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Biomedical subjects

I Horak

Publications and source records attributed to I Horak.

At least 37 records · Page 2Linked to original sources
PubMed1997

Induction of autoimmune myocarditis in interleukin-2-deficient mice.

BACKGROUND: Interleukin (IL)-2 is an important growth and survival factor for T cells and plays a crucial role in inflammation. Myosin-induced myocarditis is strictly dependent on activated T cells and is a model for postinfectious inflammatory heart disease in humans. To explore the role of IL-2 in myocarditis, we injected mice genetically deficient for IL-2 with cardiac myosin. Because it is conceivable that the lack of IL-2 either promotes or ameliorates the disease, we selected mouse strains that differ in their susceptibility to cardiac myosin-induced myocarditis. METHODS AND RESULTS: Mice from a susceptible strain (C3H) that were rendered IL-2 deficient by gene targeting (IL-2-/- mice) and littermate controls were immunized twice with purified cardiac myosin at a 7-day interval. Three weeks after the first immunization, hearts were obtained for histopathological and immunohistochemical analysis. Sera were tested for autoantibodies to the cardiac myosin isoform by enzyme-linked immunosorbent assay. The majority of C3H IL-2-/- mice developed severe myocarditis accompanied by high-titer myosin autoantibodies. In C57BL/6 mice, which develop only little myocarditis on myosin immunization, lack of IL-2 did not increase susceptibility to the disease. Moreover, the composition of the inflammatory infiltrate in C3H IL-2-/- mice was virtually identical to that seen in the wild-type strain. CONCLUSIONS: Our data provide the first genetic evidence that in cardiac myosin-immunized mice, IL-2 has no essential role for the development of autoimmune heart disease and the generation of myosin autoantibodies.

Animals↗
PubMed1997

Crucial role of interferon consensus sequence binding protein, but neither of interferon regulatory factor 1 nor of nitric oxide synthesis for protection against murine listeriosis.

Listeria monocytogenes is widely used as a model to study immune responses against intracellular bacteria. It has been shown that neutrophils and macrophages play an important role to restrict bacterial replication in the early phase of primary infection in mice, and that the cytokines interferon-gamma (IFN-gamma) and tumor necrosis factor-alpha (TNF-alpha) are essential for protection. However, the involved signaling pathways and effector mechanisms are still poorly understood. This study investigated mouse strains deficient for the IFN-dependent transcription factors interferon consensus sequence binding protein (ICSBP), interferon regulatory factor (IRF) 1 or 2 for their capacity to eliminate Listeria in vivo and in vitro and for production of inducible reactive nitrogen intermediates (RNI) or reactive oxygen intermediates (ROI) in macrophages. ICSBP-/- and to a lesser degree also IRF2-/- mice were highly susceptible to Listeria infection. This correlated with impaired elimination of Listeria from infected peritoneal macrophage (PEM) cultures stimulated with IFN-gamma in vitro; in addition these cultures showed reduced and delayed oxidative burst upon IFN-gamma stimulation, whereas nitric oxide production was normal. In contrast, mice deficient for IRF1 were not able to produce nitric oxide, but they efficiently controlled Listeria in vivo and in vitro. These results indicate that (a) the ICSBP/IRF2 complex is essential for IFN-gamma-mediated protection against Listeria and that (b) ROI together with additional still unknown effector mechanisms may be responsible for the anti-Listeria activity of macrophages, whereas IRF1-induced RNI are not limiting.

Adoptive Transfer↗
PubMed1997

Cytokine mRNA expression in intestinal tissue of interleukin-2 deficient mice with bowel inflammation.

