production by spleen cells derived from BALB/cByJ mice acutely infected with mouse hepatitis virus (MHV), strain JHM. Based on those observations, assays of in vitro antigen-presenting cell (APC) function were undertaken. APC function of unfractionated spleen cells from individual MHV-infected mice was highly variable. Experiments using pooled spleen cells derived from MHV-infected mice revealed that adherent spleen cell APC function was impaired to a much greater degree than B cell APC function. Adherent cells derived from peritoneal exudates of infected mice exhibited an APC defect that was similar in magnitude to that observed for splenic adherent cells. Splenic B cells derived from acutely infected BALB/cByJ mice harbored infectious MHV. In contrast, lysates of adherent spleen cells from acutely infected mice did not kill intracerebrally inoculated neonatal mice, but did induce seroconversion among all survivors. Despite impairment of APC function of cells derived from MHV-infected donors, neither indomethacin nor accessory cells from uninfected control mice restored concanavalin A-induced proliferative responses of spleen cells collected from acutely infected mice. These results and those of earlier studies suggest that, although APC function is impaired, in vitro T cell dysfunction exhibited by spleen cells from MHV-JHM-infected donors is probably related to an inherent proliferative defect subsequent to T cell activation. Defective concanavalin A-stimulated proliferation does not appear to be secondary to accessory cell function suppression or to inhibitory factors secreted by accessory cells.     

Gender influences infectivity in C57BL/6 mice exposed to mouse minute virus

Two natural outbreaks of mouse minute virus (MMV) are described. Observations during management of the naturally infected colonies led to a study in which 4-wk-old C57BL/6NCr and C57BL/6Tac mice were inoculated oronasally with an immunosuppressive variant of MMV (MMVi), as were adult C57BL/6NCr lactating dams or their pups (age, 10 d). By day 28 postinoculation, 100% of the 4-wk-old male C57BL/6NCr and C57BL/6Tac mice, 56.2% of 4-wk-old C57BL/6NCr female and 62.5% of 4-wk-old C57BL/6Tac female mice, 100% of adult lactating C57BL/6NCr dams, and 100% of inoculated pups (10 d) had seroconverted. Serologically positive nursing dams did not infect their nursing pups. In contrast, when nursing pups were inoculated, 100% of their dams seroconverted by 28 d postinoculation. Only 1 of 4 facility sentinels (Tac:SW female mice) seroconverted to MMVi and none of the 4 research sentinels (Tac:SW female mice) seroconverted under a once-weekly bedding transfer program. Consequently, 4 new research Tac:SW sentinels of each gender (n = 8) were placed in known-positive cages at cage-change; 100% of the male mice but 0% of the females seroconverted by day 48. Study results suggest gender influences both infectivity and the ability to detect subclinical infections of MMVi. Other factors that may influence detection of MMV include mouse strain or stock, short shedding period, and prolonged time between cage changes. In light of the data from both the natural infections and the experimental cases, cessation of breeding likely will be beneficial when trying to eradicate this virus.     

Infection of BALB/cByJ mice with the JHM strain of mouse hepatitis virus alters in vitro splenic T cell proliferation and cytokine production.

Earlier studies from this laboratory showed that infection of BALB/cByJ mice by a natural route with mouse hepatitis virus, strain JHM (MHV-JHM), results in functional splenic T cell suppression in vitro. This was evidenced by reduced concanavalin A-driven spleen cell proliferation and interleukin (IL)2 production measured after conventional intervals of cell culture (72 and 24 h, respectively). The purpose of the present work was to determine whether MHV-induced T cell dysfunction is kinetic or absolute and whether production of other T-cell derived cytokines is defective. Bioassays revealed that production of IL2, gamma interferon, and IL4 by spleen cells from acutely infected mice is suppressed and that some of the defects are kinetic as well as absolute. Proliferative responses of both CD4+ and CD8+ T cells were depressed, but neither cell type contained infectious virus. Cells that proliferated poorly in response to concanavalin A were fully capable of responding to specific virus stimulation. These results further emphasize the potential complications that MHV infection may pose to immunologic research using mice.     

