Experimental Meningococcal Sepsis in Congenic Transgenic Mice Expressing Human Transferrin

Severe meningococcal sepsis is still of high morbidity and mortality. Its management may be improved by an experimental model allowing better understanding of its pathophysiology. We developed an animal model of meningococcal sepsis in transgenic BALB/c mice expressing human transferrin. We studied experimental meningococcal sepsis in congenic transgenic BALB/c mice expressing human transferrin by transcriptional profiling using microarray analysis of blood and brain samples. Genes encoding acute phase proteins, chemokines and cytokines constituted the largest strongly regulated groups. Dynamic bioluminescence imaging further showed high blood bacterial loads that were further enhanced after a primary viral infection by influenza A virus. Moreover, IL-1 receptor–associated kinase–3 (IRAK-3) was induced in infected mice. IRAK-3 is a negative regulator of Toll-dependant signaling and its induction may impair innate immunity and hence result in an immunocompromised state allowing bacterial survival and systemic spread during sepsis. This new approach should enable detailed analysis of the pathophysiology of meningococcal sepsis and its relationships with flu infection

Interspecific Recombinant Congenic Strains Between C57BL/6 and Mice of the Mus spretus Species: A Powerful Tool to Dissect Genetic Control of Complex Traits

Complex traits are under the genetic control of multiple genes, often with weak effects and strong epistatic interactions. We developed two new collections of mouse strains to improve genetic dissection of complex traits. They are derived from several backcrosses of the Mus spretus SEG/Pas or STF/Pas strains on the C57BL/6J background. Each of the 55 interspecific recombinant congenic strains (IRCSs) carries up to eight SEG/Pas chromosomal segments with an average size of 11.7 Mb, totalizing 1.37% of the genome. The complete series covers 39.7% of the SEG/Pas genome. As a complementary resource, six partial or complete interspecific consomic strains were developed and increased genome coverage to 45.6%. To evaluate the usefulness of these strains for QTL mapping, 16 IRCSs were compared with C57BL/6J for seven hematological parameters. Strain 66H, which carries three SEG/Pas chromosomal segments, had lower red blood cell volume and higher platelet count than C57BL/6J. Each chromosomal segment was isolated in a congenic strain to evaluate individual effects. Congenic strains were combined to assess epistasis. Our data show that both traits were controlled by several genes with complex epistatic interactions. IRCSs are therefore useful to unravel QTL with small effects and gene-by-gene interactions

Behavioral effects of a deletion in Kcnn2, the gene encoding the SK2 subunit of small-conductance Ca(2+)-activated K (+) channels.

Small-conductance Ca(2+)-activated potassium (SK) channels are heteromeric complexes of SK alpha-subunits and calmodulin that modulate membrane excitability, are responsible for part of the after-hyperpolarization (AHP) following action potentials, and thus control the firing patterns and excitability of most central neurons. An engineered knockout allele for the SK2 subunit has previously been reported. The hippocampal neurons of these mice lacked the medium latency component of the AHP, but the animals were not described as presenting any overt behavioral phenotype. In this report, we describe a deletion in the 5' region of the Kcnn2 gene encoding the SK2 subunit in the mouse neurological frissonnant (fri) mutant. The frissonnant mutant phenotype is characterized by constant rapid tremor and locomotor instability. It has been suggested, based merely on its phenotype, as a potential model for human Parkinson disease. We used a positional cloning strategy to identify the mutation underlying the frissonnant phenotype. We narrowed the genetic disease interval and identified a 3,441-bp deletion in the Kcnn2 gene, one of the three candidate genes present in the interval. Expression studies showed complete absence of normal Kcnn2 transcripts while some tissue-specific abnormal truncated variants were detected. Intracellular electrophysiological recordings of central vestibular neurons revealed permanent alterations of the AHP and firing behavior that might cause the tremor and associated locomotor deficits. Thus, the fri mutation suggests a new, potentially important physiological role, which had not been described, for the SK2 subunit of small-conductance Ca(2+)-activated potassium channels

Transgenic Mice Expressing Human Transferrin as a Model for Meningococcal Infection▿

The pathogenesis of meningococcal disease is poorly understood due to the lack of a relevant animal model. Moreover, the use of animal models is not optimal as most meningococcal virulence determinants recognize receptors that are specifically expressed in human tissues. One major element of the host specificity is the system of meningococcal iron uptake by transferrin-binding proteins that bind specifically human transferrin but not murine transferrin. We developed a new mouse model for experimental meningococcal infection using transgenic mice expressing human transferrin. Intraperitoneal challenge of transgenic mice induced bacteremia for at least 48 h with an early stage of multiplication, whereas the initial inoculum was rapidly cleared from blood in wild-type mice. Inflammation in the subarachnoidal space with a high influx of polymorphonuclear cells was observed only in transgenic mice. Meningococcal mutants that were unable to use transferrin as a source of iron were rapidly cleared from both wild-type and transgenic mice. Thus, transgenic mice expressing human transferrin may represent an important advance as a new mouse model for in vivo studies of meningococcal virulence and immunogenicity factors

Mus spretus SEG/Pas mice resist virulent Yersinia pestis, under multigenic control

