Analysis of cytokine mRNA expression in Listeria-resistant C57BL/6 and Listeria-susceptible A/J mice during Listeria monocytogenes infection

Animal models of listeriosis: a comparative review of the current state of the art and lessons learned

Listeriosis is a leading cause of hospitalization and death due to foodborne illness in the industrialized world. Animal models have played fundamental roles in elucidating the pathophysiology and immunology of listeriosis, and will almost certainly continue to be integral components of the research on listeriosis. Data derived from animal studies helped for example characterize the importance of cell-mediated immunity in controlling infection, allowed evaluation of chemotherapeutic treatments for listeriosis, and contributed to quantitative assessments of the public health risk associated with L. monocytogenes contaminated food commodities. Nonetheless, a number of pivotal questions remain unresolved, including dose-response relationships, which represent essential components of risk assessments. Newly emerging data about species-specific differences have recently raised concern about the validity of most traditional animal models of listeriosis. However, considerable uncertainty about the best choice of animal model remains. Here we review the available data on traditional and potential new animal models to summarize currently recognized strengths and limitations of each model. This knowledge is instrumental for devising future studies and for interpreting current data. We deliberately chose a historical, comparative and cross-disciplinary approach, striving to reveal clues that may help predict the ultimate value of each animal model in spite of incomplete data.

Precarious balance: Th17 cells in host defense

Lineage-specific responses from the effector T-cell repertoire form a critical component of adaptive immunity. The recent identification of Th17 cells-a third, distinct lineage of helper T cells-collapses the long-accepted paradigm in which Th1 and Th2 cells distinctly mediate cellular and humoral immunity, respectively. In this minireview, we discuss the involvement of the Th17 lineage during infection by extracellular bacteria, intracellular bacteria, and fungi. Emerging trends suggest that the Th17 population bridges innate and adaptive immunity to produce a robust antimicrobial inflammatory response. However, because Th17 cells mediate both host defense and pathological inflammation, elucidation of mechanisms that attenuate but do not completely abolish the Th17 response may have powerful implications for therapy.

Clinicopathological characterization of monkey B virus (Cercopithecine herpesvirus 1) infection in mice

The purpose of this study was to establish a small animal model for monkey B virus (BV) infection. Mice were inoculated intramuscularly with several BV isolates. Comparisons were based upon the doses required to produce infection (ID50), non-central nervous system (CNS) clinical disease (CS50), CNS disease (CNSD50) and lethal effect (LD50). Strains differed in respect of the dose required to produce clinical disease in BALB/c mice. C57BL/6 mice were more resistant than BALB/c mice to CNS disease. Skin lesions at the inoculation site consisted of epidermal necrosis, ulceration, serocellular crusts and underlying dermatitis. CNS lesions included marked inflammation in the ipsilateral dorsal root ganglion and lumbar spinal cord (point of viral entry). The distribution of the lumbar spinal cord lesions suggested viral entry via sensory afferent neurons, ventral motor tracts, or both. The lesions in the more cranial spinal cord segments suggested ascension to the brain via bilateral spinothalamic and spinoreticular tracts. Brain lesions included encephalitis with neuronal necrosis and white matter destruction located consistently at the base of the brainstem, the reticular system, and rostrally to the thalamus and hypothalamus. Viral antigen was detected immunohistochemically in the lesions. The results indicated an ascending encephalomyelitis syndrome similar to that produced by BV in man.

Oral inoculation of A/J mice for detection of invasiveness differences between Listeria monocytogenes epidemic and environmental strains

Four-week-old Harlan A/J mice were orally infected with six epidemic and six environmental strains of Listeria monocytogenes. Epidemic strains were significantly more invasive as a group than were environmental strains (P < 0.05), and the intestines of some mice infected with epidemic strains had extensive hemorrhage. Mice inoculated with epidemic strains were significantly more likely to become systemically infected than mice inoculated with environmental strains (P < 0.01).

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.

