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Mucosal-associated invariant T cells (MAITs) have potent antimicrobial activity and are abundant in humans (5%-10% in blood). Despite strong evolutionary conservation of the invariant TCR-alpha chain and restricting molecule MR1, this population is rare in laboratory mouse strains (approximate to 0.1% in lymphoid organs), and lack of an appropriate mouse model has hampered the study of MAIT biology. Herein, we show that MAITs are 20 times more frequent in clean wild-derived inbred CAST/EiJ mice than in C57BL/6J mice. Increased MAIT frequency was linked to one CAST genetic trait that mapped to the TCR-alpha locus and led to higher usage of the distal V alpha segments, including V alpha 19. We generated a MAIT(hl) congenic strain that was then crossed to a transgenic Rorcgt-GFP reporter strain. Using this tool, we characterized polyclonal mouse MAITs as memory (CD44(+)) CD4(-)CD8(lo/neg) T cells with tissue-homing properties (CCR6*CCR7(-)). Similar to human MAITs, mouse MAITs expressed the cytokine receptors IL-7R, IL-18R alpha, and IL-12R beta and the transcription factors promyelocytic leukemia zinc finger (PLZF) and RAR-related orphan receptory gamma (R0R gamma t). Mouse MAITs produced Th1/2/17 cytokines upon TCR stimulation and recognized a bacterial compound in an MR1-dependent manner. During experimental urinary tract infection, MAITs migrated to the bladder and decreased bacterial load. Our study demonstrates that the MAIT(hi) congenic strain allows phenotypic and functional characterization of naturally occurring mouse MAITs in health and disease.

International audience; We have previously described SEG/Pas as the first mouse inbred strain able to survive subcutaneous injection of virulent Yersinia pestis, the agent of plague, and we identified Yprl1, Yprl2 and Yprl3 as three quantitative trait loci (QTLs) controlling this exceptional phenotype in females from a backcross between SEG/Pas and C57BL/6 strains. We have now developed congenic strains to further characterize the extent and effect of these genomic regions. In this study, we confirm the importance of two of these regions, both in males and females, while the third one may well be a spurious association. We show that no genomic region alone is able to increase the survival of C57BL/6 mice, but that C57BL/6 mice carrying both Yprl2 and Yprl3 exhibit intermediate resistance. Each of these two QTLs contains at least two subregions, which are required to increase survival. Finally, through the analysis of congenic strains in an F1 background, we establish the mode of inheritance of the SEG-derived resistance alleles. Altogether, this study has clarified and enhanced our understanding of the genetic architecture of resistance to plague in SEG/Pas mice.

International audience; 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.

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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.

International audience; The nature and lineage potential, particularly that for B cells, of thymus settling progenitors (TSP) in the adult mouse has been the subject of considerable debate. Lack of B cell potential would suggest pre-thymic, whereas its presence would suggest intra-thymic loss of B cell potential. Using limiting dilution analysis (LDA) in vitro and transfer experiments in vivo, we show that the B cell potential of TSP is critically dependent on mouse age, reaching a maximum of about 1 in 20 cells at birth, decreasing 50-fold in adult mice. Cells with a TSP phenotype can be found in the neonatal blood. Furthermore, using LDA, we show that Notch ligand signaling of TSP results in the loss of B cell potential with a half-life of approximately 12 h. Taken together, these results indicate that loss of B cell potential by TSP is an intra-thymic event and highlight the developmental pressure acting on the immune system to rapidly colonize primary lymphoid organs with functional progenitors. This critical time coincides with birth in the mouse. In the adult mouse, we estimate than only about 5 TSP cells/day would be required to maintain steady-state thymopoiesis.

