Identification and characterization of Cri1, a locus controlling mortality during Citrobacter rodentium infection in mice

Infection of inbred mouse strains with Citrobacter rodentium represents an ideal model to reveal the genetic factors controlling host resistance to noninvasive enteric bacterial pathogens. We have chosen a positional cloning approach to identify putative gene(s) that control the known difference in survival between resistant C57BL/6J and susceptible C3H/HeJ and C3H/HeOuJ mice. Our work has identified one major locus within proximal chromosome 15 that is responsible for the marked susceptibility of both C3H strains, and we formally exclude Tlr4 from control of survival to this pathogen. We have named this new host resistance locus Cri1 (Citrobacter rodentium infection 1). The Cri1 genetic interval currently spans ～16 Mb and it confers survival to the infection in a recessive manner. Transfer of the Cri1 locus from the surviving B6 mice into a congenic mouse with a C3Ou genetic background confirms its overall chromosomal localization and its highly significant effect on host survival. The C3Ou.B6-Cri1 mice thus produced have also enabled us to dissociate the control of mouse survival from the control of bacterial load early in the infection as well as from control of colonic hyperplasia.     

Bacterial virulence versus host resistance in the urinary tracts of mice.

The relative contributions of host resistance and bacterial virulence were analyzed in a mouse model for ascending urinary tract infection. The congenic mouse strains C3H/HeJ and C3H/HeN were used in parallel. They differ in their reactivity to lipopolysaccharide (LPS) and susceptibility to experimental urinary tract infection. C3H/HeJ cells are susceptible to infection and are nonresponders to LPS (Lpsd Lpsd), whereas C3H/HeN cells respond to LPS and are resistant to infection (Lpsn Lpsn). The Escherichia coli pyelonephritis isolate GR-12, serotype O75K5, expressing adhesins specific for globoseries glycolipids (P fimbriae) and for mannosides (type-1 fimbriae), and its derivatives deficient in these factors were used, either singly or in combination, to establish experimental infections. In C3H/HeN mice, the relative persistence of E. coli was inversely proportional to its phagocytosis in vitro. Loss of the O75 and K5 antigens increased the tendency toward hydrophobic interaction, promoted phagocytosis, and reduced persistence in the kidneys. This was not the case in C3H/HeJ mice, in which O75- and K5- serotypes persisted in the same extent as did the parent strain. The total number of bacteria recovered from the kidneys of C3H/HeJ mice was about 1,000-fold higher than the number recovered from kidneys of C3H/HeN mice 24 h after infection. Previous studies have demonstrated a delayed influx of polymorphonuclear leukocytes into the urinary tracts of C3H/HeJ mice. The results are consistent with the hypothesis that phagocyte activation through LPS is a major defense mechanism against E. coli in the kidney, a property in which C3H/HeJ mice are deficient.     

Dissociation of innate susceptibility to Salmonella infection and endotoxin responsiveness in C3HeB/FeJ mice and other strains in the C3H lineage.

Studies of various mouse strains in the C3H lineage have shown that there is no correlation between innate susceptibility to Salmonella infection and sensitivity to the toxic or mitogenic effects of lipopolysaccharide (LPS). C3H/HeNCrlBR mice were Salmonella resistant, but sensitive to the toxic and mitogenic effects of LPS, whereas C3HeB/FeJ mice were Salmonella susceptible as the C3H/HeJ mice, yet were mitogenically responsive to LPS and sensitive to its lethal effects. Furthermore, other mouse strains (C3H/HeTex and C3H/HeDub) displayed intermediate susceptibility to Salmonella infection and were responders to the mitogenic and toxic effects of LPS. These results are interpreted to mean that endotoxemia cannot be a major factor in the pathogenesis of Salmonella infection and provide evidence for the involvement of multiple factors in the control of innate resistance to Salmonella infection in mice of the C3H lineage.     

Susceptibility of inbred mouse strains to infection with Serpula (Treponema) hyodysenteriae.

