Different interactions of interferon-alpha subtypes at the surface of epithelial and lymphoid cells

Complex Modulation of Cell Type-Specific Signaling in Response to Type I Interferons

The type I interferons (IFNs) are pleiotropic cytokines that regulate many different cellular functions. The major signaling pathway activated by type I IFNs involves sequential phosphorylation of the tyrosine residues of the Janus kinase (JAK) and signal transducers and activators of transcription (STAT) proteins, providing the primary mechanism through which gene expression is induced. Recent work has shown that the responses are quite complex, as shown by different responses to specific subtypes of type I IFN, activation of kinases in addition to JAKs, patterns of activation of all seven STATs in different cells, and activation of transcription factors other than STATs. The type I IFNs use this complexity to regulate many different biological functions in different types of cells, by activating different specific signals and patterns of gene expression.

Amino acid substitutions in loop BC and helix C affect antigenic properties of helix D in hybrid IFN-alpha21a/alpha2c molecules

We compared the antigenic properties of human interferon-alpha2c (IFN-alpha2c), IFN-alpha21a, hybrids IFN-alpha21a/alpha2c, and their mutants, using a panel of 27 anti-IFN-alpha1, anti-IFN-alpha2, and anti-IFN-alpha8/1/8 monoclonal antibodies (mAb). After immunoanalysis by ELISA, we found parental IFN-alpha2c and IFN-alpha21a to be antigenically distinct. Lack of reactivity of anti-IFN-alpha1 mAb with IFN-alpha21a indicated an antigenic distinction between subtypes alpha1 and alpha21a. The antigenic properties of hybrid IFNs consisting of the N-terminal portion (1-75) of IFN-alpha21a and the C-terminal portion (76-166) of IFN-alpha2c were analyzed with mAb recognizing defined regions of IFN-alpha2c, IFN-alpha1, and IFN-alpha8/1/8. We found that extending the sequence of IFN-alpha21a up to position 95 in hybrid molecule decreased the immunoreactivity of mAb specific for the antigenic structure formed by residues --112-132-- (helix D) of IFN-alpha2c. Inserting the sequence 76-81 (loop BC) of IFN-alpha2c into the sequence of 1-95 of IFN-alpha21a restored the reactivity of anti-IFN-alpha2c mAb. Some amino acid substitutions at positions 86 and 90 (helix C) of hybrid IFN-alpha21a/alpha2c also affected the immunoreactivity of C-terminal-specific mAb, which recognize helix D, but did not influence the structure of C-terminus of IFN (aa 151-165). Changes in the structure of constructs affected not only their antiproliferative activity but also their antiviral activity on human cells.

Differences in lymphocyte-regulatory activity among variants of ovine IFN-tau

Interferon-tau (IFN-tau) is secreted from trophectoderm of the ruminant preimplantation conceptus and functions during pregnancy to prevent luteolysis. In addition, IFN-tau can inhibit proliferation of peripheral blood lymphocytes (PBL) and other cells. Several distinct ovine IFN-tau (OvIFN-tau) gene variants exist; three of these (IFN-tau4, IFN-tau6d, IFN-tau11) differ in their ability to prevent luteolysis (IFN-tau4 > IFN-tau6d > IFN-tau11), inhibit growth of Daudi cells (IFN-tau4 > IFN-tau6d > IFN-tau11), and induce an antiviral state (IFN-tau4 > IFN-tau6d = IFN-tau11). The present objective was to compare variants for differences in ability to inhibit proliferation of phytohemagglutinin-stimulated PBL. At equal concentrations, IFN-tau4 was more inhibitory than IFN-tau6d, IFN-tau11, or an IFN-omega control. Similar differences in potency were seen when IFN-tau variants were tested at equal antiviral concentrations. Thus, the sheep trophectoderm secretes variants of IFN-tau that differ in ability to regulate lymphocyte function. The nature of the effect of the trophectoderm on endometrial lymphocytes may depend on the relative amount of each variant produced.

