Validation of an Autoclave Procedure for Sterilization of Mouse (Mus musculus) Carcasses.

The sterilization of potentially infectious animal carcasses is an important biologic safety issue in animal facilities operating as infection or quarantine barriers. However, the literature lacks a validated protocol. Here we describe the validation of an autoclave program suitable for daily use in a small rodent biocontainment unit. We evaluated several procedures for processing mouse carcasses in a standard autoclave. Heat sensors and biologic indicators were implanted inside the peritoneal cavity of dead mice, which were loaded at various densities into IVC cages or metal boxes. Heat sensors revealed broad differences in temperature inside carcasses compared with the autoclave chamber. Achieving the appropriate sterilization temperature was considerably prolonged in carcasses compared with typical laboratory waste material. We show that for 5 cadavers placed well separated inside an IVC, a modified program for mouse cage sterilization using 134 °C for 15 min is suitable. To sterilize approximately 1 kg of carcasses in autoclavable boxes, a period of 6 h is required to reach an effective temperature of 121 °C for 60 min at the center of the waste by using an autoclave program for liquids. In conclusion, we here validated 2 protocols for the sterilization of potentially infectious mouse carcasses, to ensure the application of efficacious procedures.

A comparative phenotypic and genomic analysis of C57BL/6J and C57BL/6N mouse strains.

BACKGROUND: The mouse inbred line C57BL/6J is widely used in mouse genetics and its genome has been incorporated into many genetic reference populations. More recently large initiatives such as the International Knockout Mouse Consortium (IKMC) are using the C57BL/6N mouse strain to generate null alleles for all mouse genes. Hence both strains are now widely used in mouse genetics studies. Here we perform a comprehensive genomic and phenotypic analysis of the two strains to identify differences that may influence their underlying genetic mechanisms. RESULTS: We undertake genome sequence comparisons of C57BL/6J and C57BL/6N to identify SNPs, indels and structural variants, with a focus on identifying all coding variants. We annotate 34 SNPs and 2 indels that distinguish C57BL/6J and C57BL/6N coding sequences, as well as 15 structural variants that overlap a gene. In parallel we assess the comparative phenotypes of the two inbred lines utilizing the EMPReSSslim phenotyping pipeline, a broad based assessment encompassing diverse biological systems. We perform additional secondary phenotyping assessments to explore other phenotype domains and to elaborate phenotype differences identified in the primary assessment. We uncover significant phenotypic differences between the two lines, replicated across multiple centers, in a number of physiological, biochemical and behavioral systems. CONCLUSIONS: Comparison of C57BL/6J and C57BL/6N demonstrates a range of phenotypic differences that have the potential to impact upon penetrance and expressivity of mutational effects in these strains. Moreover, the sequence variants we identify provide a set of candidate genes for the phenotypic differences observed between the two strains.

Influence of internalin A murinisation on host resistance to orally acquired listeriosis in mice.

BACKGROUND: The bacterial surface protein internalin (InlA) is a major virulence factor of the food-born pathogen Listeria monocytogenes. It plays a critical role in the bacteria crossing the host intestinal barrier by a species-specific interaction with the cell adhesion molecule E-cadherin. In mice, the interaction of InlA with murine E-cadherin is impaired due to sequence-specific binding incompatibilities. We have previously used the approach of 'murinisation' to establish an oral listeriosis infection model in mice by exchanging two amino acid residues in InlA. This dramatically increases binding to mouse E-cadherin. In the present study, we have used bioluminescent murinised and non-murinised Listeria strains to examine the spatiotemporal dissemination of Listeria in four diverse mouse genetic backgrounds after oral inoculation. RESULTS: The murinised Listeria monocytogenes strain showed enhanced invasiveness and induced more severe infections in all four investigated mouse inbred strains compared to the non-murinised Listeria strain. We identified C57BL/6J mice as being most resistant to orally acquired listeriosis whereas C3HeB/FeJ, A/J and BALB/cJ mice were found to be most susceptible to infection. This was reflected in faster kinetics of Listeria dissemination, higher bacterial loads in internal organs, and elevated serum levels of IL-6, IFN-γ, TNF-α and CCL2 in the susceptible strains as compared to the resistant C57BL/6J strain. Importantly, murinisation of InlA did not cause enhanced invasion of Listeria monocytogenes into the brain. CONCLUSION: Murinised Listeria are able to efficiently cross the intestinal barrier in mice from diverse genetic backgrounds. However, expression of murinized InlA does not enhance listerial brain invasion suggesting that crossing of the blood brain barrier and crossing of the intestinal epithelium are achieved by Listeria monocytogenes through different molecular mechanisms.