Several inbred strains of mice were inoculated with Serpula (Treponema) hyodysenteriae B204 to determine susceptibility to infection. Challenge doses of 10(7) or 10(8) spirochetes induced cecal lesions in C3H/HeJ mice and other C3H strains of mice. However, more than a 100-fold difference existed between the dose required to induce lesions in 50% of the infected C3H/HeJ mice (8.3 x 10(7)) and that required to induce them in 50% of the infected C3H/HeN mice (5 x 10(5)). C3H/HeJ mice lack a splenocyte mitogenic response to Escherichia coli lipopolysaccharide but exhibited a mitogenic response comparable to those of other C3H strains of mice when stimulated with S. hyodysenteriae endotoxin (butanol-water extract). Different inbred strains exhibited different susceptibilities to infection, with the strain C3H/HeN being the most susceptible on the basis of colonization and development of macroscopic cecal lesions. The ity gene had no apparent effect on susceptibility of mice challenged with S. hyodysenteriae. The involvement of the H-2 haplotype with susceptibility is unclear, but the mice bearing H-2k were more susceptible than mice with the H-2b, H-2d, or H-2q haplotype. These data support the hypothesis that the host's responsiveness to lipopolysaccharide influences the susceptibility to infection with S. hyodysenteriae. However, differences in susceptibility between inbred mice exist independent of the lps locus, suggesting that there are other inherent differences between mouse strains that affect susceptibility to infection by S. hyodysenteriae.     

Difference in susceptibility to gram-negative urinary tract infection between C3H/HeJ and C3H/HeN mice

The difference in susceptibility to urinary tract infection between C3H/HeJ and C3H/HeN mice was tested for with gram-negative strains differing in lipopolysaccharide composition. Recently, impaired clearance of Escherichia coli from the kidney of C3H/HeJ compared to C3H/HeN mice was shown to be correlated with the LPS low responsiveness. In this study, a difference in clearance from the kidneys of C3H/HeJ and C3H/HeN mice was found only with lipopolysaccharide-containing bacteria. Gram-positive bacteria, e.g., Staphylococcus saprophyticus and Streptococcus agalactiae, were recovered in essentially equal numbers from the kidneys of mice of both strains. In contrast, of the lipopolysaccharide-containing strains used, all persisted in higher numbers in the kidneys of C3H/HeJ mice than in the kidneys of C3H/HeN mice. Variations in the O side chain did not eliminate this difference. E. coli Hu734 O75+K5+ and the rfb- mutant O75-K5+ remained in similar numbers in C3H/HeJ mice, although O75-K5+ was eliminated more rapidly in C3H/HeN mice. The core structure did not affect the differential persistence in the two mouse strains. The rfb mutants with R1-R4 cores were eliminated after 24 h from the C3H/HeN mice, but remained in significant numbers in the kidneys of C3H/HeJ mice. Even the Re mutant of Salmonella minnesota persisted in low numbers in C3H/HeJ mice. The relative bacterial recovery from either mouse strain was related to the overall virulence of the infecting bacterial strain, but the difference between C3H/HeJ and C3H/HeN mice was associated with responsiveness to parts of lipopolysaccharide common to the bacterial strains tested.     

Lipopolysaccharide-responder and nonresponder C3H mouse strains are equally susceptible to an induced Escherichia coli urinary tract infection.

Host defense against bacterial urinary tract infections (UTI) includes both inflammatory and immune responses to infecting bacteria. The cellular events leading up to local inflammation are thought to be under genetic control and initiated by lipopolysaccharides (LPS) of gram-negative bacteria such as Escherichia coli. It has been previously reported that mice which lack functional Lps genes are more susceptible to induced E. coli UTI than mice with normal mitogenic responses to LPS. In contrast to these findings, data in this report demonstrate that LPS-responder and nonresponder C3H mouse strains are equally susceptible to E. coli UTI. When C3H/OuJ (Lps(n)/Lps(n)) and C3H/HeJ (Lps(d)/Lps(d)) were intravesically inoculated with equal numbers of uropathogenic E. coli organisms, neither strain was able to effectively resolve the induced UTI. The inability of C3H/OuJ mice to combat the infection was not due to an impaired response to LPS, nor could defect in the local inflammatory response be identified. The results indicate that factors other than LPS responsiveness are also important in determining hose resistance to UTI.     