Neonatal lead exposure potentiates sickness behavior induced by Listeria monocytogenes infection of mice

The effects of lead (Pb) administration on infection-induced decreases in water intake, food intake, and body weight gain have been assessed as manifestations of sickness behavior using a BALB/c mouse model. Pb acetate (0.5 mM) was administered via drinking water to dams from Day 0 postpartum to weaning and to mouse pups after weaning until sacrifice. At 22 days after birth, young mice were infected with Listeria monocytogenes. Mice with blood Pb levels of less than 25 microg/dl exhibited enhanced and prolonged sickness behavior compared to mice not exposed to Pb. With this mouse model, after infection, serum levels of interleukin (IL)-1beta and IL-6 were enhanced in Pb-exposed mice. Compared with control infected mice, significant reductions in the number of thymic CD4(+)CD8(+), CD4(+), CD8(+), and CD4(-)CD8(-) T cells were observed in Pb-exposed mice. As a substitute for the infection, mice were injected with IL-1 and/or IL-6; Pb exacerbated sickness behavior only in mice injected peripherally with IL-1 and IL-6. Our data in young mice suggest that children with blood Pb levels during bacterial infection may exhibit enhanced and prolonged sickness behavior due to Pb/cytokine-dependent processes and that Pb appears to influence sickness behavior depending on the types and amounts of cytokines generated.

Tissue-level regulation of Th1 and Th2 primary and memory CD4 T cells in response to Listeria infection

Ag-specific Th1 and Th2 cytokine-producing CD4 T cells were quantitated in secondary lymphoid and tertiary tissues following oral Listeria monocytogenes infection. Although the response to Listeria was previously believed to be predominantly Th1 like, CD4 T cells producing IL-4 or IL-5 comprised a substantial proportion of the overall primary and memory response. The frequency of IFN-gamma-, IL-4-, or IL-5-producing primary effector or memory CD4 T cells was significantly higher in lung, liver, and intestinal lamina propria (LP) as compared with spleen and lymph node. However, maximum numbers of IL-4- and IL-5-producing cells were detected in the LP several days after the peak of the Th1 response, and IL-5 production was skewed toward the mucosal tissues. Remarkably, the recall response resulted in sustained Th1 and Th2 responses in tertiary, but not lymphoid tissues and long-term retention of Th1 and Th2 memory cells in equal proportions in the LP. Finally, CD40 ligand was essential for induction of IFN-gamma in the spleen and LP, but not in the liver and lung, while the IL-4 response required CD40 ligand only in the spleen. Therefore, the rules governing the effector phenotype, and the overall magnitude of the CD4 response, are regulated at the level of individual tissues.

Listeria monocytogenes infection in caspase-11-deficient mice

Caspase-11 (Cas11) is a cysteine protease involved in programmed cell death and cytokine maturation. Through activation of Cas1 (interleukin-1beta [IL-1beta]-converting enzyme), Cas11 is directly involved in the maturation of IL-1beta and IL-18. Apoptosis is mediated through Cas3. Given the role of apoptosis and cytokine signaling during the innate immune response in intracellular infection, we examined Cas11-deficient (Cas11(-/-)) mice during infection with Listeria monocytogenes. Cas11(-/-) and wild-type C57BL/6 mice were equally susceptible to intravenous infection with L. monocytogenes, resulting in similar bacterial burdens in tissue and similar survival rates. By contrast, enhanced susceptibility was observed in control mice on a mixed genetic 129/C57BL/DBA2 background. Cas11(-/-) and wild-type mice infected with Listeria had similar hepatic microabscess formation in terms of histologic appearance, size, and number. Apoptosis of L. monocytogenes-infected hepatocytes in vivo and in vitro in primary culture was not altered by the absence of Cas11. Serum IL-18 and IL-1beta levels were similar in Cas11(-/-) mice and controls. Endotoxin (lipopolysaccharide [LPS])-challenged Cas11(-/-) mice were deficient in the production of gamma interferon. IL-1beta responses in Cas11(-/-) were normal with intravenous administration of LPS but decreased with intraperitoneal administration. Our findings suggest that Cas11 deficiency does not impair the immune response to infection with L. monocytogenes. Apoptosis and maturation of IL-18 and IL-1beta were normal despite Cas11 deficiency. LPS-induced proinflammatory pathways are altered by the absence of Cas11. While Cas11-mediated Cas1 and Cas3 activation is crucial for cytokine maturation and apoptosis during inflammation, alternative pathways allow normal inflammatory and apoptotic responses during infection with L. monocytogenes.

