Tissue Tropism and Target Cells of NSs-Deleted Rift Valley Fever Virus in Live Immunodeficient Mice

Rift Valley fever, caused by a member of the Bunyaviridae family, has spread during recent years to most sub-Saharan African countries, in Egypt and in the Arabian peninsula. The virus can be transmitted by insect vectors or by direct contacts with infectious tissues. The analysis of virus replication and dissemination in laboratory animals has been hampered by the need to euthanize sufficient numbers of animals and to assay appropriate organs at various time points after infection to evaluate the viral replication. By following the bioluminescence and fluorescence of Rift Valley fever viruses expressing light reporters, we were able to track the real-time dissemination of the viruses in live immunodeficient mice. We showed that the first infected organs were the thymus, spleen and liver, but the liver rapidly became the main location of viral replication. Phagocytes also appeared as important targets, and their systemic depletion by use of clodronate liposomes decreased the number of viruses in the blood, delayed the viral dissemination and prolonged the survival of the infected mice

Identification de facteurs génétiques contrôlant la résistance de lignées de souris consanguines à une infection expérimentale par Yersinia pestis, l'agent de la peste

Plague is a zoonotic disease affecting mainly rodents and accidentally humans. The etiologic agent of bubonic and pneumonic plague is the Gram-negative bacterium Yersinia pestis. The mechanisms by which the host is able or not to resist the infection are poorly understood. We have shown that some mouse inbred strains, like C57BL/6J, die after the subcutaneous injection of 100 bacteria of a virulent strain (CO92), while others, like SEG/Pas, derived from Mus spretus, survive. A backcross between these two strains led to identification, on chromosomes 3, 4, and 6, of three QTL controlling survival rate. The first two were found only in females, while the chromosome 6 QTL was also found in males. Congenic mice carrying the SEG chromosome 6 in a C57BL/6J background were produced. After infection, they die in the same proportion as C57BL/6, but somewhat later. Bi- and tri-congenic strains are under production to assess the effect of other QTLs. We have tested a collection of 55 interspecific recombinant congenic strains between C57BL/6J and SEG/Pas. Several strains significantly differed from C57BL/6 in survival rate or time to death. The analysis of strain 120G, which dies earlier than C57BL/6J, suggests that the proximal region of chromosome 6 would be responsible for this phenotype. Altogether, our data show that genetic control of resistance to plague in SEG/Pas mice is complex, and we have identified several genomic regions which play an important role in this phenotype.La peste est une zoonose touchant principalement les rongeurs et de façon accidentelle l'Homme. L'agent responsable de la peste bubonique et pulmonaire est la bactérie Gram négative Yersinia pestis. Les mécanismes qui permettent à l'hôte de résister ou non à cette infection sont mal connus. Nous avons montré que certaines lignées consanguines de souris, comme C57BL/6J, meurent après l'injection sous cutanée de 100 bactéries d'une souche virulente (CO92) alors que d'autres, comme SEG/Pas, dérivée de Mus spretus, résistent. Un croisement en retour entre ces deux lignées a permis d'identifier, sur les chromosomes 3, 4 et 6, trois QTLs contrôlant le taux de survie. Les deux premiers ont été retrouvés uniquement chez les femelles alors que celui du chromosome 6 est commun aux deux sexes. Des souris congéniques portant le chromosome 6 de SEG dans un fonds génétique C57BL/6J ont été produites. Après infection, elles meurent dans les mêmes proportions que les souris C57BL/6, mais un peu plus tardivement. Des souris bi- et tri-congéniques sont en cours de production pour tester l'effet des autres QTLs. Nous avons testé une collection de 55 lignées recombinantes congéniques interspécifiques entre SEG/Pas et C57BL/6J. Plusieurs lignées ont montré des différences de taux ou de durée de survie significatives par rapport à C57BL/6J. L'étude de la lignée 120G, qui meurt plus rapidement que C57BL/6J, suggère que la région proximale du chromosome 6 serait responsable de ce phénotype. Nous avons ainsi montré que le contrôle génétique de la résistance à la peste chez les souris SEG/Pas est complexe, et identifié plusieurs régions génomiques qui jouent un rôle important dans ce phénotype