TLR7 contributes to the rapid progression but not to the overall fatal outcome of secondary pneumococcal disease following influenza A virus infection.

Increased risk for bacterial superinfections substantially contributes to the mortality caused by influenza A virus (IAV) epidemics. While the mechanistic basis for this lethal synergism is still insufficiently understood, immune modulation through the viral infection has been shown to be involved. Since the pattern-recognition receptor (PRR) toll-like receptor 7 (TLR7) is a major sensor for the viral genome, we studied how IAV recognition by TLR7 influences the development of secondary pneumococcal infection. In a mouse model of IAV, TLR7-deficient hosts induced a potent antiviral response and showed unchanged survival. In secondary pneumococcal infection during acute influenza, TLR7ko mice showed a fatal outcome similar to wild-type (WT) hosts, despite significantly delayed disease progression. Also, when bacterial superinfection occurred after virus clearance, WT and TLR7-deficient hosts showed similar mortality, even though we found the phagocytic activity of alveolar macrophages isolated from IAV-pre-infected hosts to be enhanced in TLR7ko over WT mice. Thus, we show that a virus-sensing PRR modulates the progression of secondary pneumococcal infection following IAV. However, the fatal overall outcome in WT as well as TLR7ko hosts suggests that processes distinct from TLR7-triggering override the contribution of this single PRR.

Schistosoma co-infection protects against brain pathology but does not prevent severe disease and death in a murine model of cerebral malaria.

Co-infections of helminths and malaria parasites are common in human populations in most endemic areas. It has been suggested that concomitant helminth infections inhibit the control of malaria parasitemia but down-modulate severe malarial disease. We tested this hypothesis using a murine co-infection model of schistosomiasis and cerebral malaria. C57BL/6 mice were infected with Schistosoma mansoni and 8-9 weeks later, when Schistosoma infection was patent, mice were co-infected with Plasmodium berghei ANKA strain. We found that a concomitant Schistosoma infection increased parasitemia at the beginning of the P. berghei infection. It did not protect against P. berghei-induced weight loss and hypothermia, and P. berghei-mono-infected as well as S. mansoni-P. berghei-co-infected animals showed a high case fatality between days 6 and 8 of malarial infection. However, co-infection significantly reduced P. berghei-induced brain pathology. Over 40% of the S. mansoni-P. berghei-co-infected animals that died during this period were completely protected against haemorrhaging, plugging of blood vessels and infiltration, indicating that mortality in these animals was not related to cerebral disease. Schistosoma mansoni-P. berghei-co-infected mice had elevated plasma concentrations of IL-5 and IL-13 and on day 6 lower levels of IFN-γ, IL-10, monocyte chemoattractant protein-1 (MCP-1) and monokine induced by IFN-γ (MIG) than P. berghei-mono-infected mice. We conclude that in P. berghei infections, disease and early death are caused by distinct pathogenic mechanisms, which develop in parallel and are differentially influenced by the immune response to S. mansoni. This might explain why, in co-infected mice, death could be induced in the absence of brain pathology.

Microfilariae of the filarial nematode Litomosoides sigmodontis exacerbate the course of lipopolysaccharide-induced sepsis in mice.