Experimental autoimmune myocarditis in A/J mice is an interleukin-4-dependent disease with a Th2 phenotype

Myocarditis in humans is often associated with an autoimmune process in which cardiac myosin (CM) is a major autoantigen. Experimental autoimmune myocarditis (EAM) is induced in mice by immunization with CM. We found that EAM in A/J mice exhibits a Th2-like phenotype demonstrated by the histological picture of the heart lesions (eosinophils and giant cells) and by the humoral response (association of IgG1 response with disease and up-regulation of total IgE). Blocking interleukin (IL)-4 with anti-IL-4 monoclonal antibody (mAb) reduced the severity of EAM. This reduction in severity was associated with a shift from a Th2-like to a Th1-like phenotype represented by a reduction in CM-specific IgG1; an increase in CM-specific IgG2a; an abrogation of total IgE response; a decrease in IL-4, IL-5, and IL-13; as well as a dramatic increase in interferon (IFN)-gamma production in vitro. Based on the latter finding, we hypothesized that IFN-gamma limits disease. Indeed, IFN-gamma blockade with a mAb exacerbated disease. The ameliorating effect of IL-4 blockade was abrogated by co-administration of anti-IFN-gamma mAb. Thus, EAM represents a model of an organ-specific autoimmune disease associated with a Th2 phenotype, in which IL-4 promotes the disease and IFN-gamma limits it. Suppression of IFN-gamma represents at least one of the mechanisms by which IL-4 promotes EAM.

Differences in interleukin-12 and -15 production by dendritic cells at the early stage of Listeria monocytogenes infection between BALB/c and C57 BL/6 mice

The mechanisms responsible for the resistance of C57BL/6 mice and for the susceptibility of BALB/c mice to infection with Listeria monocytogenes were studied by comparing early IL-12 and IL-15 production by dendritic cells (DC) after infection with L. monocytogenes. Splenic DC expressing CD11b(low) and CD11c(+) obtained from C57BL/6 mice at 3 and 6 h after L. monocytogenes infection expressed higher levels of IL-12 p40 mRNA and IL-12 p40 protein than did those from BALB/c mice. Concurrently, a larger amount of IFN-gamma was produced by the splenic T cells from C57BL/6 mice in response to immobilized anti-TCRalphabeta mAb than by those from BALB/c mice, while the splenic T cells from BALB/c mice produced a higher level of IL-4 upon TCR alphabeta stimulation than did those of C57BL/6 mice. IL-15 mRNA and intracellular IL-15 protein were detected more abundantly in the DC from C57BL/6 mice than in those from BALB/c mice on day 3 after infection. CD3(+) IL2Rbeta (+) cells in the spleen were increased in C57BL/6 mice but not in BALB/c mice at the early stage after infection. Furthermore, IL-12Rbeta2 gene expression was up-regulated in T cells from C57BL/6 mice but not in those from BALB/c mice at the early stage after listerial infection. These results suggest that the difference in early production of IL-12 and IL-15 by DC may at least partly underlie the difference in susceptibility to L. monocytogenes between C57BL/6 and BALB/c mice.

Resistance to Coccidioides immitis in mice after immunization with recombinant protein or a DNA vaccine of a proline-rich antigen

Two inbred strains of mice (BALB/c and C57BL/6) were vaccinated with either recombinant expression protein of a Coccidioides immitis spherule-derived proline-rich antigen (rPRA) in monophosphoryl lipid A-oil emulsion adjuvant or a DNA vaccine based on the same antigen. Four weeks after vaccination, mice were infected intraperitoneally with arthroconidia. By 2 weeks, groups of mice receiving saline or plasmids with no PRA insert exhibited significant weight loss, and quantitative CFUs in the lungs ranged from 5.9 to 6.4 log10. In contrast, groups of mice immunized with either rPRA or DNA vaccine had significantly smaller pulmonary fungal burdens, ranging from 3.0 to 4.5 log10 fewer CFUs. In vitro immunologic markers of lymphocyte proliferation and gamma interferon (IFN-gamma) release after splenocytes were stimulated with rPRA correlated with protection. Also, plasma concentrations of rPRA-specific total immunoglobulin G (IgG), IgG1, and IgG2a showed increases in vaccinated mice. These studies expand earlier work by demonstrating protection in mice which differ in H-2 background, by using an adjuvant that is potentially applicable to human use, and by achieving comparable protections with a DNA-based vaccine. Our in vitro results substantiate a Th1 response as evidenced by IFN-gamma release and increased IgG2a. However, IgG1 was also stimulated, suggesting some Th2 response as well. PRA is a promising vaccine candidate for prevention of coccidioidomycosis and warrants further investigation.