Citrobacter rodentium lifA/efa1 is essential for colonic colonization and crypt cell hyperplasia in vivo

Previously, we have identified a large gene (lifA, for lymphocyte inhibitory factor A) in enteropathogenic Escherichia coli (EPEC) encoding a protein termed lymphostatin that suppresses cytokine expression in vitro. This protein also functions as an adhesion factor for enterohemorrhagic E. coli (EHEC) and Shiga toxin-producing E. coli and is alternatively known as efa1 (EHEC factor for adherence 1). The lifA/efa1 gene is also present in Citrobacter rodentium, an enteric pathogen that causes a disease termed transmissible murine colonic hyperplasia (TMCH), which induces colitis and massive crypt cell proliferation, in mice. To determine if lifA/efa1 is required for C. rodentium-induced colonic pathology in vivo, three in-frame mutations were generated, disrupting the glycosyltransferase (GlM12) and protease (PrMC31) motifs and a domain in between that does not encode any known activity (EID3). In contrast to infection with wild-type C. rodentium, that with any of the lifA/efa1 mutant strains did not induce weight loss or TMCH. Enteric infection with motif mutants GlM12 and PrM31 resulted in significantly reduced colonization counts during the entire 20-day course of infection. In contrast, EID3 was indistinguishable from the wild type during the initial colonic colonization, but cleared rapidly after day 8 of the infection. The colonic epithelium of all infected mice displayed increased epithelial regeneration. However, significantly increased regeneration was observed by day 20 only in mice infected with the wild-type in comparison to those infected with lifA/efa1 mutant EID3. In summary, lifA/efa1 is a critical gene outside the locus for enterocyte effacement that regulates bacterial colonization, crypt cell proliferation, and epithelial cell regeneration.     

Time Course and Host Responses to Escherichia coli Urinary Tract Infection in Genetically Distinct Mouse Strains

Recurrent urinary tract infections (UTIs) are a significant clinical problem for many women; however, host susceptibility factors have not been completely defined. The mouse model of induced UTI provides an experimental environment in which to identify specific host characteristics that are important in initial bacterial colonization of the urinary tract and in resolution of an infection. This study examined initial susceptibility, bacterial clearance, and host defense mechanisms during induction and resolution of Escherichia coli UTIs in genetically distinct strains of mice. Of the ten inbred strains tested, six (BALB/c, C3H/HeN, C57BL/6, DBA.1, DBA.2, and AKR) showed progressive resolution of bladder infections over a 14-day period. A constant, low-level bladder infection was observed in SWR and SJL mice. High bladder infection levels persisted over the 14-day study period in C3H/HeJ and C3H/OuJ mice. Kidney infection levels generally correlated with bladder infection levels, especially in C3H/HeJ and C3H/OuJ mice, the two most susceptible strains, in which infections became more severe with time after challenge. The degree of inflammation in bladder and kidneys, as well as antibody-forming cell responses, positively correlated with infection intensity in all strains except C3H/HeJ, which had minimal inflammation despite high infection levels. These results demonstrate two important aspects of host defense against UTI. First, the innate immune response to an infection in the bladder or kidneys consists primarily of local inflammation, which is followed by an adaptive response characterized in part by an antibody response to the infecting bacteria. Second, a UTI will be spontaneously resolved in most cases; however, in mice with specific genetic backgrounds, a UTI can persist for an extended length of time. The latter result strongly suggests that the presence or absence of specific host genes will determine how effectively an E. coli UTI will be resolved.     

