Post-transcriptional regulation of interferon-alpha 4 subtype production by lymphoblastoid cells

Decreased Type I Interferon Production by Plasmacytoid Dendritic Cells Contributes to Severe Dengue

The clinical presentation of dengue virus (DENV) infection is variable. Severe complications mainly result from exacerbated immune responses. Type I interferons (IFN-I) are important in antiviral responses and form a crucial link between innate and adaptive immunity. Their contribution to host defense during DENV infection remains under-studied, as direct quantification of IFN-I is challenging. We combined ultra-sensitive single-molecule array (Simoa) digital ELISA with IFN-I gene expression to elucidate the role of IFN-I in a well-characterized cohort of hospitalized Cambodian children undergoing acute DENV infection. Higher concentrations of type I IFN proteins were observed in blood of DENV patients, compared to healthy donors, and correlated with viral load. Stratifying patients for disease severity, we found a decreased expression of IFN-I in patients with a more severe clinical outcome, such as dengue hemorrhagic fever (DHF) or dengue shock syndrome (DSS). This was seen in parallel to a correlation between low IFNα protein concentrations and decreased platelet counts. Type I IFNs concentrations were correlated to frequencies of plasmacytoid DCs, not DENV-infected myloid DCs and correlated inversely with neutralizing anti-DENV antibody titers. Hence, type I IFN produced in the acute phase of infection is associated with less severe outcome of dengue disease.

Differential expression of IFN-alpha subtypes in human PBMC: evaluation of novel real-time PCR assays

Studies of the human IFN-alpha subtype system have been hampered by the lack of efficient procedures to quantify and differentiate the expression of the highly homologous IFN-alpha subtypes. Here we evaluate four novel real-time PCR assays for the specific detection and quantification of IFN-alpha mRNA for the subtypes alpha(2), alpha(6), alpha(8) and alpha(1/13) in a combined assay in human peripheral blood mononuclear cells (PBMC). This included (a) the selection of beta-glucuronidase (GUS) as a suitable housekeeping gene for relative quantification; (b) verification of the specificity by using human DNA of different IFN-alpha subtypes; and (c) comparison of the amplification efficiencies among the different assays. This highly sensitive method allows the detection of low-level, constitutive IFN-alpha mRNA and shows differences in the composition of constitutive IFN-alpha subtypes compared to other cell types (HeLa and HEp-2). The in vitro stimulation of PBMC with Newcastle disease virus (NDV), Respiratory syncytial virus (RSV) or an inactivated Herpes simplex (HSV) preparation leads to the transcriptional induction of all IFN-alpha subtypes investigated but to different expression levels. Among the subtypes detected, IFN-alpha(13/1) and alpha(2) are the major transcripts followed by alpha(8), and finally alpha(6) as a minor transcribed subtype. Time-kinetics of IFN-alpha transcriptional activation also revealed variations in the course of IFN-alpha transcription between NDV, RSV or HSV. The data obtained from the real-time PCR assays correlated well with IFN-alpha(2) protein release. In conclusion, we have demonstrated the suitability and reliability of new real-time PCR assays for the rapid and efficient analysis of IFN-alpha subtype expression.

Alpha/beta interferons increase host resistance to murine AIDS

Murine AIDS (MAIDS) is caused by a defective retrovirus present in the LP-BM5 murine leukemia virus mixture. Strains of inbred mice differ in resistance to MAIDS development; some are susceptible (e.g., C57BL/6), while others are resistant (e.g., CBA and B10.BR). As an early block to viral replication in resistant mice has been demonstrated previously by PCR studies, we postulated that alpha/beta interferons (IFN-alpha/beta) may be involved in resistance to MAIDS. Susceptible C57BL/6 mice infected with LP-BM5 were treated with IFN-alpha/beta or Newcastle disease virus. Newcastle disease virus induces high endogenous IFN-alpha/beta production in mice. Both treatments delayed the development of MAIDS, as assessed by splenomegaly and T- and B-cell proliferation. In addition, an IFN-alpha/beta response was detected by reverse transcription-PCR and dot blotting 3, 6, and 9 h after LP-BM5 infection in resistant mice but not in susceptible mice. These results suggest that the ability to produce IFN-alpha/beta in response to LP-BM5 infection may contribute to host resistance to MAIDS.

