Cytokines play a critical role in modulating the innate and adaptive immune systems. Here, we have identified from the human genomic sequence a family of three cytokines, designated interleukin 28A (IL-28A), IL-28B and IL-29, that are distantly related to type I interferons (IFNs) and the IL-10 family. We found that like type I IFNs, IL-28 and IL-29 were induced by viral infection and showed antiviral activity. However, IL-28 and IL-29 interacted with a heterodimeric class II cytokine receptor that consisted of IL-10 receptor beta (IL-10Rbeta) and an orphan class II receptor chain, designated IL-28Ralpha. This newly described cytokine family may serve as an alternative to type I IFNs in providing immunity to viral infection.

Cytokines are important in the regulation of haematopoiesis and immune responses, and can influence lymphocyte development. Here we have identified a class I cytokine receptor that is selectively expressed in lymphoid tissues and is capable of signal transduction. The full-length receptor was expressed in BaF3 cells, which created a functional assay for ligand detection and cloning. Conditioned media from activated human CD3+ T cells supported proliferation of the assay cell line. We constructed a complementary DNA expression library from activated human CD3+ T cells, and identified a cytokine with a four-helix-bundle structure using functional cloning. This cytokine is most closely related to IL2 and IL15, and has been designated IL21 with the receptor designated IL21 R. In vitro assays suggest that IL21 has a role in the proliferation and maturation of natural killer (NK) cell populations from bone marrow, in the proliferation of mature B-cell populations co-stimulated with anti-CD40, and in the proliferation of T cells co-stimulated with anti-CD3.

Protease-activated receptors 1-3 (PAR1, PAR2, and PAR3) are members of a unique G protein-coupled receptor family. They are characterized by a tethered peptide ligand at the extracellular amino terminus that is generated by minor proteolysis. A partial cDNA sequence of a fourth member of this family (PAR4) was identified in an expressed sequence tag database, and the full-length cDNA clone has been isolated from a lymphoma Daudi cell cDNA library. The ORF codes for a seven transmembrane domain protein of 385 amino acids with 33% amino acid sequence identity with PAR1, PAR2, and PAR3. A putative protease cleavage site (Arg-47͞Gly-48) was identified within the extracellular amino terminus. COS cells transiently transfected with PAR4 resulted in the formation of intracellular inositol triphosphate when treated with either thrombin or trypsin. A PAR4 mutant in which the Arg-47 was replaced with Ala did not respond to thrombin or trypsin. A hexapeptide (GYPGQV) representing the newly exposed tethered ligand from the amino terminus of PAR4 after proteolysis by thrombin activated COS cells transfected with either wild-type or the mutant PAR4. Northern blot showed that PAR4 mRNA was expressed in a number of human tissues, with high levels being present in lung, pancreas, thyroid, testis, and small intestine. By f luorescence in situ hybridization, the human PAR4 gene was mapped to chromosome 19p12.

A third member of the metallothionein (MT) gene family, designated MT-HI, was cloned by virtue of its homology to a human protein that was shown previously to inhibit neuronal survival in culture and to be deficient in the brains of people with Alzheimer disease. Human and mouse MT-Ms have two insertions relative to all other known mammalian MTs: a threonine after the fourth amino acid and a block of six amino acids near the carboxyl terminus. The genes encoding MT-r resemble all other mammalian MT genes in their small size and exon/intron organization. The MT-Il genes are closely linked to the other functional MT genes on human chromosome 16 and mouse chromosome 8. Mouse MT-HI gene expression appears to be restricted to brain; in addition, it fails to respond to zinc, cadmium, dexamethasone, or bacterial endotoxin in vivo, thereby distinguishing MT-rn from other known MTs.Neurofibrillary tangles, which are paired helical arrays of modified X proteins, are one of the characteristic features observed in brains of individuals with Alzheimer disease (AD). Uchida et al.(1) hypothesized that these tangles, which occur in neurites, might result from inappropriate control of a neuronal growth factor. In pursuing this hypothesis, they identified, and then purified and sequenced, a protein that inhibits survival of cultured rat neurons. That protein, which they called growth inhibitory factor (GIF), resembles metallothioneins (MTs) in that it is short (68 amino acids), contains 20 cysteine residues, and binds zinc and copper. Immunocytochemistry revealed that GIF is present in glial (astrocyte) cells of normal aged individuals but is depleted in individuals with AD (1). These observations suggested that this MT-like protein normally plays a role in preventing neuronal sprouting and development of neurofibrillary tangles, but they raise the tantalizing question of how this might occur.The MT-like protein that Uchida et al. (1) sequenced differs from all other mammalian MTs in having two insertions of amino acids. The structure of the traditional MTs has been solved by NMR and x-ray crystallographic methods, which confirmed that 20 cysteines coordinate 7 metal atoms in a tetrahedral configuration (reviewed in ref. 2). Thus, one can view the structure as a metal-cysteine core with several short loops of amino acids connecting the cysteines. In this view, one ofthe loops ofGIF would be extended by one amino acid, while another would be extended by six amino acids. Considering that traditional MTs do not substitute for GIF in their bioassay, the modified loops may be responsible for its particular function.To gain additional insight into the relationship of this MT-like protein to traditional MTs, we cloned the mouse and human genes encoding these proteinst and compared them with traditional MT genes. This analysis revealed that these genes retain all the characteristics of the traditional MT genes, suggesting that they be designated MT-III rather than GIF. MATERIALS AND METHODSIsolation of Mouse MT-rn (mMT-rn) cDNA C...

A structural, profile-based algorithm was used to identify interleukin 20 (IL-20), a novel IL-10 homolog. Chromosomal localization of IL-20 led to the discovery of an IL-10 family cytokine cluster. Overexpression of IL-20 in transgenic (TG) mice causes neonatal lethality with skin abnormalities including aberrant epidermal differentiation. Recombinant IL-20 protein stimulates a signal transduction pathway through STAT3 in a keratinocyte cell line, demonstrating a direct action of this ligand. An IL-20 receptor was identified as a heterodimer of two orphan class II cytokine receptor subunits. Both receptor subunits are expressed in skin and are dramatically upregulated in psoriatic skin. Taken together, these results demonstrate a role in epidermal function and psoriasis for IL-20, a novel cytokine identified solely by bioinformatics analysis.

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