Monoclonal antibody cure and prophylaxis of lethal Sindbis virus encephalitis in mice

Neuroadapted Sindbis virus (NSV) causes acute encephalitis and paralyzes and kills adult mice unless they are treated with primary immune serum after infection. To study the nature and specificity of curative antibodies, we gave mice 30 different monoclonal antibodies (MAbs) against Sindbis virus (SV) 24 h after lethal intracerebral inoculation of NSV. By the time of MAb treatment, NSV replication in the brain had been well established (7.5 X 10(7) PFU/g). Seventeen MAbs directed against multiple biological domains on the NSV E1 and E2 envelope glycoproteins prevented paralysis and death. Anticapsid MAbs failed to protect. Altogether, 15 of 17 curative MAbs either neutralized NSV infectivity or lysed NSV-infected cells with complement, but neither ability was necessary or sufficient to guarantee recovery. All 5 protective anti-E2 MAbs neutralized NSV infectivity; 6 of 10 protective anti-E1 MAbs neutralized NSV; 4 did not. Plaque assay or immunohistochemical staining showed that neutralizing and nonneutralizing curative MAbs decreased NSV in the brain, brainstem, and spinal cord. Despite high neutralization titers, hyperimmune anti-SV and anti-NSV mouse sera prevented only 6 and 30% of deaths, respectively, while primary immune sera prevented 50 (SV) and 90% (NSV) of deaths. Secondary intravenous immunization with a live virus apparently diminished, obscured, or failed to boost a class of protective antibodies. When separate mouse groups were given these 30 MAbs 24 h before lethal intracerebral inoculation of NSV, a slightly different set of 17 neutralizing or nonneutralizing anti-E1 and anti-E2 antibodies protected. Two nonneutralizing MAbs and hyperimmune anti-SV serum, which had failed to promote recovery, prophylactically protected 100% of the mice. The antibody requirements or mechanisms of prophylaxis and recovery may differ.     

Resistance of Interleukin-1β-Deficient Mice to Fatal Sindbis Virus Encephalitis

Interleukin-1β (IL-1β) concentrations are frequently elevated in central nervous system (CNS) viral infections, but the pathophysiologic significance of such elevations is not known. To examine the role of IL-1β in CNS viral pathogenesis, we compared the natural histories of IL-1β-deficient and wild-type 129 SV(ev) mice infected with a neurovirulent viral strain, neuroadapted Sindbis virus (NSV). We found that the incidence of severe paralysis and death was markedly decreased in NSV-infected IL-1β^−/− mice compared to NSV-infected wild-type mice (4 versus 88%, P < 0.001). Despite this marked difference in clinical outcome, no differences in numbers of apoptotic cells or presence of histopathologic lesions in the brains of moribund wild-type mice and those of clinically healthy IL-1β^−/− mice could be detected. These results suggest that IL-1β deficiency is protective against fatal Sindbis virus infection by a mechanism that does not involve resistance to CNS virus-induced apoptosis or histopathology.     

Differences between C57BL/6 and BALB/cBy mice in mortality and virus replication after intranasal infection with neuroadapted Sindbis virus

Neuroadapted Sindbis virus (NSV), given intranasally, caused fatal encephalitis in 100% of adult C57BL/6 mice and 0% of BALB/cBy mice. Most C57BL/6 mice developed severe kyphoscoliosis followed by hind-limb paralysis, while BALB/cBy mice did not. In situ hybridization for detecting NSV RNA and immunohistochemistry for detecting NSV antigen indicated that virus delivered by this route infected neurons of the olfactory region and spread caudally without infection of ependymal cells. Virus antigen was more abundant and infectious virus increased more rapidly and reached higher levels in C57BL/6 mice than in BALB/cBy mice. Surprisingly, infectious virus was cleared faster in C57BL/6 mice, and this was associated with more rapid production of neutralizing antibody. However, viral RNA was cleared more slowly in C57BL/6 mice. In both mouse strains, more infectious virus was present in the lumbar spinal cord than in the cervical spinal cord. These data suggest that genetic susceptibility to fatal NSV encephalomyelitis is determined at least in part by the efficiency of viral replication and spread in the central nervous system. The differences identified in this study provide possible phenotypes for mapping genetic loci involved in susceptibility.     