Helminths facilitate their own survival by actively modulating the immune systems of their hosts. We investigated the impacts that different life cycle stages of the rodent filaria Litomosoides sigmodontis have on the inflammatory responses of mice injected with sublethal doses of lipopolysaccharide (LPS). Mice infected with female adult worms from prepatent infections, worms which have not yet started to release microfilariae, developed lower levels of proinflammatory cytokines in the peripheral blood after LPS challenge than sham-treated controls, demonstrating that female adult worms can mitigate the innate immune response. The presence of microfilariae in mice, however, through either direct injection or implantation of microfilaria-releasing adult female worms, turned the LPS challenge fatal. This lethal outcome was characterized by increased plasma levels of gamma interferon (IFN-gamma), tumor necrosis factor alpha (TNF-alpha), interleukin 12 (IL-12), and IL-6, greater numbers of macrophages and granulocytes in the peripheral blood, and decreased body temperatures in microfilaria-infected mice. Microfilaria-infected mice deficient in IFN-gamma receptor and TNF receptor 1 had increased survival rates after LPS challenge compared to immune-competent mice, suggesting that microfilariae worsen LPS-induced sepsis through actions of IFN-gamma and TNF-alpha. In summary, we have demonstrated that infection of mice with L. sigmodontis female adult worms from prepatent infections protects mice injected with LPS whereas microfilariae worsen LPS-induced sepsis through the induction of proinflammatory cytokines and upregulation of granulocytes, NK cells, and monocytes in the peripheral blood.

Extending the host range of Listeria monocytogenes by rational protein design.

In causing disease, pathogens outmaneuver host defenses through a dedicated arsenal of virulence determinants that specifically bind or modify individual host molecules. This dedication limits the intruder to a defined range of hosts. Newly emerging diseases mostly involve existing pathogens whose arsenal has been altered to allow them to infect previously inaccessible hosts. We have emulated this chance occurrence by extending the host range accessible to the human pathogen Listeria monocytogenes by the intestinal route to include the mouse. Analyzing the recognition complex of the listerial invasion protein InlA and its human receptor E-cadherin, we postulated and verified amino acid substitutions in InlA to increase its affinity for E-cadherin. Two single substitutions increase binding affinity by four orders of magnitude and extend binding specificity to include formerly incompatible murine E-cadherin. By rationally adapting a single protein, we thus create a versatile murine model of human listeriosis.

Vitamin D receptor signaling contributes to susceptibility to infection with Leishmania major.

We have previously reported that 1alpha,25-dihydroxyvitamin D3 (1alpha,25(OH)2D3) can selectively suppress key functions of interferon-gamma (IFN-gamma) activated macrophages. To further explore this mechanism for its relevance in vivo, we investigated an infection model that crucially depends on the function of IFN-gamma activated macrophages, the infection with the intracellular protozoan Leishmania major. 1Alpha,25(OH)2D3 treatment of L. major infected macrophages demonstrated a vitamin D receptor (Vdr) dependent inhibition of macrophage killing activity. Further analysis showed that this was a result of decreased production of nitric oxide by 1alpha,25(OH)2D3-treated macrophages due to Vdr-dependent up-regulation of arginase 1 expression, which overrides NO production by Nos2. When analyzing the course of infection in vivo, we found that Vdr-knockout (Vdr-KO) mice were more resistant to L. major infection than their wild-type littermates. This result is in agreement with an inhibitory influence of 1alpha,25(OH)2D3 on the macrophage mediated host defense. Further investigation showed that Vdr-KO mice developed an unaltered T helper cell type 1 (Th1) response on infection as indicated by normal production of IFN-gamma by CD4+ and CD8+ T cells. Therefore, we propose that the absence of 1alpha,25(OH)2D3-mediated inhibition of macrophage microbicidal activity in Vdr-KO mice results in increased resistance to Leishmania infection.

The wild-derived inbred mouse strain SPRET/Ei is resistant to LPS and defective in IFN-beta production.

Although activation of Toll-like receptor 4 (TLR4)-positive cells is essential for eliminating Gram-negative bacteria, overactivation of these cells by the TLR4 ligand LPS initiates a systemic inflammatory reaction and shock. Here we demonstrate that SPRET/Ei mice, derived from Mus spretus, exhibit a dominant resistance against LPS-induced lethality. This resistance is mediated by bone marrow-derived cells. Macrophages from these mice exhibit normal signaling and gene expression responses that depend on the myeloid differentiation factor 88 adaptor protein, but they are impaired in IFN-beta production. The defect appears to be specific for IFN-beta, although the SPRET/Ei IFN-beta promoter is normal. In vivo IFN-beta induction by LPS or influenza virus is very low in SPRET/Ei mice, but IFN-beta-treatment restores the sensitivity to LPS, and IFN type 1 receptor-deficient mice are also resistant to LPS. Because of the defective induction of IFN-beta, these mice are completely resistant to Listeria monocytogenes and highly sensitive to Leishmania major infection. Stimulation of SPRET/Ei macrophages leads to rapid down-regulation of IFN type 1 receptor mRNA expression, which is reflected in poor induction of IFN-beta-dependent genes. This finding indicates that the resistance of SPRET/Ei mice to LPS is due to disruption of a positive-feedback loop that amplifies IFN-beta production. In contrast to TLR4-deficient mice, SPRET/Ei mice resist both LPS and sepsis induced with Klebsiella pneumoniae.

