Down-regulation of oxytocin-induced cyclooxygenase-2 and prostaglandin F synthase expression by interferon-tau in bovine endometrial cells.
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Oxytocin (OT) is responsible for the episodic release of luteolytic prostaglandin (PG) F2alpha from the uterus in ruminants. The attenuation of OT-stimulated uterine PGF2alpha secretion by interferon-tau (IFN-tau) is essential for prevention of luteolysis during pregnancy in cows. To better understand the mechanisms involved, the effect of recombinant bovine IFN-tau (rbIFN-tau) on OT-induced PG production and cyclooxygenase-2 (COX-2) and PGF synthase (PGFS) expression in cultured endometrial epithelial cells was investigated. Cells were obtained from cows at Days 1-3 of the estrous cycle and cultured to confluence in RPMI medium supplemented with 5% steroid-free fetal calf serum. The cells were then incubated in the presence or absence of either 100 ng/ml OT or OT+100 ng/ml rbIFN-tau for 3, 6, 12, and 24 h. OT significantly increased PGF2alpha and PGE2 secretion at all time points (p < 0.01), while rbIFN-tau inhibited the OT-induced PG production and reduced OT receptor binding in a time-dependent manner. OT increased the steady-state level of COX-2 mRNA, measured by Northern blot, which was maximal at 3 h (9-fold increase) and then decreased with time (p < 0.01). OT also caused an increase in COX-2 protein, which peaked at 12 h (11-fold increase), as measured by Western blot. Addition of rbIFN-tau suppressed the induction of COX-2 mRNA (89%, p < 0.01) and COX-2 protein (50%, p < 0.01) by OT. OT also increased PGFS mRNA, and this stimulation was attenuated by rbIFN-tau (p < 0.01). To ensure that the decrease in COX-2 was not solely due to down-regulation of the OT receptor, cells were stimulated with a phorbol ester (phorbol 12-myristate 13-acetate; PMA) in the presence and absence of rbIFN-tau. The results showed that rbIFN-tau also decreased PMA-stimulated PG production and COX-2 protein. It can be concluded that rbIFN-tau inhibition of OT-stimulated PG production is due to down-regulation of OT receptor, COX-2, and PGFS. (+info)
Type I IFN sets the stringency of B cell repertoire selection in the bone marrow.
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Locally produced type I interferon (IFN-I) enhances the sensitivity of bone marrow B cell to IgM receptor ligation. The establishment of B cell repertoires, on the other hand, seems to involve selective processes that are critically dependent on B cell receptor (BCR) ligation. In order to assess the importance of BCR triggering thresholds on the selection of polyclonal unmanipulated B cell populations, we compared VH gene expression and reactivity repertoires in various B cell compartments of wild-type and IFN-I receptor-deficient mice (IFN-I-R-/-). These analyses demonstrate that increased B cell sensitivity to BCR ligation mediated by IFN-I in the bone marrow (BM) has consequences on the stringency of B cell repertoire selection. Thus, the normal counter-selection of both VH7183 gene family expression and multireactivity was impaired among immature BM B cells from mutant mice. Furthermore, as a result of reduced efficiency of BCR ligation-dependent inhibition of terminal differentiation, IFN-I-R-/- animals produce, in BM and thymus, higher numbers of plasma cells secreting antibodies that are more multireactive than wild-type animals. Finally, mutant serum IgM natural antibodies display a more reactive repertoire than controls, a likely reflection of the BM resident plasma cell repertoire. The present observations demonstrate, therefore, that local modulation of BCR triggering thresholds leads to important modifications in the generation and/or selection of normal B cell populations. (+info)
Ontogeny of hepatitis C virus (HCV) hypervariable region 1 (HVR1) heterogeneity and HVR1 antibody responses over a 3 year period in a patient infected with HCV type 2b.