Identification de facteurs génétiques contrôlant la résistance de lignées de souris consanguines à une infection expérimentale par Yersinia pestis, l'agent de la peste

La peste est une zoonose touchant principalement les rongeurs et de façon accidentelle l'Homme. L'agent responsable de la peste bubonique et pulmonaire est la bactérie Gram négative Yersinia pestis. Les mécanismes qui permettent à l'hôte de résister ou non à cette infection sont mal connus. Nous avons montré que certaines lignées consanguines de souris, comme C57BL/6J, meurent après l'injection sous cutanée de 100 bactéries d'une souche virulente (CO92) alors que d'autres, comme SEG/Pas, dérivée de Mus spretus, résistent. Un croisement en retour entre ces deux lignées a permis d'identifier, sur les chromosomes 3, 4 et 6, trois QTLs contrôlant le taux de survie. Les deux premiers ont été retrouvés uniquement chez les femelles alors que celui du chromosome 6 est commun aux deux sexes. Des souris congéniques portant le chromosome 6 de SEG dans un fonds génétique C57BL/6J ont été produites. Après infection, elles meurent dans les mêmes proportions que les souris C57BL/6, mais un peu plus tardivement. Des souris bi- et tri-congéniques sont en cours de production pour tester l'effet des autres QTLs. Nous avons testé une collection de 55 lignées recombinantes congéniques interspécifiques entre SEG/Pas et C57BL/6J. Plusieurs lignées ont montré des différences de taux ou de durée de survie significatives par rapport à C57BL/6J. L'étude de la lignée 120G, qui meurt plus rapidement que C57BL/6J, suggère que la région proximale du chromosome 6 serait responsable de ce phénotype. Nous avons ainsi montré que le contrôle génétique de la résistance à la peste chez les souris SEG/Pas est complexe, et identifié plusieurs régions génomiques qui jouent un rôle important dans ce phénotypePlague is a zoonotic disease affecting mainly rodents and accidentally humans. The etiologic agent of bubonic and pneumonic plague is the Gram-negative bacterium Yersinia pestis. The mechanisms by which the host is able or not to resist the infection are poorly understood. We have shown that some mouse inbred strains, like C57BL/6J, die after the subcutaneous injection of 100 bacteria of a virulent strain (CO92), while others, like SEG/Pas, derived from Mus spretus, survive. A backcross between these two strains led to identification, on chromosomes 3, 4, and 6, of three QTL controlling survival rate. The first two were found only in females, while the chromosome 6 QTL was also found in males. Congenic mice carrying the SEG chromosome 6 in a C57BL/6J background were produced. After infection, they die in the same proportion as C57BL/6, but somewhat later. Bi- and tri-congenic strains are under production to assess the effect of other QTLs. We have tested a collection of 55 interspecific recombinant congenic strains between C57BL/6J and SEG/Pas. Several strains significantly differed from C57BL/6 in survival rate or time to death. The analysis of strain 120G, which dies earlier than C57BL/6J, suggests that the proximal region of chromosome 6 would be responsible for this phenotype. Altogether, our data show that genetic control of resistance to plague in SEG/Pas mice is complex, and we have identified several genomic regions which play an important role in this phenotypePARIS-AgroParisTech Centre Paris (751052302) / SudocSudocFranceF

Protective or Deleterious Role of Scavenger Receptors SR-A and CD36 on Host Resistance to <i>Staphylococcus aureus</i> Depends on the Site of Infection

