Stimulation of interferon and cytokine gene expression by imiquimod and stimulation by Sendai virus utilize similar signal transduction pathways

The imidazoquinolineamine derivative 1-(2-methyl propyl)-1H-imidazole [4,5-c]quinoline-4-amine (imiquimod) has been shown to induce alpha interferon (IFN-alpha) synthesis both in vivo and in peripheral blood mononuclear cells in vitro. In this study, we show that, in these cells, imiquimod induces expression of several IFNA genes (IFNA1, IFNA2, IFNA5, IFNA6, and IFNA8) as well as the IFNB gene. Imiquimod also induced the expression of interleukin (IL)-6, IL-8, and tumor necrosis factor alpha genes. Expression of all these genes was transient, independent of cellular protein synthesis, and inhibited in the presence of tyrosine kinase and protein kinase C inhibitors. Infection with Sendai virus led to expression of a similar set of cytokine genes and several of the IFNA genes. Imiquimod stimulates binding of several induction-specific nuclear complexes: (i) the NF-kappa B-specific complexes binding to the kappa B enhancer present in the promoters of all cytokine genes, but not in IFNA genes, and (ii) the complex(es) binding to the A4F1 site, 5'-GTAAAGAAAGT-3', conserved in the inducible element of IFNA genes. These results indicate that imiquimod, similar to viral infection, stimulates expression of a large number of cytokine genes, including IFN-alpha/beta, and that the signal transduction pathway induced by both of these stimuli requires tyrosine kinase and protein kinase activity.

Priming does not change promoter sequence requirements for IFN induction or correlate with the expression of IFN regulatory factor-1

Pretreatment of L929 cells with IFN enhances Sendai virus-mediated induction of IL-6, TNF-alpha, and IFNA and IFNB genes. The priming effect could be demonstrated at both the RNA and protein levels and the former did not require cellular protein synthesis. Priming increased the Sendai virus-mediated induction of a murine IFNA4 promoter-chloramphenicol acetyltransferase gene hybrid plasmid (A4CAT) in transiently transfected cells, and deletion analysis showed that the identical DNA sequence was required for the inducibility in primed and unprimed cells. Cotransfection of A4CAT plasmid with interferon regulatory factor-1 (IRF-1) expression plasmid increased CAT expression, however, the IRF-1-mediated expression was further enhanced by priming. These results show that the identical inducible element present in the promoter region of IFNA4 gene is required for both the inducibility and the priming effect; however, no direct correlation between the enhancement of expression of the IRF-1 gene and enhancement of expression of IFN, IL-6, and TNF-alpha genes in the primed cells was observed. We suggest that priming facilitates inducer-mediated posttranscriptional modulation of various transcriptional factors that play a role in stimulation of transcription of these genes.

Priming does not change promoter sequence requirements for IFN induction or correlate with the expression of IFN regulatory factor-1

Pretreatment of L929 cells with IFN enhances Sendai virus-mediated induction of IL-6, TNF-alpha, and IFNA and IFNB genes. The priming effect could be demonstrated at both the RNA and protein levels and the former did not require cellular protein synthesis. Priming increased the Sendai virus-mediated induction of a murine IFNA4 promoter-chloramphenicol acetyltransferase gene hybrid plasmid (A4CAT) in transiently transfected cells, and deletion analysis showed that the identical DNA sequence was required for the inducibility in primed and unprimed cells. Cotransfection of A4CAT plasmid with interferon regulatory factor-1 (IRF-1) expression plasmid increased CAT expression, however, the IRF-1-mediated expression was further enhanced by priming. These results show that the identical inducible element present in the promoter region of IFNA4 gene is required for both the inducibility and the priming effect; however, no direct correlation between the enhancement of expression of the IRF-1 gene and enhancement of expression of IFN, IL-6, and TNF-alpha genes in the primed cells was observed. We suggest that priming facilitates inducer-mediated posttranscriptional modulation of various transcriptional factors that play a role in stimulation of transcription of these genes.

Mouse genotype affects inducible expression of cytokine genes

The levels of circulating IFN in mice infected with Newcastle disease virus (NDV) are regulated by the If-1 locus. In this study we show that in NDV-infected C57BL/6 mice, which carry the If-1h allele and produce high levels of IFN, high levels of both IFN-alpha and -beta mRNA can be detected in the spleen. In contrast, only very low levels of IFN mRNA could be detected in spleens of infected BALB/c mice containing the If-1l allele and producing low levels of IFN or in B6.C-H28c mice that are congenic for the If-1l allele. The relative levels of all individual IFN-alpha 1, alpha 4, and alpha 6 mRNA in spleens of infected BALB/c were lower than in spleens of infected C57BL/6 mice, indicating that the If-1 locus affects the expression of all IFN-alpha subtypes and is not associated with the deletion or inactivation of a specific IFN gene. The relative levels of IFN regulatory factor-1 mRNA in infected mice carrying the If-1l and If-1h loci were comparable, suggesting that the If-1 regulation is not associated with the altered expression of the IFN regulatory factor-1 gene. Quantitative difference in the expression of IFN-alpha and -beta genes was also observed in in vitro-infected peritoneal macrophages isolated from either C57BL/6 or BALB/c mice. A surprise finding was that the If-1 locus also affected the NDV-induced expression of two other cytokine genes, TNF-alpha and IL-6. Priming of the macrophage cultures with murine IFN enhanced the expression of all cytokine genes, and the relative levels of IFN, TNF-alpha, and IL-6 mRNA induced by NDV in macrophages derived from C57BL/6 and BALB/c mice were comparable. We propose that the If-1 locus affects the early stages of a signal transduction pathway which are common to the virus-mediated induction of IFN, TNF-alpha, and IL-6 genes.