Interleukin-12 has a role in mediating resistance of murine strains to Tyzzer's disease

Clostridium piliforme induces enterohepatic disease in many domestic and laboratory animal species. Susceptibility to infection is known to vary with the immune status and strain of the host, but little is known about specific immune mechanisms that regulate this disease. To evaluate host control of C. piliforme infection, we examined the role of interleukin-12 (IL-12) both in the control of and in the response to murine C. piliforme infection. For this study, 3-week-old C. piliforme-resistant C57BL/6 or -susceptible DBA/2 mice were infected intravenously with either the toxic H1 or the nontoxic M1 C. piliforme isolate. Serum and liver samples were collected prior to C. piliforme inoculation (day 0) and at days 1, 3, 7, 14, and 28 postinoculation. Evaluation of hepatic IL-12 p40 mRNA expression by reverse transcription-PCR and of total-IL-12 protein levels in serum by enzyme-linked immunosorbent assay revealed that C. piliforme induced elevations in both hepatic p40 mRNA and serum total-IL-12 levels at all times postinoculation. Elevations were similar with both toxic and nontoxic C. piliforme isolates. Levels of total IL-12 in serum were significantly (P < 0.05) higher in C57BL/6 mice than in DBA/2 mice. Additional experiments were performed in which polyclonal antibody treatment was used to neutralize IL-12 in mice of both strains prior to intravenous inoculation with toxic C. piliforme H1. IL-12 neutralization increased the severity of Tyzzer's disease at day 3 postinoculation in both mouse strains, but the degree of increase was greater in C57BL/6 mice than in DBA/2 mice.

Listeria monocytogenes and Serratia marcescens infections as models for Th1/Th2 immunity in laboratory cats

Five species of bacteria known to be naturally-occurring pathogens of cats were screened for their ability to grow in feline macrophages in vitro, and to induce antibodies and delayed type hypersensitivity (DTH) responses in vivo. Two of these organisms, L. monocytogenes and S. marcescens, were selected for further study based on clear-cut differences in their in vitro and in vivo behavior. Listeria was macrophage tropic, induced DTH, and evoked poor antibody responses post-recovery, whereas Serratia remained extracellular, did not induce a DTH reaction, and produced high titer of antibodies. Young specific pathogen free cats were then inoculated subcutaneously into the drainage areas of the right and left popliteal and auricular lymph nodes with either L. monocytogenes or S. marcescens. Each of the four lymph nodes were then removed in sequence over a two week period, weighed, cultured for viable bacteria, and RNA extracted for Th1/Th2 cytokine mRNA quantitation. Antibody responses and delayed type hypersensitivity responses were also measured. Identical to pilot studies, cats infected with Serratia developed very high levels of antibody compared to Listeria infected cats but no DTH, while Listeria infected cats produced negligible or low titers of antibodies and strong DTH. Immunity to Listeria occurred around 168 h post infection as evidenced by the disappearance of living bacteria from the nodes, while immunity to Serratia took over 264 h. Pronounced lymph node hyperplasia occurred in both infections, but persisted longer for Serratia. Enlargement of Serratia infected nodes was associated with marked follicular, primary and secondary germinal center and medullary hyperplasia. Germinal center formation in Listeria stimulated nodes was much less intense and dense accumulations of macrophages dissected between follicles downward from the subcapsular sinuses. Although functional and histologic studies showed a clear-cut cell-mediated vs. humoral response in the respective Listeria and Serratia infections, preferential cytokine mRNA upregulation was observed for only two of the five major Th1/Th2 cytokines measured. Interferon-gamma, a Th1 cytokine, was much more elevated in the Listeria stimulated nodes, but TNF-alpha (also a Th1 cytokine) was more elevated in Serratia infected nodes. Interleukin-12, an important Th1 cytokine, was elevated to equal levels in both infections as were the Th2 cytokines IL-4 and IL-10.

