Dysregulated inflammatory response to Candida albicans in a C5-deficient mouse strain

Experimental infection of inbred mouse strains with Candida albicans provides a good model system to identify host genetic determinants that regulate onset of, response to, and ultimate outcome of disseminated candidiasis. The A/J mouse strain is exquisitely sensitive to infection with C. albicans, while the C57BL/6J strain is relatively resistant, as measured by survival following intravenous injection of Candida blastospores. This differential susceptibility is caused by an A/J-specific loss-of-function mutation in the C5 component of the complement pathway. C5 plays several critical roles in host response to infection, including target lysis and phagocyte recruitment. Therefore, to determine which of its functions were required for host resistance to candidiasis, a detailed comparative analysis of pathophysiology and host response to acute C. albicans infection was conducted in A/J and C57BL/6J mice. C5-sufficient C57BL/6J mice were found to succumb late in infection due to severe kidney pathology, typified by fungal replication and robust neutrophil-based inflammatory response associated with extensive tissue damage. In contrast, A/J mice were moribund within 24 h postinfection but displayed little if any kidney damage despite an inability to mobilize granulocytes and a high fungal load in the kidney. Rather, C5 deficiency in A/J mice was associated with higher levels of circulating cytokines tumor necrosis factor alpha, interleukin-6, monocyte chemotactic protein 1 (MCP-1), MCP-5, and eotaxin in response to C. albicans. Transfer of the C5-defective allele from A/J onto a C57BL/6J genetic background in recombinant congenic strain BcA17 recapitulated the phenotypic aspects of the susceptibility of A/J mice to C. albicans, confirming the causative role of C5 deficiency in the dysregulated cytokine response.     

Cardiac failure in C5-deficient A/J mice after Candida albicans infection

The effect of a deficiency in the C5 component of complement on the pathophyisology of infection with the fungal pathogen Candida albicans was studied by using the A/J inbred mouse strain and the BcA17 congenic mouse strain. Acute infection caused by intravenous injection of C. albicans blastospores is associated with rapid fungal replication in the heart, brain, and, in particular, kidneys of C5-deficient mice. Histological studies and analysis of markers for tissue damage indicated that the heart is the organ that is most affected and that it ultimately fails in C5-deficient mice. In A/J and BcA17 mice, tissue damage is associated with (i) cellular infiltration in the heart, which is not seen in the kidney despite the higher fungal load in the latter organ, and (ii) a very strong inflammatory response, including elevated levels of many cytokines and chemokines. This results in cardiomyopathy, which is associated with elevated levels of creatine kinase and cardiac troponin I in the circulation. Damage to the cardiac muscle is associated with metabolic changes, including hypoglycemia, decreased lipid utilization resulting in elevated levels of cardiac triglycerides, and unproductive glucose utilization linked to a dramatic increase in the level of pyruvate dehydrogenase kinase 4 (Pdk4), a negative regulator of the pyruvate dehydrogenase complex.     

Genetics of resistance to infection with Candida albicans in mice.

To determine differences in susceptibility, 234 naive mice including xid and beige mutants were infected intravenously with Candida albicans and monitored with survival analysis and quantitative culture of the kidneys. By using survival time as the criterion, animals of seven inbred strains were separated into three groups. C3H/HeJ and Dw/+ were most susceptible; C57BR/cdJ, BRVR and CBA/N (xid) were intermediate in susceptibility; C57BL/KsJ and C57BL/6J were least susceptible. Mean survival times (MST) were markedly influenced by the number of Candida cells injected while the ranking of mouse strains by survival alone was unchanged. There was a dissimilar behaviour of the strains to produce organ weight changes in response to infection when compared with uninfected mice which were matched for age and genetic lineage. Black mice had lower colony forming units (CFU) per mg of tissue at the time of death than animals of other genetic lineage. Nevertheless, the finding that MST and CFU studies were loosely correlated in a few strains of mice indicated that the proliferation of the fungus in the kidneys was not always the major cause of death. The beige mutation was found to determine an increased susceptibility to systemic Candida infection. The differences in survival for beige and nonbeige mice were influenced by the genetic lineage of the host, being much greater in the C57BL/6 strain (36.7 days) than in the C3H/He strain (5 days). C57BL/6 beige-J had significantly higher CFU per organ and per unit of weight than C57BL/6 +/+ mice. These data evinced an important contribution of host genetic factors to resistance to systemic candidiasis. It is suggested that innate resistance genes regulate the differentiation in the bone marrow and the function of cells of granulocyte-macrophage lineage.     