BACKGROUND: Mice deficient in interleukin-2 (IL-2) develop inflammatory bowel disease resembling ulcerative colitis in humans. Recent studies provided evidence that alpha beta T cells, particularly CD4 T cells, rather than B cells, are involved in the pathogenesis of bowel inflammation of IL-2 deficient mice. AIM: To analyse the pattern of expression of cytokine mRNA in intestinal tissue of normal and IL-2 deficient mice. METHODS: Expression of beta-actin, IL-1 alpha, IL-1 beta, IL-6, IL-10, tumour necrosis factor alpha (TNF-alpha), interferon gamma (IFN-gamma) and transforming growth factor beta 1 (TGF-beta 1) mRNA was analysed in colon and small intestinal tissue of both IL-2 deficient (IL-2-/-) mice and normal (wild type) litter mates (IL-2+/+) at different ages by using qualitative, as well as semiquantitative, competitive reverse transcription polymerase chain reaction (RT-PCR). Results were correlated with the phase of progression of the disease, as determined by histology. RESULTS: IL-2-/- mice had expressed low levels of IL-1 alpha, IL-1 beta, IL-6, TNF-alpha, and IFN-gamma mRNA in the colon by 1.5 weeks of age. In advance of the development of histologically and clinically detectable bowel inflammation, expression of IL-1 alpha, IL-1 beta, IL-6, TNF-alpha, IFN-gamma, and IL-10, but not TGF-beta 1, mRNA increased in the colon of IL-2 deficient mice. In contrast, IL-2+/+ mice expressed TGF-beta 1 mRNA in colon tissue at 13 and 23 weeks of age, but not IL-1 alpha, IL-1 beta, IL-6, TNF-alpha, IL-10, or IFN-gamma mRNA. Levels of expression of cytokine mRNA in tissue from the small intestine were comparable in IL-2-/- and IL-2+/+ mice. CONCLUSIONS: Bowel inflammation in IL-2 deficient mice is preceded by an increase in IL-1 alpha, IL-1 beta, TNF-alpha, and IFN-gamma mRNA expression in colon tissue. Low levels of TGF-beta 1, but high levels of IL-1 alpha, IL-1 beta, IL-6, TNF-alpha, IFN-gamma, and IL-10 mRNA expression correlate with the manifestation of severe colitis, and suggest that T cells and macrophages are involved in bowel inflammation of IL-2 deficient mice.

Actins↗
PubMed1996

Immunodeficiency and chronic myelogenous leukemia-like syndrome in mice with a targeted mutation of the ICSBP gene.

Interferon consensus sequence binding protein (ICSBP) is a transcription factor of the interferon (IFN) regulatory factor (IRF) family. Mice with a null mutation of ICSBP exhibit two prominent phenotypes related to previously described activities of the IRF family. The first is enhanced susceptibility to virus infections associated with impaired production of IFN(gamma). The second is deregulated hematopoiesis in both ICSBP-/- and ICSBP+/- mice that manifests as a syndrome similar to human chronic myelogenous leukemia. The chronic period of the disease progresses to a fatal blast crisis characterized by a clonal expansion of undifferentiated cells. Normal mice injected with cells from mice in blast crisis developed acute leukemia within 6 weeks of transfer. These results suggest a novel role for ICSBP in regulating the proliferation and differentiation of hematopoietic progenitor cells.

Animals↗
PubMed1996

The mouse poly(C)-binding protein exists in multiple isoforms and interacts with several RNA-binding proteins.

The murine poly(C)-binding protein (mCBP) was previously shown to belong to the group of K-homology (KH) proteins by virtue of its homology to hnRNP-K. We have isolated cDNA-splice variants of mCBP which differ by two variable regions of 93 bp and/or 39 +/- 3 bp respectively. Both variable regions are located between the second and third KH-domain of mCBP. The characterization of a partial genomic clone enabled us to propose a model for the generation of the second variable region by the use of a putative alternative splice signal. The mCBP mRNA is expressed ubiquitously and the protein is found predominantly in the nucleus with the exception of the nucleoli. We have identified five proteins which interact with mCBP in the yeast two hybrid system: mouse y-box protein 1 (msy-1), y-box-binding protein, hnRNP-L, filamin and splicing factor 9G8. The interaction between mCBP and splicing factor 9G8 was confirmed in vivo. These results suggest a function of mCBP in RNA metabolism.