<div><p><i>Staphylococcus aureus</i> is a major human opportunistic pathogen responsible for a broad spectrum of infections ranging from benign skin infection to more severe life threatening disorders (e.g. pneumonia, sepsis), particularly in intensive care patients. Scavenger receptors (SR-A and CD36) are known to be involved in <i>S. aureus</i> recognition by immune cells in addition to MARCO, TLR2, NOD2 and α5β1 integrin. In the present study, we further deciphered the contribution of SR-A and CD36 scavenger receptors in the control of infection of mice by <i>S. aureus</i>. Using double SR-A/CD36 knockout mice (S/C-KO) and <i>S. aureus</i> strain HG001, a clinically relevant non-mutagenized strain, we showed that the absence of these two scavenger receptors was protective in peritoneal infection. In contrast, the deletion of these two receptors was detrimental in pulmonary infection following intranasal instillation. For pulmonary infection, susceptible mice (S/C-KO) had more colony-forming units (CFU) in their broncho-alveolar lavages fluids, associated with increased recruitment of macrophages and neutrophils. For peritoneal infection, susceptible mice (wild-type) had more CFU in their blood, but recruited less macrophages and neutrophils in the peritoneal cavity than resistant mice. Exacerbated cytokine levels were often observed in the susceptible mice in the infected compartment as well as in the plasma. The exception was the enhanced compartmentalized expression of IL-1β for the resistant mice (S/C-KO) after peritoneal infection. A similar mirrored susceptibility to <i>S. aureus</i> infection was also observed for MARCO and TLR2. <i>Marco and tlr2</i> -/- mice were more resistant to peritoneal infection but more susceptible to pulmonary infection than wild type mice. In conclusion, our results show that innate immune receptors can play distinct and opposite roles depending on the site of infection. Their presence is protective for local pulmonary infection, whereas it becomes detrimental in the peritoneal infection.</p></div

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

Resistance to plague of Mus spretus SEG/Pas mice requires the combined action of at least four genetic factors

International audienceWe 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

Cytokine levels (IL-6, KC, IL-10 and IL-1β) in peritoneal lavage (PL) fluids and in plasma after peritoneal injection of 5×10⁷ CFU of <i>S. aureus</i>/g of mice.

<p>Samples from C57BL/6 (B6J) and double SR-A/CD36 knockout (S/C-KO) were harvested 1.5 h and 3 h after infection. (R) and (S) stand for resistant and susceptible mice. All data acquired after 1.5 h are the mean of n = 5 mice, data acquired after 3 h are the mean of 10 and 5 mice in the peritoneal cavity and in the blood compartment, respectively. * <i>P</i><0.05.</p

Cytokine levels (IL-6, KC, IL-10 and IL-1β) in broncho-alveolar lavage (BAL) fluids and in plasma after intranasal inoculation of 10⁹ CFU of <i>S. aureus</i>.

<p>Samples from C57BL/6 (B6J) and double SR-A/CD36 knockout (S/C-KO) were harvested 1.5 h and 3 h after infection. (R) and (S) stand for resistant and sensitive mice. All data acquired after 1.5 h are the mean of n = 5 mice, and all data acquired after 3 h are the mean of 10 mice. * <i>P</i><0.05 ; ** <i>P</i><0.01 ; *** <i>P</i><0.001 between wild type and deficient mice.</p

Bacterial counts in broncho-alveolar lavage (BAL) fluids (after intranasal inoculation of 10⁹ CFU of <i>S. aureus</i>), in peritoneal lavage (PL) fluids (after peritoneal injection of 5×10⁷ CFU of <i>S. aureus</i>/g of mice, and in blood for both types of infection.

<p>Samples from C57BL/6 (B6J) and double SR-A/CD36 knockout (S/C-KO) were harvested 1.5 h and 3 h after infection. (R) and (S) stand for resistant and susceptible mice depending on the route of infection. All data acquired after 1.5 h are the mean of n = 5 mice, data acquired after 3 h are the mean of 10, 10, 7 and 5 mice in the peritoneal cavity, the broncho-alveolar lavages, and in the blood (after intra-nasal infection and intraperitoneal infection), respectively. * <i>P</i><0.05; ** <i>P</i><0.01 between wild type and deficient mice.</p

Survival curves.

<p>Survival curves of C57BL/6 (B6J) and double SR-A/CD36 knockout (S/C-KO) mice after a pulmonary infection following an intranasal inoculation (IN) of 10⁹ CFU of <i>S. aureus</i> (upper panel) or a peritoneal injection (IP) of 5×10⁷ CFU of <i>S. aureus</i>/g of mice (lower panel). The results have been acquired with n = 14 B6/J and n = 14 S/C-KO for lung infection, and n = 15 B6/J and n = 15 S/C-KO for peritoneal infection.</p