Genetics of resistance to infection with Candida albicans in mice

To determine differences in susceptibility, 234 naive mice including xid and beige mutants were infected intravenously with Candida albicans and monitored with survival analysis and quantitative culture of the kidneys. By using survival time as the criterion, animals of seven inbred strains were separated into three groups. C3H/HeJ and Dw/+ were most susceptible; C57BR/cdJ, BRVR and CBA/N (xid) were intermediate in susceptibility; C57BL/KsJ and C57BL/6J were least susceptible. Mean survival times (MST) were markedly influenced by the number of Candida cells injected while the ranking of mouse strains by survival alone was unchanged. There was a dissimilar behaviour of the strains to produce organ weight changes in response to infection when compared with uninfected mice which were matched for age and genetic lineage. Black mice had lower colony forming units (CFU) per mg of tissue at the time of death than animals of other genetic lineage. Nevertheless, the finding that MST and CFU studies were loosely correlated in a few strains of mice indicated that the proliferation of the fungus in the kidneys was not always the major cause of death. The beige mutation was found to determine an increased susceptibility to systemic Candida infection. The differences in survival for beige and nonbeige mice were influenced by the genetic lineage of the host, being much greater in the C57BL/6 strain (36.7 days) than in the C3H/He strain (5 days). C57BL/6 beige-J had significantly higher CFU per organ and per unit of weight than C57BL/6 +/+ mice. These data evinced an important contribution of host genetic factors to resistance to systemic candidiasis. It is suggested that innate resistance genes regulate the differentiation in the bone marrow and the function of cells of granulocyte-macrophage lineage.     

A/J mice are susceptible and C57BL/6 mice are resistant to Listeria monocytogenes infection by intragastric inoculation

Previous studies demonstrated that the innate resistance of mice to Listeria monocytogenes infection by intravenous or intraperitoneal inoculation is regulated principally by the Hc locus on mouse chromosome 2. The A/J and C57BL/6 mouse strains were identified as prototype L. monocytogenes-susceptible and -resistant strains, respectively. In the present study, we compared the relative susceptibilities of A/J and C57BL/6 mice to intragastric (i.g.) inoculation with L. monocytogenes. The results of our study indicate that A/J mice are significantly more susceptible than C57BL/6 mice to an i.g. challenge with L. monocytogenes. This was reflected in the estimated 50% lethal doses for the two strains (10(6) and 10(8) CFU for A/J and C57BL/6 mice, respectively) and a more rapid and severe dissemination of the infection to the spleen and liver in A/J mice than in C57BL/6 mice. Histopathological examination of tissues from the infected mice confirmed the greater severity of disease in A/J mice. Clearance of a primary infection enhanced the resistance of both A/J and C57BL/6 mice to reinfection with L. monocytogenes via the gastrointestinal tract. However, the relative difference in susceptibility between the two strains was evident even after immunization. The A/J mouse holds promise as a model for investigating the pathogenesis of gastrointestinal listeriosis because of its ability to develop systemic infection following challenge with numbers of organisms similar to those recovered from some L. monocytogenes-contaminated food products.     

