Colonization and pathogenesis of Cryptococcus neoformans in gnotobiotic mice.

Congenitally immunodeficient nude (nu/nu) mice and their immunocompetent littermates (nu/+) were used to determine whether the absence of thymus-matured T cells would alter the capacity of Cryptococcus neoformans to colonize their mucosal surfaces or enhance their susceptibility to systemic cryptococcosis, or both, following oral challenge. We present data demonstrating that an encapsulated strain of C. neoformans serotype A colonized the alimentary tracts of germfree, conventional, and antibiotic-treated conventional nu/nu mice. Scanning electron microscopy showed that C. neoformans adhered to the epithelial surfaces of the oral cavities, esophagi, and gastrointestinal tracts of monoassociated nu/nu and nu/+ mice, and culture data showed that there were more viable C. neoformans cells in the alimentary tracts of nu/nu mice than of nu/+ mice. Tetracycline-treated conventional nu/nu, but not nu/+, mice were also colonized with C. neoformans following intragastric challenge. C. neoformans-monoassociated and tetracycline-treated conventional nu/nu mice succumbed to disseminated cryptococcosis with cerebral involvement 3 to 4 weeks after oral challenge, whereas no mortality was observed for similarily challenged nu/+ mice. These results demonstrate that an encapsulated strain of C. neoformans can colonize mucosal surfaces and cause systemic cryptococcosis in immunodeficient nu/nu mice, suggesting that the alimentary tract can be a portal of entry for C. neoformans in an immunodeficient host. These data also indicate that functional T cells play an important role in resistance to systemic cryptococcosis of endogenous origin.     

Genetic resistance to murine cryptococcosis: the beige mutation (Chédiak-Higashi syndrome) in mice

The influence of the bgJ and bg2J mutations on the susceptibility of mice to experimental cryptococcosis was studied in inbred mice of the C57BL/6J and C3H/HeJ strains. Although infected animals with the bg/bg genotype had a significantly shorter lifespan than bg/+ or +/+ animals, C3H/He beige-2J mice were less susceptible than C57BL/6 beige-J mice when compared with nonbeige mice of similar background. On days 18 and 19 after infection, quantitation of cryptococci in the brain, liver, and spleen revealed that the overall burden of organisms in infected C57BL/6 beige-J mice was in excess of one log unit above that found in the brain, liver, and spleen of infected C57BL/6 +/+ mice. At that time, C57BL/6 beige-J mice showed a 53% increase in mean brain weight, a 67.8% decrease in mean liver weight, and a 58.6% decrease in mean spleen weight, when compared with uninfected animals of the same age and genetical lineage. The corresponding figures for C57BL/6 +/+ mice were a 32% increase in mean brain weight, a 41.4% decrease in mean liver weight, and a 23.4% decrease in mean spleen weight. From these data, it is concluded that the beige mutation in mice is associated with increased susceptibility to cryptococcosis, the accrued susceptibility of the beige mutant is related to more rapid changes in the weight profile of the target organs as well as to a higher rate of growth or decreased clearance of Cryptococcus neoformans or both, and other autosomal genes are likely to be involved in the genetic control of susceptibility to murine cryptococcosis.     

Role of natural killer cells in resistance to systemic cryptococcosis

These studies demonstrate that Cryptococcus neoformans infection induced a dose-dependent augmentation of splenic natural killer (NK) cell activity by bg/+, but not bg/bg mice. To directly assess the role of NK cells in resistance to C. neoformans, bg/+ and bg/bg mice were treated with anti-NK-1.1 monoclonal antibody (mAb). Anti-NK-1.1-treatment abrogated the augmented NK cell activity observed during C. neoformans infection in bg/+ mice. Anti-NK-1.1-treated bg/+ mice had higher C. neoformans colony forming units (CFU) in their lungs on days 3 and 7 after intravenous (i.v.) challenge than control bg/+ mice. Moreover, the number of C. neoformans CFU in the lungs of anti-NK-1.1-treated bg/+ mice on days 3 and 7 were similar to those observed for infected bg/bg mice. By day 14, however, no differences in C. neoformans CFU were evident in the lungs of anti-NK-1.1-treated and control bg/+ mice. Anti-NK-1.1-treatment did not alter either the growth of C. neoformans in the spleens, livers, kidneys, or brain of bg/+ mice or the susceptibility of bg/bg mice to systemic cryptococcosis. These studies suggest that NK cells do not play a role in resistance to systemic cryptococcosis in the spleen, but do appear to play an early, but transient role in resistance to C. neoformans in the lungs. Overall, congenital defects in polymorphonuclear neutrophils (PMNs) and macrophages (M phi s), in addition to defects in NK cells, contribute to the enhanced susceptibility of bg/bg mice to systemic cryptococcosis.     