Differential susceptibility to actively induced experimental allergic encephalomyelitis and experimental allergic orchitis among BALB/c substrains

Experimental allergic orchitis (EAO) and experimental allergic encephalomyelitis (EAE) are animal models of organ-specific autoimmune disease. In this study, BALB/cByJ and BALB/cAnNCr mice were susceptible to both autoimmune diseases whereas BALB/cJ subline mice were resistant. Disease resistance in BALB/cJ mice did not appear to be a reflection of either (i) a nonspecific generalized impairment of cellular immunity or (ii) an alteration in the phenotypic expression of Bordetella pertussis-induced histamine sensitization, a phenotype which has been shown to be associated with susceptibility to both diseases. Susceptibility to both EAE and EAO was inherited as a dominant trait in F1 hybrid animals. Segregation analysis in a (BALB/cByJ X BALB/cJ) X BALB/cJ backcross population suggested that disease resistance may be associated with a single genotypic difference in a common regulatory gene affecting susceptibility to both diseases. Linkage analysis of the backcross population failed to demonstrate an association of disease resistance with the mutant raf-1b allele carried by BALB/cJ mice. The results of these studies support previous observations that multiple genotypic differences may in fact exist in mice of the BALB/cJ subline and that such differences play a significant role in the genetic control of susceptibility to EAE and EAO.     

Experimental allergic orchitis in mice. V. Resistance to actively induced disease in BALB/cJ substrain mice is mediated by CD4 + T cells

Previous studies have shown that differential susceptibility to actively induced experimental allergic orchitis (EAO) exists among various BALB/c substrains. Of 13 substrains studied, BALB/cJ mice consistently exhibit greater resistance to disease induction. Such resistance is associated with a single recessive genotypic difference in an immunoregulatory locus which is unlinked to any of the known alleles distinguishing the BALB/cJ substrain. In this study, gene complementation protocols were used to study the genetics of susceptibility and resistance to EAO. The results indicate that resistance in BALB/cJ mice is not due to a mutation in theH-2D ^d linked gene which governs the phenotypic expression of autoimmune orchitis. The mechanistic basis for disease resistance was examined using reciprocal bone marrow radiation chimeras generated between the disease-susceptible BALB/ cByJ (ByJ) substrain and BALB/cJ (Jax) mice. All constructs, including Jax - Jax and Jax - ByJ, developed severe EAO following inoculation with mouse testicular homogenate (MTH) and adjuvants whereas control chimeras immunized with adjuvants alone did not. These results suggest that an active immunoregulatory mechanism rather than a passive one, such as the lack of T cells and/or B cells with receptors for the aspermatogenic autoantigens relevant in the induction of EAO, is responsible for disease resistance in BALB/cJ mice. The role of immunoregulatory cells was examined by pretreating BALB/cJ mice with either cyclophosphamide (20 mg/kg) or low-dose whole body or total lymphoid irradiation (350 rads) 2 days prior to inoculation. BALB/cJ mice immunized with MTH plus adjuvants generate immunoregulatory spleen cells (SpCs) that, when transferred to naive BALB/cByJ recipients, significantly reduce the severity of autoimmune orchitis observed during actively induced EAO. Treatment of such cells with either cytotoxic monoclonal anti-Thy-1.2 or anti-CD4 plus C' before transfer abrogates the ability of BALB/cJ spleen cells to inhibit disease. In contrast, neither SpCs from adjuvantimmunized BALB/cJ nor MTH plus adjuvant-primed BALB/cByJ donors significantly influenced the severity of disease observed in recipients. Taken together, these results suggest that genetically controlled resistance to EAO in BALB/cJ mice is associated with a mutation in an immunoregulatory locus whose effects appear to be mediated through a cyclophosphamide and low-dose radiation-sensitive CD4⁺ T-cell population.     

Induction of apoptosis by Sindbis virus occurs at cell entry and does not require virus replication

Sindbis virus (SV) is an alphavirus that causes encephalitis in mice and can lead to the apoptotic death of infected cells. To determine the step in virus replication during which apoptosis is triggered, we used UV-inactivated SV, chemicals that block virus fusion or protein synthesis, and cells that do and do not express heparan sulfate, the initial binding molecule for SV infection of many cells. In initial experiments, UV-inactivated neuroadapted SV (NSV) induced apoptosis in Chinese hamster ovary (CHO) cells lacking heparan sulfate in the presence of cycloheximide. When fusion of prebound UV-inactivated NSV was rapidly induced at the plasma membrane by exposure to acidic pH, apoptosis was induced in CHO cells with or without heparan sulfate in the presence or absence of cycloheximide in a virus dose-dependent manner. In N18 neuroblastoma cells, the relative virulence of the virus strain was an important determinant of apoptosis induced by UV-inactivated SV. Treatment of N18 cells with monensin to prevent endosomal acidification an hour before, but not 2 h after, exposure to live NSV blocked the induction of cell death, as did treatment with NH(4)Cl or bafilomycin A1. These studies indicate that SV can induce apoptosis at the time of fusion with the cell membrane and that virus replication is not required.     