Immunolocalisation of interferon-alpha in hepatitis C patients and its correlation with response to interferon-alpha therapy

Localised interferon-alpha production was investigated in hepatitis C patients entered into a trial of interferon-alpha-2a therapy. Antibodies capable of reacting specifically with interferon-alpha-2, interferon-alpha-4 or with all interferon-alpha subtypes were used as immunohistochemical and immunofluorescence probes to study interferon-alpha production in liver biopsy tissue, and peripheral blood mononuclear cells prior to and after stimulation with Sendai virus. Measurement of cytoplasmic interferon-alpha, specifically interferon-alpha-2 and interferon-alpha-4, in peripheral blood mononuclear cells isolated from the hepatitis C patients and of total interferon-alpha secreted into culture supernatants by these cells showed interferon-alpha production similar to that of peripheral blood mononuclear cells isolated from normal individuals. Interferon-alpha-positive cells were observed in the infiltrating mononuclear cells of the liver biopsy tissue obtained from 8 of the 14 patients. Lymphocytes, fibroblasts, Kupffer cells, polymorphonuclear cells and monocytes stained positive for interferon-alpha, and specifically interferon-alpha-4, in all of the eight patients. The cytoplasm of hepatocytes also stained weakly positive in three of these patients. Interferon-alpha positive cells showed a good correlation with the degree of histological damage observed in the liver biopsies but not with presence of antibodies towards hepatitis C virus or levels of serum alanine aminotransferase measured prior to interferon-alpha-2a therapy. Interestingly, response to therapy seemed linked to local interferon-alpha production status. Those patients who responded best to therapy displayed no or only low levels of interferon-alpha positive cells in liver biopsy tissue. Thus patients with a lower activation of their endogenous interferon-alpha system may benefit from administration of exogenous interferon-alpha.

Detection of interferon-alpha expression by PCR in patients with chronic hepatitis C and hepatitis non-A, non-B

The polymerase chain reaction (PCR) was used to examine expression of interferon-alpha (IFN A) genes in general and the expression of messenger RNA (mRNA) encoding the subtypes IFN-alpha-2 and IFN-alpha-4 in blood and liver biopsy samples from patients with chronic hepatitis C or hepatitis non-A, non-B (HC/HNANB) infection entered into a trial of IFN-alpha-2a therapy. Peripheral blood mononuclear cells (PBMC) from healthy controls and HC/HNANB infected patients were studied for their capacity to produce transcripts encoding IFN-alpha after stimulation with Sendai virus. Expression at the level of mRNA for IFN A and the subtypes IFN A2 and A4 was detected in both controls and HC/HNANB infected patients PBMC and no significant difference was seen in expression of IFN A transcripts or level of total IFN-alpha secreted into culture supernatants between controls and patients. Interferon A, and specifically IFN A2 and IFN A4 transcripts were detected in a high proportion of liver biopsies from patients with HC/HNANB infection. The presence of IFN A mRNA (and specifically IFN A2 and IFN A4) showed no correlation to histological improvement nor response to therapy. The use of PCR to detect those IFN A genes that are not expressed, thereby identifying subtypes that may be lacking, could be the key to the choice of IFN-alpha subtypes that are used for effective therapy.

Expression of IFN A genes in subpopulations of peripheral blood cells

The polymerase chain reaction (PCR) was used to detect the expression of IFN A genes in general (with 'universal' primers) and specifically the expression of mRNA transcripts encoding the subtypes IFN-alpha-1, -alpha-2, -alpha-4, -alpha-5 and -alpha-14 (with gene specific primers) in normal human peripheral blood mononuclear cells (PBMC) and PBMC subpopulations. Our examination revealed that all transcripts tested for could be detected not only following induction with inducers such as Sendai virus, Semliki Forest virus and poly(I):poly(C), but also in the absence of induction. IFN A1, IFN A2 and IFN A4 mRNAs were found to constitute the major transcripts of Sendai virus and poly(I):poly(C) induced PBMC. Fractionation of PBMC into T cells, B cells, adherent cells, mononuclear (MN) cells and polymorphonuclear (PMN) cells revealed that these cell populations all contain specific IFN A mRNA transcripts both in the absence of an inducer and following induction with Sendai virus. The proportion of IFN A transcripts detected was dependent on the cell type investigated. IFN A1, IFN A2 and IFN A4 transcripts constituted the major RNA species present in PBMC and PMN cells. In MN cells IFN A5 transcripts were also present as a major IFN RNA species. Expression of the IFN A transcripts tested for in T cells, B cells and adherent cells did not vary significantly. These results emphasize the importance of identifying IFN A subtype expression in order to further our understanding of the biological significance of differential regulation and expression of particular IFN-alpha subtypes.