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Biomedical subjects

J E Rehg

Publications and source records attributed to J E Rehg.

At least 19 recordsLinked to original sources
PubMed2001

Dmp1 is haplo-insufficient for tumor suppression and modifies the frequencies of Arf and p53 mutations in Myc-induced lymphomas.

Loss of Dmp1, an Arf transcriptional activator, leads to spontaneous tumorigenesis in mice, causing death from various forms of cancer by two years of age. Retention and expression of the wild-type Dmp1 allele in tumors arising in Dmp1(+/-) mice demonstrate that Dmp1 can be haplo-insufficient for tumor suppression. The mean latency of E(mu)-Myc-induced B-cell lymphomas is halved on a Dmp1(-/-) or Dmp1(+/-) genetic background. Although p53 mutations or Arf deletion normally occur in approximately 50% of E(mu)-Myc-induced lymphomas, Dmp1 loss obviates selection for such mutations, indicating that Dmp1 is a potent genetic modifier of the Arf-p53 pathway in vivo.

Age Factors↗
PubMed2001

Control of spermatogenesis in mice by the cyclin D-dependent kinase inhibitors p18(Ink4c) and p19(Ink4d).

Male mice lacking both the Ink4c and Ink4d genes, which encode two inhibitors of D-type cyclin-dependent kinases (Cdks), are infertile, whereas female fecundity is unaffected. Both p18(Ink4c) and p19(Ink4d) are expressed in the seminiferous tubules of postnatal wild-type mice, being largely confined to postmitotic spermatocytes undergoing meiosis. Their combined loss is associated with the delayed exit of spermatogonia from the mitotic cell cycle, leading to the retarded appearance of meiotic cells that do not properly differentiate and instead undergo apoptosis at an increased frequency. As a result, mice lacking both Ink4c and Ink4d produce few mature sperm, and the residual spermatozoa have reduced motility and decreased viability. Whether or not Ink4d is present, animals lacking Ink4c develop hyperplasia of interstitial testicular Leydig cells, which produce reduced levels of testosterone. The anterior pituitary of fertile mice lacking Ink4c or infertile mice doubly deficient for Ink4c and Ink4d produces normal levels of luteinizing hormone (LH). Therefore, the failure of Leydig cells to produce testosterone is not secondary to defects in LH production, and reduced testosterone levels do not account for infertility in the doubly deficient strain. By contrast, Ink4d-null or double-null mice produce elevated levels of follicle-stimulating hormone (FSH). Because Ink4d-null mice are fertile, increased FSH production by the anterior pituitary is also unlikely to contribute to the sterility observed in Ink4c/Ink4d double-null males. Our data indicate that p18(Ink4c) and p19(Ink4d) are essential for male fertility. These two Cdk inhibitors collaborate in regulating spermatogenesis, helping to ensure mitotic exit and the normal meiotic maturation of spermatocytes.

Animals↗
PubMed2000

p53-independent functions of the p19(ARF) tumor suppressor.

The p19(ARF) tumor suppressor antagonizes Mdm2 to induce p53-dependent cell cycle arrest. Individual TKO (triple knock out) mice nullizygous for ARF, p53, and Mdm2 develop multiple tumors at a frequency greater than those observed in animals lacking both p53 and Mdm2 or p53 alone, demonstrating that p19(ARF) can act independently of the Mdm2-p53 axis in tumor surveillance. Reintroduction of ARF into TKO mouse embryo fibroblasts (MEFs), but not into those lacking both p53 and ARF, arrested the cell division cycle in the G1 phase. Inhibition of the retinoblastoma protein had no effect on the ability of ARF to arrest TKO MEFs. Thus, in the absence of Mdm2, p19(ARF) interacts with other targets to inhibit cell proliferation.

Animals↗
PubMed2000

Disruption of the ARF transcriptional activator DMP1 facilitates cell immortalization, Ras transformation, and tumorigenesis.