Mouse genotype affects inducible expression of cytokine genes

The levels of circulating IFN in mice infected with Newcastle disease virus (NDV) are regulated by the If-1 locus. In this study we show that in NDV-infected C57BL/6 mice, which carry the If-1h allele and produce high levels of IFN, high levels of both IFN-alpha and -beta mRNA can be detected in the spleen. In contrast, only very low levels of IFN mRNA could be detected in spleens of infected BALB/c mice containing the If-1l allele and producing low levels of IFN or in B6.C-H28c mice that are congenic for the If-1l allele. The relative levels of all individual IFN-alpha 1, alpha 4, and alpha 6 mRNA in spleens of infected BALB/c were lower than in spleens of infected C57BL/6 mice, indicating that the If-1 locus affects the expression of all IFN-alpha subtypes and is not associated with the deletion or inactivation of a specific IFN gene. The relative levels of IFN regulatory factor-1 mRNA in infected mice carrying the If-1l and If-1h loci were comparable, suggesting that the If-1 regulation is not associated with the altered expression of the IFN regulatory factor-1 gene. Quantitative difference in the expression of IFN-alpha and -beta genes was also observed in in vitro-infected peritoneal macrophages isolated from either C57BL/6 or BALB/c mice. A surprise finding was that the If-1 locus also affected the NDV-induced expression of two other cytokine genes, TNF-alpha and IL-6. Priming of the macrophage cultures with murine IFN enhanced the expression of all cytokine genes, and the relative levels of IFN, TNF-alpha, and IL-6 mRNA induced by NDV in macrophages derived from C57BL/6 and BALB/c mice were comparable. We propose that the If-1 locus affects the early stages of a signal transduction pathway which are common to the virus-mediated induction of IFN, TNF-alpha, and IL-6 genes.

Interferon pretreatment regulates interferon and interleukin-6 production in L929 cells in a coordinated manner

Two sublines of L929 cells with different interferon (IFN)-producing capacities synthesized IFN and interleukin-6 (IL-6) simultaneously in response to Sendai virus infection. IFN pretreatment primed the production of both cytokines. However, the difference in IL-6 production between the "high and low producer" L-cell sublines was about one magnitude of order larger than in the case of their IFN production. The determination of the corresponding mRNA levels also reflected this difference.

The effects of various cytokines on interleukin-6 and interferon-alpha synthesis in human peripheral blood mononuclear cells

The effect of various recombinant cytokines on the induction of interleukin-6 (IL-6) synthesis induced in adherent and nonadherent cells of human peripheral blood mononuclear cells (PBMNC) by bacterial lipopolysaccharide (LPS) or concanavalin A (CA) was studied. The results showed that human interferon-(HuIFN)-alpha, -beta, and gamma at a concentration of 100-10,000 IU/ml enhanced the LPS-induced IL-6 production in the adherent cell fraction of PBMNC. However, in nonadherent cells, treatment with HuIFN-alpha or -beta inhibited the CA-stimulated IL-6 production in a dose-dependent manner. Recombinant (r) IL-2 enhanced the IL-6 production of the adherent cells, while rIL-1 alone in the absence of other inducer induced IL-6 production in the nonadherent cell fraction. Other cytokines such as the recombinant tumor necrosis factor-alpha (rTNF-alpha) or rIL-6 itself did not modulate IL-6 production in human PBMNC. TNF and the interleukins studied did not affect the Sendai virus-induced IFN production in the adherent cells. In contrast, the different IFNs exerted a significant priming effect.

The localization of influenza virus: minimal infectious dose determinations and single cycle kinetic studies on organ cultures of respiratory and other ferret tissues

A comprehensive survey of ferret tissues in organ culture showed that influenza virus (A/Moscow/1019/65 (H₂N₂)) can infect bladder, uterus, oviduct and conjunctiva in addition to respiratory tissues. Alimentary tract tissues were insusceptible, except oesophagus and pharynx which were infected at high inocula. Muscle, reticuloendothelial tissues, blood vessels and kidney were also insusceptible.

Minimal infectious dose determinations on the susceptible tissues showed significant differences in the ease of initiation of infection in the order nasal turbinates > bladder > uterus > trachea > lung > conjunctiva > oviduct > oesophagus. On the other hand, the susceptible tissues were similar with respect to the kinetics of virus replication over one infection cycle, new virus appearing from all tissues at about the same time (5-6 hours) after inoculation.

Large inocula of virus disappeared very quickly from the blood stream of ferrets in vivo, yet in vitro ferret blood could not inactivate large quantities of virus although it inhibited smaller quantities.

The results are discussed in relation to the degree of confinement of influenza infection to the respiratory tract.