A new IFN-like cytokine, limitin, modulates the immune response without influencing thymocyte development

Characterization of the bovine type I IFN locus: rearrangements, expansions, and novel subfamilies

BACKGROUND

The Type I interferons (IFN) have major roles in the innate immune response to viruses, a function that is believed to have led to expansion in the number and complexity of their genes, although these genes have remained confined to single chromosomal region in all mammals so far examined. IFNB and IFNE define the limits of the locus, with all other Type I IFN genes except IFNK distributed between these boundaries, strongly suggesting that the locus has broadened as IFN genes duplicated and then evolved into a series of distinct families.

RESULTS

The Type I IFN locus in Bos taurus has undergone significant rearrangement and expansion compared to mouse and human, however, with the constituent genes separated into two sub-loci separated by >700 kb. The IFNW family is greatly expanded, comprising 24 potentially functional genes and at least 8 pseudogenes. The IFNB (n = 6), represented in human and mouse by one copy, are also present as multiple copies in Bos taurus. The IFNT, which encode a non-virally inducible, ruminant-specific IFN secreted by the pre-implantation conceptus, are represented by three genes and two pseudogenes. The latter have sequences intermediate between IFNT and IFNW. A new Type I IFN family (IFNX) of four members, one of which is a pseudogene, appears to have diverged from the IFNA lineage at least 83 million years ago, but is absent in all other sequenced genomes with the possible exception of the horse, a non-ruminant herbivore.

CONCLUSION

In summary, we have provided the first comprehensive annotation of the Type I IFN locus in Bos taurus, thereby providing an insight into the functional evolution of the Type I IFN in ruminants. The diversity and global spread of the ruminant species may have required an expansion of the Type I IFN locus and its constituent genes to provide broad anti-viral protection required for foraging and foregut fermentation.

Type I IFN receptor signals directly stimulate local B cells early following influenza virus infection

Rapidly developing Ab responses to influenza virus provide immune protection even during a primary infection. How these early B cell responses are regulated is incompletely understood. In this study, we show that the first direct stimulatory signal for local respiratory tract B cells during influenza virus infection is provided through the type I IFNR. IFNR-mediated signals were responsible for the influenza infection-induced local but not systemic up-regulation of CD69 and CD86 on virtually all lymph node B cells and for induction of a family of IFN-regulated genes within 48 h of infection. These direct IFNR-mediated signals were shown to affect both the magnitude and quality of the local virus-specific Ab response. Thus, ligand(s) of the type I IFNR are direct nonredundant early innate signals that regulate local antiviral B cell responses.

IFN-zeta/ limitin: a member of type I IFN with mild lympho-myelosuppression

Interferon (IFN)-Zeta/limitin has been considered as a novel type I IFN by the Nomenclature Committee of the International Society for Interferon and Cytokine Research. IFN-Zeta/limitin shows some sequence homology with IFN-alpha and IFN-beta, has a globular structure with five alpha-helices and four loops, and recognizes IFN-alpha/beta receptor. Although IFN-zeta/limitin displays antiviral, immunomodulatory, and antitumor effects, it has much less lympho-myelosuppressive activities than IFN-alpha. Treatment of cells with type I IFNs induces and/or activates a number of molecules, which regulate cell cycle and apoptosis. It is noteworthy that IFN-zeta/limitin activates the Tyk2-Daxx and Tyk2-Crk pathways weaker than IFN-alpha. Because experiments using antisense oligonucleotides have revealed their essential role in type I IFN-related suppression of lympho-hematopoiesis, little ability of IFN-zeta/limitin to activate the Tyk2-dependent signaling pathway may explain its uniquely narrow range of biological activities. Further analysis of structure-function relationship of type I IFNs will establish an engineered cytokine with useful features of IFN-zeta/limitin.

The role of type I interferons in non-viral infections

For a long time, the family of type I interferons (IFN-alpha/beta) has received little attention outside the fields of virology and tumor immunology. In recent years, IFN-alpha/beta regained the interest of immunologists, due to the phenotypic and functional characterization of IFN-alpha/beta-producing cells, the definition of novel immunomodulatory functions and signaling pathways of IFN-alpha/beta, and the observation that IFN-alpha/beta not only exerts antiviral effects but is also relevant for the pathogenesis or control of certain bacterial and protozoan infections. This review summarizes the current knowledge on the production and function of IFN-alpha/beta during non-viral infections in vitro and in vivo.