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.     

Chronic giardiasis in B-cell-deficient mice expressing the xid gene.

The role of antibody in immunity to Giardia muris infection was investigated by studying B-cell-deficient CBA/N mice expressing the xid gene. After gastric administration of infective G. muris cysts, CBA/N male and female mice developed prolonged G. muris infection, whereas BALB/c mice eliminated their infection in 6 to 8 weeks. Male F1 progeny obtained from matings between female CBA/N mice and male BALB/c mice expressed the xid gene and developed prolonged infections. In contrast, all other F1 progeny of CBA/N and BALB/c matings, which did express the xid gene, eliminated G. muris. The link between the xid gene and prolonged infection was confirmed by studies of C57BL/6 mice congenic for the xid gene. When compared with BALB/c or F1 mice, CBA/N mice produced large quantities of immunoglobulin A (IgA) anti-G. muris antibody in serum and gut secretions during prolonged infection. Serum IgG anti-G. muris antibody levels were reduced in CBA/N and F1 male mice that expressed the xid gene. The inability of xid mice to eliminate G. muris is consistent with the importance of antibody in the development of immunity to G. muris. We hypothesize that mice bearing the xid gene fail to produce IgA antibody of appropriate specificity to an antigen or antigens whose recognition by antibody is critical for successful elimination of the parasite.     

Pathogenesis of Cryptococcus neoformans in congenitally immunodeficient beige athymic mice.

Mortality after intravenous challenge with 10(4) Cryptococcus neoformans demonstrated that doubly immunodeficient beige athymic (bg/bg nu/nu) mice were more susceptible to systemic cryptococcosis than either bg/bg or nu/nu mice. Infected bg/bg nu/nu mice also had a shortened lifespan compared with their bg/bg nu/+ littermates. Beige athymic (bg/bg nu/nu) but not bg/bg nu/+mice developed cryptococcal lesions in the skin, demonstrating that C. neoformans is dermatotropic in a T-cell-deficient host. Higher numbers of C. neoformans were isolated from the lungs and spleen of infected bg/bg nu/nu than bg/bg nu/+ mice as early as day 3 after challenge, indicating that in lymphoid-rich organs, T cells can alter the course of systemic cryptococcosis early in the infection. Despite extensive abscess formation in the brains of bg/bg nu/+ mice, dissemination and growth rate of C. neoformans in the brain was similar in both genotypes. The primary histopathological feature in tissues from bg/bg nu/nu mice infected with C. neoformans consisted of foci of encapsulated yeast cells with minimal to no inflammatory response. In contrast to bg/bg nu/nu mice, bg/bg nu/+ mice mounted a vigorous inflammatory response to C. neoformans that progressed from acute to chronic inflammation. Beige athymic mice are a new animal model that will be useful in clarifying the innate and acquired immune factors important in resistance to cryptococcosis.     

Defective immunoglobulin M responses to vaccination or infection with Schistosoma mansoni in xid mice.