Plasmodium chabaudi chabaudi: B-1 cell expansion correlates with semiresistance in BALB/cJ mice

The largest obstacle impeding the development of an effective malaria vaccine is the incomplete understanding of how the immune response is regulated during infection. B-1a cells, a poorly understood subcategory of B lymphocytes, produce nonpathologic autoantibodies of low affinity which have been shown to have distinct immunoregulatory capabilities. What the exact activity of B-1a cells are during the course of malaria has yet to be determined. By use of flow cytometry, it was observed that B-1a cells significantly expand by day 3 postinfection in the spleen and peritoneum of Plasmodium chabaudi chabaudi semiresistant BALB/cJ mice, but not until day 8 postinfection in the spleen of P. chabaudi chabaudi fully susceptible BALB/cByJ mice. The activation of B-1a cells was also demonstrated by the measurement of natural autoantibody IgM production from the serum and cultured peritoneal B-1a cells. Infected semiresistant BALB/cJ mice generated higher levels of anti-ssDNA IgM antibodies than infected fully susceptible BALB/cByJ mice. The preliminary data presented here suggest a possible roll of B-1 cells in contributing to the successful survival of murine malarial infection.     

Influence of the preimplantation-embryo-development (ped) gene on mouse blastocyst differentiation

Mouse preimplantation embryonic cleavage rate is dependent upon the presence or absence of the Preimplantation-embryo-development (Ped) gene; which is linked to the Qa-2 subregion of the H-2 complex. Expression of Qa-2 antigens by fast developing mouse embryos correlates with Ped gene pheno-type: Qa-2(a). It is not known if the Ped gene (Qa-2(a)) participates in cell differentiation in the preimplantation mouse blastocyst. Therefore, the study objective was to determine the differentiation of cells to the inner cell mass (ICM) and trophectoderm (TE) in Qa-2(a) positive (Ped +) and Qa-2(a) negative (Ped -) mouse blastocysts. One-cell stage embryos were recovered from the excised oviducts of PMSG (5 IU) and hCG (5 IU) primed virgin female (3-4 weeks) BALB/cByJ (Qa-2(a): Ped -) and BALB/cJ (Qa-2(a): Ped +) mice mated to fertile males (12+ weeks). Embryos were collected, 14 hr after hCG, and cultured in modified alpha-MEM, to the hatched blastocyst stage in an atmosphere of 5% CO2 in air, 95% relative humidity at 37 degrees C. Cell differentiation was determined by differential staining (bis-benzimide and propidium iodide) and fluorescence microscopy. Data were analyzed by Students t-test. There was no significant difference in total cell number between BALB/cJ (mean 139) and BALB/cByJ (mean 143) embryos. A significant difference (p < 0.001) was found in the number of cells differentiating to the ICM between BALB/cJ (mean 59.0) and BALB/cByJ (mean 29.0) mouse embryos. The number of cells differentiating to the TE, between BALB/cJ (mean 80.0) and BALB/cByJ (mean 114) embryos, approached significance (p = 0.062). The results suggest that the Ped gene (Qa-2(a)) may have an influential role in preimplantation blastocyst cell differentiation. Additional studies are warranted to further elucidate the role of the Ped gene in preimplantation embryo development and blastocyst formation.     

