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There are several interferon-alpha (IFN-alpha) subtypes. Mechanism of disparity in biological effects among members of IFN-alpha subtypes remains unexplained. Biological activity of IFN-alpha is mediated in part by induction of intracellular antiviral proteins. We studied whether differences in biologic effects of IFN-alpha subtypes may rely on their antiviral protein inducing effect. Intracellular induction of MxA protein and anti-virus-induced cytopathic effect (CPE) activity of 11 IFN-alpha subtypes in human amnion WISH cells have been studied. MxA protein quantitation in cell lysates was performed by immunochemiluminescence assay and anti-virus-induced CPE activity was assessed by protection against vesicular stomatitis virus (VSV)-induced CPE. Range of MxA values was high when cells were treated with 10 and 100 IU/ml of each IFN-alpha subtype. Levels of MxA correlated with anti-VSV-induced CPE obtained with 10 IU/ml IFN-alpha subtype. Together our data show a disparity in MxA-inducing activity of IFN-alpha subtypes and suggest that differences in anti-VSV-induced CPE of IFN-alpha subtypes in WISH cells can be related to their different ability to induce MxA.

Type I interferon system is an important part of host's innate defense mechanisms against viral infections. The type I interferons mediate in part their antiviral effect via induction of various proteins. Among them the most widely known are 2'-5' oligoadenylate synthetase (2'-5' OAS) and a protein kinase (PKR). MxA, an other antiviral protein, is specifically induced by the type I interferons. The MxA protein contains the dynamin signature, which is implicated in transport processes. The MxA protein appears to block the replication of certain viruses at poorly defined steps. There are substantial differences in the antiviral activity of MxA between virus types. Indeed, the replication of vesicular stomatitis virus and influenza virus is inhibited by MxA, but not the one of type I herpes simplex virus. Measurements of interferon alpha and MxA levels may be of high value in clinical practice. Interferon alpha can be detected by using a bioassay based on the interferon alpha ability to protect cultured cells from the cytopathic effect caused by a selected challenged virus, or by using immunological techniques. The current bioassays are the most sensitive methods but they are cumbersome and lengthy, even though simplifications have been proposed. Immunological techniques are easier, however they do not explore the biological activity of the circulating interferon. The presence of type I interferon in biological samples (serum, plasma, cerebro-spinal fluid, cultured cell supernatants) can be indirectly assessed by capability of interferon alpha to induce in vitro the synthesis of MxA in a dose dependent manner in cultured cells. Following to the lysis of the cells, the induced MxA can be quantitated and hence the type I-interferon concentration can be determinated in samples. The quantitation of MxA protein in peripheral blood lysates can be useful as a specific marker of acute viral infections. A minute amount of whole blood (15 mul) is sufficient which facilitates its use in pediatrics. The specifically type-I-interferons inducible MxA protein is also a potential useful marker in the management of interferon alpha-treatment. Moreover, the detection of interferon alpha and antiviral proteins constitute an indirect approach for investigating the hypothesis of the role of viruses in chronic diseases with suspected infectious aetiology.

We investigated the biological properties of interferon (IFN)-alpha produced by Sendai virus (SV)-activated whole blood cultures in 20 patients infected with human immunodeficiency virus (HIV)-1 and 24 healthy controls. Supernatants of cultures were assayed for IFN-alpha by using an immunological method (DELFIA), biological methods and an in-vitro MxA induction assay. The levels of intracellular MxA protein were detected by an immunochemiluminescence assay. The levels of IFN-alpha in patients measured by DELFIA were significantly lower than those in healthy controls (P < 0.0001), but the antiviral activity of IFN-alpha in patients infected with HIV-1 was lower than predicted from DELFIA. The IFN-alpha produced by cells of patients infected with HIV-1 was able to induce MxA protein in human amnions WISH cells but was unable to protect these cells against Vesicular Stomatitis Virus (VSV)-induced cytopathic effects. A relative increased capability to induce the production of MxA protein in vitro was observed with the IFN-alpha contained in culture supernatant of virus-activated whole blood of HIV-1-infected patients with increased levels of MxA in their peripheral blood. These data suggest that biological properties of IFN-alpha produced in the course of HIV-1 infection are different from those observed with IFN-alpha of healthy subjects.

The immune response against viral pathogens include specific and non specific mechanisms. Cytokines are peptides which can play a role in the non specific immunity. Type I interferons (IFNalpha/beta) are the most effective antiviral cytokines. Interferons alpha are represented by a large familly of structurally related genes while the IFNbeta is encoded by a single gene. Type I interferon genes are located on the chromosome 9, and are segregated in a "modern" and an "ancestral" group with distinctive effects onto the cells. Type I interferons consist of 5 alpha helices, 4 of which are closely held together. Type I interferons receptor is a member of the class II cytokine receptor familly. It is a heterodimer composed of polypeptidic chains naimed IFNAR-1 and IFNAR-2. The type I interferons inducers are viruses, inactivated viruses and certain synthetic molecules. The molecular mechanisms of the induction of IFNbeta have been extensively described whereas the factors that play a role in the regulation of IFNalpha are not so well characterized. Two regulating domains located on the IFNbeta gene promotor are involved. The activation of these regulating domains leads to adverse effects by interacting with two intracellular factors (IRF1 and IRF2). IRF1 enhances the synthesis of IFNbeta but other pathways may be involved as well. The different IFNalpha sub-types have not only synergistic but also antagonistic effects. The synthesis of the different subtypes depends on cell lines and IFNalpha inducers. The N terminal part of IFNalpha is a major determinant in the diversity of the biological effects of IFNalpha sub-types which probably involve changes of the conformation of the type I receptor resulting from interactions between the receptor and its ligand. The type I interferons confer resistance to viruses, especially by enhancing the synthesis of intracellular antiviral proteins.

Interferon-alpha (IFN-alpha) is an important molecule in the antiviral response, but cells from HIV-1-infected individuals show a reduced ability to secrete IFN-alpha. We investigated an association between an imbalance of type 1/type2 cytokines and the production of IFN-alpha in HIV-1 infection. We used whole blood culture to study the cytokine production profile, interferon-gamma (IFN-gamma) and interleukin-4 (IL-4), in response to HIV-1 antigens and to study the Sendai Virus and HSV-1-induced-production of IFN-alpha in seven HIV-1-infected patients. An impaired synthesis of IFN-alpha was obtained in patients with a predominant IL-4 production (IL-4 > IFN-gamma), and we found a positive correlation between the ex vivo production of IFN-alpha and the IFN-gamma/IL-4 ratio but not with the HIV RNA copy number in plasma. We investigated the role of T-cell-derived cytokines in the in vitro production of IFN-alpha by PBMC from eight healthy donors, activated with Sendai Virus or HSV-1. Whereas type 2 cytokines (IL-4, IL-13) inhibited virus-induced IFN-alpha synthesis, on the contrary, type 1 cytokines (IL-2, IFN-gamma) enhanced it. A disarray in the T-cell-derived cytokine response may play a role in the defect of IFN-alpha production in HIV-1-infected individuals. Further investigations are needed to explore this hypothesis.