Mice vaccinated with irradiated Schistosoma mansoni cercariae develop a persistent immunoglobulin M (IgM) antischistosomulum antibody response. To investigate the possible role of antilarval IgM antibodies in the effector mechanism of vaccine-induced immunity, CBA/N mice, which have an X-linked genetic defect resulting in impaired IgM antibody responses to certain antigens, were analyzed for their resistance to a challenge infection. When either infected with unattenuated parasites or vaccinated with irradiated cercariae, mice of this inbred strain failed to produce detectable IgM antibodies to schistosomulum surface membrane and soluble worm antigens. To analyze the effect of this IgM deficiency on immunity, F1 hybrids were constructed between CBA/N females and nondefective C57BL/6J males. As expected, vaccinated (CBA/N X C57BL/6J)F1 females, as well as (CBA/J X C57BL/6J)F1 males and females, produced normal IgM antibodies to both surface antigens and worm antigen extracts. However, such antibodies were not produced by (CBA/N X C57BL/6J)F1 males (hemizygous for xid). Nevertheless, (CBA/N + C57BL/6J)F1 males displayed the same high levels of immunity to challenge infection as (CBA/N X C57BL/6J)F1 females and (CBA/J X C57BL/6J)F1 males and females. These results indicate that vaccine-induced immunity is not dependent on an IgM response to schistosome antigens.     

A monoclonal antibody to gamma interferon blocks augmentation of natural killer cell activity induced during systemic cryptococcosis.

These studies demonstrate that the cytotoxic activity of splenic natural killer (NK) cells is augmented in both nu/nu and nu/+ mice during systemic cryptococcosis. Both the kinetics and the regulation of NK cell activity differed in Cryptococcus neoformans-infected nu/nu and nu/+ mice. Greater augmentation was observed following challenge with 10(5) cells than with smaller inocula, and augmented NK cell activity was not always associated with enhanced control of systemic cryptococcosis. Infection with a nonencapsulated strain of C. neoformans induced an early but transient increase in splenic NK cell activity in nu/nu and nu/+ mice. Injection of capsular polysaccharide induced a transient augmentation of splenic NK cell activity in nu/+ mice but caused a persistent increase in splenic NK cell activity in nu/nu mice. In vivo treatment with monoclonal antibody to gamma interferon abrogated the augmentation of splenic NK cell activity induced during cryptococcal infections in both nu/nu and nu/+ mice and enhanced the susceptibility of nu/+ mice to C. neoformans to a greater extent than it did that of nu/nu mice. These results suggest that gamma interferon is an important mediator of resistance to C. neoformans.     

Strain-Dependent Differences in Murine Susceptibility to Coccidia

Differences in susceptibility of strains of mice to Eimeria ferrisi were observed by infecting eight strains of mice with six infectious dose levels and comparing the mortality rate among the strains for a period of 12 days. Mice of the C57BL/6 and HA/ICR strains were susceptible, and those of A/He, AKR, BALB/c, CBA, C3H/Anf, and DBA/2 strains were resistant to coccidial infection. Resistance was a dominant genetic expression, as indicated by the resistant response of F(1) hybrids of susceptible C57BL/6 and resistant CBA, C3H/Anf, or DBA/2 strains. An E. ferrisi infection in congenitally athymic nu/nu mice and phenotypically normal heterozygous nu/+ mice was used to determine how thymus-dependent immunoincompetence in cell-mediated immunity of the nu/nu mouse affected resistance to infection in a genetic background of the resistant BALB/c mouse. Results of primary and challenge infections in these two strains of mice suggested that resistance is thymus dependent. Furthermore, impairment of thymus-dependent cell-mediated immunity in resistant AKR mice by treatment with mouse antithymus serum led to partial susceptibility. However, susceptible C57BL/6 and HA/ICR strains are phenotypically normal mice, and previous evidence showed that C57BL/6 mice are not completely immunoincompetent in cell-mediated reactivity to coccidia. Collectively, our data show that cell-mediated immunity is necessary for resistance but may be subjected to modification by genetic expression of the host. The possible role of immune response genes in the control of coccidial immunity is discussed.     

Biochemical Characterization of the T-Cell Mitogen Derived from Mycoplasma arthritides.