Phenotypic instability between the near isogenic substrains BALB/cJ and BALB/cByJ

Closely related substrains of inbred mice often show phenotypic differences that are presumed to be caused by recent mutations. The substrains BALB/cJ and BALB/cByJ, which were separated in 1935, have been reported to show numerous highly significant behavioral and morphological differences. In an effort to identify some of the causal mutations, we phenotyped BALB/cJ and BALB/cByJ mice as well as their F1, F2, and N2 progeny for behavioral and morphological phenotypes. We also generated whole-genome sequence data for both inbred strains (~3.5× coverage) with the intention of identifying polymorphic markers to be used for linkage analysis. We observed significant differences in body weight, the weight of the heart, liver, spleen and brain, and corpus callosum length between the two substrains. We also observed that BALB/cJ animals showed greater anxiety-like behavior in the open field test, less depression-like behavior in the tail suspension test, and reduced aggression compared to BALB/cByJ mice. Some but not all of these physiological and behavioral results were inconsistent with prior publications. These inconsistencies led us to suspect that the differences were due to, or modified by, non-genetic factors. Thus, we did not perform linkage analysis. We provide a comprehensive summary of the prior literature about phenotypic differences between these substrains as well as our current findings. We conclude that many differences between these strains are unstable and therefore ill-suited to linkage analysis; the source of this instability is unclear. We discuss the broader implications of these observations for the design of future studies.     

Responses of mice susceptible or resistant to lethal infection with mouse hepatitis virus, strain JHM, after exposure by a natural route

CF1 mice were resistant and BALB/cByJ mice were susceptible to the lethal effects of MHV-JHM infection after intranasal inoculation. Virus was recovered rarely from tissues of CF1 mice. In contrast, MHV-JHM was pantropic in BALB/cByJ mice. The peak systemic interferon response of Balb/cByJ mice occurred 30 hours later than that of CF1 mice. Exogenously administered interferon resulted in partial protection of Balb/cByJ mice challenged with MHV-JHM. Prior immunization of susceptible mice with MHV-JHM protected against challenge with homologous or heterologous (MHV-3) virus.     

A new mouse model reveals a critical role for host innate immunity in resistance to Rift Valley fever

Rift Valley fever (RVF) is an arthropod-borne viral disease repeatedly reported in many African countries and, more recently, in Saudi Arabia and Yemen. RVF virus (RVFV) primarily infects domesticated ruminants, resulting in miscarriage in pregnant females and death for newborns and young animals. It also has the ability to infect humans, causing a feverish syndrome, meningoencephalitis, or hemorrhagic fever. The various outcomes of RVFV infection in animals and humans argue for the existence of host genetic determinants controlling the disease. We investigated the susceptibility of inbred mouse strains to infection with the virulent RVFV ZH548 strain. Compared with classical BALB/cByJ mice, wild-derived Mus m. musculus MBT/Pas mice exhibited earlier and greater viremia and died sooner, a result in sharp contrast with their resistance to infection with West Nile virus and influenza A. Infection of mouse embryonic fibroblasts (MEFs) from MBT/Pas mice with RVFV also resulted in higher viral production. Microarray and quantitative RT-PCR experiments showed that BALB/cByJ MEFs displayed a significant activation of the type I IFN pathway. In contrast, MBT/Pas MEFs elicited a delayed and partial type I IFN response to RVFV infection. RNA interference-mediated inhibition of genes that were not induced by RVFV in MBT/Pas MEFs increased viral production in BALB/cByJ MEFs, thus demonstrating their functional importance in limiting viral replication. We conclude that the failure of MBT/Pas murine strain to induce, in due course, a complete innate immune response is instrumental in the selective susceptibility to RVF.     

Molecular analysis of neurovirulent strains of Sindbis virus that evolve during persistent infection of scid mice.

To understand the role of tissue-specific adaptation and antibody-induced selectional pressures in the evolution of neurovirulent viruses, we analyzed three strains of Sindbis virus isolated from the brains of persistently infected scid mice and four strains of Sindbis virus isolated from the brains of scid mice with viral reactivation following immune serum treatment. For each viral isolate, we tested neurovirulence in weanling BALB/c mice and sequenced regions of the E2 and E1 envelope glycoprotein genes that are known to contain important determinants of Sindbis virus neurovirulence. One strain isolated from a persistently infected scid mouse and two strains isolated from scid mice with viral reactivation were neurovirulent, resulting in mortality in 80 to 100% of weanling BALB/c mice. All three neurovirulent strains contained an A-->U change at nucleotide 8795, which predicts a Gln-->His substitution at E2 amino acid position 55. No nucleotide changes were detected in the other sequenced regions of the E2 and E1 envelope glycoprotein genes or in the avirulent isolates. Our findings indicate that tissue-specific adaptations, rather than antibody-induced selectional pressures, are a critical determinant of the evolution of neurovirulent strains of Sindbis virus and provide evidence that E2 His-55 is an important neuroadaptive mutation that confers neurovirulence properties on Sindbis virus.     