Animals↗
PubMed1996

Analysis of the determinants of neurotropism and neurotoxicity of HFV in transgenic mice.

The Bel-1 protein of human foamy virus (HFV) is a transactivator acting on the U3 region of the long terminal repeat and on an internal promoter (IP) immediately upstream of the bel genes. An HFV transgene called delta gpe, containing both promoters and all bel genes, is expressed in the central nervous system and induces neurodegeneration in mice. To dissect the role of individual promoters and bel genes on transgene expression and neurotoxicity we generated transgenic mice with a construct termed pL-bel1, which lacks the IP and the ancillary genes except bel-1. L-bel1 mice transcribed the HFV transgene in more tissues than delta gpe mice, suggesting that CNS specificity is dictated by cis-acting elements not present in the pLbel-1 construct. Unlike delta gpe mice, L-bel1 mice did not develop neurodegenerative changes and did not show induction of nitric oxide synthase expression, although both strains expressed Bel-1 in the brain. Therefore, Bel-1 expression is not sufficient for neurotoxicity. Our results suggest that Bet, a fusion protein between bel-1 and bel-2 which is highly expressed in delta gpe but not in L-bel1 mice, is a candidate for neurotoxicity.

Animals↗
PubMed1996

Interleukin-2 is indispensable for development of immunological self-tolerance.

Interleukin-2-deficient mice (IL-2(-/-)) manifest severe immune system abnormalities characterized by an uncontrolled activation and proliferation of lymphocytes. A systemic autoimmune syndrome results, and hemolytic anemia leads to early death especially in mice derived from a BALB/c genotype. Remarkably, IL-2 treatment prevents both the activation of the immune system and the development of autoimmune disease. Moreover, adoptive transfer of lymphocytes from IL-2-treated IL-2(-/-) animals confers protection to IL-2(-/-) mice, suggesting that IL-2 induces a postnatal differentiation/maturation of regulatory cells necessary for self- and non-self-discrimination.

Anemia, Hemolytic, Autoimmune↗
PubMed1996

[Generalized autoimmune diseases in BALB/c mice with a genetically dependent interleukin-2 deficiency].

Il-2 has been described as a key cytokine regulating the growth, differentiation and function of lymphocytes. To better understand its in vivo function Il-2 deficient mouse mutants were generated on a mixed (129/Ola x C57BL6) genetic background which predominantly develop an ulcerative colitis-like disease (10). To further elucidate the complex disease syndrome of Il-2-/-mice and to study the possible contribution of genetic factors in its pathogenesis we have bred the IL-2-/-mice to various genetic backgrounds. The resulting phenotypes were analyzed clinically and morphologically and the status of their immune system was assessed. Il-2-/-mice backcrossed to BALB/c genetic background develop a generalized autoimmune disease, which becomes manifest as hemolytic anemia, follicular hyperplasia of lymphoid organs, inflammatory changes of pancreas, liver, heart, lungs and thoracal blood vessels but not of the colon (11). The mutants all die within 5 weeks of age. The changes of the immune system are dominated by an uncontrolled polyclonal activation and proliferation of T and B cells, associated with an increased production of autoantibodies. Treatment of Il-2-/-Balb/c mice with anti-gp39 (CD40L) antibody inhibited activation of B cells and CD8+ T cells, however, it did not affect the activation of CD4+ T cells. In such treated mice amelioration of hemolytic anemia but not of inflammatory lesions in most of the affected organs could be recognized. The primary immunologic change of Il-2-/-mice is obviously an uncontrolled proliferation of CD4+ T cells. It suggests that the in vivo function of IL-2 which is not compensated by other cytokines is the maintenance of self tolerance.

Animals↗
PubMed1995

T cells, but not B cells, are required for bowel inflammation in interleukin 2-deficient mice.