Differential effects of a novel IFN-ζ/limitin and IFN-α on signals for Daxx induction and Crk phosphorylation that couple with growth control of megakaryocytes

OBJECTIVE

Although a novel IFN-zeta/limitin uses IFN-alpha/beta receptor, it lacks some common activities of type I IFNs. We compared effects on megakaryocyte proliferation and differentiation as well as signals for their biological activities.

MATERIALS AND METHODS

Recombinant IFN-zeta/limitin and IFN-alpha titrated with a cytopathic effect dye binding assay, were used in this study. Colony assays and serum-free suspension cultures for megakaryocytes were performed to compare their growth inhibitory effects. To analyze signals, megakaryocytes cultured in serum-free suspension cultures were stimulated and Western blotted with the indicated antibody.

RESULTS

Both IFN-zeta/limitin and IFN-alpha suppressed the proliferation of megakaryocyte progenitors without influencing their differentiation. However, much higher concentrations of IFN-zeta/limitin were required for the growth inhibition than IFN-alpha. The growth inhibition by IFN-zeta/limitin and IFN-alpha was significantly reduced when either Tyk2 or STAT1 was disrupted. In addition, the antisense oligonucleotides against Crk and Daxx, downstream molecules of Tyk2, greatly rescued the IFN-zeta/limitin- and IFN-alpha-induced reduction of megakaryocyte colony numbers. In cultured megakaryocytes, IFN-zeta/limitin induced the expression of SOCS-1 as strongly as IFN-alpha. However, IFN-zeta/limitin induced weaker phosphorylation of Crk and lower induction of Daxx than IFN-alpha.

CONCLUSIONS

Weaker signals for Crk and Daxx may participate in less megakaryocyte suppressive activity of IFN-zeta/limitin and may distinguish IFN-zeta/limitin from IFN-alpha in megakaryocytes. Our results extend the understanding about thrombocytopenia in patients with IFN-alpha treatment as well as the possibility for the clinical application of human homologue of IFN-zeta/limitin or an engineered cytokine with useful features of the IFN-zeta/limitin structure.

Interferon-3/Limitin: Novel Type I Interferon That Displays a Narrow Range of Biological Activity

Interferon zeta (IFN-zeta)/limitin has been regarded as a novel type I IFN by the Nomenclature Committee of the International Society for Interferon and Cytokine Research. IFN-zeta/limitin, which has some sequence homology with IFN-alpha and IFN-beta, has a globular structure with 5 alpha helices and 4 loops and recognizes IFN-alpha/beta receptor. Although it displays antiviral, immunomodulatory, and antitumor effects, IFN-zeta/limitin has much less lymphomyelosuppressive activity than IFN-alpha. Unique interactions between IFN-zeta/limitin and the receptor probably led to the narrow range of signals and biological activities. A human homologue of IFN-zeta/limitin may be clinically more effective than IFN-alpha and IFN-beta because it has fewer adverse effects. Moreover, further analysis of the structure-function relationship may establish an engineered cytokine with the useful features of IFN-zeta/limitin.

A new interferon, limitin, displays equivalent immunomodulatory and antitumor activities without myelosuppressive properties as compared with interferon-alpha

OBJECTIVE

Limitin is a new member of type I interferon (IFN) identified with an expression cloning based on the growth suppression of a myelomonocytic leukemia cell line WEHI3. Although limitin uses the IFN-alpha/beta receptor, its signal transduction pathways to express the antiviral effects are different from those of IFN-alpha. To clarify the characteristics of limitin, we compared the biological activities of limitin, such as the antiviral, immunomodulatory, antitumor, and myelosuppressive effects, with IFN-alpha.

MATERIALS AND METHODS

Limitin and IFN-alpha were titered with a cytopathic effect dye binding assay. Induction of MHC class I on a keratinocyte cell line PAM212 was estimated with flow cytometry. Induction of OVA-restricted cytotoxic T lymphocyte (CTL) activity was analyzed with 51Cr release assay. Antiproliferative effects were evaluated with 3H-thymidine incorporation assay using WEHI3 and a lymphoblast cell line L1210. Myelosuppresive effects were evaluated with colony assay. In vivo side effects were estimated after the injection of limitin or IFN-alpha.