Molecular basis of Sindbis virus neurovirulence in mice.

We examined a variety of strains of Sindbis virus for the genetic changes responsible for differences in neurovirulence in mice. SV1A (a low passage of the AR339 strain of Sindbis virus), a neuroadapted Sindbis virus (NSV), and two laboratory strains of Sindbis virus (HRSP and Toto1101) were examined. NSV causes severe encephalomyelitis with hind-limb paralysis and high mortality after intracerebral inoculation in weanling mice. In contrast, SV1A causes only mild, nonfatal disease in weanling mice; however, in suckling mice, SV1A causes a fatal encephalomyelitis after either intracerebral or subcutaneous inoculation. The two laboratory strains used have a greatly reduced neurovirulence for suckling mice and are avirulent for weanling mice. The nucleotide sequences and encoded amino acid sequences of the structural glycoproteins of these four strains were compared. Hybrid genomes were constructed by replacing restriction fragments in a full-length cDNA clone of Sindbis virus, from which infectious RNA can be transcribed in vitro, with fragments from cDNA clones of the various strains. These recombinant viruses allowed us to test the importance of each amino acid difference between the various strains for neurovirulence in weanling and suckling mice. Glycoproteins E2 and E1 were of paramount importance for neurovirulence in adult mice. Recombinant viruses containing the nonstructural protein region and the capsid protein region from an avirulent strain and the E1 and E2 glycoprotein regions from NSV were virulent, although they were less virulent than NSV. Furthermore, changes in either E2 (His-55 in NSV to Gln in SV1A) or E1 (Ala-72 in NSV to Val in SV1A and Asp-313 in NSV to Gly in SV1A) reduced virulence. For virulence in suckling mice, we found that a number of changes in E2 and E1 can lead to decreased virulence and that in fact, a gradient of virulence exists.     

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.     

Streptobacillus moniliformis epizootic in barrier-maintained C57BL/6J mice and susceptibility to infection of different strains of mice

We report a Streptobacillus moniliformis epizootic in barrier-maintained SPF mice. Although various inbred and F1 hybrid strains of mice have been kept in this animal facility, only C57BL/6J Han [corrected] mice showed clinical signs of disease. During the course of the epizootic, 825 breeding animals (approximately 36% of the breeders) died or had to be killed because of severe clinical signs. Although sequential treatment with ampicillin and chlortetracycline gave good therapeutic results, the animal facility was vacated in order to exclude any risk of cross-contamination of the other rodent colonies in our institute. The source and route of transmission of S. moniliformis could not be elucidated. To investigate strain dependent differences experimental infection of different strains of mice with our S. moniliformis isolate was performed. After oral infection only C57BL/6J showed the typical signs of a cervical lymphadenitis and gave an immunological response. BALB/cJ, C3H/He, DBA/2J, CB6F1 and B6D2F1 mice were not affected except in two cases of DBA/2J and B6D2F1 mice where seroconversion was observed. After intravenous infection of C57BL/6J, DBA/2J [corrected] and BALB/cJ all animals showed positive titers in the indirect immunofluorescence test (IIF). One hundred percent of the C57BL/6J, forty percent of the DBA/2J, and none of the BALB/cJ mice developed severe symptoms. The results demonstrate that the susceptibility to streptobacillosis is predominantly influenced by genetic factors.     

The immune response to mouse hepatitis virus: expression of monocyte procoagulant activity and plasminogen activator during infection in vivo

After infection with 10(3) plaque-forming units of mouse hepatitis virus strain 3 (MHV-3) in vivo, peripheral blood mononuclear cells and splenic cells expressed procoagulant activity (PCA) in a pattern directly correlating with susceptibility to disease. Mononuclear cells from BALB/cJ mice, a strain which is fully susceptible to MHV-3, expressed a greater than 500-fold increase in PCA. PCA was first detected within 12 hr of infection; prior to histologic evidence of disease and viral replication, it reached maximal levels 48 hr post-infection (p.i.) and persisted until the death of the animals 5 to 7 days p.i. Mononuclear cells from C3HeB/FeJ mice expressed a significant but lesser titer of PCA, with elevated PCA persisting throughout the chronically infected state until death of the animals 4 to 6 mo p.i. Basal levels of PCA were detected in mononuclear cells from fully resistant A/J mice despite the presence of large amounts of virus in livers, spleens, and sera from these animals. When mononuclear cells expressing high PCA were subfractionated, monocytes were found to be the cellular source of greater than 96% of the PCA activity. Increased plasminogen activator activity was found in monocytes from resistant A/J mice at the time when PCA was markedly elevated in BALB/cJ and C3HeB/FeJ mice. This activity persisted for 5 to 7 days p.i., but was undetectable 10 days p.i. at a time when the mice had cleared the virus from their blood streams. These observations suggest that monocyte PCA may be important in the pathogenesis of MHV-3 disease, whereas the production of monocyte plasminogen activators may contribute to resistance of A/J mice to MHV-3-induced liver disease.     