Mousepox in inbred mice innately resistant or susceptible to lethal infection with ectromelia virus. I. Clinical responses

Clinical responses to infection with ectromelia virus strain NIH-79 were determined in several strains of inbred mice. All mice were equally susceptible to infection, but mortality was strain dependent. BALB/c AnNCr, A/JNCr, DBA/2NCr and C3H/He/NCr MTV- mice were highly susceptible to lethal infection whereas AKR/NCr and SJL/NCr mice were moderately susceptible and C57BL/6NCr mice were highly resistant. Death rates were influenced strongly by virus dose and by route of inoculation. High doses were associated with early and high mortality. For a given dose, intraperitoneal inoculation resulted in the highest mortality and death rates were progressively reduced in mice inoculated by the footpad, subcutaneous and intranasal routes. Footpad swelling was prominent in resistant mice and in survivors among susceptible strains. Deaths among AKR and SJL mice were sporadic and often occurred late irrespective of virus dose. It is suggested that this pattern could be influenced by secondary contact infections or by immunologic injury associated with host responses to ectromelia virus.     

Kinetics of ectromelia virus (mousepox) transmission and clinical response in C57BL/6j, BALB/cByj and AKR/J inbred mice

Research was undertaken to answer basic questions on susceptibility, clinical response and transmission of ectromelia virus in selected strains of inbred mice. C57BL/6J and AKR/J were found to be markedly more resistant to a virulent strain of ectromelia virus (isolated during the 1979-80 outbreak at the National Institutes of Health) than C57LJ, BALB/cByJ, DBA/2J, A.By/SNJ and C3H/HeJ when infected by footpad inoculation. In C57BL/6J and AKR/J the LD50 was about 7 logs higher than the ID50. With one exception, C57LJ, the LD50 and ID50 titers in the other strains were about equal. In C57LJ the LD50 titer was intermediate. Following intragastric inoculation, virus was isolated from feces of C57BL/6J mice for as long as 46 days and up to 29 days from BALB/cByJ mice. Transmission to cage mates from intragastrically infected C57BL/6J and BALB/cByJ occurred up to 36 and 30 days respectively after infection. Virus was isolated from the spleen in 2 of 5 BALB/cByJ mice and 1 of 7 C57BL/6J mice tested 95 days after gastric inoculation. Following footpad inoculation, BALB/cByJ mice consistently transmitted virus to cage mates before death at 10-12 days. C57BL/6J mice transmitted between days 8 and 17, but not beyond. Virus was maintained in C57BL/6J mice by exposure to infected cage mates for seven passages, which was the most attempted. Clinical signs in infected C57BL/6J mice were usually subtle or inapparent.     

NaCl taste thresholds in 13 inbred mouse strains

Molecular mechanisms of salty taste in mammals are not completely understood. We use genetic approaches to study these mechanisms. Previously, we developed a high-throughput procedure to measure NaCl taste thresholds, which involves conditioning mice to avoid LiCl and then examining avoidance of NaCl solutions presented in 48-h 2-bottle preference tests. Using this procedure, we measured NaCl taste thresholds of mice from 13 genealogically divergent inbred stains: 129P3/J, A/J, BALB/cByJ, C3H/HeJ, C57BL/6ByJ, C57BL/6J, CBA/J, CE/J, DBA/2J, FVB/NJ, NZB/BlNJ, PWK/PhJ, and SJL/J. We found substantial strain variation in NaCl taste thresholds: mice from the A/J and 129P3/J strains had high thresholds (were less sensitive), whereas mice from the BALB/cByJ, C57BL/6J, C57BL/6ByJ, CE/J, DBA/2J, NZB/BINJ, and SJL/J had low thresholds (were more sensitive). NaCl taste thresholds measured in this study did not significantly correlate with NaCl preferences or amiloride sensitivity of chorda tympani nerve responses to NaCl determined in the same strains in other studies. To examine whether strain differences in NaCl taste thresholds could have been affected by variation in learning ability or sensitivity to toxic effects of LiCl, we used the same method to measure citric acid taste thresholds in 4 inbred strains with large differences in NaCl taste thresholds but similar acid sensitivity in preference tests (129P3/J, A/J, C57BL/6J, and DBA/2J). Citric acid taste thresholds were similar in these 4 strains. This suggests that our technique measures taste quality-specific thresholds that are likely to represent differences in peripheral taste responsiveness. The strain differences in NaCl taste sensitivity found in this study provide a basis for genetic analysis of this phenotype.     