The DMP1 transcription factor induces the ARF tumor suppressor gene in mouse fibroblasts, leading to cell cycle arrest in a p53-dependent manner. We disrupted sequences encoding the DNA-binding domain of DMP1 in mouse embryonic stem cells and derived animals lacking the functional protein. DMP1-null animals are small at birth, and males develop more slowly than their wild-type littermates. Some adult animals exhibit seizures and/or obstuctive uropathy, each of unknown cause. The growth of explanted DMP1-null mouse embryo fibroblasts (MEFs) is progressively retarded as cells are passaged in culture on defined transfer protocols; but, unlike the behavior of normal cells, p19(ARF), Mdm2, and p53 levels remain relatively low and DMP1-null MEFs do not senesce. Whereas the establishment of cell lines from MEFs is usually always accompanied by either p53 or ARF loss of function, continuously passaged DMP1-null cells readily give rise to established 3T3 and 3T9 cell lines that retain wild-type ARF and functional p53 genes. Early-passage DMP1-null cells, like MEFs from either ARF-null or p53-null mice, can be morphologically transformed by oncogenic Ha-Ras (Val-12) alone. Splenic lymphocytes harvested from both DMP1-null and ARF-null mice exhibit enhanced proliferative responses in long-term cultures when stimulated to divide with antibody to CD3 and interleukin-2. Although only 1 of 40 DMP1-null animals spontaneously developed a tumor in the first year of life, neonatal treatment with dimethylbenzanthracene or ionizing radiation induced tumors of various histologic types that were not observed in similarly treated DMP1(+/+) animals. Karyotypic analyses of MEFs and lymphomas from DMP1-null animals revealed pseudodiploid chromosome numbers, consistent with the retention of wild-type p53. Together, these data suggest that ARF function is compromised, but not eliminated, in animals lacking functional DMP1.

3T3 Cells↗
PubMed2000

Effect of CD40 ligand and other immunomodulators on Pneumocystis carinii infection in rat model.

The corticosteroid-treated animal is well established as an experimental model for the study of Pneumocystis carinii pneumonitis (PCP). Latent or acquired infection with P. carinii in the murine lung progresses to fatal pneumonitis when the host is profoundly immunocompromized. In this study the effects of five immunomodulators; recombinant CD40 ligand (CD40L), bryostatin 1, recombinant FLT3 ligand (FLT3L), recombinant granulocyte colony-stimulating factor (G-CSF) and recombinant interleukin-15 (IL-15) were investigated against PCP in a dexamethasone immunosuppressed Sprague-Dawley rat model. The majority of rats (70%) treated with CD40L at the onset of dexamethasone immunosuppression were protected against PCP. When CD40L was given after 10 days of immunosuppression, only 40% of the rats resolved the infection. However, 95% of the control animals developed PCP. Immunosuppressed rats treated with bryostatin 1, an immune activator had a partial (50%) protection against P. carinii infection. In contrast, daily administration of FLT3L, IL-15 or G-CSF provided no protection against P. carinii infection.

Adjuvants, Immunologic↗
PubMed2000

Protection from Cryptosporidium parvum infection by gammadelta T cells in mice that lack alphabeta T cells.

BACKGROUND AND PURPOSE: Cryptosporidium parvum establishes a parasitic relationship with epithelial cells of the intestine. Infection with this protozoan is resolved in the immunocompetent host, but persistent life-threatening infection develops in the immunocompromised host. We propose that gammdelta T cells in the intestinal mucosa play a role in immunity to C. parvum. METHODS: Intestinal intra-epithelial lymphocyte and lamina propria T-cell subsets were examined in mice infected with C. parvum. The mice are homozygous for a deletion of the TCRalpha chain gene, TCRalpha(-/-) and, therefore, lack conventional alphabeta T cells, but retain a population of T cells with gammadelta T-cell receptors. To examine the contribution of gammadelta T cells to immunity, these mice were treated with monoclonal antibody GL3-3A, specific for this T-cell receptor, then were inoculated with C. parvum oocysts. Lymphocyte subsets and hematoxylin and eosin (H&E)-stained intestinal sections from untreated mice were compared with those from mice treated with either a low dose of GL3-3A for 6 weeks, or a high dose of GL3-3A for 16 weeks. RESULTS: The proportion of gammadelta T cells in the lamina propria increased in infected mice. In mice treated with a low dose of GL3-3A, a population of gammadelta T cells that had characteristics of activated cells, was still evident 6 weeks after inoculation. No C. parvum developmental forms were identified in the intestinal sections of mice under these conditions. However, TCRalpha(-/-) mice treated with a high dose of GL3-3A were depleted of gammadelta T cells, and 50% of the mice were infected with C. parvum. CONCLUSIONS: The gammadelta T cells contribute to protection against C. parvum infection. In the absence of conventional T cells, activation of intestinal gammadelta T cells may prevent infection with this organism.