Th1 response in Salmonella typhimurium-infected mice with a high or low rate of bacterial clearance

Previous studies have shown that the capacity to clear an attenuated strain of Salmonella typhimurium after the second week of infection varies widely among mouse strains. Bacterial clearance is mediated by CD4+ T cells and is regulated in part by the H-2 complex. The aim of the present study was to compare the patterns of cytokine mRNA expression in the spleens of C57BL/6 (H-2b) and CBA (H-2k) mice, which exhibit a low and a high rate of bacterial clearance, respectively. A transient increase in interleukin-12 (IL-12) mRNA levels was found in both mouse strains. Gamma interferon (IFN-gamma) gene expression was higher and more sustained in C57BL/6 than in CBA mice. No increase in IL-4 mRNA was detected. A transient increase in IL-10 mRNA was found in C57BL/6 mice. Separation of spleen cells into CD4+ and CD4- fractions showed that CD4+ T cells produced the bulk of IFN-gamma in both mouse strains and of IL-10 in C57BL/6 mice. Infection of H-2 congenic mice induced a higher level of IFN-gamma mRNA expression by CD4+ T cells in mice with a low rate of clearance (H-2b) than in mice with a high rate of clearance (H-2q). Treatment of infected C57BL/6 mice with anti-IFN-gamma or anti-CD4 monoclonal antibodies indicated that IFN-gamma participates in resistance in the early phase of infection, but not in bacterial clearance, and that CD4+ T cells mediate bacterial clearance during the 3rd week of infection. Taken together, these results suggest that defective bacterial clearance in H-2b mice is not linked to defective IFN-gamma production and that CD4+ T cells mediate bacterial clearance by an IFN-gamma-independent mechanism.

Interleukin-4 and listeriosis

Experimental infection of mice with Listeria monocytogenes (L. monocytogenes) has served as an appropriate model for analyzing Th1-cell-driven immune responses. Generally, Th2 responses are absent and IL-4 is not detectable. Here, we describe experimental settings under which IL-4 is detectable in listeriosis. Our data suggest that IL-4 is rapidly produced after infection. This prompt IL-4 burst seems to stimulate chemokine responses and, therefore, may participate in the regulation of the early antilisterial host response. Soon thereafter, IL-4 production wanes. At least partially this seems to be caused by downregulation of IL-4-producing CD4+ NK1+ TCR alpha beta int lymphocytes by IL-12. In the absence of IFN-gamma responsiveness, IL-4 production is demonstrable during acquired immunity against L monocytogenes, and this elevated IL-4 production apparently contributes to disease exacerbation. In conclusion, the data are consistent with a detrimental role of IL-4 in listeriosis and active control of IL-4 synthesis by the antilisterial immune response. The rapid, but transient, IL-4 burst in listeriosis probably contributes to host defense without impairing development of the acquired T-cell response because of its shortness.

Dietary fish oil enhances circulating interferon-gamma in mice during listeriosis without altering in vitro production of this cytokine

The objective of this study was to investigate the impact of feeding mice a diet rich in n-3 polyunsaturated fatty acids (PUFA) from fish oil on the interferon-gamma (IFN-gamma) response during an active infection with Listeria monocytogenes. Weanling female C3H/Hen mice were fed experimental diets containing 20% by weight one of the following fats: soybean oil, lard, or a mixture of menhaden fish oil and corn oil (17:3, w/w). After 4 weeks, mice were injected with 10(5) live L. monocytogenes, and the concentration of IFN-gamma in serum and spleen was determined 0, 2, 4, and 7 days postinfection by enzyme-linked immunosorbent assay (ELISA). Fish oil-fed mice showed significantly higher IFN-gamma in their blood at 2 and 4 days postchallenge compared with mice fed the soybean oil-containing or lard-containing diets (p < 0.001). A higher concentration of IFN-gamma was also found in the spleen homogenate of fish oil-fed mice on day 4 postchallenge (p < 0.005). To examine in vitro IFN-gamma production, splenocytes were isolated from fish oil-fed and soybean oil-fed mice on day 4 postchallenge and cultured with concanavalin A (1 microgram/ml and 10 micrograms/ml) for 24 and 48 h. There were no significant differences in the IFN-gamma concentration in cell culture supernatants between these diet treatments. This study demonstrated that the elevation in the concentration of IFN-gamma in blood and spleen during murine listeriosis is accentuated and prolonged by dietary n-3 PUFA, and these effects may not be due to changes in IFN-gamma production.