International audience; The Tmevp3 locus controls the load of Theiler's virus RNA during persistent infection of the mouse central nervous system (CNS). We identified a candidate gene at this locus, Tmevpg1, by using a positional cloning approach. Tmevpg1 and its human ortholog, TMEVPG1, are expressed in the immune system and encode what appears to be a noncoding RNA. They are located in a cluster of cytokine genes that includes the genes for gamma interferon and one or two homolog of interleukin-10. We now report that Tmevpg1 is expressed in CNS-infiltrating immune cells of resistant B10.S mice, but not in those of susceptible SJL/J mice, following inoculation with Theiler's virus. The pattern of expression of Tmevpg1 is the same in B10.S mice and in SJL/J mice congenic for the resistant B10.S haplotype of Tmevp3. Nineteen polymorphisms were identified when the Tmevpg1 genes of B10.S and SJL/J mice were compared. Interestingly, Tmevpg1 is down regulated after in vitro stimulation of murine CD4 or CD8 splenocytes, whereas Ifng is up regulated. Similar patterns of expression of TMEVPG1 and IFNG were observed in human NK cells and CD4 and CD8 T lymphocytes. Therefore, Tmevpg1 is a strong candidate gene for the Tmevp3 locus and may be involved in the control of Ifng gene expression. After intracranial inoculation, the DA strain of Theiler's virus replicates for approximately 2 weeks in neurons of the mouse brain and spinal cord, regardless of the mouse's genetic background. Some genetically resistant mice clear the infection at this stage. Others, which are susceptible to persistence of the infection, remain infected for life (26). However, in this case, the virus does not persist in neurons. Instead, it is found in glial cells of the white matter of the spinal cord. Persistent infection of the white matter induces chronic inflammation and primary demyelination similar to those seen in multiple sclerosis (25). Susceptibility to viral persistence varies greatly among inbred strains of mice. The viral genome load during persistent infection is controlled mainly by the H2D class I gene (4-6, 24). However, the SJL/J strain is the only inbred strain among 16 examined for which the viral genome load is greater than that predicted by its H2 s haplotype (13). Studies of bone marrow chimeras of the SJL/J and B10.S strains, which both bear an H2 s haplotype, showed that susceptibility loci with major effects on persistence are expressed in cells of the immune system (3). Some non-H2 susceptibility loci were mapped by using a backcross and congenic mice between the SJL/J and B10.S strains. Two susceptibility loci, Tmevp2 and Tmevp3, were located on chromosome 10 close to the Ifng locus (8, 12). However , immunological studies indicated that the Ifng gene does not explain the effects of the Tmevp2 or the Tmevp3 locus (30). Instead, the Tmevpg1 gene was recently identified by positional cloning of the Tmevp3 locus. It is located telomeric to a cluster of cytokines, which includes the Ifng and IL-22/Il-Tif genes (36). Tmevpg1 has six exons and appears to encode a noncod-ing RNA. It is expressed at a low level in the spleen and thymus, and occasionally in the liver and kidneys, of B10.S mice but never in the central nervous system (CNS) of these animals. Tmevpg1 has a human ortholog, TMEVPG1, with ho-mologies to the mouse gene only in exon 1 and the region surrounding it. In the present paper, we show that Tmevpg1 is a strong candidate gene for the Tmevp3 locus and analyze its expression in the immune system.

Brucella,the causative agent of brucellosis in animals and humans, can survive and proliferate within macrophages. Macrophages mediate mouse resistance to various pathogens through the expression of theNramp1gene. The role of this gene in the control ofBrucellainfection was investigated. When BALB/c mice (Nramp1s) and C.CB congenic mice (Nramp1r) were infected withBrucella melitensis,the number ofBrucellaorganisms per spleen was significantly larger in the C.CB mice than in the BALB/c mice during the first week postinfection (p.i.). ThisNramp1-linked susceptibility toBrucellawas temporary, since similar numbers ofBrucellawere recovered from the two strains of mice 2 weeks p.i. The effect ofNramp1expression occurred within splenocytes intracellularly infected byBrucella.However, there was no difference between in vitro replication rates ofBrucellain macrophages isolated from the two strains of mice infected in vivo or inNramp1RAW264 transfectants. In mice, infection withBrucellainduced an inflammatory response, resulting in splenomegaly and recruitment of phagocytes in the spleen, which was amplified in C.CB mice. Reverse transcription-PCR (RT-PCR), performed 5 days p.i., showed that inducible nitric oxide synthase, tumor necrosis factor alpha (TNF-α), interleukin-12 p40 (IL-12p40), gamma interferon (IFN-γ), and IL-10 mRNAs were similarly induced in spleens of the two strains. In contrast, the mRNA of KC, a C-X-C chemokine, was induced only in infected C.CB mice at this time. This pattern of mRNA expression was maintained at 14 days p.i., with IFN-γ and IL-12p40 mRNAs being more intensively induced in the infected C.CB mice, but TNF-α mRNA was no longer induced. The higher recruitment of neutrophils observed in the spleens of infected C.CB mice could explain the temporary susceptibility of C.CB mice toB. melitensisinfection. In contrast to infections withSalmonella, Leishmania,andMycobacterium,the expression of theNramp1gene appears to be of limited importance for the natural resistance of mice toBrucella.

International audience; Background: Genetic determinism of cranial morphology in the mouse is still largely unknown, despite the localization of putative QTLs and the identification of genes associated with Mendelian skull malformations. To approach the dissection of this multigenic control, we have used a set of interspecific recombinant congenic strains (IRCS) produced between C57BL/6 and mice of the distant species Mus spretus (SEG/Pas). Each strain has inherited 1.3% of its genome from SEG/Pas under the form of few, small-sized, chromosomal segments.Results: The shape of the nasal bone was studied using outline analysis combined with Fourier descriptors, and differential features were identified between IRCS BcG-66H and C57BL/6. An F2 cross between BcG-66H and C57BL/6 revealed that, outof the three SEG/Pas-derived chromosomal regions present in BcG-66H, two were involved. Segments on chromosomes 1~32 Mb) and 18 (~13 Mb) showed additive effect on nasal bone shape. The three chromosomal regions present in BcG-66H were isolated in congenic strains to study their individual effect. Epistatic interactions were assessed in bicongenicstrains.Conclusions: Our results show that, besides a strong individual effect, the QTL on chromosome 1 interacts with genes onchromosomes 13 and 18. This study demonstrates that nasal bone shape is under complex genetic control but can beefficiently dissected in the mouse using appropriate genetic tools and shape descriptors.