Genetic control of susceptibility to pulmonary infection with Chlamydia pneumoniae in the mouse

A mouse model was used to study the genetic control of differential host response to pulmonary infection with Chlamydia pneumoniae. The A/J and C57BL/6 strains show differential response to intranasal infection with respect to their ability to clear pulmonary bacterial load and the extent of lung pathology developed by 2 weeks post infection. The genetic basis of this interstrain difference was studied by whole-genome scan in an informative [A/J x C57BL/6J] F2 cross using the pulmonary microbial load as a phenotypic readout of host response. We detected a highly significant linkage (LOD score=11.5) on chromosome 17 that overlaps with the major histocompatibility (MHC) locus. This quantitative trait locus (QTL) accounts for approximately 30% of the phenotypic variance with B6 alleles conferring susceptibility and inherited in a recessive fashion. Significant linkage was also detected to chromosome 5 in female mice, while chromosome 6 showed suggestive linkage in male mice, pointing to additional complexity in the genetic control of the difference in susceptibility observed in A/J and C57BL/6J.     

Low responsiveness to MLM bacilli associated with an impaired macrophage function in CBA/J mice

It has previously been reported that susceptibility to Mycobacterium lepraemurium (MLM) infection (subcutaneous inoculation) differs markedly between CBA/J and C57BL/6 mice. The high susceptibility of CBA/J mice was shown to be due to the generation of cyclophosphamide-sensitive, I-Jk-positive suppressor T cells. In the present study, we attempt to show functional differences between splenic macrophages of both strains of mice in terms of their phagocytic and antigen-presenting activities against MLM bacilli. The results show that (a) the secondary MLM-induced T-cell proliferative response is dependent on Ia-positive antigen-presenting cells (APC), (b) macrophages of CBA/J mice are able to present antigens to F1 T cells, and yet (c) they show an extremely low phagocytic activity, (d) antigen presentation by APC of CBA/J mice lasted for a longer period than that of C57BL/6 mice after MLM infection. These results suggest that there is a functional difference in CBA/J and C57BL/6 APC, which could account for the phenotypic difference in immune responsiveness to MLM bacilli.     

Complexity in the host response to Salmonella Typhimurium infection in AcB and BcA recombinant congenic strains

The host response to Salmonella infection is controlled by its genetic makeup. Using the mouse model of typhoid fever, several genes were found to influence the outcome of Salmonella infection, including Nramp1 (Slc11a1). In order to improve our knowledge of genetic determinants of the mouse response to acute Salmonella Typhimurium infection, we performed a systematic screening of a set of A/J and C57BL/6J recombinant congenic strains (RCS) for their resistance to infection. While we knew that the parental strains differ in their susceptibility to Salmonella because C57BL/6J mice carry a non-functional allele at Nramp1, we hypothesized that other genes would influence the response to Salmonella and segregate in the RCS. We identified several RCS that showed a non-expected phenotype given their known Nramp1 genotype proving that the response to Salmonella in A/J and C57BL/6J mice is complex. Based on these findings, we selected two RCS for generation of fully informative F2 crosses, (AcB61 x 129S6) and (AcB64 x DBA/2J). Genetic analyses performed on these crosses identified five novel Salmonella susceptibility QTL mapping to chromosomes 3 (Ity4), 2 (Ity5), 14 (Ity6), 7 (Ity7) and 15 (Ity8). These results illustrate the genetic complexity associated with the mouse response to Salmonella Typhimurium.     

Strain-dependent differences in host response to Candida albicans infection in mice are related to organ susceptibility and infectious load.

After systemic infection with the yeast Candida albicans, inbred mice show substantial differences in mortality, organ colonization, and severity of tissue damage. To examine the relationships between these variables, which are not directly correlated with each other, fungal colonization of the kidneys and brain was enumerated in six inbred strains that exhibit different patterns of tissue damage and mortality. Mice lacking the fifth component of complement (C5) are highly susceptible to lethal challenge, and A/J and DBA/2 mice, both C5 deficient, showed the highest colony counts in the kidneys after challenge with 10(5) blastoconidia. In contrast, colony counts in the brain of all six strains were equivalent at this challenge dose. A/J and DBA/2 mice died after challenge with 3 x 10(5) blastoconidia, but other strains showed an increase in kidney colonization, and strain-dependent differences in clearance from the brain became evident. The data suggest that mortality in A/J and DBA/2 mice is related to an unusual susceptibility of the kidneys to colonization by C. albicans and that there may be tissue-specific differences in host protective mechanisms.     

