Influence of mouse genotype and bacterial virulence in the generation of interferon-gamma-producing cells during the early phase of Salmonella typhimurium infection.

Interferon-gamma (IFN-gamma) is known to play a major role in resistance to Salmonella typhimurium infection. In this study, the IFN-gamma production in spleens of mice infected with S. typhimurium was analysed at the single cell level using an ELISPOT method. The in vivo IFN-gamma production during the early phase of infection with virulent and avirulent S. typhimurium strains was examined in four mouse strains. Data show that infection with a virulent strain of S. typhimurium caused a much greater enhancement in the frequency of IFN-gamma-producing cells in innately resistant (ltyr) mice (CBA and DBA/2) than in susceptible (ltys) mice (C57BL/6 and BALB/c). In contrast, infection with an avirulent strain of S. typhimurium induced a clear increase in the number of IFN-gamma-producing cells in susceptible mice which was even greater than in resistant ones. These results indicate that both the host genetic background and bacterial virulence play a critical role in the regulation of IFN-gamma production during the early phase of S. typhimurium infection.     

The full expression of the ity phenotype in ityr mice requires C3 activation by Salmonella lipopolysaccharide.

Our previous study has shown that the rapid and sufficient activation of complement by Salmonella lipopolysaccharide occurs in genetically resistant (Ityr) A/J mice. To assess whether the level of complement activation by a virulent strain of Salmonella typhimurium regulates the level of murine natural resistance, we compared levels of serum complement activation by S. typhimurium and kinetics of serum-opsonized S. typhimurium grown in macrophages using several strains of resistant (Ityr) and susceptible (Itys) mice. Itys macrophages killed intracellular S. typhimurium to the same extent as did Ityr macrophages when the pathogen was opsonized with Ityr serum. Opsonization of S. typhimurium with Itys serum reduced intracellular killing activity in Ityr macrophages to the same level as seen with Itys macrophages. Incubation of S. typhimurium with 25% Mg2+ EGTA (5 mm MgCl2-3 mm ethylene glycol-bis (beta-aminotheyl either)-N,N,N',N'-tetraacetic acid)-chelated Ityr serum resulted in higher levels of C3 deposition onto the surface of this bacteria, C3b generation and also C3 consumption, compared with that with Mg2+ EGTA-chelated Itys serum. Opsonization of S. typhimurium with A/J serum prior to infection increased early resistance in Itys mice. Infection with a virulent strain of S. typhimurium induced the expression of interleukin-10 (IL-10) mRNA at higher levels in C57BL/6 mice than in A/J mice. However, opsonization of S. typhimurium with A/J serum decreased bacterial growth in the spleen of C57BL/6 mice to the same level as observed for A/J mice in association with decreased expression levels of IL-10 mRNA. Moreover, administration of anti-C3 antibodies reduced the resistance of A/J mice in association with a decrease in serum levels of C3. These results indicate that the high level of complement activation via the alternative pathway in Ityr serum by a virulent strain of S. typhimurium reduces the virulence of this pathogen, which may contribute to the full expression of Ity phenotype in Ityr mice.     

Genetic control of in vitro natural cell-mediated activity against Salmonella typhimurium by intestinal and splenic lymphoid cells in mice.

In vitro natural anti-bacterial activity against Salmonella typhimurium by lymphocytes from Peyer's patches and spleens was assessed in several mouse strains. C3H/HeN and CBA/J mice, which are resistant to S. typhimurium infections, showed a natural anti-bacterial activity significantly higher than BALB/c, C57BL/10, C57BL/6 and C3H/HeJ mice, i.e. strains susceptible to the in vivo bacterial infection. In these susceptible strains and also in A/J mice, a significantly higher natural activity was observed in females compared to males. The sex control of natural anti-bacterial activity was further stressed by the fact that orchidectomy could induce a strong activity in low responder C57BL/10 male mice. With the exception of Beige mice, a low natural killer (NK) strain also with no natural activity against S. typhimurium in both sexes, the genetic distribution of natural anti-bacterial activity was extremely different from that of the NK activity. Thus, these results further stress the difference between natural anti-bacterial activity and NK cytotoxicity. Furthermore, our data establish a possible link, although with some exceptions, between in vivo susceptibility to S. typhimurium infections and in vitro natural activity against these bacteria.     

The Salmonella typhimurium virulence plasmid increases the growth rate of salmonellae in mice.