A biochemical procedure is described to purify the T-cell mitogen in the supernatant of cultured Mycoplasma arthritidis organisms. The mitogenic material was bound on an affigel blue column. The eluate of this column was then acylated at 0 degrees C for 1.5 h and subsequently chromatography on a Sepharose Cl 6B and a Superose 12HR column were performed. SDS-PAGE showed a major band at MW 26,000 and some minor bands at 50,000. With this material biological tests were performed, including induction of lymphoproliferation and interferon induction in murine spleen cell cultures. Purified Mycoplasma arthritidis supernatant (MAS) vigorously stimulated spleen cell cultures of A/J, CBA, C3H/He, and DBA/2 mice, whereas a low-grade but definitive response was observed in C57BL/6 spleen cells. Cultures of Balb/c nu/nu mice, in contrast to those of their euthymic littermates, were non-reactive. When induction of interferon was tested, a marked response to purified MAS was observed in CBA and C3H/HeJ spleen cell cultures, whereas C57BL/6 spleen cells were non-reactive.     

Genetic Analysis of the Low Responsiveness to Dextran B512 in CB A/N and C57BL/10ScCr Mice

CBA/N and C57BL/10ScCr mice are low responders to the antigen dextran B512. This is due to the Xid gene in CBA/N mice and to unknown genes in C57BL/10ScCr mice, although this strain is unresponsive to lipopolysaccharide (LPS) due to a defective gene in the fourth chromosome. The female F1 hybrids (C57BL/10ScCr X CBA/N) and (CBA/N X C57BL/10ScCr) were low responders to dextran, although the Xid gene is not expressed in these hybrids, indicating lack of genetic complementation. In contrast, female F1 hybrids between the dextran high-responder strains CBA or C57BL/10 as one parental strain and the low-responder strains CBA/N or C57BL/10ScCr as the other parental strain, respectively, were responders to dextran. The C57BL/10ScCr mice did not appear to have an X-linked gene determining low responsiveness to dextran. The findings suggest that the only defect in CBA/N mice cannot be the Xid gene and the only defect in C57BL/10ScCr mice cannot be the gene determining unresponsiveness to LPS.     

Cytotoxic cell populations in normal and alloimmunized pregnant mice

Cytotoxic cell activity directed against paternal alloantigens was investigated in primiparous C57BL/10 and CBA/Ca mice using a microcytotoxicity assay. Most allogeneically or syngeneically mated females lacked effector cells in their spleens or paraaortic lymph nodes both during pregnancy and immediately postpartum. However, spleen, cells from 33% of C57BL/10 females mated to CBA/Ca males exhibited low levels of paternal target cell killing (P less than 0.05-0.01). Alloimmunization of virgin mice prior to mating resulted in only allogeneically mated females producing cytotoxic cells and alloantibody. These responses were not detectable during pregnancy but appeared immediately postpartum. The ability of pregnancy to induce memory cell formation was tested by allowing females one successful pregnancy before challenging them postpartum with allogeneic spleen cells. Kinetic studies of cytotoxic cell production showed that C57BL/10 females that had borne (C57BL/10 X CBA/Ca)F1 litters responded earlier than their syngeneically mated sisters giving a peak response at 4 days compared to 7 days after immunization. This indicates that a single allogeneic pregnancy can prime the mother against paternal alloantigens suggesting that the conceptus is weakly immunogenic.     