Interleukin-2 (IL-2)-deficient (IL-2-/-) mice develop anemia and colonic inflammatory bowel disease. To elucidate the mechanism of this disease, we have bred IL-2-/- mice to two strains of immunodeficient mice, RAG-2-deficient (RAG-2-/-, lacking B and T cells) and JH-deficient mice (JH-/-, lacking B cells). IL-2-/-, RAG-2-/- double-mutant mice are disease free, while IL-2-/-, JH-/- double-mutant mice succumb to bowel disease at the same rate as IL-2-/- littermates. IL-2-/-, JH-/- mice do not, however, succumb to anemia. Thus, spontaneous intestinal inflammation in IL-2-/- mice requires mature T cells, not B cells, while anemia is dependent on B cells.

Anemia, Hemolytic, Autoimmune↗
PubMed1995

Generalized autoimmune disease in interleukin-2-deficient mice is triggered by an uncontrolled activation and proliferation of CD4+ T cells.

Interleukin-2-deficient mice (IL-2-/-) crossed to a BALB/c genetic background develop a lymphoproliferative syndrome with severe hemolytic anemia and die within 5 weeks of age. The presence of autoantibodies of various specificities and inflammatory lesions in several organs are indicative of a generalized auto-immune disease. No alterations of the immune system were observed in 6-day-old animals, but 10-day-old mice already showed an increased proliferation and polyclonal activation of lymphocytes. The treatment of IL-2-/- mice with anti-gp39(CD40L) antibody prevented the disease and indicated that the appearance of activated CD4- T cells (CD44high, CD69-) represents the first alteration of the immune system in IL-2-/- mice. Collectively, our results suggest that an essential role of IL-2 in vivo, which is not compensated by other cytokines, is the maintenance of self tolerance.

Anemia, Hemolytic, Autoimmune↗
PubMed1995

Immunodeficiency in IL-2-knockout mice.

Interleukin-2-deficient mice (IL-2-/-) generated by targeted mutagenesis proved to be an excellent system to study the function of this lymphokine in the context of whole immune system. In addition, they provide an animal model of a primary immunodeficiency caused by a single-gene defect. Our results indicate that the essential degect in IL-2-/- mice is the lack of a negative regulatory function, which leads to breakdown of self tolerance. The development of autoimmune diseases in IL-2-deficient mice stresses the link between autoimmunity and primary immunodeficiencies.

Animals↗
PubMed1995

Antiviral immune responses in mice deficient for both interleukin-2 and interleukin-4.

Antiviral immune responses of mice lacking interleukin-2 (IL-2) or IL-4 or both IL-2 and IL-4 (IL-2/4) were compared by using different viruses. Primary cytotoxic T-lymphocyte (CTL) responses against lymphocytic choriomeningitis virus (LCMV) were only moderately reduced in mice lacking IL-2 and were normal in mice lacking IL-4. Mice deficient in both interleukins exhibited variable and more strongly reduced but nevertheless in vivo protective LCMV-specific CTL responses. Similar results were obtained with vaccinia virus. Upon virus-specific restimulation in vitro, spleen cells from IL-2- and IL-2/4-deficient mice failed to generate CTL responses against virus-infected target cells, whereas the response of mice deficient in only IL-4 was comparable to that of control mice. The addition of IL-2 during in vitro restimulation completely restored the responses of both IL-2 and IL-2/4-deficient mice. T-helper-cell-independent immunoglobulin M and T-helper-cell-dependent immunoglobulin G antibody responses against vesicular stomatitis virus glycoprotein were within normal ranges for the various mutant mice. After LCMV infection, specific antibody responses against LCMV nucleoprotein were reduced four- to eightfold. These results show that mice lacking IL-2/4 have an overall tendency to exhibit more severely reduced CTL responses than IL-2- or IL-4-deficient mice. Nevertheless, and surprisingly, in vivo protective immune responses were mounted in the absence of IL-2/4, suggesting that besides a minor contribution from IL-4, other interleukins compensate in vivo for the lack of IL-2 in IL-2-deficient mice.