The virulence plasmids of Salmonella typhimurium and other invasive Salmonella serovars have long been associated with the ability of these bacteria to cause systemic infection beyond the intestines in orally inoculated animals. Genetic analysis of virulence genes on the high-molecular-weight plasmids has revealed that no more than five genes spanning a 6.2-kb region are sufficient to replace the entire plasmid for conferring virulence. However, the exact virulence function(s) encoded by these genes has not been elucidated. In this report, we measured the possible effect of the virulence plasmid on the growth rate of S. typhimurium in mice by two complementary procedures. The first procedure used segregation of a temperature-sensitive plasmid in vivo to provide a measure of bacterial divisions and the number of recovered marker plasmid-containing salmonellae as a measure of killing. In the second procedure, aroA deletions were transduced into virulence plasmid-containing and plasmid-cured S. typhimurium. Since AroA- salmonellae are inhibited for growth in vivo, if the virulence plasmid affected only growth rate, no difference in the recoveries of the paired AroA- strains would be seen. Virulence plasmid-containing S. typhimurium segregated the marker plasmid more rapidly than did the virulence plasmid-cured strain, and AroA- derivatives of both strains were recovered equally from mice. Therefore, the S. typhimurium virulence plasmid increased growth rate but had no detectable effect on killing or bacterial movement into deep tissues. To examine whether the plasmid accomplished this function by affecting the intracellular/extracellular location of bacteria, orally infected mice were injected with gentamicin to kill the extracellular bacteria. Wild-type and plasmid-cured S. typhimurium strains were equally resistant to gentamicin in vivo and hence most likely located intracellularly to equal degrees. When wild-type and plasmid-cured S. typhimurium strains were sequestered within peritoneal chambers in mice, the resulting extracellular growth was equal. Therefore, the virulence plasmid increases the growth rate of S. typhimurium in mice, probably within mouse cells.     

Genetics of natural resistance to salmonellae in mice.

The genetics of natural resistance to salmonellae were studied in F1 hybrid and backcross mice. Overall resistance to Salmonella typhimurium C5 is complex, but one parameter, the early net growth rate of the organism in vivo, is controlled by a single autosomal gene or cluster of genes. 'Slow' net growth rate is necessary but insufficient, for resistance to S. typhimurium C5. Resistance requires the participation of other mechanisms, detectable by the end of the first week, which presumably involve an immune response. F1 hybrids bred from parents of low, intermediate and high natural resistance showed either high or low resistance. Most of the F1 hybrids were of a similar high resistance, and were bred from pairs in which at least one parent showed slow net growth rate. Hybrids of low resistance were only obtained when neither parent showed slow net growth rate. No hybrid was less resistant than the parents, many were more resistant. Backcross analysis on two hybrids challenged with S. typhimurium C5 supports the hypothesis of complex genetic control of overall resistance but with single gene control of the early net growth rate of the organism. Similar experiments were performed using a much more virulent organism, S. enteritidis 5694. All mouse strains were very susceptible (LD 50 less than ten organisms) to this strain given either i.v. or s.c. This organism produced an overwhelming infection which did not allow the cell-mediated immune response time to develop. This, however, did not interfere with the mechanism controlling early net growth rate, and genetic analysis using this organism gave similar results to those obtained with S. typhimurium C5. These results suggest that the mechanism regulating early net growth rate does not operate via the cell-mediated immune response, which develops later in the course of the infection.     

Genetic control of Salmonella typhimurium-induced depression of delayed-type hypersensitivity to sheep erythrocytes in mice.

Infection of mice with a temperature-sensitive mutant of Salmonella typhimurium C5TS allowed the survival of genetically susceptible mice. The ability to mount a delayed-type hypersensitivity (DTH) response to sheep erythrocytes during infection with C5TS was studied in various inbred mouse strains, recombinant inbred strains derived from C57BL/6 (susceptible) and A/J (resistant) mice, and C3H congenic mice. Suppression of the DTH response to sheep erythrocytes was found in mice that carried the Itys allele, the H-2b haplotype, or both. These genes are known to increase susceptibility to S. typhimurium infection. In contrast, no DTH response suppression was observed in mouse strains that carried other genes that increased susceptibility to S. typhimurium, e.g., DBA/2 and C3H/HeJ. Apart from a transient suppression in A/J mice, the DTH responses of resistant mice (A/J and CBA) were normal or increased. The DTH response to sheep erythrocytes could be restored in immunodepressed mice by increasing the immunizing dose, suggesting the possible role of activated macrophages in depression of the DTH response.     