Inverse relationship between severity of experimental pyelonephritis and nitric oxide production in C3H/HeJ mice

The contribution of nitric oxide to host resistance to experimental pyelonephritis is not well understood. We examined whether the inhibition of nitric oxide synthesis alters the sensitivity of lipopolysaccharide (LPS) responder (C3H/HeN) and nonresponder (C3H/HeJ) mice to experimental Escherichia coli pyelonephritis. C3H/HeJ and C3H/HeN mice were implanted subcutaneously with minipumps containing an inhibitor of nitric oxide, NG-nitro-L-arginine methyl ester (L-NAME), or a corresponding vehicle. Ascending urinary tract infection by bladder catheterization with two strains of E. coli, an O75 strain bearing Dr fimbriae and an O75 strain bearing P fimbriae, was developed in tested animals. Twenty-four hours following bladder infection, the kidneys of C3H/HeN and C3H/HeJ mice were colonized at a similar rate. However, 5 weeks postinoculation, C3H/HeN mice cleared infection while C3H/HeJ mice showed persistent colonization. Twenty-four hours following infection, C3H/HeN mice treated with L-NAME showed no significant increase of renal tissue infection compared to the saline-treated control group. However, L-NAME-treated C3H/HeJ mice showed an approximately 100-fold increase in E. coli infection rate compared to the saline-treated controls in the Dr+ group but showed no change compared to those in the P+ group. Dissemination of Dr+ E. coli but not P+ E. coli to the liver and uterus was significantly enhanced with L-NAME treatment in C3H/HeJ mice only. Nitric oxide had no direct killing effect on E. coli in vitro. Nitrite production by various organs was found to be significantly lower in C3H/HeJ mice than in C3H/HeN mice. Alteration of nitric oxide and LPS responsiveness was significantly associated with the increased sensitivity of C3H/HeJ mice to experimental Dr+ but not to P+ E. coli pyelonephritis. These findings are consistent with the hypothesis that nitric oxide synthase activity in concert with LPS responsiveness may participate in the antibacterial defense mechanisms of the C3H mouse urinary tract. This phenomenon is strain dependent and possibly related to the invasive properties of E. coli.     

Immunosuppression induced by attenuated Salmonella: effect of LPS responsiveness on development of suppression.

A live, avirulent strain of Salmonella typhimurium, SL3235, was previously shown to afford protection against virulent Salmonella challenge in three mouse strains of the C3H lineage, C3H/HeJ, C3HeB/FeJ, and C3H/HeNCrlBR, which differ in their innate susceptibility to Salmonella infection, as well as in their responsiveness to lipopolysaccharide (LPS). Concurrent with protection, however, SL3235 was found to induce greater than 90% reduction in proliferative responses of splenocytes from immunized mice to a panel of B and T cell mitogens. Suppression appeared to be independent of susceptibility to Salmonella infection, since the mitogenic responses of hypersusceptible C3H/HeJ and C3HeB/FeJ, as well as resistant C3H/HeNCrlBR mice, were suppressed. The suppressor cell population in immunized C3HeB/FeJ mice was recently shown to be of monocytic lineage. Using transwell plates, co-culture studies indicated that suppression was mediated by soluble factors. In the present study, the effect of LPS responsiveness on susceptibility to SL3235-induced suppression was evaluated in C3H mice by studying their ability to mount plaque-forming cell (PFC) responses to sheep red blood cells (SRBC) and in vivo antibody responses to tetanus toxoid. Comparison of PFC responses as a function of SL3235 dose in C3HeB/FeJ and C3H/HeJ mice, revealed that the latter strain was markedly more resistant to the development of suppression, as evidenced by the significantly higher (10-35-fold) SL3235 doses needed to achieve comparable suppression to those seen in C3HeB/FeJ mice. In contrast to C3HeB/FeJ mice, suppression in C3H/HeJ mice required direct cell-cell contact. In both mouse strains, suppression was alleviated by pre-treatment of immune splenocytes with either mitomycin C or x-irradiation, indicating that actively proliferating cells are required for suppressor function. Resistance of C3H/HeJ mice to SL3235-induced suppression was not due to a lesser bacterial load in vivo, since a higher number of SL3235 organisms were seen in C3H/HeJ spleens compared to C3HeB/FeJ mice. Rather, resistance of C3H/HeJ mice correlated with their reduced ability to recruit macrophages and other inflammatory cells into the spleen, as evidenced by the significantly smaller degree of splenomegaly induced in these mice following immunization with SL3235.     