Influence of genetic background on host resistance to experimental murine tularemia.

The host response to experimental murine tularemia was examined in different inbred mouse strains. The kinetics of growth of Francisella tularensis live vaccine strain (LVS) in the livers and spleens of A and C57BL/6 mice were monitored, and it was observed that mice of the A strain were more susceptible to the proliferation of LVS than were C57BL/6 mice. The difference was most marked 5 days following infection, when the number of bacteria isolated from the spleens of A mice was found to exceed that of C57BL/6 mice by 100-fold. In addition, the C57BL/6 strain exhibited a more pronounced splenomegaly 8 days after infection than did the A strain. When the response of other inbred strains was evaluated by determining the splenic count of LVS on day 5 postinfection, several levels of antiularemic resistance were observed. Mice of the AKR, BALB/cBy, C57BL/10, and SJL strains were found to be most resistant, while SM mice were most susceptible to the proliferation of LVS. The DBA/2, CBA, 129, C3H/HeJ, and A strains expressed a resistance phenotype which was intermediate between the two extremes, with A and C3H/HeJ mice being somewhat more susceptible than DBA/2, CBA, or 129 mice. The trait of resistance or susceptibility was analyzed genetically in (C57BL/6 x A)F1 hybrid mice and in F2 generation and recombinant inbred (RI) mouse strains derived from C57BL/6 (resistant) and A (susceptible) strain progenitors. The F1 progeny exhibited a level of resistance to infection which was similar to that of the resistant parent. In both the F2 generation mice and the RI strains, a continuous spectrum of resistance levels was observed. The results of these experiments indicate that the genetic background of the host influences host resistance to experimental murine tularemia and that multiple genetic loci are involved in this response.     

Differential mechanisms of resistance to sublethal systemic Aspergillus fumigatus infection in immunocompetent BALB/c and C57BL/6 mice

Studies of systemic and pulmonary Aspergillus fumigatus infection demonstrated differential susceptibility of inbred mice of various genetic background to lethal outcome, with an opposite pattern of Th1 cytokine interferon-γ (IFN-γ) and Th2 cytokine interleukin-4 (IL-4) in susceptible vs resistant mice. We have shown recently reciprocal IFN-γ and IL-4 expression in spleens of Th1-prone C57BL/6 mice in sublethal systemic aspergillosis. In this study, resistance to systemic (i.v.) A. fumigatus infection was investigated in Th2-prone BALB/c mice by survival rate at different fungal inocula, efficiency of reduction of visceral organ and spleen fungal burden at sublethal conidia dose and splenic immune response to this dose and compared to C57BL/6 mice. No strain differences in survival were noted at three A. fumigatus doses, with similar extent and dynamics of fungal eradication from all organs following sublethal conidia dose injection. Progressive decrease in spleen fungal burden was associated with different dynamics and quality of changes in spleen activity of BALB/c and C57BL/6 mice. Increased spleen mass and cellularity was noted in both strains, with higher values in BALB/c mice at some time points what might be ascribed to peripheral blood cell recruitment, as well as hematopoietic activity and red pulp upgrowth. Infection tipped the balance towards pro-inflammatory antifungal splenic response by a highly increasing IFN-γ and without changing the IL-4 expression in BALB/c mice, in contrast to down-regulating anti-inflammatory (IL-4) and a moderately increasing IFN-γ response in C57BL/6 mice. Jointly, stimulation of IL-17 expression noted in both strains provided an optimal inflammatory milieu in the spleen of infected mice that might have contributed to efficient removal of conidia.     