Genetic control of resistance to Salmonella typhimurium infection in high and low antibody responder mice.

Mice selected by Biozzi for high and low responses to sheep erythrocytes were investigated for resistance to subcutaneous Salmonella typhimurium infection. The resistance was measured by LD50 values, viable bacterial counts in liver and spleen at 10 days, and the kinetics of infection over 4 weeks. High responder mice were susceptible to S. typhimurium injected subcutaneously (LD50 less than 10) and low line resistant (LD50 3 x 10(6)). Control of natural resistance to S. typhimurium in inbred mice is primarily by a single gene. Ity, on chromosome 1. Results with hybrid generations of Biozzi mice with either BALB/c (sensitive) or CBA (resistant) inbred mice indicated additional genetic control of resistance in Biozzi mice. Analysis of resistance data of backcrosses of (high x low)F1 with either parental strain showed this genetic control to be at least one other gene in the Biozzi mice, not linked to Ity. The antibody responses in the hybrid generations and inbred and Biozzi parental strains were tested by haemagglutination assays and ELISA. After specific stimulation of the mice there was an inverse relationship between resistance to S. typhimurium and antibody levels.     

Locating salmonella resistance gene on mouse chromosome 1.

The inherited resistance of inbred mouse strains to Salmonella typhimurium injected subcutaneously has been reported to be controlled primarily by a single gene designated Ity. Resistant mice have the dominant allele Ityr and sensitive mice are homozygous for the recessive allele Itys. This paper describes studies undertaken to locate the gene using readily distinguishable phenotypes as chromosome markers. Appropriate F1 backcross and F2 generations of hybrids between resistant and susceptible inbred strains of mice, with or without the particular phenotypic markers, were tested both for susceptibility to salmonella sci and presence of the marker. Independent segregation of the characteristics eliminated all chromosomes except Chromosome 1. C57L mice resistant to S. typhimurium, Ityr Ityr and leaden, ln ln, located on Chromosome 1, were crossed with BALB/c mice sensitive to S. typhimurium and non-leaden. In the F2 generation mice, ln always segregated with Ityr. The presence of only one leaden mouse sensitive to S. typhimurium out of sixty leaden F2 mice tested linked Ityr closely with ln on Chromosome 1. This result will be of use in further experiments with hybrid populations by enabling us to predetermine resistance or sensitivity to S. typhimurium without infecting the mice, so permitting experiments on the nature of the inheritance in unsensitized mice.     

Natural resistance to Salmonella typhimurium in different inbred mouse strains.

The mechanisms of natural resistance to intravenous challenge with Salmonella typhimurium C5 are complex. LD50 determinations showed inbred mouse strains of low, intermediate and high natural resistance, with BALB/c and B10 strains the most susceptible, A/J the most resistant. Delayed (footpad) hypersensitivity was not by itself a measure of natural resistance. Resistant mouse strains sensitized either s.c. or i.v. with an attenuated salmonella strain showed positive 48 h footpad reactions when tested 8 days later with a salmonella extract, but three very susceptible strains also showed positive reactions. Determinations of the in vivo net growth rate of salmonellae in the liver and spleen during the first phase of the infection (up to day 4) arrange the different mouse strains into two categories of fast and slow net growth rate. All fast net growth rate strains are susceptible, but not all slow net growth rate strains are resistant. Besides slow net growth rate, resistance requires the participation of other factors appearing in the second phase of the infection (towards the end of the first week) probably involving the cellular immune response, which halts further bacterial growth. Not all slow net growth rate strains are equally capable of suppressing bacterial growth in this second phase. The host mechanism determining slow net growth rate is inherited as a dominant trait, and appears to be operating before the main cellular immune response. The influence of this mechanism on net growth rate is reflected in the time to death following a given dose of salmonellae. The present results suggest that overall resistance to salmonellae is polygenic, but that the mechanism responsible for the differences in early net growth rate is less complex.     

Early haemopoietic responses to Salmonella typhimurium infection in resistant and susceptible mice.