Animals↗
PubMed2000

Toxicity evaluation of prophylactic treatments for mites and pinworms in mice.

The detection of external and internal parasites in laboratory mice is a particularly problematic aspect of animal health evaluation. Because these organisms must be detected by direct examination of the feces or hair coat, low-level infestation or sporadic shedding can make them difficult to detect, thereby undermining confidence that negative reports are truly negative. Prophylactic treatment of suspect colonies with anthelminthics and/or insecticides may therefore be indicated under some circumstances. However, when considering the use of prophylactic treatments, the potential for toxicity is an important factor, especially in genetically modified strains of mice. To evaluate the potential toxicity of prophylactic anti- parasitic treatments on strains of mice that are commonly used as experimental models and in genetic engineering in our facility, we surveyed a number of strains and ages of mice for toxic reactions during treatment regimens that combine anthelminthic and anti-acaricidal agents. Three experimental protocols (ivermectin, piperazine, and dichlorvos in combination; ivermectin alone; and fenbendazole/permethrin or fenbendazole/dichlorvos) were evaluated. Our data suggest a potential for toxicity associated with these treatments and indicate to us that prophylactic treatment regimens should be initiated with caution.

Animals↗
PubMed1998

Effects of sleep deprivation and other stressors on the immune and inflammatory responses of influenza-infected mice.

Many stressors have well-documented effects on host immune competence. However, two important stressors that have not been extensively characterized in terms of their immune-modulatory properties are sleep deprivation and alterations in light:dark cycles. We therefore evaluated the effects of these stressors on the immune and inflammatory responses of mice inoculated intranasally with influenza virus. In contrast to a previous report, sleep deprivation did not significantly alter viral clearance or antibody titers of either virus-naive or immunized mice. Exposure to constant light also failed to affect these variables. However, repeated overnight restraint, a well-characterized stressor, reduced the pulmonary inflammatory response elicited by influenza virus, as previously reported. The data indicate that sleep deprivation and altered light cycles do not markedly influence selected host defense responses to influenza infection under the conditions tested.

Amyloid↗
PubMed1998

Rodent quarantine programs: purpose, principles, and practice.

In animal research, validity and reproducibility of data are critically influenced by the microbial status of the experimental animals. One of the most crucial aspects of assuring quality in animal research is providing research personnel with confidence that experimental results will not be invalidated due to interference caused by infectious disease. An effective quarantine program is essential to providing this assurance. Quarantine programs are generally instituted to prevent the introduction of rodent pathogens into established specific-pathogen-free colonies in a facility. Therefore, programs should be designed to isolate newly acquired rodents until their health status can be determined and to maximize the probability that microorganisms of interest will be detected before the animals are introduced into (and thus, could potentially contaminate) established colonies. Important principles that are critical to designing an effective quarantine program will be discussed here, as will the practical implementation of these principles. Although quarantine programs may be costly in terms of time and effort, these costs must be balanced against the potential costs of disease outbreaks that could invalidate long-term studies, alter normal biological baselines, and cause the loss or necessitate re-derivation of rare or valuable strains of rodents. Reducing the incidence of quarantine failures through appropriate program design and implementation helps to maintain the confidence of research personnel in the value of quarantine programs and in our competence as specialists in laboratory animal management and as partners in the research process.

Animal Husbandry↗
PubMed1997

Efficacy of lasalocid against murine Pneumocystis carinii pneumonitis.

The efficacy of the ionophore lasalocid against Pneumocystis carinii pneumonitis in corticosteroid-immunosuppressed Sprague-Dawley rats was investigated. Lasalocid was effective in the prevention of the pneumonitis in a dose-dependent manner. At dosages of 0, 5, 10, and 20 mg/kg/day, P. carinii infection rates were 92, 60, 20, and 0%, respectively, during dexamethasone immunosuppression. Also, lasalocid compared favorably with other drugs known to have anti-P. carinii activity, including trimethoprim-sulfamethoxazole, atovaquone, and dapsone-trimethoprim.