Macronutrient diet selection in thirteen mouse strains

The strain distribution for macronutrient diet selection was described in 13 mouse strains (AKR/J, NZB/B1NJ, C57BL/6J, C57BL/6ByJ, DBA/2J, SPRET/Ei, CD-1, SJL/J, SWR/J, 129/J, BALB/cByJ, CAST/Ei, and A/J) with the use of a self-selection protocol in which separate carbohydrate, fat, and protein diets were simultaneously available for 26-30 days. Relative to carbohydrate, nine strains consumed significantly more calories from the fat diet; two strains consumed more calories from carbohydrate than from fat (BALB/cByJ, CAST/Ei). Diet selection by SWR/J mice was variable over time, resulting in a lack of preference. One strain (A/J) failed to adapt to the diet paradigm due to inadequate protein intake. Comparisons of proportional fat intake across strains revealed that fat selection/consumption ranged from 26 to 83% of total energy. AKR/J, NZB/B1NJ, and C67BL/6J mice self-selected the highest proportion of dietary fat, whereas the CAST/Ei and BALB/cByJ strains chose the lowest. Finally, epididymal fat depot weight was correlated with fat consumption. There were significant positive correlations in AKR/J and C57BL/6J mice, which are highly sensitive to dietary obesity. However, absolute fat intake was inversely correlated with epididymal fat in two of the lean strains: SWR/J and CAST/Ei. We hypothesize that the SWR/J and CAST/Ei strains are highly sensitive to a negative feedback signal generated by increasing body fat, but the AKR/J and C67BL/6J mice are not. The variation in dietary fat selection across inbred strains provides a tool for dissecting the complex genetics of this trait.     

Comparison of lipids in total brain tissue from five mouse genotypes.

Brain tissue from adult male and female mice of the C57BL/6J, C57BL/6J-AW-J, BALB/cJ, SJL/J, and DBA/2J genotypes was examined for brain weight, total protein, total lipid, cholesterol, phospholipid, plasmalogen, sulfatide, nonganglioside-glycolipid sphingosine, and ganglioside N-acetyl neuraminic acid, fatty acid, and sphingosine. No significant differences were found between sexes for any of these constituents. When compared to the overall average obtained for other animals, the DBA/2J, C57BL/6J-AW-J, and BALB/cJ mice contained lower quantities of plasmalogen and sulfatide compared to the overall averages obtained for the other genotypes. In addition, the sterol content in DBA/2J mice was significantly higher than the overall average value obtained for the other animals.     

Mousepox in inbred mice innately resistant or susceptible to lethal infection with ectromelia virus. II. Pathogenesis

The pathogenesis of mousepox due to infection with ectromelia virus strain NIH-79 was characterized in genetically susceptible (BALB/cAnNCr) and genetically resistant (C57BL/6NCr) mice. BALB/c mice inoculated subcutaneous (s.c.) or intranasally (i.n.) had high mortality. Most mice died within 7 days from severe necrosis of the spleen and liver. Necrotic foci in livers of BALB/c mice that survived beyond 7 days often were accompanied by mononuclear cell infiltrates and by hyperplasia of lymphoid tissues. C57BL/6 mice inoculated by either route remained asymptomatic and necrotic lesions were mild or absent, whereas focal non-suppurative hepatitis and lymphoid hyperplasia were prominent. Infectious virus and viral antigen were distributed widely in tissues of BALB/c mice, but had limited distribution in C57BL/6 mice. Both mouse strains had infection of the respiratory tract, genital tract, oral tissues and bone marrow, and BALB/c mice also had infection of the intestines. Both strains also developed serum antibody to vaccinia virus antigen after infection. The results show that ectromelia virus occurs in tissues conducive to mouse to mouse transmission and that the severity and character of mousepox lesions correlate directly with resistance and susceptibility to infection. They also support the concept that cellular immunity contributes to survival from infection.     

Mouse susceptibility to mouse hepatitis virus infection is linked to viral receptor genotype.