The response of colony forming cells in the bone marrow and spleen of resistant (CBA) and susceptible (C57BL) mice to Salmonella typhimurium infection was studied for 4 days after infection. The number and size of the colonies were assessed. The resistant strain exhibited an immediate response to challenge, sharply increasing the number of colonies to 2.5 times normal over 2-3 days after infection. In contrast the susceptible strain gave a slowly increased response to the same challenge, which never exceeded 1.2 times normal and fell to 0.8 times the normal. When mouse strains were immunized there was a clear distinction between the splenic and bone marrow cellularity. Immunization appeared to enhance the splenic cellularity in resistant mice but failed to in susceptible mice. In the bone marrow of susceptible mice, however, there was some evidence of an elevated response.     

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.     

Inbred mouse strain resistance to Mycobacterium lepraemurium follows the Ity/Lsh pattern.

Inbred mouse strains and their F1 hybrids infected intravenously with Mycobacterium lepraemurium showed different mean survival times (MST). BALB/c and C57BL mice were particularly susceptible, whereas C3H, CBA and DBA/2 mice were relatively resistant. Resistance as judged by MST was dominant in the F1 hybrids. A similar ranking order was obtained by comparing the doubling time of the bacillus in the bone marrow, the increase in spleen weight between 4 and 12 weeks after infection, and the pathology of the liver during infection. The general pattern suggests that mouse resistance to M. lepraemurium is, at least in part, controlled by a gene with the same strain distribution as the genes for resistance to Salmonella typhimurium (Ity') and Leishmania donovani (Lsh') and the gene controlling resistance to Mycobacterium bovis BCG (Bcg). Ity, Lsh and Bcg are all known to be on chromosome 1, suggesting a centre controlling reactions to intracellular infections.     

Resistance to murine cytomegalovirus linked to the major histocompatibility complex of the mouse.

Studies of the resistance patterns to infection with a murine cytomegalovirus in inbred strains of mice revealed the existence of resistant and susceptible strains. Resistance was found to be associated with possession of the H-2k allele at the major histocompatibility locus of the mouse. The F1 hybrid between a resistant strain (C3H/HeJ) and a susceptible strain (BALB/c) was found to have a resistance intermediate between that of both parents, indicating that the gene(s) controlling resistance is partly dominant. Susceptible BALB/c mice could be made resistant to lethal infection by pre-treatment with thioglycollate broth but not by pre-treatment with endotoxin or BCG. Resistant C3H/HeJ mice could be made susceptible to lethal infection by pre-treatment with cyclophosphamide.     

伤寒杆菌耐药质粒pRST98介导细菌毒力的研究

目的 研究伤寒杆菌耐药质粒pRST98能否介导细胞毒力。方法 将pRST98导入鼠伤寒杆菌低毒株RIA，经口和腹腔感染小鼠，测定半数致死量（LD50）；口饲细菌后检测在体内播散、繁殖及引起脏器的组织学改变；在体外对其进行细胞的粘附和侵袭试验。分别用含pRST98的野生伤寒杆菌、消除pRST98的突变体菌株及pRST98再重新导入突变体的菌株，研究对人、兔及鼠血清杀菌的低抗力。结果 导入pRST98的鼠伤寒杆菌口服和腹腔注射组LD50比阴性对照分别降低约700锐和75倍；在小鼠肠系膜淋巴结、脾和肝脏内增殖（P＜0.05）并引起脏器严重病变；但在体外不影响鼠伤寒杆菌对HEp－2、CHO和HeLa细胞的粘附和侵袭。携带pRST98的伤寒杆菌在血清中的抵抗力是同于无此质粒的菌株（P＜0.05）。结论 伤寒杆菌耐药质粒pRST98不但介导对药物的抗性，同时还能使宿主菌的毒力增强。     

Impaired resistance to infection does not increase the virulence of Salmonella htrA live vaccines for mice.

We have described a new class of live attenuated salmonella vaccines harbouring lesions in htrA, a stress protein gene previously. The virulence and invasiveness of Salmonella htrA mutants was investigated in three models of increased susceptibility to Salmonella infection. These included BALB/c mice, either given sublethal whole body irradiation (350 R) or administered rabbit anti-TNF alpha antiserum, and (CBA/NfemaleXBALB/cmale)F1 male mice which express the xid sex-linked B cell defect of CBA/N mice and are more susceptible to salmonellae than female littermates. Salmonella typhimurium htrA mutants derived from virulent strains, C5046 (C5 htrA::TnphoA) and BRD726 (SL1344 delta htrA) were not more invasive in immunosuppressed mice than in normal controls in the three mouse models of defective immunity. The results indicate that susceptibility to S. typhimurium htrA vaccines derived from virulent parents is not enhanced by conditions of impaired resistance to infection.     