Experimental Pneumocystis carinii pneumonia in C3H/HeJ and C3HeB/FeJ mice

C3H mice develop heavier degrees of Pneumocystis carinii pneumonia than other mouse strains tested. We have compared P. carinii pneumonia in two strains of C3H mice: C3H/HeJ mice, which are unresponsive to the effects of bacterial lipopolysaccharide (LPS), have defects in macrophage function, and have increased antibody responses to orally administered T-dependent antigens; and C3HeB/FeJ mice, which are immunologically normal. P. carinii pneumonia was induced by corticosteroids, and the intensity of the infection was judged by a semiquantitative histopathologic scoring system. Heavier degrees of infection were found in C3H/HeJ mice than in C3HeB/FeJ mice. Serum antibodies to P. carinii, measured by an indirect fluorescent antibody technique, were mainly of the IgG class in both strains of mice and varied inversely with the intensity of P. carinii infection in the lungs. Antibody levels were significantly higher in C3H/HeJ mice than in C3HeB/FeJ mice. These data suggest that C3H/HeJ have increased susceptibility to the effects of steroids of host defenses against P. carinii, and heightened serum antibody responses to the organism.     

Infection of different strains of mice with Lawsonia intracellularis derived from rabbit or porcine proliferative enteropathy

This report describes intestinal lesions in five strains of mice infected orally with Lawsonia intracellularis-infected tissue homogenates from rabbits or pigs (RLI and PLI). BALB/cA, C3H/HeJ, C57BL/6J and ICR mice were susceptible to infection with RLI, whereas only C3H/HeJ, C57BL/6J and ICR strains were susceptible to PLI. In susceptible mice, crypt epithelial hyperplasia occurred in association with an inflammatory reaction, as in proliferative enteropathy (PE) in other species. The intestinal changes in the infected mice varied from mild to severe. Unlike rabbit or porcine PE, in which the changes are confined to the ileum, the lesions in mice were located in the caecum. Immunolabelling of L. intracellularis antigen was abundant in early infection when the epithelial hyperplasia was mild or absent. When the hyperplasia had become severe, however, immunolabelling was weak. For this reason, it is suggested that transitory infection of the epithelium induces epithelial hyperplasia. Genetic differences between mouse strains appeared to play an important role in the response to L. intracellularis infection. Moreover, the susceptibility of BALB/cA mice to RLI but not to PLI suggests that there are significant biological differences between L. intracellularis isolates from rabbit PE and porcine PE.     

Formation of interferon-gamma and tumor necrosis factor in mice during Salmonella typhimurium infection

Formation of interferon-gamma (IFN-gamma) and tumor necrosis factor (TNF) during Salmonella typhimurium infection was investigated in lipopolysaccharide (LPS)-sensitive C3H/HeN and C57BL/10ScSn(B10ScSn), and LPS-resistant (lpsd mutant) C3H/HeJ and C57BL/10ScCr(B10ScCr) mice. When infected with 50 colony-forming units (CFU) of S. typhimurium C5, C3H/HeN and B10ScSn mice became hypersensitive to the lethal effect of LPS. In the case of lpsd mutants, only C3H/HeJ mice became hypersensitive to LPS, while B10ScCr mice remained resistant. C3H/HeJ as well as B10ScSn mice produced significant amounts of plasma IFN-gamma on day 3 after infection. By this time bacterial CFU in the liver of B10ScSn and C3H/HeJ mice were 10(6.7) and 10(7.1), respectively. In B10ScCr mice, however, IFN-gamma was not detectable although bacteria present in the liver exceeded 10(8) CFU. On the other hand, plasma TNF was not detectable in any of the mouse strains during S. typhimurium infection. When S. typhimurium-infected mice were challenged with LPS on day 3, significant amounts of plasma TNF were measured in C3H/HeN and B10ScSn mice, while in the lpsd mutant C3H/HeJ and B10ScCr mice plasma TNF was undetectable.     