International audienceLaboratory mice are well known to be highly susceptible to virulent strains of Yersinia pestis in experimental models of bubonic plague. We have found that Mus spretus-derived SEG/Pas (SEG) mice are exceptionally resistant to virulent CO92 and 6/69 wild type strains. Upon subcutaneous injection of 10(2) colony-forming units (CFU), 90% of females and 68% of males survived, compared with only an 8% survival rate for both male and female C57BL/6 mice. Furthermore, half of the SEG mice survived a challenge of up to 10(7) CFU. The time required for mortality was similar between B6 and SEG, suggesting that survival is dependent on early rather than late processes. The analysis of 322 backcross mice identified three significant quantitative trait loci (QTLs) on chromosomes 3, 4 and 6, with dominant SEG protective alleles. Each QTL increased the survival rate by approximately 20%. The three QTLs function additively, thereby accounting for 67% of the difference between the parental phenotypes. Mice heterozygous for the three QTLs were just as resistant as SEG mice to Y. pestis challenge. The SEG strain therefore offers an invaluable opportunity to unravel mechanisms and underlying genetic factors of resistance against Y. pestis infection

Emergence of New Virulent Neisseria meningitidis Serogroup C Sequence Type 11 Isolates in France.

International audienceIn France, there have been variations in the incidence of invasive meningococcal infection due to serogroup C isolates. Infection peaks were observed in 1992 and 2003 that involved isolates of phenotypes C:2a:P1.5,2 and/or C:2a:P1.5, which belong to the sequence type 11 (ST-11) clonal complex. We report an emergence of isolates belonging to the ST-11 clonal complex since 2003. These isolates displayed a new phenotype, C:2a:P1.7,1, caused infections that occurred as clusters, and were associated with increased infection severity and high virulence in mice. These isolates may be responsible for a peak in the incidence of serogroup C meningococcal infection in France, for which there is no routine vaccination to date

Early Systemic Bacterial Dissemination and a Rapid Innate Immune Response Characterize Genetic Resistance to Plague of SEG Mice

International audienceBackground. Although laboratory mice are usually highly susceptible to Yersinia pestis, we recently identified a mouse strain (SEG) that exhibited an exceptional capacity to resist bubonic plague and used it to identify immune mechanisms associated with resistance.Methods. The kinetics of infection, circulating blood cells, granulopoiesis, lesions, and cellular populations in the spleen, and cytokine production in various tissues were compared in SEG and susceptible C57BL/6J mice after subcutaneous infection with the virulent Y. pestis CO92.Results. Bacterial invasion occurred early (day 2) but was transient in SEG/Pas mice, whereas in C57BL/6J mice it was delayed but continuous until death. The bacterial load in all organs significantly correlated with the production of 5 cytokines (granulocyte colony-stimulating factor, keratinocyte-derived chemokine (KC), macrophage cationic peptide-1 (MCP-1), interleukin 1a, and interleukin 6) involved in monocyte and neutrophil recruitment. Indeed, higher proportions of these 2 cell types in blood and massive recruitment of F4/801CD11b2 macrophages in the spleen were observed in SEG/Pas mice at an early time point (day 2). Later times after infection (day 4) were characterized in C57BL/6J mice by destructive lesions of the spleen and impaired granulopoiesis.Conclusion. A fast and efficient Y. pestis dissemination in SEG mice may be critical for the triggering of an early and effective innate immune response necessary for surviving plague

Dissemination of <i>N. meningitidis</i> in BALB/c congenic mice that were infected by intraperitoneal injection of 5*10⁶ CFU of <i>N. meningitidis</i> (Nm) strain NM0804 expressing the luciferase.

<p>Mice were then analyzed for bioluminescence at the indicated times. Images depict photographs overlaid with colour representations of luminescence intensity, measured in photons/second and indicated on the scales, where red is most intense and blue is least intense. (Top row) (A) Ventral views of a three transgenic mice expressing human transferrin (hTf/+) and two wild type mice (+/+) at the indicated times. The framed region of the first transgenic mice is shown below for more details of the bioluminescence imaging in the skull. (B) Dorsal view of the skull of one transgenic mouse expressing human transferrin and one wild type mouse. The substrate of firefly luciferase was injected directly into the lateral ventricle after 6 h of bacterial intraperitoneal challenge. (C) The luminescence of the hTf/+ and (+/+) mice from A and D was quantified and expressed as means ± SD from each category at the indicated times by defining specific representative region of interest encompassing the entire animal.(D) Ventral views of a three transgenic mice expressing human transferrin (hTf/+) and two wild type mice (+/+) at the indicated times. Mice were first infected by influenza A virus (IAV) by intranasal inhalation. Mice were then infected after 7 days by <i>N. meningitidis</i> (Nm) strain NM0804 by intraperitoneal injection. The framed region of the first transgenic mice is shown below for more details of the bioluminescence imaging in the skull.</p

Ex-vivo images of organs from mouse infected by influenza A virus (IAV) intranasal inhalation and by Nm at day 7 by intraperitoneal injection.

<p>Mouse was dissected to determine which organs were the sources of bioluminescence. The spleen, liver and brain were hence removed and the mixture containing the substrate of firefly luciferase was added. Dynamic bioluminescence imaging from noninfected (A) or infected organs (B) are shown.</p

Major groups of upregulated genes in blood and brain of infected mice.

*<p>Genes that are also analyzed by RT-PCR.</p>**<p>Log10 of the ratio of intensity of infected/non infected mice after correction for the background.</p