RESULTS

Limitin had relatively higher antiviral activity than IFN-alpha. Limitin induced the surface expression of MHC class I, the enhancement of CTL activity, and the growth inhibition of lymphohematopoietic cell lines as strong as IFN-alpha. Nevertheless, the treatment of mice with limitin showed neither myelosuppression nor fever that are common adverse effects of IFN-alpha.

CONCLUSIONS

Strong immunomodulatory, antitumor, and antiviral effects with weak myelosuppressive and weak acute toxic effects of limitin indicate that it may be useful as a new therapeutic drug for virus-hepatitis and cancers.

The Class II cytokine receptor (CRF2) family: overview and patterns of receptor–ligand interactions

Expanded genomic information has driven the discovery of new members of the human Class II family of cytokine receptors (CRF2), which now includes 12 proteins. The corresponding cytokines have been identified, paired with their receptors and initially characterized for function. These cytokines include: a new human Type I IFN, IFN-kappa; molecules related to IL-10 (IL-19, IL-20, IL-22, IL-24, IL-26); and IFN-lambdas (IL-28/29), which have antiviral and cell stimulatory activities reminiscent of Type I IFNs, but act through a distinct receptor. In response to ligand binding, the CRF2 proteins form heterodimers, leading to cytokine-specific cellular responses; these diverse physiological functions are just beginning to be explored. Progress in structural and mutational analysis of ligand-receptor interactions now presents a more reliable framework for understanding receptor-ligand interactions, and for predicting key regions in less well studied members of the CRF2 family. The relationships between the CRF2 proteins will be summarized, as will the progress in identifying patterns of receptor interactions with ligands.

Antiviral activity of limitin against encephalomyocarditis virus, herpes simplex virus, and mouse hepatitis virus: diverse requirements by limitin and alpha interferon for interferon regulatory factor 1

Limitin has sequence homology with alpha interferon (IFN-alpha) and IFN-beta and utilizes the IFN-alpha/beta receptor. However, it has no influence on the proliferation of normal myeloid and erythroid progenitors. In this study, we show that limitin has antiviral activity in vitro as well as in vivo. Limitin inhibited not only cytopathic effects in encephalomyocarditis virus- or herpes simplex virus (HSV) type 1-infected L929 cells, but also plaque formation in mouse hepatitis virus (MHV) type 2-infected DBT cells. In addition, administration of limitin to mice suppressed MHV-induced hepatitis and HSV-induced death. The antiviral activity may be mediated in part by 2',5'-oligoadenylate synthetase, RNA-dependent protein kinase, and Mx protein, which inhibit viral replication or degrade viral components, because limitin induced their mRNA expression and enzyme activity. While limitin has antiviral activity as strong as that of IFN-alpha in vitro (the concentration that provided 50% inhibition of cytopathic effect is approximately 30 pg/ml), IFN regulatory factor 1 (IRF-1) dependencies for induction of an antiviral state were different for limitin and IFN-alpha. In IRF-1-deficient fibroblasts, a higher concentration of limitin than of IFN-alpha was required for the induction of antiviral activity and the transcription of proteins from IFN-stimulated response element. The unique signals and the fewer properties of myelosuppression suggest that a human homolog of limitin may be used as a new antiviral drug.

Links between innate and adaptive immunity via type I interferon

Type I interferon (IFN-alpha/beta) is expressed rapidly following exposure to a wide variety of infectious agents and plays a key role in innate control of virus replication. Recent studies have demonstrated that dendritic cells both produce IFN-alpha/beta and undergo maturation in response to IFN-alpha/beta. Moreover, IFN-alpha/beta has been shown to potently enhance immune responses in vivo through the stimulation of dendritic cells. These findings indicate that IFN-alpha/beta serves as a signal linking innate and adaptive immunity.

Cytokine signaling in 2002: new surprises in the Jak/Stat pathway

The importance of Jak-Stat pathway signaling in regulating cytokine-dependent gene expression and cellular development/survival is well established. Nevertheless, advances continue to be made in defining Jak-Stat pathway effects on different cellular processes and in different organisms. This review focuses on recent advances in the field and highlights some of the most active areas of Jak-Stat pathway research.