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Hypervariable region 1 (HVR1) sequences of 96 clones at six time-points representing 27 variants in two major and one minor group were identified in a patient with chronic hepatitis C virus (HCV) infection over 3 years. Major and selected minor variants were used to design synthetic peptides corresponding to the HVR1 C terminus. Peptide ELISA reactivity with IgG was plotted against the corresponding clone frequency, and three patterns emerged: (1) three peptides were unreactive; (2) antibodies against two peptides followed emergence of the corresponding variant, suggesting isolate-specificity; (3) antibodies against four peptides preceded the appearance of the corresponding variant, indicating cross-reactivity or previous exposure. Cross-reactivity was investigated further: sera from six time-points were tested against 11 unrelated HVR1 peptides, seven of which (63.6%) showed cross-reactivity at all time-points. Cross-reactivity of nine patient-specific peptides tested against a panel of 45 heterologous sera from chronic HCV carriers ranged between 0 and 20%. Only three of 27 variants appeared at more than one time-point and in two cases specific and/or cross-reactive HVR1 antibodies coexisted with the corresponding variant, consistent with emergence of escape mutants. In addition, analysis of HVR1 IgG reactivity within a group of closely related patient-specific peptides revealed a loss of reactivity in one peptide attributable to a single amino acid substitution. Interferon-alpha treatment considerably reduced viral RNA but, paradoxically, heterogeneity increased. (+info)
Inhibition of IL-4-inducible gene expression in human monocytes by type I and type II interferons.
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The Th2-type cytokines, interleukin-4 (IL-4) and interleukin-13 (IL-13), induce expression of a distinct subset of genes in human monocytes, including FcepsilonRIIb (CD23), 15-lipoxygenase, IL-1 receptor antagonist (IL-1ra), and type I and type II IL-1 receptors (IL-1R). Type I interferons (IFN-alpha and IFN-beta) and type II interferon (IFN-gamma) inhibit induction of these genes by IL-4 and IL-13. However, the mechanism by which IFNs mediate this inhibition has not been defined. In this overview, we discuss the role of the transcription factor, STAT6 (signal transducer and activator of transcription-6) in mediating IL-4- and IL-13-induced gene expression in monocytes. We also discuss our recent findings that type I and type II IFNs suppress IL-4/IL-13-inducible gene expression by inhibiting tyrosine phosphorylation and nuclear translocation of STAT6. The ability of type I and type II IFNs to inhibit IL-4/IL-13-induced STAT6 activity is dose- and time-dependent, and is not unique to monocytes because IFNs induce the same effects in fibroblasts. Inhibition of STAT6 activity is not evident unless cells are preincubated with IFN for at least 1 h before IL-4 stimulation. Furthermore, inhibition can be blocked by actinomycin D, indicating a requirement for de novo transcription. We propose a model in which stimulation of monocytes by IFN activates de novo synthesis of an inhibitory factor, possibly one or more members of the SOCS/ SSI/CIS gene family, capable of suppressing activation of STAT6 by IL-4 and IL-13. Because STAT6 activation plays an essential role in IL-4/IL-13-induced gene expression, the ability of IFN-beta and IFN-gamma to inhibit STAT6 activity provides an explanation for how IFNs can suppress IL-4/IL-13-inducible gene expression. (+info)
Interferon-induced guanylate binding protein-1 (GBP-1) mediates an antiviral effect against vesicular stomatitis virus and encephalomyocarditis virus.
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A cDNA encoding the human guanylate binding protein-1 (hGBP-1) was expressed in HeLa cells using a constitutive expression vector. Stably transfected clones expressing hGBP-1 exhibited resistance to the cytopathic effect mediated by both vesicular stomatitis virus (VSV) and encephalomyocarditis virus (EMCV) and produced less viral progeny than control cells following infection with these viruses. To study the role hGBP-1 plays in the IFN-mediated antiviral effect, cells were stably transfected with a construct expressing antisense RNA for hGBP-1. VSV infection of IFN-alpha-treated antisense RNA-expressing cells produced an amount of virus comparable to that produced in the parental cell line, while EMCV infection of the IFN-alpha-treated transfected cells and VSV and EMCV infection of the IFN-gamma-treated transfected cells produced far more virus than was produced in the parental cell line. These results demonstrate that GBP-1 mediates an antiviral effect against VSV and EMCV and plays a role in the IFN-mediated antiviral response against these viruses. (+info)
Protective effects of type I and type II interferons toward Rous sarcoma virus-induced tumors in chickens.