Differential regulation of cytokine and cytokine receptor mRNA expression upon infection of bone marrow-derived macrophages with Listeria monocytogenes

Cytokine and cytokine receptor mRNA expression was analyzed by PCR-assisted amplification of RNA extracted from bone marrow-derived macrophages (BMM phi) at different time points after infection with Listeria monocytogenes. The mRNAs for the cytokines interleukin-1 alpha (IL-1 alpha), IL-1 beta, and tumor necrosis factor alpha (TNF-alpha) were induced early after infection, whereas IL-6 mRNA appeared later and even nonhemolytic Listeria strains, which are unable to grow inside eukaryotic cells, induced the same cytokine mRNAs at levels similar to those of the wild-type strain. In most cases, the amounts of cytokines determined by various bioassays correlated with the level of mRNA induction. Inhibition of phagocytic uptake of L. monocytogenes by cytochalasin D treatment resulted in adherent bacteria which still induced the proinflammatory cytokines. In BMM phi, the level of IL-1 receptor II mRNA was unaffected, whereas mRNA expression of the two subtypes of tumor necrosis factor receptors (TNF-RI and TNF-RII) was differentially regulated upon infection: transcription of TNF-RI was reduced, and that of TNF-RII mRNA was induced. Similar to the decreased TNF-RI mRNA expression, gamma interferon receptor mRNA was downregulated in L. monocytogenes-infected BMM phi. This dose- and time-dependent induction or downregulation of cytokine receptor mRNA following L. monocytogenes infection of BMM phi was not observed upon infection of established macrophage-like cell lines J774 and P388D1. Induction of IL-6 mRNA as well as IL-1 alpha/beta and TNF-alpha mRNAs upon L. monocytogenes infection of BMM phi occurs independently of autocrine TNF-alpha signaling via TNF-RI or TNF-RII, as shown by infection of TNF-RI- and TNF-RII-deficient macrophages derived from mutant B6 x 129 mice. In contrast to gamma interferon receptor mRNA, both TNF receptor subtype mRNAs were not influenced by L. monocytogenes infection of hybrid (B6 x 129) mouse macrophages. Whereas the proinflammatory cytokine mRNAs were even induced after infection with the nonpathogenic species L. innocua, no alteration of cytokine receptor mRNA expression was observed after challenge of BMM phi with this nonpathogenic species, suggesting that the modulation of cytokine and cytokine receptor expression by L. monocytogenes could be an important way of inhibition of macrophage stimulation.

Gamma interferon and interleukin-10 gene expression in innately susceptible and resistant mice during the early phase of Salmonella typhimurium infection

Previous studies have shown that gamma interferon (IFN-gamma) plays a major role in natural resistance to Salmonella typhimurium during the early phase of infection. To assess whether the level of natural resistance in mice is related to the level of IFN-gamma gene expression, we compared IFN-gamma mRNA levels by means of reverse transcriptase-PCR in the spleens of genetically susceptible Itys (C57BL/6 and BALB/c) and resistant Ityr (CBA and DBA/2) mice during the first 5 days of infection. The mRNA expression of interleukin-10 (IL-10), a cytokine which antagonizes IFN-gamma effects, was also investigated. Mice were infected with 10(3) CFU of the virulent strain S. typhimurium C5, a dose which is lethal within a week for susceptible mice only. IFN-gamma mRNA increased to similar levels in both susceptible and resistant mice, suggesting that susceptibility to S. typhimurium infection is not related to defective IFN-gamma gene expression. In contrast, IL-10 mRNA reached much higher levels in susceptible than in resistant mice. Similar results were found in Ity congenic mice, confirming a link between the presence of the Itys allele and a high level of IL-10 gene expression during infection. High levels of IL-10 mRNA in susceptible mice correlated with high IL-10 serum levels (on day 5), whereas IL-10 was not detectable in the sera of resistant mice. However, administration of neutralizing anti-IL-10 monoclonal antibodies did not modify the course of infection. To evaluate the influence of bacterial multiplication on IL-10 mRNA expression, susceptible mice were infected with an attenuated strain of S. typhimurium. This strain induced a low level of IL-10 mRNA expression. When susceptible mice were immunized with an attenuated strain and challenged with the virulent strain, they inhibited the growth of the challenge bacteria and exhibited a low level of IL-10 mRNA. In contrast, when resistant mice were infected with a high (lethal) dose of the virulent strain, they exhibited a high level of IL-10 mRNA. Taken together, these results indicate that the level of IL-10 gene expression correlates with the level of bacterial multiplication in the organs and that the high level of IL-10 mRNA in Itys mice is a consequence rather than the cause of their susceptibility to S. typhimurium infection.