Distinct granuloma responses in C57BL/6J and BALB/cByJ mice in response to pristane

Granuloma formation is an inflammatory response of the host against invading pathogens or indigestible substances. We generated mesenteric oil granulomas by injecting pristane into the peritoneal cavity (PC) of mice, and compared oil granuloma formation in the C57BL/6J and BALB/cByJ strains of mice. The formation and kinetics of oil granulomas were distinct between the two strains. In C57BL/6J mice, injected pristane induced oil granuloma formation at both the mesenteric centers (MG) and margins (SG). MG was resolving by 11 weeks, and SG persisted. In BALB/cByJ mice, MG developed slower but persisted longer than in C57BL/6J mice, and SG resolved sooner than in C57BL/6J mice. Injection of India ink revealed that phagocytes were localised mainly to the SG in C57BL/6J mice, but were located diffusely in both MG and SG of BALB/cByJ mice. SG cells expressed more monocyte chemotactic protein‐1 (MCP‐1) mRNA than MG cells in C57BL/6J mice, but there was no difference in MCP‐1 expression between the MG and SG in BALB/cByJ mice. These observations suggest that the recruitment of inflammatory leucocytes under the direction of chemokines differentiates the patterns of granuloma responses to pristane in C57BL/6J and BALB/cByJ mice.     

Macrophage activation during Plasmodium chabaudi AS infection in resistant C57BL/6 and susceptible A/J mice.

Macrophage activation was examined in resistant C57BL/6 and susceptible A/J mice during the course of blood-stage infection with Plasmodium chabaudi AS. Three parameters of macrophage activation (lipopolysaccharide [LPS]- and malaria antigen-induced tumor necrosis factor [TNF] production in vitro, phorbol myristate acetate [PMA]-induced production of oxygen metabolites in vitro, and Ia antigen expression) were assessed during infection in populations of peritoneal and splenic macrophages recovered from infected mice of the two strains. The peak level of LPS-induced TNF production in vitro by splenic macrophages from both infected C57BL/6 and infected A/J mice occurred on day 7, which was 3 days before the peak of parasitemia. Although the kinetics of TNF production in vitro in response to either LPS, soluble malaria antigen, or intact parasitized erythrocytes varied in some of the other macrophage populations during infection, there was no significant difference in the peak level of production. Peritoneal and splenic macrophages from infected C57BL/6 mice exhibited significantly increased PMA-induced production of H2O2 in vitro on day 7. Peritoneal macrophages from infected A/J mice also exhibited significant PMA-induced H2O2 production on day 7, while production by splenic macrophages from these hosts was not increased in comparison with production by cells from normal animals. Only peritoneal macrophages from infected C57BL/6 mice produced significantly increased levels of O2-, and this occurred on day 7 postinfection. Ia antigen expression by both peritoneal and splenic macrophages from resistant C57BL/6 and susceptible A/J mice was significantly increased during P. chabaudi AS infection. However, the percentage of Ia+ peritoneal macrophages on days 8 and 10 postinfection and Ia+ splenic macrophages on day 3 postinfection was significantly higher in C57BL/6 than in A/J mice. Thus, these results demonstrate that macrophages from P. chabaudi AS-infected A/J mice exhibit defects in oxygen metabolism and Ia antigen expression which may contribute to the susceptibility of these hosts to this intraerythrocytic parasite. The cause-and-effect relationship between these defects and the susceptibility of A/J mice to P. chabaudi AS is unknown.     

Role of complement C5 and T lymphocytes in pathogenesis of disseminated and mucosal candidiasis in susceptible DBA/2 mice

The aims of the study were to compare the pathogenesis of Candida albicans infection in various organs and anatomical regions of C5-deficient (DBA/2) and C5-sufficient (BALB/c) mice, and to evaluate the importance of complement C5 and T lymphocytes as factors that determine host susceptibility or resistance. The kidneys of DBA/2 mice showed higher colonisation and more severe tissue damage than those of BALB/c, but infection at other sites, including oral and vaginal mucosa, was generally similar in the two strains. Passive transfer of C5-sufficient serum into DBA/2 mice decreased the fungal burden in the kidney, and prolonged survival of the reconstituted animals. Depletion of CD4(+) and/or CD8(+) cells did not exacerbate either systemic or mucosal infection when compared to controls, and passive transfer of splenocytes from infected donors caused only a small and transient reduction in numbers of yeasts recovered from the kidney of sub-lethally infected recipients. It is concluded that the acute susceptibility of the kidneys in this mouse strain is due to C5 deficiency expressed on a susceptible genetic background. T lymphocytes, however, appear to have minimal influence on recovery from systemic infection with this isolate of C. albicans.     