We have reported that the receptor for mouse hepatitis virus (MHV) expressed in MHV-susceptible BALB/c mice (MHVR1) has 10 to 30 times the virus-binding activity of the MHV receptor expressed in MHV-resistant SJL mice (MHVR2) (N. Ohtsuka, Y. K. Yamada, and F. Taguchi, J. Gen. Virol. 77:1683-1992, 1996). This fact indicates the possibility that the difference in MHV susceptibility between BALB/c and SJL mice is determined by the virus-binding activity of the receptor. To test this possibility, we have examined MHV susceptibility in mice with the homozygous MHVR1 gene (R1/R1 genotype), mice with the MHVR1 and MHVR2 genes (R1/R2 genotype), and mice with the homozygous MHVR2 gene (R2/R2 genotype) produced by cross and backcross mating between BALB/c and SJL mice. All 63 F2 and backcrossed mice with the MHVR1 gene (R1/R1 and R1/R2) were susceptible to MHV infection, and all 57 with the homozygous MHVR2 gene (R2/R2) were resistant. We have also examined the MHV receptor genotypes of several mouse strains that were reported to be susceptible to MHV infection. All of those mice had the MHVR1 gene. These results suggest the possibility that the viral receptor determines the susceptibility of the whole animal to MHV infection.     

Activation of murine T cells by staphylococcal enterotoxin E: requirement of MHC class II molecules expressed on accessory cells and identification of V beta sequence of T cell receptors in T cells reactive to the toxin

We investigated a mechanism leading to activation of murine T cells by staphylococcal enterotoxin E (SEE). L cells transfected with I-Ab genes but not control L cells supported IL-2 production by SEE-induced C57BL/6 T lymphoblasts upon restimulation with SEE. mAb to I-Ab markedly inhibited the above response. Flow cytometric analyses showed that SEE-induced C57BL/6 T lymphoblasts are composed of both CD4+ T cells and CD8+ T cells, and that larger parts of them bore V beta 11 (40-75%). mAb to V beta 11 markedly inhibited the SEE-induced proliferative response and IL-2 production by T cells. Analysis of SEE-induced IL-2 production in spleen cells from various mouse strains showed that C57BL/6 and B10.A(4R) mice (I-E, not expressed; V beta 11+ T cells, normally generated) are highly responsive to SEE. In contrast, BALB/c, C3H/HeN, (C57BL/6 x BALB/c or C3H/HeN) F1 mice (I-E, normally expressed and V beta 11+ T cells, deleted), and SJL and C57L mice (V beta 11 genes, deleted) are weakly responsive to SEE. The results indicate that SEE activates mainly T cells bearing V beta 11 in physical association with MHC class II molecules expressed on AC. In addition, the results indicate that SEE activates both CD4+ T cells and CD8+ T cells.     

Differences in antibody production against mouse hepatitis virus (MHV) among mouse strains

Several strains of mice were examined for antibody production after intranasal inoculation with a low virulence strain of mouse hepatitis virus (MHV), MHV-NuU. C57BL/6N mice were shown to be high responders in the production of complement fixing (CF) antibody as compared to C3H/HeN, BALB/c-AnN, DBA/2N mice. F1 hybrids B6C3 and BDF1 from C57BL/6N mice, showed CF antibody responses as high as C57BL/6N, suggesting that high responsiveness is genetically controlled. All these mouse strains were able to produce high titred neutralizing antibody to MHV.     

IL-10 limits parasite burden and protects against fatal myocarditis in a mouse model of Trypanosoma cruzi infection

Chagas' disease is a zoonosis prevalent in Latin America that is caused by the protozoan Trypanosoma cruzi. The immunopathogenesis of cardiomyopathy, the main clinical problem in Chagas' disease, has been extensively studied but is still poorly understood. In this study, we systematically compared clinical, microbiologic, pathologic, immunologic, and molecular parameters in two mouse models with opposite susceptibility to acute myocarditis caused by the myotropic Colombiana strain of T. cruzi: C3H/HeSnJ (100% mortality, uncontrolled parasitism) and C57BL/6J (<10% mortality, controlled parasitism). T. cruzi induced differential polarization of immunoregulatory cytokine mRNA expression in the hearts of C57BL/6J versus C3H/HeSnJ mice; however, most differences were small. The difference in IL-10 expression was exceptional (C57BL/6J 8.7-fold greater than C3H/HeSnJ). Consistent with this, hearts from infected C57BL/6J mice, but not C3H/HeSnJ mice, had a high frequency of total IL-10-producing CD8(+) T cells and both CD4(+) and CD8(+) subsets of IFN-γ(+)IL-10(+) double-producing T cells. Furthermore, T. cruzi infection of IL-10(-/-) C57BL/6J mice phenocopied fatal infection in wild-type C3H/HeSnJ mice with complete loss of parasite control. Adoptive transfer experiments indicated that T cells were a source of protective IL-10. Thus, in this system, IL-10 production by T cells promotes T. cruzi control and protection from fatal acute myocarditis.     

