Tumor necrosis factor and IFN induce a common set of proteins

The treatment of cells with TNF or IFN results in the development of an antiviral state and in the induction of a common set of proteins with m.w. of 80,000, 67,000, and 56,000. The induction of the 80,000- and 56,000-Da proteins after TNF treatment is dependent on the synthesis of an intermediary protein, whereas the induction of the 67,000-Da protein appears to occur as a direct result of the TNF treatment. The effects of antibodies to IFN on the TNF-mediated effects have been evaluated and reveal that the incubation of TNF-treated cells with antibody to rIFN-beta 1 greatly reduces the antiviral effectiveness of the TNF treatment and blocks the ability of TNF to induce the 80,000-Da protein. Incubation with antibodies to either IFN-alpha or IFN-gamma failed to affect the TNF-mediated responses. Thus, the induction by TNF of each of the proteins is regulated differently and is mediated through both IFN-dependent and IFN-independent mechanisms.     

Differential regulation of IFNα, IFNβ and IFNε gene expression in human cervical epithelial cells

Interferonε (IFNε) is a unique type I IFN that has distinct functions from IFNα/β. IFNε is constitutively expressed at mucosal tissues, including the female genital mucosa, and is reported to be modulated by estrogen and seminal plasma. However, its regulation by cytokines, including TNFα, IL-1β, IL-6, IL-8, IL-17, IL-22 and IFNα, which are commonly present in the female genital mucosa, is not well documented in freshly isolated primary cervical cells from tissues. We determined the effect of these cytokines on gene expression of type I IFNs in an immortalized endocervical epithelial cell line (A2EN) and in primary cervical epithelial cells. Several pro-inflammatory cytokines were found to induce IFNε, and TNFα induced the strongest response in both cell types. Pretreatment of cells with the IκB inhibitor, which blocks the NF-κB pathway, suppressed TNFα-mediated IFNε gene induction and promoter activation. Expression of IFNα, IFNβ, and IFNε was differentially regulated in response to various cytokines. Taken together, our results show that regulation of these IFNs depends on cell type, cytokine concentration, and incubation time, highlighting the complexity of the cytokine network in the cervical epithelium.     

Factors inhibiting IFN activity

Several factors may inhibit the activity of IFNs. Some of these occur naturally, others are therapy-induced or artificial. Naturally occurring antibodies appear to have a much broader reactivity than therapy-induced antibodies. Naturally induced antibodies are reported in patients suffering from chronic graft-versus-host disease after bone marrow transplantation. Differences in the reported immunogenicity between interferons may not be due to the minor variation in amino acid sequence. The clinical significance of therapy-induced antibodies has been unclear. In patients treated for chronic hepatitis C, antibody formation is closely related to relapse. In animal studies the efficacy of treatments targeting the IFN receptor interaction has been shown. Soluble IFN- receptor inhibits the development of autoimmune diseases in mice. Monoclonal antibodies to the IFN- receptor protects against allograft rejections in monkeys. Two naturally occurring inhibitors of IFN action were reported. The clinical significance and structure of these inhibitors remain elusive.     

Antibodies against IFN gamma-binding proteins recognize a member of IFN alpha R complex

Recombinant human IFN alpha 2b coupled to a silica support was used for the purification of the IFN alpha-binding proteins from placental cell membrane extracts. The 100-kDa (p100) and 64-kDa (p64) proteins, which bind preferentially to an IFN alpha 2b-silica matrix, were identified. Using a monoclonal antibody (A6) against IFN-gammaR1, it was able to isolate p100 and p70, but only if IFN alpha 2b was present during chromatography. Similar interactions were observed using polyclonal antibody anti-IFN gamma binding proteins, as assayed in Western blot. These interactions were identified as conformation dependent. We speculate that IFN alpha 2b receptor complex shares an IFN gamma receptor complex epitope.     

Murine gammaherpesvirus targets type I IFN receptor but not type III IFN receptor early in infection

The innate immune response represents a primary line of defense against invading viral pathogens. Since epithelial cells are the primary site of gammaherpesvirus replication during infection in vivo and there are no information on activity of IFN-III signaling against gammaherpesviruses in this cell type, in present study, we evaluated the expression profile and virus-host interactions in mouse mammary epithelial cell (NMuMG) infected with three strains of murine gammaherpesvirus, MHV-68, MHV-72 and MHV-4556. Studying three strains of murine gammaherpesvirus, which differ in nucleotide sequence of some structural and non-structural genes, allowed us to compare the strain-dependent interactions with host organism. Our results clearly demonstrate that: (i) MHV-68, MHV-72 and MHV-4556 differentially interact with intracellular signaling and dysregulate IFN signal transduction; (ii) MHV-68, MHV-72 and MHV-4556 degrade type I IFN receptor in very early stages of infection (2–4 hpi), but not type III IFN receptor; (iii) type III IFN signaling might play a key role in antiviral defense of epithelial cells in early stages of murine gammaherpesvirus replication; (iv) NMuMG cells are an appropriate model for study of not only type I IFN signaling, but also type III IFN signaling pathway. These findings are important for better understanding of individual virus-host interactions in lytic as well as in persistent gammaherpesvirus replication and help us to elucidate IFN-III function in early events of virus infection.     