Increased susceptibility of complement factor B/C2 double knockout mice and mannan-binding lectin knockout mice to systemic infection with Candida albicans

Candida albicans is the major cause of systemic fungal infections in immunocompromised patients. We investigated the susceptibility of mice deficient in complement factor B and C2 (Bf/C2(-/-)), C1q (C1qa(-/-)), and mannan-binding lectin (MBL)-A (MBL-A) and MBL-C (MBL-A/C(-/-)) to systemic infection with C. albicans. Animals were infected i.p. with 10(8)C. albicans blastoconidia and monitored for mortality. Bf/C2(-/-) mice showed high mortality (over 90%) within the study period of 3 weeks. In contrast, mortality in C1qa(-/-) mice was below 15% whereas that of MBL-A/C(-/-) mice was 40% (P<0.001). Intravenous infection of mice with 8x10(5) blastoconidia resulted in the same trend with Bf/C2(-/-) mice being highly susceptible compared to the other strains. Histology of kidney sections of infected Bf/C2(-/-) mice showed widespread mycelia confirming the high CFU counts from cultured tissue homogenates. In C1qa(-/-), MBL-A/C(-/-) and wild type C57BL/6 mice hyphal growth was limited. However, massive inflammatory infiltration was apparent, which was not seen in Bf/C2(-/-) mice. The ability of the mouse sera to opsonize C. albicans was determined by quantification of phagocytosis of C. albicans by peritoneal phagocytes. Whilst phagocytosis mediated by Bf/C2(-/-) mouse serum was low (10.6%), more phagocytosis could be seen in MBL-A/C(-/-) (19.9%), C1qa(-/-) mice (23.9%) and wild type mice (29%). Deficiency of classical pathway activation has only a low impact whereas the lectin pathway contributes to the host defence against candidosis. The more pronounced lack of complement activation in Bf/C2(-/-) mice leads to uncontrolled infection due to an opsonophagocytic defect.     

Quantitative, not qualitative, differences in CD8(+) T cell responses to Theiler's murine encephalomyelitis virus between resistant C57BL/6 and susceptible SJL/J mice

Theiler's murine encephalomyelitis virus (TMEV) infection of the CNS induces an immune-mediated demyelinating disease in susceptible mouse strains and serves as a relevant infection model for human multiple sclerosis. However, it is not yet clear what immunological parameters determine the susceptibility of SJL/J mice compared to resistant mice. We have here compared the TMEV-specific CD8(+) T cell responses in highly susceptible SJL/J mice with those of highly resistant C57BL/6 mice. Our results clearly indicate that the levels of initial responses of infiltrating CD8(+) T cells to viral capsid proteins are higher in resistant C57BL/6 mice compared to susceptible SJL/J mice. However, the level of virus-specific CD8(+) T cells was much more rapidly reduced in resistant C57BL/6, resulting in a higher CD8(+) T cell level in SJL/J mice later in viral infection. The activation states, cytokine production, as well as the cytolytic function of the CD8(+) T cells were similar to each other in these mice. These results suggest that an initial induction of a vigorous CD8(+) T cell response to TMEV is critically important for the resistance to virally induced demyelinating disease.     

Wallerian degeneration in C57BL/6J and A/J mice: differences in time course of neurofilament and myelin breakdown, macrophage recruitment and iNOS expression