Comparison of lipids in total brain tissue from five mouse genotypes

Brain tissue from adult male and female mice of the C57BL/6J, C57BL/6J-A^w—J, BALB/cJ, SJL/J, and DBA/2J genotypes was examined for brain weight, total protein, total lipid, cholesterol, phospholipid, plasmalogen, sulfatide, nonganglioside—glycolipid sphingosine, and ganglioside N-acetyl neuraminic acid, fatty acid, and sphingosine. No significant differences were found between sexes for any of these constituents. When compared to the overall average obtained for other animals, the DBA/2J, C57BL/6J-A^w−J, and BALB/cJ mice contained lower quantities of nonganglioside—glycolipid sphingosine. The DBA/2J and C57BL/6J-A^w−J mice also contained lower quantities of plasmalogen and sulfatide compared to the overall averages obtained for the other genotypes. In addition, the sterol content in DBA/2J mice was significantly higher than the overall average value obtained for the other animals.     

The receptor for mouse hepatitis virus in the resistant mouse strain SJL is functional: implications for the requirement of a second factor for viral infection.

The SJL mouse strain is resistant to infection by some strains of the murine coronavirus mouse hepatitis virus (MHV), such as JHM and A59. The block to virus infection has been variously attributed to defects in virus receptors or virus spread. Since the cellular receptors for MHV, mmCGM1 and mmCGM2, have recently been identified as members of the carcinoembryonic antigen family, we reexamined the possible defectiveness of the MHV receptors in SJL mouse strain. Cloning and sequencing of the cDNAs of both mmCGMs RNAs from SJL mice revealed that they were identical in size to those of the susceptible C57BL/6 (B6) mouse. There was some sequence divergence in the N terminus of the mmCGM molecules between the two mouse strains, resulting in a different number of potential glycosylation sites. This was confirmed by in vitro translation of the mmCGM RNAs, which showed that the glycosylated mmCGM2 of SJL was smaller than that of B6 mice. However, transfection of either mmCGM1 or mmCGM2 from SJL mice into MHV-resistant Cos 7 cells rendered the cells susceptible to MHV infection. The ability of the SJL mmCGM molecules to serve as MHV receptors was comparable to that of those from B6. These molecules are expressed in SJL mouse brain and liver in a similar ratio and in amounts equivalent to those in the B6 mouse. Furthermore, we demonstrated that an SJL-derived cell line was susceptible to A59 but resistant to JHM infection. We concluded that the MHV receptor molecules in the SJL mouse are functional and that the resistance of SJL mice to infection by some MHV strains most likely results from some other factor(s) required for virus entry or some other step(s) in virus replication.     

Host genetic background affects regulatory T-cell activity that influences the magnitude of cellular immune response against Mycobacterium tuberculosis

Using two mouse strains with different abilities to generate interferon (IFN)-γ production after Mycobacterium tuberculosis infection, we tested the hypothesis that the frequency and activity of regulatory T (Treg) cells are influenced by genetic background. Our results demonstrated that the suppressive activity of spleen Treg cells from infected or uninfected BALB/c mice was enhanced, inhibiting IFN-γ and interleukin (IL)-2 production. Infected C57BL/6 mice exhibited a decrease in the frequency of lung Treg cells and an increased ratio CD4(+):CD4(+)Foxp3(+) cells compared with infected BALB/c mice and uninfected C57BL/6 mice. Moreover, infected C57BL/6 mice also had a decrease in the immunosuppressive capacity of spleen Treg cells, higher lung IFN-γ and IL-17 production, and restricted the infection better than BALB/c mice. Adoptive transfer of BALB/c Treg cells into BALB/c mice induced an increase in bacterial colony-forming unit (CFU) counts. Furthermore, BALB/c mice treated with anti-CD25 antibody exhibited lung CFU counts significantly lower than mice treated with irrelevant antibody. Our results show that in BALB/c mice, the Treg cells have a stronger influence than that in C57BL/6 mice. These data suggest that BALB/c and C57BL/6 mice may use some different mechanisms to control M. tuberculosis infection. Therefore, the role of Treg cells should be explored during the development of immune modulators, both from the perspective of the pathogen and the host.     