IFN regulatory factor family members differentially regulate the expression of type III IFN (IFN-lambda) genes

Virus replication induces the expression of antiviral type I (IFN-alphabeta) and type III (IFN-lambda1-3 or IL-28A/B and IL-29) IFN genes via TLR-dependent and -independent pathways. Although type III IFNs differ genetically from type I IFNs, their similar biological antiviral functions suggest that their expression is regulated in a similar fashion. Structural and functional characterization of the IFN-lambda1 and IFN-lambda3 gene promoters revealed them to be similar to IFN-beta and IFN-alpha genes, respectively. Both of these promoters had functional IFN-stimulated response element and NF-kappaB binding sites. The binding of IFN regulatory factors (IRF) to type III IFN promoter IFN-stimulated response element sites was the most important event regulating the expression of these genes. Ectopic expression of the components of TLR7 (MyD88 plus IRF1/IRF7), TLR3 (Toll/IL-1R domain-containing adapter-inducing factor), or retinoic acid-inducible gene I (RIG-I) signal transduction pathways induced the activation of IFN-lambda1 promoter, whereas the IFN-lambda3 promoter was efficiently activated only by overexpression of MyD88 and IRF7. The ectopic expression of Pin1, a recently identified suppressor for IRF3-dependent antiviral response, decreased the IFN promoter activation induced by any of these three signal transduction pathways, including the MyD88-dependent one. To conclude, the data suggest that the IFN-lambda1 gene is regulated by virus-activated IRF3 and IRF7, thus resembling that of the IFN-beta gene, whereas IFN-lambda2/3 gene expression is mainly controlled by IRF7, thus resembling those of IFN-alpha genes.     

Type I IFN protects against murine lupus

Both the type I (IFN-alpha beta) and type II (IFN-gamma) IFNs have been heavily implicated in the pathogenesis of systemic lupus erythematosus. To test the relative roles of these systems, congenic lupus-prone MRL/CD95(lpr/lpr) (MRL/lpr) mice lacking the type I IFN receptor (IFN-RI), type II IFN receptor (IFN-RII), or both, were derived. As expected, deficiency for IFN-RII protected MRL/lpr mice from the development of significant autoimmune-associated lymphadenopathy, autoantibodies, and renal disease. However, deficiency for the IFN-RI surprisingly worsened lymphoproliferation, autoantibody production, and end organ disease; animals doubly deficient for IFN-RI and IFN-RII developed an autoimmune phenotype intermediate between wild-type and IFN-RII-deficient animals, all correlating with an ability of type I IFN to suppress MRL B cell activation. Thus, type I IFNs protect against both the humoral and end organ autoimmune syndrome of MRL/lpr mice, independent of IFN-gamma. These findings warrant caution in the use of type I IFN antagonists in the treatment of autoimmune diseases and suggest further investigation into the interplay between the types I and II IFNs during the ontogeny of pathogenic autoantibodies.     

Synergistic production of TNFα and IFNα by human pDCs incubated with IFNλ3 and IL-3

In this study, we investigated whether IFNλ3 and IL-3 reciprocally influence their capacity to activate various functions of human plasmacytoid dendritic cells (pDCs). In fact, we preliminarily observed that IFNλ3 upregulates the expression of the IL-3Rα (CD123), while IL-3 augments the expression of IFNλR1 in pDCs. As a result, we found that combination of IFNλ3 and IL-3 induces a strong potentiation in the production of TNFα, IFNα, as well as in the expression of Interferon-Stimulated Gene (ISG) mRNAs by pDCs, as compared to either IFNλ3 or IL-3 alone. In such regard, we found that endogenous IFNα autocrinally promotes the expression of ISG mRNAs in IL-3-, but not in IFNλ3 plus IL-3-, treated pDCs. Moreover, we uncovered that the production of IFNα by IFNλ3 plus IL-3-treated pDCs is mostly dependent on endogenously produced TNFα. Altogether, our data demonstrate that IFNλ3 and IL-3 collaborate to promote, at maximal levels, discrete functional responses of human pDCs.     

Guanylate binding protein 4 negatively regulates virus-induced type I IFN and antiviral response by targeting IFN regulatory factor 7

IRF7 is known as the master regulator in virus-triggered induction of type I IFNs (IFN-I). In this study, we identify GBP4 virus-induced protein interacting with IRF7 as a negative regulator for IFN-I response. Overexpression of GBP4 inhibits virus-triggered activation of IRF7-dependent signaling, but has no effect on NF-κB signaling, whereas the knockdown of GBP4 has opposite effects. Furthermore, the supernatant from Sendai virus-infected cells in which GBP4 have been silenced inhibits the replication of vesicular stomatitis virus more efficiently. Competitive coimmunoprecipitation experiments indicate that overexpression of GBP4 disrupts the interactions between TRAF6 and IRF7, resulting in impaired TRAF6-mediated IRF7 ubiquitination. Our results suggest that GBP4 is a negative regulator of virus-triggered IFN-I production, and it is identified as a novel protein targeting IRF7 and inhibiting its function.     

IFN regulation and functions in myeloid dendritic cells

A central issue in dendritic cells (DC) biology is to understand how type I IFNs modulate the immuno-regulatory properties of DC. In this review I will address this issue in light of the recent experimental evidence on the expression and function of these cytokines in myeloid DC. This knowledge may have important therapeutic implications in infectious and neoplastic diseases and open new perspectives in the use of IFNs as vaccine adjuvants and in the development of DC-based vaccines.