Mice vaccinated with a non-virulent, aromatic-dependent mutant of Salmonella choleraesuis die from challenge with its virulent parent but survive challenge with Salmonella typhimurium

BALB/c mice given a live vaccine of an aroA mutant of Salmonella choleraesuis by intraperitoneal (i.p.) injection were not protected against i.p. challenge with its virulent parental strain but were protected against i.p. challenge with either of two virulent strains of Salmonella typhimurium (O [1], 4, [5], 12). Vaccination with a live vaccine of S. typhimurium aroA protected against challenge with S. typhimurium but not with S. choleraesuis. Intraperitoneal administration of either aroA strain evoked high levels of serum antibody against the homologous lipopolysacharide (LPS) as determined by an enzyme immunoassay. Sera from vaccinated mice also reacted with heterologous LPS but at dilutions at least seven-fold lower than homologous endpoint titres. The vaccination schedule employed with either live-vaccine strain conferred an equal degree of resistance to challenge with Listeria monocytogenes. After mixed infection of mice with equal numbers of virulent S. typhimurium and S. choleraesuis by the i.p. route, the former was isolated in numbers at least 50,000 times greater than the latter from the liver and spleen between days 1 and 5. When mice were vaccinated i.p. with S. choleraesuis aroA, L. monocytogenes or P. multocida before mixed infection, neither serotype showed more than a slight predominance in the liver and spleen during the same period. Thus, in relative terms, vaccination with S. choleraesuis aroA or inoculation with unrelated bacteria suppressed the growth of virulent S. typhimurium in mice but allowed virulent S. choleraesuis to multiply. These results clearly show that S. choleraesuis 38(1) can multiply to kill immunised BALB/c mice.     

O antigen and lipid A phosphoryl groups in resistance of Salmonella typhimurium LT-2 to nonoxidative killing in human polymorphonuclear neutrophils.

We have compared the intraleukocytic survival of isogenic strains of Salmonella typhimurium, whose outer membrane lipopolysaccharide differed in O antigen and lipid A composition and whose susceptibility to nonoxidative antimicrobial granule proteins of human polymorphonuclear neutrophilis (PMN) could be established. We found that the order of resistance to the bactericidal activity of intact PMN of the three bacterial strains utilized closely resembled their ordered resistance to the purified human cationic antimicrobial 57,000-dalton protein (CAP57). LT-2, a smooth wild-type strain, was far more resistant than SH9178, its rough (Rb LPS) mutant. It was most significant that SH7426, a polymyxin B-resistant pmrA mutant of SH9178, not only was substantially more resistant to CAP57 and to intraphagocytic killing than SH9178 but also came close to being as resistant as LT-2. These experiments confirm earlier work that showed the importance of the glycosyl groups of O antigens of S. typhimurium for their resistance to O2-independent antimicrobial phagocytosis by PMN. The surprising result was that a rough strain, very susceptible to bactericide, became substantially more resistant when a mutation led to its lipid A phosphoryl groups being 100% substituted with amino pentoses. Yet unresolved is whether the protection is due to the loss of negative charges on the lipid A, the substitution of sugar molecules in vulnerable loci in the outer membrane, or both.     

Immunity to Salmonella typhimurium infection in C3H/HeJ and C3H/HeNCrlBR mice: studies with an aromatic-dependent live S. typhimurium strain as a vaccine