Animals↗
PubMed1994

Murine protein which binds preferentially to oligo-C-rich single-stranded nucleic acids.

Two single-stranded nucleic acid binding proteins mCBP and mCTBP were identified by means of their binding to a potential recombination hotspot in LTRs of mouse retro-transposons. Both are nuclear proteins of 35 and 55 kDa respectively. mCBP binds preferentially to oligo dC, mCTBP to oligo dCdT. mCBP was purified and its cDNA was isolated and sequenced.

Amino Acid Sequence↗
PubMed1994

Development and proliferation of lymphocytes in mice deficient for both interleukins-2 and -4.

Interleukin (IL)-2 and IL-4 are considered as important regulators of growth and differentiation of lymphocytes. We report that in mice made deficient for both IL-2 and IL-4 by gene targeting all major T cell subsets and B cells were normal, indicating that IL-2 and IL-4 are not essential for development of the immune system. Paradoxically, proliferation of T cells was increased in both IL-2 and IL-4-deficient homozygous mice.

Animals↗
PubMed1994

T cell subset distribution and B cell hyperreactivity in mice expressing interleukin-4 under the control of major histocompatibility complex class I regulatory sequences.

Transgenic mice in which interleukin-4 (IL-4) is expressed under the control of the major histocompatibility complex (MHC) class I regulatory sequences show low level expression of IL-4 in all organs investigated. Several weeks after birth the animals develop thymus hypoplasia with a loss of CD4+CD8+ double-positive cells and a relative increase in the mature population, especially, and in contrast to previously published lines, the CD4+ single-positive cells. In the periphery, T lymphocytes eventually decline, CD8+ cells being more strongly affected. Many of the residual T cells exhibit the CD44highMel-14low phenotype of antigenically experienced T cells. B cells also show an activated phenotype with respect to size, MHC class II and CD23 expression, are more readily stimulated by anti-mu F(ab')2 antibodies than are B cells from control littermates, and show a higher spontaneous and antigen-induced production of IgG1 and IgE.

Animals↗
PubMed1994

Thymic selection and peptide-induced activation of T cell receptor-transgenic CD8 T cells in interleukin-2-deficient mice.

The requirement for interleukin-2 (IL-2) in repertoire selection and peripheral activation of CD8 T cells was tested in mice rendered IL-2 deficient by gene targeting and expressing a transgenic T cell receptor (TcR) (F5) specific for influenza nucleoprotein (NP) 366-374 + H-2Db. Positive selection of the transgenic F5 TcR into the CD8 compartment proceeded normally. Both in vivo and in vitro, the antigenic peptide induced depletion of immature thymocytes and proliferation of mature CD8 T cells regardless of the presence of an intact IL-2 gene. In contrast, cytotoxic T lymphocyte (CTL) activity was only generated by T cells from IL-2+ F5 transgenic mice. Exogenous IL-2 was able to fully restore the CTL response of IL-2-/- responder cells in vitro. Thus, both in vivo and in vitro, clonal expansion of CD8 T cells can proceed in the absence of IL-2, whereas in peptide-immunized F5 transgenic mice, induction of cytotoxic effector function is IL-2 dependent.

Animals↗
PubMed1993

Immune responses in interleukin-2-deficient mice.

The role of costimulatory signals in T cell induction was evaluated in mice lacking the interleukin-2 (IL-2) gene. In vitro secondary antiviral T cell responses were absent unless IL-2 was added, confirming the crucial role of IL-2 in vitro. In vivo, primary and secondary cytotoxic T cell responses against vaccinia and lymphocytic choriomeningitis virus were within normal ranges. B cell reactivity to vesicular stomatitis virus was not impaired. T helper cell responses were delayed but biologically functional. Natural killer cell activity was markedly reduced but inducible. These normal in vivo immune responses in IL-2-deficient mice question the importance of IL-2 as defined by in vitro studies.

Animals↗