Roles of gamma interferon and interleukin-4 in genetically determined resistance to Coccidioides immitis

The profiles of gamma interferon (IFN-gamma) and interleukin-4 (IL-4) production were evaluated during the course of coccidioidomycosis in two inbred mouse strains which differ in their susceptibility to Coccidioides immitis. Cytokine responses, measured at the molecular and protein levels, showed increased levels of IFN-gamma in lung extracts from mice of the resistant DBA/2 strain after a pulmonary challenge, whereas the susceptible BALB/c strain manifested a predominant IL-4 response. The importance of these cytokines in host defense against C. immitis was established by treating the mice with recombinant cytokines or neutralizing anticytokine monoclonal antibodies. Treatment of the susceptible BALB/c mice with recombinant murine IFN-gamma significantly protected mice against systemic challenge, and in the reciprocal experiment, the administration of an anti-IFN-gamma monoclonal antibody to the resistant DBA/2 mice significantly decreased their capacity to control disease. Although the treatment of DBA/2 mice with recombinant IL-4 did not alter the disease, neutralization of endogenous IL-4 in infected BALB/c mice by administration of a neutralizing anti-IL-4 antibody led to a significant reduction in the fungal load in their tissues. These results, taken together, establish that IFN-gamma plays a pivotal role in resistance to C. immitis, whereas IL-4 down-regulates protective immunity against C. immitis.

A quantitative analysis of antigen-presenting cell function: activated B cells stimulate naive CD4 T cells but are inferior to dendritic cells in providing costimulation

Ligation of CD28 on CD4 Th1 clones and freshly isolated mixtures of naive and memory CD4 T cells triggered their T cell receptors (TCR) is sufficient to induce the costimulatory signals necessary for interleukin 2 (IL-2) production by these cells. CTLA-4-reactive ligands expressed on antigen-presenting cells (APC) are critical in providing costimulatory signals to these T cell populations. We demonstrate that these activation characteristics apply equally to purified naive CD4 T cells. Because B cell blasts express CTLA-4-reactive ligands and high levels of adhesion and major histocompatibility complex class II molecules, they would be expected to engage both the TCR and CD28 and consequently stimulate IL-2 production by naive CD4 T cells. Using purified populations of cells in limiting dilution cultures, we have carried out a quantitative analysis of the interaction between naive CD4 T cells and either activated B or dendritic cells. We demonstrate that B cell blasts stimulate a high frequency of naive CD4 T cells. Slight differences in TCR signaling efficiency between the two APC types were observed. Even at optimal peptide concentrations, however, the amount of IL-2 made by individual T cells was fourfold lower in response to B cell blasts than to dendritic cells. This relative deficiency of activated B cells was due to their inability to optimally costimulate naive CD4 T cells.

Early gamma interferon mRNA expression is associated with resistance of mice against Yersinia enterocolitica

T cells in cooperation with macrophages play an important role in resolution of primary Yersinia enterocolitica infection in mice. Previous work from this laboratory demonstrated that gamma interferon (IFN-gamma) and tumor necrosis factor alpha (TNF-alpha) are essential mediators of these processes. In an attempt to elucidate early mechanisms of resistance, we investigated cytokine mRNA production, including that for interleukin-1 beta (IL-1 beta), IL-2, IL-4, IL-6, IL-10, TNF-alpha, and IFN-gamma, after primary as well as secondary Y. enterocolitica infection in Yersinia-susceptible BALB/c mice and Yersinia-resistant C57BL/6 mice. In both strains of mice, proinflammatory cytokines such as IL-1 beta, IL-6, and TNF-alpha were expressed rapidly and to comparable degrees, while IFN-gamma expression was enhanced two- to eightfold in C57BL/6 mice, as revealed by semiquantitative reverse transcription PCR. Similar results were found in both mouse strains after secondary Y. enterocolitica infection. IL-2 mRNA was detected only during secondary infection and disappeared rapidly in BALB/c mice. IL-4 mRNA expression was detectable in C57BL/6 but not BALB/c mice. The levels of cytokine mRNA expression correlated closely with the number of injected bacteria. The findings reported here support the hypothesis that early and enhanced production of IFN-gamma may be associated with a state of heightened resistance against Y. enterocolitica infection.