The type I interferon receptor: structure, function, and evolution of a family business

Recent results indicate that coherent models of how multiple interferons (IFN) are recognized and signal selectively through a common receptor are now feasible. A proposal is made that the IFN receptor, with its subunits IFNAR-1 and IFNAR-2, presents two separate ligand binding sites, and this double structure is both necessary and sufficient to ensure that the different IFN are recognized and can act selectively. The key feature is the duplication of the extracellular domain of the IFNAR-1 subunit and the configurational geometry that this imposes on the intracellular domains of the receptor subunits and their associated tyrosine kinases.

Identification of a linear epitope of interferon-alpha2b recognized by neutralizing monoclonal antibodies

Four monoclonal antibodies (mAbs) directed against the recombinant human interferon-alpha2b (IFN-alpha2b) were used as probes to study the interaction of the IFN molecule to its receptors. The [125I]IFN-alpha2b binding to immobilized mAbs was completely inhibited by IFN-alpha2b and IFN-alpha2a but neither IFNbeta nor IFNgamma showed any effect. Gel-filtration HPLC of the immune complexes formed by incubating [125I]IFN-alpha2b with paired mAbs revealed the lack of simultaneous binding of two different antibodies to the tracer, suggesting that all mAbs recognize the same IFN antigenic domain. Furthermore, the mAbs were also able to neutralize the IFN-alpha2b anti-viral and anti-proliferative activities as well as [125I]IFN-alpha2b binding to WISH cell-membranes. As [125I]mAbs did not recognize IFN exposed epitopes in the IFN:receptor complexes, mAb induction of a conformational change in the IFN binding domain impairing its binding to receptors was considered unlikely. In order to identify the IFN region recognized by mAbs, IFN-alpha2b was digested with different proteolytic enzymes. Immunoreactivity of the resulting peptides was examined by Western blot and their sequences were established by Edman degradation after blotting to poly(vinylidene difluoride) membranes. Data obtained indicated that the smallest immunoreactive region recognized by mAbs consisted of residues 107-132 or 107-146. As this zone includes the sequence 123-140, which has been involved in the binding to receptors, and our mAbs did not show an allosteric behaviour, it is concluded that they are directed to overlapping epitopes located close to or even included in the IFN binding domain.

IFN-α Activates Stat6 and Leads to the Formation of Stat2:Stat6 Complexes in B Cells

IFN-α consists of a family of highly homologous proteins, which exert pleiotropic effects on a wide variety of cell types. The biologic activities of IFN-α are mediated by its binding to a multicomponent receptor complex resulting in the activation of the Janus kinase-STAT signaling pathway. In most cell types, activation of Stat1 and Stat2 by IFN-α leads to the formation of either STAT homo-/heterodimers or of the IFN-stimulated gene factor 3 complex composed of Stat1, Stat2, and p48, a non-STAT protein. These distinct transcriptional complexes then target two different sets of cis-elements, γ-activated sites and IFN-stimulated response elements. Here, we report that IFN-α can activate complexes containing Stat6, which, until now, has been primarily associated with signaling by two cytokines with biologic overlap, IL-4 and IL-13. Induction of Stat6 complexes by IFN-α appears to be cell type specific, given that tyrosine phosphorylation of Stat6 in response to IFN-α is predominantly detected in B cells. Activation of Stat6 by IFN-α in B cells is accompanied by the formation of novel Stat2:Stat6 complexes, including an IFN-stimulated gene factor 3-like complex containing Stat2, Stat6, and p48. B cell lines resistant to the antiproliferative effects of IFN-α display a decrease in the IFN-α-mediated activation of Stat6. Activation of Stat6 as well as of Stat2:Stat6 complexes by IFN-α in B cells may allow modulation of target genes in a cell type-specific manner.