Innate immune responses in NF-kappaB-repressing factor-deficient mice.

NF-kappaB-repressing factor (NRF) is a transcriptional silencer protein that specifically counteracts the basal activity of several NF-kappaB-dependent promoters by direct binding to specific neighboring DNA sequences. In cell culture experiments, the reduction of NRF mRNA leads to a derepression of beta interferon, interleukin-8, and inducible nitric oxide synthase transcription. The X chromosome-located single-copy NRF gene is ubiquitously expressed and encodes a protein of 690 amino acids. The N-terminal part contains a nuclear localization signal, the DNA-binding domain, and the NF-kappaB-repressing domain, while the C-terminal part is responsible for double-stranded RNA binding and nucleolar localization. To study the function of NRF in a systemic context, transgenic mice lacking the NRF gene were created. Against predictions from in vitro experiments, mice with a deletion of the NRF gene are viable and have a phenotype that is indistinguishable from wild-type mice, even after challenge with different pathogens. The data hint towards an unexpected functional redundancy of NRF.

Sex-dependent susceptibility to Listeria monocytogenes infection is mediated by differential interleukin-10 production.

It is well documented that sex-dependent factors affect susceptibility to infection, with most mouse models demonstrating higher resistance in females. We made the unexpected observation that infection with the intracellular bacterium Listeria monocytogenes showed an opposite pattern in several commonly used inbred mouse strains: female C57BL/6J, BALB/c, C3H/HeN, and CBA/J mice were significantly more susceptible to Listeria infection. The pronounced sensitivity of females to Listeria, which was revealed by significantly higher lethality rates, correlated also with increased bacterial numbers in organ tissues (spleen and liver) and several immunological changes in peripheral blood samples. Surprisingly, increased severity of infection in females was associated with elevated interleukin-10 (IL-10) levels in plasma. Experiments using Il10 knockout mice, for which no differences between the susceptibilities of males and females to Listeria infection could be detected, confirmed the important role of this immunosuppressive cytokine for the outcome of disease. Our findings are likely to have clinical relevance, since similar sex differences with regard to infection with Listeria monocytogenes and other intracellular pathogens have been reported for humans.

Evaluation of Cx26/GJB2 in German hearing impaired persons: mutation spectrum and detection of disequilibrium between M34T (c.101T>C) and -493del10.

Mutations in the connexin 26 gene (GJB2) are responsible for the major part of nonsyndromic autosomal recessive or apparently sporadic prelingual deafness in Caucasians (DFNB1). We screened 228 German hearing-impaired persons for mutations in the GJB2 gene by sequence analysis. Homozygous or compound heterozygous GJB2 mutations were detected in 38/228 (16.7%) of hearing impaired persons. The most frequently occurring mutation was the c.35delG mutation, which was found in 71.1% of the mutated alleles. The next frequent mutation detected in the group of hearing impaired persons was the c.101T>C mutation (9/76 alleles; 11.8%). One new mutation, c.567delA, was observed. We further studied the presence of a 10bp deletion in the 5' UTR of the GJB2 gene (c.-493del10) which was assumed to occur together with the c.101T>C mutation. Ten out of thirteen patients (76.9%) were found to be carriers of both the c.101T>C mutation and the 10bp variant and in 7/14 alleles a linkage disequilibrium between c.101T>C and the 10bp deletion was proven. In 4/14 alleles the linkage was ruled out and for the remaining 3 cases the phase determination was not possible. Seventy one controls were screened for the prevalence of Cx26 mutations and for the c.-493del10 variant. Heterozygosity frequency in the control group was for c.35delG 4.2%, for c.101T>C 1.4% and for c.-493del10 it was 5.6%.