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Growth of tumors induced by Rous sarcoma virus (RSV) is controlled by alleles at the major histocompatibility complex locus in chickens, indicating that immunological host defense mechanisms play a major role. We show here that the resistance phenotype of CB regressor chickens can be partially reverted by treating the animals with a monoclonal antibody that neutralizes the major serotype of chicken type I interferon, ChIFN-alpha. Injection of recombinant ChIFN-alpha into susceptible CC progressor chickens resulted in a dose-dependent inhibition of RSV-induced tumor development. This treatment was not effective, however, in CC chickens challenged with a DNA construct expressing the v-src oncogene, suggesting that the beneficial effect of type I interferon in this system resulted from its intrinsic antiviral activity and probably not from indirect immunmodulatory effects. By contrast, recombinant chicken interferon-gamma strongly inhibited tumor growth when given to CC chickens that were challenged with the v-src oncogene, indicating that the two cytokines target different steps of tumor development. (+info)
Role of interferon and interferon regulatory factors in early protection against Venezuelan equine encephalitis virus infection.
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To investigate the role of type I interferon (IFN) and its regulatory transacting proteins, interferon regulatory factors (IRF-1 and IRF-2), in early protection against infection with virulent Venezuelan equine encephalitis virus (VEE), we utilized mice with targeted mutations in the IFN-alpha/beta receptor, IRF-1, or IRF-2 genes. IFN-alpha/beta-receptor knockout mice are highly susceptible to peripheral infection with virulent or attenuated VEE, resulting in their death within 24 and 48 h, respectively. Treatment of normal macrophages with anti-IFN-alpha/beta antibody prior to and during infection with molecularly cloned virulent VEE resulted in increased VEE replication. However, treatment with high doses of IFN or IFN-inducing agents failed to alter percentage mortality or average survival times in mice challenged with a low dose of virulent VEE. In IRF-1 and IRF-2 knockout mice (IRF-1(-/-) and IRF-2(-/-)), the 100% protection against virulent VEE that is conferred by attenuated VEE within 24 h in control C57BL/6 mice was completely absent in IRF-2(-/-) mice, whereas 50% of IRF-1(-/-) mice were protected. IRF-2(-/-) mice were deficient in clearing VEE virus from the spleen and the brain compared to the heterozygous IRF-2(+/-) knockout or C57BL/6 (+/+) mice. Furthermore, a distinct pattern of histopathological changes was observed in brains of IRF-2(-/-) mice after VEE exposure. Taken together, these findings imply that the altered immune response in IRF-1 and IRF-2 knockout mice results in altered virus dissemination, altered virus clearance, and altered virus-induced pathology. Thus, type I interferon, as well as IRF-1 and IRF-2, appears to play an important and necessary role in the pathogenesis of, and protection against, VEE infection. (+info)
HTLV-I-infected T cells evade the antiproliferative action of IFN-beta.
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Human T-cell lymphotropic virus type I (HTLV-I)-infected T-cell clones enter the S-phase of the cell cycle in the absence of exogenous IL-2. The pathway by which HTLV-I activates the host T cell may circumvent normal immunoregulatory mechanisms and thus be important for the pathogenesis of HTLV-I-induced diseases. The early control of viral infections is in part mediated by interferons (IFNs), which possess both antiviral and antiproliferative functions. In order to investigate the antiproliferative effect of IFN-beta on HTLV-I-induced T-cell activation, we generated T-cell clones from patients with HTLV-I-associated myelopathy/tropical spastic paraparesis by single-cell cloning under limiting dilution conditions. Here we demonstrate that HTLV-I-induced T-cell proliferation is resistant to the antiproliferative action of IFN-beta. Moreover, HTLV-I-infected T-cell clones continue to constitutively secrete IFN-gamma in the presence of high doses of IFN-beta. HTLV-I-infected T cells express normal levels of IFNAR1 and are able to respond to IFN-beta by phosphorylation of STAT1 on Tyr701, although they display a relative increase in phosphorylation of the transcriptionally inactive STAT1beta when compared with STAT1alpha. Thus, HTLV-I promotes cell cycle progression in G1 by a mechanism that overcomes inhibitory signals, thereby circumventing an innate immune defense mechanism. (+info)