Protective efficacy of antigenic fractions in mouse models of cryptococcosis

Infections due to the encapsulated fungus Cryptococcus neoformans are a significant cause of morbidity and mortality in patients with impaired T-cell function, particularly those with AIDS. Presumably then, T-cell responses to cryptococcal antigens are critical for protection against this ubiquitous fungus. To test the protective efficacy of these antigens as vaccine candidates, secreted cryptococcal antigens were separated by concanavalin A affinity chromatography into adherent (mannoprotein [MP]) and nonadherent (flowthrough [FT]) fractions, and the fractions were tested in murine models of disseminated cryptococcosis. Compared with adjuvant alone, C57BL/6 mice that received two inoculations of MP and FT exhibited prolonged survival and reduced brain and kidney fungal loads following intravenous challenge with C. neoformans strain B3501. MP-immunized animals had increased brain levels of tumor necrosis factor alpha, gamma interferon, and interleukin-2. Histopathologic examination revealed that compared with organs from mice that received only adjuvant, MP-immunized mice were able to recruit a stronger cellular infiltrate in brain, kidney, and liver in response to cryptococcal infection. Conjugated O-linked glycans were necessary for optimal MP-mediated protection, because chemical O deglycosylation reduced the protective efficacy of MP immunization. FT and MP immunization protected B-cell-deficient, but not T-cell-deficient mice, suggesting that protection was T-cell mediated. CBA/J mice also benefited from immunization with FT and MP, although the benefits were more modest than those seen with C57BL/6 mice. Thus, both MP and FT fractions of C. neoformans contain components that protect mice from disseminated cryptococcosis, and this protection appears to be T-cell mediated.     

The capsule of Bacillus anthracis behaves as a thymus-independent type 2 antigen

Bacillus anthracis elaborates a homopolymeric capsule composed of gamma-D-glutamic acid residues. Mice were immunized with formalin-fixed encapsulated B. anthracis bacilli, and the serum antibody response to a gamma-D-glutamyl capsular epitope was measured. Antiglutamyl antibodies were elicited in athymic BALB/c Nu/Nu, BALB/c Nu/+, and CBA/J mice but not in CBA/N xid mice. These response patterns define the capsule of B. anthracis as a thymus-independent type 2 antigen.     

Analysis of peripheral immune tolerance uncovers a mouse strain-dependent in situ type of graft tolerance

We screened various mouse strains [C57BL / 6, BALB / c, DBA / 2, CBA / Ca, (CBAxC57L / 6)F1, SJL, C3H] for induction of peripheral immune tolerance. Only CBA / Ca mice treated with anti-CD4 + CD8 monoclonal antibodies and grafted with allogeneic skin showed long-term graft survival (150 to > 200 days). Interestingly, T cells from the tolerant CBA / Ca mice rejected bone marrow / spleen cells of the skin graft donor strain and caused lethal graft-versus-host disease when transplanted to the donor strain. Furthermore, peripheral tolerance was easily broken: CBA / Ca mice could be reactivated to reject their tolerated grafts via immunization with (graft donor x recipient strain)F1 bone marrow cells. Thus, in contrast to the generalized nature of central tolerance, our experiments show that peripheral immune tolerance is strain dependent and locally restricted to graft tissue.     

Experimental Cryptosporidium parvum infections in immunosuppressed adult mice.

Five strains of adult mice were immunosuppressed with the synthetic glucocorticosteroid dexamethasone (DEX), administered either orally or intraperitoneally. The strains of mice used were C57BL/6N, DBA/2N, CBA, C3H/HeN, and BALB/cAnN. All mice were evaluated for susceptibility to Cryptosporidium parvum after intragastric inoculation with 10(6) oocysts per mouse. The DBA/2N, CBA, C3H/HeN, and BALB/cAnN mice given 0.25 micrograms of DEX per g per day orally (the dose and route previously used to infect rats with C. parvum) failed to develop chronic infections. However, the C57BL/6N mice sustained light infections during the entire 28-day experiment. The five strains of mice were also administered DEX intraperitoneally at concentrations ranging from 62.5 to 500 micrograms/day. Only the C57BL/6N mice given DEX at 125 micrograms/day developed chronic infections which persisted over 10 weeks, suggesting that the genetic background of the mouse plays a role in determining susceptibility to cryptosporidosis following immunosuppression with DEX. We believe that the C57BL/6N mouse model will prove to be superior to other animal models for evaluating potential anticryptosporidial agents, as well as for elucidating the immunological defects that allow C. parvum to establish chronic infections, because of cost effectiveness and ease in maintenance, breeding, and handling. We also evaluated the C3H/HeJ/beige mouse (lacks natural killer cell activity) and the C57BL/6N mouse maintained on a low-protein diet to induce immunosuppression. Neither of these mice exhibited heavy cryptosporidial infections.     