The lower regeneration potential reported for C57BL/6J mice strain after peripheral nerve lesion may result from alterations in crucial events during Wallerian degeneration. We analysed neurofilament and myelin breakdown, macrophage recruitment, NADPH-diaphorase reaction and inducible nitric oxide synthase (iNOS) expression in transected sciatic nerves of C57BL/6J and A/J mice. The neurofilament volume density was lower in C57BL/6J strain mice at 1 and 3 days after lesion, and later equalled the density observed in A/J. C57BL/6J mice presented a high number of cells containing myelin debris, 3 and 5 days after the lesion. In both strains iNOS immunoreactivity was intense in macrophages and less evident in Schwann cells. However, a delay in macrophage recruitment and a lower percentage of iNOS-expressing macrophages on the third day were observed in C57BL/6J mice. NADPH-diaphorase reaction disclosed a similar pattern for both strains until the seventh day. However, at 5 days, cells with slender processes involving ellipsoid segments showed a well-defined cytoplasmic labelling in C57BL/6J whereas in A/J most of these cells exhibited a more granular and disperse labelling. We propose that these differences between A/J and C57BL/6J strains during Wallerian degeneration may be implicated in the lower regeneration potential observed in the latter.     

Influence of muramyl dipeptide on renal candidiasis in genetically distinct mice.

Susceptible (DBA/2) and resistant (C57BL/6) mice were inoculated intravenously with Candida albicans to evaluate the effect of a four-day prophylaxis with muramyl dipeptide (MDP) on the renal burden of organisms during the first week after infection. In sham-treated DBA/2 mice injected with 8 x 10(4) candida cells, renal CFU (LOG10 +/- SEM) on days 1, 4 and 7 after infection were found to average 5.050 +/- 0.109, 4.882 +/- 0.133 and 5.482 +/- 0.245. In sham-treated C57BL/6 mice injected with 2 x 10(5) candida cells, renal CFU on days 1, 4 and 7 reached only 3.610 +/- 0.118, 3.404 +/- 0.107 and 4.176 +/- 0.580. MDP-treated DBA/2 mice achieved significant reduction in CFU of C. albicans on day 1 (1.3 log units) and day 4 (0.6 log unit), while MDP-treated C57BL/6 mice had significant reduction in CFU of C. albicans only on day 1 (0.6 log unit) after infection. Sham-treated mice of both strains had a 28.6 to 30% increase in kidney weights on day 4 only, a transient change not seen in MDP-treated mice. Histopathological examination on days 8, 15 and 21 after infection revealed a higher incidence of renal papillary necrosis in DBA/2 mice than C57BL/6 mice (approximately 70% vs 10%). The incidence of granulomas and of chronic interstitial inflammation was much higher in MDP-treated mice. We conclude that the genetic makeup of the host influences the potential effectiveness of MDP as a biological response modifier.     

Multigenic control and sex bias in host susceptibility to spore-induced pulmonary anthrax in mice

Mechanisms underlying susceptibility to anthrax infection are unknown. Using a phylogenetically diverse panel of inbred mice and spores of Bacillus anthracis Ames, we investigated host susceptibility to pulmonary anthrax. Susceptibility profiles for survival time and organ pathogen load differed across strains, indicating distinct genetic controls. Tissue infection kinetics analysis showed greater systemic dissemination in susceptible DBA/2J (D) mice but a higher terminal bacterial load in resistant BALB/cJ (C) mice. Interestingly, the most resistant strains, C and C57BL/6J (B), demonstrated a sex bias for susceptibility. For example, BALB/cJ females had a significantly higher survival time and required 4-fold more spores for 100% mortality compared to BALB/cJ males. To identify genetic regions associated with differential susceptibility, survival time and extent of organ infection were assessed using mice derived from two susceptibility models: (i) BXD advanced recombinant inbred strains and (ii) F2 offspring generated from polar responding C and D strains. Genome-wide analysis of BXD strain survival identified linkage on chromosomes 5, 6, 9, 11, and 14. Quantitative trait locus (QTL) analysis of the C×DF2 population revealed a significant QTL (designated Rpai1 for resistance to pulmonary anthrax infection, locus 1) for survival time on chromosome 17 and also identified a chromosome 11 locus for lung pathogen burden. The striking difference between genome-wide linkage profiles for these two mouse models of anthrax susceptibility supports our hypothesis that these are multigenic traits. Our data provide the first evidence for a differential sex response to anthrax resistance and further highlight the unlikelihood of a single common genetic contribution for this response across strains.