Lack of B cell leakiness in BALB/cA-nu, scid double mutant mice.

BALB/cA mice homozygous for both nu and scid mutations (BALB/cA-nu/nu, scid/scid) were developed by mating between BALB/cA-scid and BALB/cA-nu. These mice have greater longevity than C.B-17-scid because no thymic lymphoma occurs in them unlike in the latter. C.B-17-scid is known to show the leaky phenomenon in which a few clones of functional T and B cells develop in aged C.B-17-scid. Unexpectedly, the leaky B cells and T cells were absent or suppressed in BALB/cA-nu, scid mice when cytokine expressions were determined by RT-PCR, lymphocyte phenotypes by flow cytometry and serum immunoglobulin levels by ELISA. These results indicate that B cell leakiness may be induced by leaked T cells. BALB/cA-nu, scid mice may be useful as a recipient in allo- and xeno-transplantation experiments because of the absence of both thymic lymphomas and leakiness, in addition to lack of hair.     

Immunization with nonstructural proteins promotes functional recovery of alphavirus-infected neurons.

The encephalitic alphaviruses are useful models for understanding virus-neuron interactions. A neurovirulent strain of Sindbis virus (NSV) causes fatal paralysis in mice by infecting motor neurons and inducing apoptosis of these nonrenewable cells. Antibodies to the surface glycoproteins suppress virus replication, but other recovery-promoting components of the immune response have not been recognized. We assessed the effect on the outcome of NSV-induced encephalomyelitis of immunization of mice with nonstructural proteins (nsPs) by using recombinant vaccinia viruses. Mice immunized with vaccinia virus expressing nsPs and challenged with NSV initially developed paralysis similar to unimmunized mice but then recovered neurologic function. Mice preimmunized with vaccinia virus expressing structural proteins were completely protected from paralysis. Mice immunized with vaccinia virus alone showed paralysis with little evidence of recovery. Vaccinia virus expressing only nsP2 was as effective as vaccinia virus expressing all the nsPs. Protection provided by immunity to nsPs was not associated with a reduction in virus replication or with improved antibody responses to structural proteins. Protection could not be passively transferred with nsP immune serum. The depletion of T cells at the time of NSV infection decreased protection. The data show that antiviral immune responses can improve the ability of neurons to survive infection and to recover function without altering virus replication.     

Visual detection, pattern discrimination and visual acuity in 14 strains of mice

Based on the procedure of Prusky et al. (2000, Vision Research, 40, 2201-2209), we used a computer-based, two-alternative swim task to evaluate visual detection, pattern discrimination and visual acuity in 14 strains of mice from priority groups A and B of the JAX phenome project (129S1/SvImJ, A/J, AKR/J, BALB/cByJ, BALB/cJ, C3H/HeJ, C57BL/6J, CAST/Ei, DBA/2J, FVB/NJ, MOLF/Ei, SJL/J, SM/J and SPRET/Ei). Each mouse was tested for eight trials/day for 8 days on each of the three tests. There was a significant strain difference in visual ability in all three tests. Mice with reported normal vision (129S1/SvImJ, C57BL/6J and DBA/2J) and one albino strain (AKR/J) performed very well in these tasks. The other albino strains (A/J, BALB/cByJ and BALB/cJ) took longer to learn the tasks than mice with normal vision and did not reach the criterion of 70% correct. Mice with retinal degeneration (C3H/HeJ, FVB/NJ, MOLF/Ei and SJL/J) performed only at chance levels as did the three strains with unknown visual abilities (CAST/Ei, SM/J and SPRET/Ei). Because many behavioral tasks for rodents rely on visual cues, we suggest that the visual abilities of mice should be evaluated before they are tested in commonly used visuo-spatial learning and memory tasks.