Comparison of susceptibility of inbred and outbred infant mice to Escherichia coli heat-stable enterotoxin STa.

Comparison of the susceptibility of outbred OF1 and inbred BALB/c, C57BL/6, DBA/2, and CBA mice to heat-stable toxin (STa) of enterotoxigenic Escherichia coli was made at different levels of induced secretion. STa was able to elicit fluid accumulation into the intestine of each strain of mice; however, quantitatively different results were obtained. Results were as usual expressed by gut weight/remaining body weight ratios. Fluid accumulation weight and fluid accumulation weight/remaining body weight ratios were also estimated. Values obtained for BALB/c and OF1 mice were never significantly different, but values for OF1 mice were significantly higher than those for DBA and C57BL/6 mice at the highest concentrations of toxin (toxin dilutions of 1/2, 1/4, and 1/5). At the highest toxin concentration, gut weight/remaining body weight ratio in C57BL/6 mice was significantly lower than that for every other strain, but the fluid accumulation value obtained for DBA mice did not differ from that for C57BL/6 mice. Fluid accumulation values for DBA mice were also significantly lower at toxin dilutions of 1/5 and 1/8 than those for every other strain, and this was also the case when estimating the fluid accumulation weight/remaining body weight ratio at a dilution of 1/8. Although the intestine of each strain of mice was able to respond to STa by fluid accumulation, differences in susceptibility of the STa receptor could exist and make DBA mice more resistant to enterotoxigenic E. coli diarrhea.     

Cellular requirements for anti-DNA production induced in mice by immunization with bacterial DNA

To further define DNA immunization as a model for anti-DNA production, we investigated the cellular requirements for this response in mice immunized with single-stranded DNA from E. coli. The anti-DNA responses of genetically immune-deficient mice and congenic controls were measured by ELISA after immunization with E. coli DNA as complexes with methylated bovine serum albumin in complete Freund's adjuvant. T cell-deficient BALB/c-nu/nu mice failed to produce IgG anti-DNA by this protocol despite high backgrounds of IgM anti-DNA. In contrast, CBA/N mice expressing the xid defect displayed IgG anti-DNA responses comparable to those of CBA/J mice despite a reduced IgM response; the specificity of CBA/N and CBA/J anti-DNA antibodies was similar as determined by binding to synthetic DNA and RNA antigens. These results suggest that the anti-DNA response stimulated by DNA immunization is dependent on T cells but not the B cell population affected by xid. The intact IgG response of immunized xid mice differs from that of lupus mice bearing xid where this gene defect leads to significant reduction of spontaneous anti-DNA production.     

Sex differences in the genetic architecture of susceptibility to Cryptococcus neoformans pulmonary infection

Cryptococcus neoformans is a major cause of fungal pneumonia, meningitis and disseminated disease in the immune compromised host. Here we have used a clinically relevant model to investigate the genetic determinants of susceptibility to progressive cryptococcal pneumonia in C57BL/6J and CBA/J inbred mice. At 5 weeks after infection, the lung fungal burden was over 1000-fold higher in C57BL/6J compared to CBA/J mice. A genome-wide scan performed on 210 male and 203 female (CBA/J x C57BL/6J) F2 progeny using lung colony-forming units as a quantitative trait revealed a sex difference in genetic architecture with three loci (designated Cnes1-Cnes3) associated with susceptibility to cryptococcal pneumonia. Single locus analysis identified significant loci on chromosomes 3 (Cnes1) and 17 (Cnes2) with logarithm of the odds (LOD) scores of 4.09 (P=0.0110) and 7.30 (P<0.0001) that explained 8.9 and 15.9% of the phenotypic variance, respectively, in female CBAB6F2 and one significant locus on chromosome 17 (Cnes3) with a LOD score of 4.04 (P=0.010) that explained 8.6% of the phenotypic variance in male CBAB6F2 mice. Genome-wide pair-wise analysis revealed significant quantitative trait locus interactions in both the female and male CBAB6F2 progeny that collectively explained 43.8 and 19.5% of phenotypic variance in each sex, respectively.