Differences in interleukin-12 and -15 production by dendritic cells at the early stage of Listeria monocytogenes infection between BALB/c and C57 BL/6 mice

The mechanisms responsible for the resistance of C57BL/6 mice and for the susceptibility of BALB/c mice to infection with Listeria monocytogenes were studied by comparing early IL-12 and IL-15 production by dendritic cells (DC) after infection with L. monocytogenes. Splenic DC expressing CD11b(low) and CD11c(+) obtained from C57BL/6 mice at 3 and 6 h after L. monocytogenes infection expressed higher levels of IL-12 p40 mRNA and IL-12 p40 protein than did those from BALB/c mice. Concurrently, a larger amount of IFN-gamma was produced by the splenic T cells from C57BL/6 mice in response to immobilized anti-TCRalphabeta mAb than by those from BALB/c mice, while the splenic T cells from BALB/c mice produced a higher level of IL-4 upon TCR alphabeta stimulation than did those of C57BL/6 mice. IL-15 mRNA and intracellular IL-15 protein were detected more abundantly in the DC from C57BL/6 mice than in those from BALB/c mice on day 3 after infection. CD3(+) IL2Rbeta (+) cells in the spleen were increased in C57BL/6 mice but not in BALB/c mice at the early stage after infection. Furthermore, IL-12Rbeta2 gene expression was up-regulated in T cells from C57BL/6 mice but not in those from BALB/c mice at the early stage after listerial infection. These results suggest that the difference in early production of IL-12 and IL-15 by DC may at least partly underlie the difference in susceptibility to L. monocytogenes between C57BL/6 and BALB/c mice.     

Inhibition of nitric oxide synthesis increases mortality in Sindbis virus encephalitis.

Sindbis virus (SV) is an alphavirus that causes acute encephalomyelitis in mice. The outcome is determined by the strain of virus and by the age and genetic background of the host. The mortality rates after infection with NSV, a neurovirulent strain of SV, were as follows v: 81% (17 of 21) in BALB/cJ mice; 20% (4 of 20) in BALB/cByJ mice (P < 0.001); 100% in A/J, C57BL/6J, SJL, and DBA mice; and 79% (11 of 14) in immunodeficient scid/CB17 mice. Treatment with Nomega-nitro-L-arginine methyl ester (L-NAME), a nitric oxide synthetase (NOS) inhibitor, increased mortality to 100% (P < 0.05) in NSV-infected BALB/cJ mice, to 95% (P < 0.001) in BALB/cByJ mice, and to 100% in scid/CB17 mice. BALB/cJ and BALB/cByJ mice had similar levels of inducible NOS mRNA in their brains, which were not affected by L-NAME or NSV infection. Brain NOS activity was similar in BALB/cJ and BALB/cByJ mice before and after infection and was markedly inhibited by L-NAME. NSV replication in the brains of BALB/cJ mice, BALB/cByJ mice, and mice treated with L-NAME was similar. Treatment of N18 neuroblastoma cells with NO donors S-nitroso-N-acetylpenicillamine or sodium nitroprusside in vitro before infection increased cell viability at 42 to 48 h compared with untreated NSV-infected N18 cells with little effect on virus replication. These data suggest that NO protects mice from fatal encephalitis by a mechanism that does not directly involve the immune response or inhibition of virus growth but rather may enhance survival of the infected neuron until the immune response can control virus replication.     

Modulatory effect of zinc on the proliferative response of murine spleen cells to polyclonal T cell mitogens

To study the effect of zinc on the proliferative response to polyclonal T cell mitogens, spleen cells from C57BL/6 mice were cultured with or without ZnCl2 and stimulated with graded doses of concanavalin A or phytohemagglutinin. Addition of 10(-4) M ZnCl2 inhibited proliferation whereas 10(-5) to 10(-6) M ZnCl2 did not modify the response to suboptimal doses of mitogen but increased DNA synthesis in cultures stimulated with high doses of mitogen (10 or 20 micrograms/ml of concanavalin A and 10 or 25 microliters/ml of phytohemagglutinin) which are supraoptimal for C57BL/6 mice, and inhibited proliferation in cultures of spleen cells from animals of this strain, low responder to T cell mitogens. In contrast, supplementation with ZnCl2 did not enhance the response to mitogen of spleen cells from high responder BALB/c mice. The enhancing effects of ZnCl2 on the proliferative response of C57BL/6 cells were not observed following depletion of adherent cells or in cultures supplemented with 5 X 10(-5) M 2-mercaptoethanol, both conditions capable of abrogating the inhibitory effect of high mitogen doses on the response of C57BL/6 cells.