The endotoxin of Helicobacter pylori is a modulator of host-dependent gastritis.

Atrophic gastritis caused by Helicobacter pylori is the precursor lesion in the development of intestinal-type gastric adenocarcinoma. In animal models, atrophic gastritis induced by Helicobacter felis has been shown to be host dependent, developing in some mouse strains and not in others. The lipopolysaccharide (LPS) of H. pylori has been suggested to play a role in the induction of gastritis. The goal of this study was to compare the inflammation induced by long-term infection of the C3H/He and the C3H/HeJ strains of mice with H. felis. C3H/HeJ mice are unresponsive to LPS. Six months after infection, severe atrophic gastritis had developed in the body mucosae of all infected C3H/He mice, with replacement of parietal and chief cells. Atrophy was associated with a loss of the H. felis from the antral mucosa. In contrast, no atrophy was seen in the infected C3H/HeJ non-LPS responder animals, and heavy colonization of the antrum remained. There were no significant differences between both the quantitative and qualitative serum immunoglobulin G (IgG) and salivary IgA levels in both strains of mice. The main difference between the two strains of long-term-infected mice was a lack of macrophage infiltration in the lamina propria. Immunization induced good protective immunity to challenge with viable H. felis. Helicobacter-induced, host-dependent gastritis is likely to be cell mediated. The C3H/He and C3H/HeJ mouse model provides an excellent opportunity to investigate the cellular basis of atrophic gastritis.     

Toll-like receptor 4-defective C3H/HeJ mice are not more susceptible than other C3H substrains to infection with Mycobacterium tuberculosis

Mycobacterium tuberculosis produces a variety of molecules capable of activating Toll-like receptors, a family of pattern recognition receptors expressed by macrophages and a variety of other cells. To determine whether Toll-like receptor 4 (TLR4) was critical in resistance to M. tuberculosis infection, we compared the morbidity and mortality of TLR4-defective C3H/HeJ mice to those of TLR4-sufficient C3H mouse substrains. TLR4-defective C3H/HeJ mice and TLR4-sufficient C3H/HeSnJ, C3HeB/FeJ, and C3H/HeOuJ mice were infected by the aerosol route with M. tuberculosis. TLR4-defective C3H/HeJ mice had levels of cytokines in their bronchoalveolar lavage fluids and in vitro mycobacterial antigen-specific recall responses similar to those of other C3H mouse substrains. In addition, bacterial replication and long-term survival of mice following infection appeared to be independent of TLR4. Interestingly, C3HeB/FeJ mice were significantly more susceptible to M. tuberculosis infection, indicating that genetic heterogeneity among inbred C3H mouse substrains modifies resistance to infection. Therefore, cautious interpretation is required when the C3H/HeJ strain is used as a model of a TLR4-defective mouse strain, as there are significant allelic differences between C3H/HeJ and other C3H mouse substrains in response to M. tuberculosis infection. With this caveat, our data indicate that TLR4 may not be required for optimal immunity of mice to M. tuberculosis.     

Induction of immune and adjuvant immunoglobulin G responses in mice by Brucella lipopolysaccharide

The immunogenic and adjuvant properties of Brucella abortus and Escherichia coli lipopolysaccharides (LPSs) were studied in endotoxin-responsive, athymic, and euthymic BALB/c mice and in responsive C3H/HeAu mice and congenic nonresponsive C3H/HeJ mice. Consistent with previous reports, E. coli LPS did not stimulate significant primary or secondary antibody responses in C3H/HeJ mice and induced the production of immunoglobulin M (IgM) and low levels of IgG in C3H/HeAu mice. In contrast, B. abortus smooth and rough LPS stimulated primary and secondary antibody responses and induced the production of IgM and high levels of IgG in both responsive and nonresponsive strains of C3H/He mice and in nude mice. When used as adjuvant, B. abortus LPS augmented the IgG plaque-forming-cell response of C3H/HeAu and BALB/c euthymic mice to the T-dependent antigen sheep erythrocytes. E. coli LPS augmented only the IgM plaque-forming-cell response in the same mouse strains. Neither B. abortus nor E. coli LPS was adjuvant for C3H/HeJ or nude mice. The dichotomy between the antibody and adjuvant responses of both C3H/HeJ mice and athymic mice to B. abortus LPS may be a function of the true thymus independence and dependence of these responses. In addition, the refractiveness of C3H/HeJ and nude mice to B. abortus LPS as adjuvant, but not as mitogen or polyclonal B cell activator, clearly dissociates these phenomena.     