Animals↗
PubMed1997

Disruption of T-cell differentiation precedes T-cell tumor formation in LMO-2 (rhombotin-2) transgenic mice.

Transgenic mice expressing LMO-2 (rhombotin-2) were constructed by placing the LMO-2 gene under control of the metallothionein promoter. Thymic tumors developed in approximately 15% of the transgenic mice between 37 and 71 weeks. Only T-cell tumors were found in the transgenic mice despite high expression of LMO-2 in all tissues. The thymic tumors were aggressive and were invariably associated with metastasis to non-lymphoid organs. In approximately 50% of apparently healthy transgenic mice there was up to a 10-fold expansion of CD4-CD8- double negative (DN) cells. Expansion of the DN cells was accompanied by the compensatory decrease in CD4+CD8+ double positive (DP) cells, indicating that breach of homeostasis within the thymus had not occurred in these animals. The increase in DN cells was associated with a clonal expansion of thymocytes, and increased proliferation within the thymus. Our data indicate that the ectopic expression of LMO-2 in T-cells disrupts normal T-cell differentiation by selectively expanding the DN thymocyte population prior to breach of homeostasis and overt leukemia/lymphoma.

Adaptor Proteins, Signal Transducing↗
PubMed1996

Lethal synergism between influenza infection and staphylococcal enterotoxin B in mice.

Superantigen hyperactivation of the immune system has variable, sometimes lethal consequences for the host. Here we show that concurrent influenza infection enhanced the effects of the bacterial superantigen staphylococcal enterotoxin B (SEB) in mice. The effect was T cell-dependent, and maximal synergism was observed when SEB was administered 7 days after the virus, a timepoint during infection associated with high viral titers, a vigorous cytotoxic T cell response, and extensive lung pathology. The influenza infection enhanced the SEB-induced cytokine response in terms of higher absolute levels of cytokine, sustained secretion, and localization to the respiratory tract. In particular, TNF and IFN-gamma were implicated in the mechanism of death because their neutralization protected the mice from death, and recombinant IFN-gamma and TNFalpha mimicked the lethal effect of SEB in influenza-infected mice. This lethal synergism between concurrent influenza infection and superantigen exposure points to the danger of secondary bacterial involvement in viral pneumonia, and suggests mechanisms that may contribute to sudden and unexpected death from influenza infection. In addition, these data demonstrate that the in vivo effects of superantigen exposure can be strongly influenced by the immune activation status of the host.

Animals↗
PubMed1996

A gene transfer strategy for making bone marrow cells resistant to trimetrexate.

Trimetrexate (TMTX) is an anticancer drug with potential advantages over the more commonly used antifolate, methotrexate (MTX); however, its use has been limited by severe myelosuppression. Retroviral vectors containing mutant dihydrofolate reductase (DHFR) genes have been used to protect bone marrow cells from MTX, suggesting a similar approach could be used for TMTX. We first screened six variants of human DHFR to determine which allowed maximal TMTX resistance in fibroblasts. A variant enzyme containing a Leu-to-Tyr mutation in the 22nd codon (L22Y) was best, allowing a 100-fold increase in resistance over controls. Murine hematopoietic progenitor cells transduced with an L22Y-containing retroviral vector also showed high-level TMTX resistance in vitro. Mice reconstituted with L22Y-transduced bone marrow cells were challenged with a 5-day course of TMTX to determine whether hematopoiesis could be protected in vivo. Transfer of the L22Y vector resulted in consistent protection from TMTX-induced neutropenia and reticulocytopenia at levels that correlated with the proviral copy number in circulating leukocytes. We conclude that the L22Y vector is highly effective in protecting hematopoiesis from TMTX toxicity and may provide a means for increasing the therapeutic utility of TMTX in certain cancers.

Animals↗
PubMed1996

Effect of interferon-gamma in experimental Cryptosporidium parvum infection.