Immunization with avirulent Salmonella typhimurium strain SL3235, a smooth, aroA- derivative, was shown to induce high levels of resistance to challenge with virulent S. typhimurium in innately hypersusceptible C3H/HeJ mice and inherently resistant C3H/HeNCrlBR mice. Strain SL3235 is one of a class of avirulent aroA- derivatives made from various strains and species of Salmonella that are being considered as vaccine candidates for cattle and humans. This paper supports their efficacy and potential utility in this regard. In C3H/HeJ mice, immunity against over 1,000 50% lethal doses of virulent S. typhimurium was evident as early as 3 days after immunization and persisted for at least 7 months. Further, the vaccine was effective over a broad spectrum of doses, ranging from 10(4) to 10(6) organisms. Infection with SL3235 led to marked splenomegaly in both mouse strains. The relationship of splenomegaly to the growth kinetics and colonization by SL3235 in the spleens of infected C3H/HeJ and C3H/HeNCrlBR mice was followed. SL3235 initially multiplied slowly in the spleens of both mouse strains and then was rapidly cleared. Less multiplication was seen in the resistant C3H/HeNCrlBR mice than in C3H/HeJ mice. Maximum splenomegaly occurred after clearance of the organism had begun. Protection against virulent S. typhimurium persisted after virtually all of the SL3235 vaccine strain had been cleared from the spleen. Cross-protection against Listeria monocytogenes was evident, but had a later onset, waned by 21 days, and was not detectable by 1 month after vaccination. Demonstration of this cross-protection is consistent with the interpretation that SL3235 induces cellular immunity. One-week immune spleen cells adoptively transferred anti-S. typhimurium and anti-L. monocytogenes immunity. T cell-enriched fractions were ineffective in adoptive transfer, as were spleen cells taken 2 weeks or later after immunization. Protective capacity was in the adherent cell fraction and seemed to be associated with macrophages. Evidence for induction of a population of sensitized T cells was obtained by using a peritoneal exudate T-lymphocyte proliferation assay on peritoneal T lymphocytes collected 1 to 3 months after SL3235 infection.     

Yersinia enterocolitica infection in resistant and susceptible strains of mice.

We investigated natural resistance in mice to Yersinia enterocolitica, an enteric bacterial pathogen of humans, with a view to determine host genetic factors that are important in resistance. Most mouse strains studied (C3H/HeN, BALB/c, BALB.B, DBA/2, A, Swiss, and SWR) were highly susceptible to infection (50% lethal dose [LD50], 2 X 10(2) to 6 X 10(2) Y. enterocolitica administered intravenously [i.v.]). In contrast, C57BL/6 mice were highly resistant (LD50, 2 X 10(5) Y. enterocolitica administered i.v.). Resistance to i.v. Yersinia infection did not appear to be related to the Ity locus (which codes for resistance to Salmonella typhimurium and other pathogens) because Ityr mice (C3H/HeN, DBA/2, A, and SWR) were more susceptible to Y. enterocolitica than were Itys (C57BL/6) mice. In addition, because BALB.B mice (congenic to C57BL/6 mice at the H-2 locus) were susceptible, resistance was probably not H-2 linked. BALB/c X C57BL/6 F1 mice were intermediate in their resistance to Y. enterocolitica infection (LD50, 3 X 10(4) organisms administered i.v.), suggesting that resistance to Y. enterocolitica depends on a gene dosage affect or a resistance gene(s) interaction between susceptible and resistant parents. Further studies with C57BL/6 and BALB/c mice as prototype resistant and susceptible strains were undertaken. A time course study of Y. enterocolitica growth in various organs following i.v. infection revealed no strain difference in bacterial growth during the first 48 h of infection. Thereafter, however, C57BL/6 mice were capable of restricting Y. enterocolitica growth in all tissues (liver, lung, spleen, kidneys), whereas extensive bacterial proliferation occurred in BALB/c mice tissues. BALB/c mice were also more susceptible to oral Y. enterocolitica infection than were C57BL/6 mice, demonstrating increased mortality and greater numbers of bacteria in the Peyer's patches. Finally, whereas thymus-bearing C57BL/6 X BALB/c F1 mice were resistant to infection, athymic (nude) C57BL/6 X BALB/c F1 mice were susceptible. These studies provide a model to investigate natural immunity to enteric pathogens at mucosal surfaces, as well as provide the basis for clarifying the role of host genotype in Y. enterocolitica resistance.     

Influence of the Bcg locus on macrophage response to the dimorphic fungus Candida albicans.

The Bcg/Ity/Lsh gene (candidate Nramp) controls natural resistance to several parasites, such as Mycobacterium bovis, Leishmania donovani, and Salmonella typhimurium. Using two macrophage (M phi) cell lines (B10R and B10S) derived from mouse strains congenic at Bcg, we found that M phi s from resistant mice (B10R M phi s) act more effectively against the two morphogenetic forms of the dimorphic fungus Candida albicans compared with M phi s from susceptible mice (B10S M phi s). Moreover, when assessed for tumor necrosis factor secretion in response to the hyphal form of C. albicans, B10R M phi s are significantly more effective at expressing this secretory function than are B10S M phi s, closely resembling the trend of response to lipopolysaccharide. Overall, these results provide insight into the influence of the Bcg locus on the M phi response to C. albicans.