Structure-activity of type I interferons

Type I IFNs constitute a family of proteins exhibiting high homology in primary, secondary, and tertiary structures. They interact with the same receptor and transmit signals to cellular nucleus through a similar mechanism, eliciting roughly homogeneous biological activity. Nevertheless, the members of that family, IFN alpha species, IFN beta and IFN omega, due to local differences in the structure sometime show distinct properties. From the reported data it results that even minute changes or differences in the primary sequences could be responsible for a significant variety of biological actions, thus inducing to the hypothesis that Type I IFNs, rather than to be the result of a redundant replication during the evolution play definite roles in the defense of living organisms to foreign agents.

The biologic activity and molecular characterization of a novel synthetic interferon-alpha species, consensus interferon

Consensus interferon (Infergen) is a wholly synthetic type I interferon (IFN), developed by scanning several interferon-alpha nonallelic subtypes and assigning the most frequently observed amino acid in each position, resulting in a consensus sequence. The antiviral, antiproliferative, NK cell activation activity, cytokine induction, and interferon-stimulated gene-induction activity of consensus interferon has been compared with naturally occurring type I interferons. In all of these comparisons, consensus interferon had a higher activity when compared, on a mass basis, with IFN-alpha 2a and IFN-alpha 2b, although the activity was the same for all of these parameters on an antiviral unit basis. That a synthetic type I interferon could have higher activities than naturally occurring molecules is surprising and may be a result of the higher affinity for the array of type I interferon receptors demonstrated for consensus interferon when compared with IFN-alpha. In contrast, consensus interferon was shown to be an inferior inducer of IL-1 beta when compared with IFN-alpha. These results may reflect differential binding to multiple accessory proteins interacting with a type I interferon receptor. These unique biologic properties may lead to a favorable clinical benefit for consensus interferon when compared with the naturally occurring recombinant molecules. Ongoing clinical trials will ascertain whether consensus interferon can be used in a wide array of disease situations, such as chronic viral infections and certain malignancies.

Aberrant activation of JAK/STAT pathway components in response to G-CSF, interferon-alpha/beta and interferon-gamma in NFS-60 cells

There is evidence that the cellular responses to cytokines, such as granulocyte colony stimulating factor (G-CSF) and interferons, depend on prior activation of components of the JAK/STAT signalling pathway. We report here that the myeloid cell line NFS-60 shows aberrant JAK/STAT signalling yet elicits expected biological responses to G-CSF and interferons-alpha/beta and gamma. Instead of increased phosphorylation of JAK1 and JAK2 in response to G-CSF and interferon-gamma, and JAK1 and Tyk2 in response to interferon-alpha/beta, we observed only an increase of phosphorylation of Tyk2 in response to all of these cytokines in NFS-60 cells. The subset of STAT proteins being activated in response to these cytokines was unusual as well. G-CSF activated STAT3 and STAT5A, whereas interferons activated, in addition to STAT1 and STAT5 other, as yet unidentified, DNA binding proteins. However, NFS-60 cells show normal biological responses to these cytokines, such as proliferation in response to G-CSF, and reduction of proliferation, induction of an anti-viral response and induction of specific genes in response to interferons.

Sensitive antiproliferative neutralization assay for the detection of neutralizing IFN-alpha and IFN-beta antibodies

Antibodies to interferon (IFN) may compromise IFN treatment in some patients. In tumor therapy, a critical function of type I IFNs is their antiproliferative effect. For the quantification of neutralizing IFN antibodies we have developed an antiproliferative neutralization assay (APA) based on the reduction of IFN-mediated growth inhibition of Daudi cells by IFN-alpha and IFN-beta antibodies. Proliferation was quantified by [3H]thymidine incorporation, and the neutralizing potency of IFN antibody-positive sera was expressed as the neutralizing titer inhibiting 50% of the antiproliferative activity of 10 IU/ml of IFN (NT50). The APA is easy to perform, reproducible, and more sensitive than a well-established antiviral neutralization assay (AVA). All 30 sera with recombinant IFN-alpha 2a-binding antibodies proved to be neutralizing antibody-positive in the APA whereas seven were scored antibody-negative or uninterpretable in the AVA. The APA is recommended as a second or third line assay for the estimation of the neutralizing potency of spontaneous or treatment-induced IFN-alpha and IFN-beta-specific antibodies.