The activity of recombinant murine interferon-gamma (IFN-gamma) against infection by Cryptosporidium parvum was evaluated in immunosuppressed rats. Daily intraperitoneal doses of at least 125,000 U/kg significantly (P < .05) reduced the intensity of subsequent ileal infection. In addition, daily administration of 500,000 U/kg significantly (P < .05) inhibited colonization of the biliary tract. When administered for 11 days to rats with established C. parvum infection, IFN-gamma significantly (P < .05) reduced the number of parasites in the small intestine, but this treatment was ineffective against infection of the biliary tract and large intestine. Although the parasite loads in the common bile duct and large intestine were not significantly reduced, there were fewer cases of infection among the treated rats than in the control group. The data suggest that treatment with IFN-gamma may limit cryptosporidiosis of the small intestine.

Animals↗
PubMed1996

Comparative evaluation of several techniques for purification of Cryptosporidium parvum oocysts from rat feces.

Three methods of isolating Cryptosporidium parvum oocysts from rat feces were evaluated. Oocysts were initially isolated by sucrose density gradient centrifugation. They were further purified by passage through a glass bead column or a Percoll gradient or by dialysis. Although oocysts recovered from the glass bead column and by dialysis were relatively free of fecal debris, only oocysts recovered from the Percoll gradient were free of bacteria. Recovered oocysts retained their antigenicity and infectivity. The ability to effectively recover oocysts from rat feces suggests that the laboratory rat may be a convenient substitute for ruminants in the propagation and maintenance of C. parvum oocysts for in vitro and in vivo use.

Animals↗
PubMed1996

Effect of diethyldithiocarbamate on Cryptosporidium parvum infection in immunosuppressed rats.

Diethyldithiocarbamate was the only immune modulator of 7 evaluated to show activity against Cryptosporidium parvum in immunosuppressed rats. The model was then used to assess the drug's activity further. When administered prophylactically, oral doses > or = 75 mg/kg/day significantly (P < or = 0.05) reduced the severity of ileal infection and doses > or = 300 mg/kg/day significantly (P < or = 0.05) inhibited infection of the biliary tract. When administered to rats with established infection, the drug significantly (P < or = 0.05) reduced the parasite burden in the ileum but was ineffective against biliary tract infection. The data suggest that diethyldithiocarbamate is effective for treating cryptosporidiosis of the small intestine but is probably ineffective against chronic cryptosporidiosis involving the large intestine or biliary tract.

Adjuvants, Immunologic↗
PubMed1995

Ectopic expression of rhombotin-2 causes selective expansion of CD4-CD8- lymphocytes in the thymus and T-cell tumors in transgenic mice.

Although the proto-oncogene rhombotin-2 (RBTN-2) is widely expressed in most tissues, it is not expressed in T cells. We investigated the potential for overexpression of RBTN-2 to cause tumors in T cells and other tissues by constructing transgenic mice that expressed RBTN-2 under control of the metallothionein-1 promoter. Despite overexpression of RBTN-2 in all tissues, transgenic mice developed T-cell tumors only, thus indicating that tumorigenesis caused by RBTN-2 is T-cell-specific. Thymic tumors were found between 37 and 71 weeks and were invariably associated with metastasis to nonlymphoid organs. Thymuses from apparently healthy transgenic mice were also examined. In some mice there was an 10-fold increase in the CD4-CD8- thymocyte subset, yet the total number of thymocytes was the same as that in wild-type mice. Thymic homeostasis was maintained by a compensatory reduction in the CD4+CD8+ subset. The expansion of CD4-CD8- thymocytes was associated with increased expression of RBTN-2 and with increased cell proliferation. No differences were found in the proportion of thymocytes undergoing apoptosis in transgenic mice. Furthermore, RBTN-2-induced expansion of CD4-CD8- cells did not block differentiation of these cells. Thymuses with 30% CD4-CD8- cells were essentially monoclonal, indicating that all thymic immunophenotypes were derived from a single clone. Overall, our data are consistent with the following scenario: (1) RBTN-2 expression in T cells causes selective and polyclonal proliferation of CD4-CD8- thymocytes accompanied by a compensatory decrease in other thymocyte subsets; (2) a clone with growth advantage and differentiation potential is selected and populates the thymus; and (3) this clone eventually breaches homeostasis of the thymus, accompanied or followed by metastasis to other organs.

Adaptor Proteins, Signal Transducing↗