Is TNF alpha involved in early susceptibility of Trypanosoma cruzi-infected C3H/He mice?

Early wasting and subsequent mortality may occur in mice of some inbred strains following infection with Trypanosoma cruzi. It was hypothesized that TNF alpha/cachectin might be involved in this process. Thus, sera collected from mice of strains differing in their susceptibility or resistance to Trypanosoma cruzi infection were checked for the presence and level of TNF alpha, a cytokine able to exert acute toxic effects. C3H/HeJ or C3H/HePas (susceptible), BALB/c (intermediate) and C57BL/6 (resistant) mice were infected with the CL or Colombian strain of Trypanosoma cruzi, and TNF activity was measured in the sera during the acute phase of the infection. Only serum collected from infected C3H/He mice contained TNF activity. However, TNF activity could be measured in serum of all strains, following LPS infection, indicating that the infection was able to prime macrophages of infected mice to secrete TNF alpha. The TNF alpha/cachectin release in the sera of C3H mice may play a role in the early wasting and death of these mice after Trypanosoma cruzi infection.     

Genetic analysis of susceptibility to Chlamydia trachomatis in mouse

Chlamydia trachomatis is a bacterial pathogen that is a major cause of blindness and infertility in diverse populations across the world. In an effort to model genetic complexities that are observed in human populations and to identify novel genes involved in susceptibility to C. trachomatis, we have adapted a murine model of systemic infection for use in genetic analysis. In this model, chlamydial colonization and replication is measured in the spleens of mice shortly after intravenous delivery of C. trachomatis L2. Here, we show that C57BL/6J and C3H/HeJ inbred mice are differentially susceptible to this systemic infection. Additionally, fibroblasts cultured from C57BL/6J and C3H/HeJ embryos are differentially permissive for chlamydial replication. We have taken advantage of this natural variation to map quantitative trait loci on Chromosomes 2, 3, and 11 that segregate with the bacterial load in F2 cross progeny during the acute phase of C. trachomatis infection in vivo. To validate our mapping results, we also generated mice that are congenic for a portion of Chromosome 11 from the susceptible parent. This congenic interval confers increased susceptibility to C. trachomatis, both in vivo and in vitro, suggesting that our screen identified at least one gene that is involved in cellular resistance to C. trachomatis replication.     

Susceptibility of inbred mice to rickettsiae of the spotted fever group.

A mouse strain susceptible to lethal infection with Rickettsia conorii was required for testing vaccine efficacy and for studying the immunology and pathogenesis of infection. Among 20 strains of inbred mice inoculated intraperitoneally with the Malish strain of R. conorii, the C3H/HeJ mouse strain was the most susceptible, with a 50% lethal dose of approximately 10 PFU. Infection of all mouse strains resulted in a measurable antibody response; the highest titers correlated with the greatest degree of rickettsial replication as measured by plaque assay of infected spleen homogenates. Inoculation of C3H/HeJ mice with 5.0 log10 organisms of strain Malish by the subcutaneous route did not result in lethal infection. The Casablanca and Moroccan strains of R. conorii were not lethal for C3H/HeJ mice and, in addition, produced plaques in L-929 cells morphologically distinct from those produced by the Malish strain. The only other spotted fever group rickettsia tested which produced a lethal infection in C3H/HeJ mice was Rickettsia sibirica. Sublethal infection with any of the spotted fever rickettsiae tested protected against lethal infection with R. conorii. These data established a lethal challenge system for examining the protective efficacy of spotted fever immunogens and presented evidence of biological variation among strains of R. conorii.