Harold Dickensheets

IFN-λs mediate antiviral protection through a distinct class II cytokine receptor complex

We report here the identification of a ligand-receptor system that, upon engagement, leads to the establishment of an antiviral state. Three closely positioned genes on human chromosome 19 encode distinct but paralogous proteins, which we designate interferon-λ1 (IFN-λ1), IFN-λ2 and IFN-λ3 (tentatively designated as IL-29, IL-28A and IL-28B, respectively, by HUGO). The expression of IFN-λ mRNAs was inducible by viral infection in several cell lines. We identified a distinct receptor complex that is utilized by all three IFN-λ proteins for signaling and is composed of two subunits, a receptor designated CRF2-12 (also designated as IFN-λR1) and a second subunit, CRF2-4 (also known as IL-10R2). Both receptor chains are constitutively expressed on a wide variety of human cell lines and tissues and signal through the Jak-STAT (Janus kinases–signal transducers and activators of transcription) pathway. This receptor-ligand system may contribute to antiviral or other defenses by a mechanism similar to, but independent of, type I IFNs.

The interleukin-10 signal transduction pathway and regulation of gene expression in mononuclear phagocytes.

Interleukin-10 (IL-10) activates a diverse array of functional responses in mononuclear phagocytes. Functional IL-10 receptor (IL-10R) complexes are tetramers consisting of two IL-10R1 polypeptide chains and two IL-10R2 chains. Binding of IL-10 to the extracellular domain of IL-10R1 activates phosphorylation of the receptor-associated Janus tyrosine kinases, JAK1 and Tyk2. These kinases then phosphorylate specific tyrosine residues (Y446 and Y496) on the intracellular domain of the IL-10R1 chain. Once phosphorylated, these tyrosine residues (and their flanking peptide sequences) serve as temporary docking sites for the latent transcription factor, STAT3 (signal transducer and activator of transcription-3). STAT3 binds to these sites via its SH2 (Src homology 2) domain, and is, in turn, tyrosine-phosphorylated by the receptor-associated JAKs. It then homodimerizes and translocates to the nucleus where it binds with high affinity to STAT-binding elements (SBE) in the promoters of various IL-10-responsive genes. One of these genes, SOCS-3 (Suppressor of Cytokine Signaling-3) is a member of a newly identified family of genes that inhibit JAK/STAT-dependent signaling. Moreover, the ability of IL-10 to induce de novo synthesis of SOCS-3 in monocytes correlates with its ability to inhibit expression of many genes in these cells, including endotoxin-inducible cytokines such as tumor necrosis factor-alpha (TNF-alpha) and IL-1. Thus, the ability of IL-10 to inhibit gene expression in monocytes is associated with its ability to rapidly induce synthesis of SOCS-3.

Cloning, expression and initial characterisation of interleukin-19 (IL-19), a novel homologue of human interleukin-10 (IL-10)

Interleukin-10 (IL-10) is a pleiotropic cytokine with important immunoregulatory functions whose actions influence activities of many of the cell-types in the immune system. We report here identification and cloning of a gene and corresponding cDNAs encoding a novel homologue of IL-10, designated IL-19. IL-19 shares 21% amino acid identity with IL-10. The exon/intron structure of IL-19 is similar to that of the human IL-10 gene, comprising five exons and four introns within the coding region of the IL-19 cDNA. There are at least two distinct IL-19 mRNA species that differ in their 5′-sequences, suggesting the existence of an intron in the 5′-sequences of coding portion of the IL-19 gene. The longer 5′-sequence contains an alternative initiating ATG codon that is in-frame with the rest of the coding sequence. The expression of IL-19 mRNA can be induced in monocytes by LPS-treatment. The appearance of IL-19 mRNA in LPS-stimulated monocytes was slightly delayed compared to expression of IL-10 mRNA: significant levels of IL-10 mRNA were detectable at 2 h post-stimulation, whereas IL-19 mRNA was not detectable until 4 h. Treatment of monocytes with IL-4 or IL-13 did not induce de novo expression of IL-19, but these cytokines did potentiate IL-19 gene expression in LPS-stimulated monocytes. In addition, GM-CSF was capable of directly inducing IL-19 gene expression in monocytes. IL-19 does not bind or signal through the canonical IL-10 receptor complex, suggesting existence of an IL-19 specific receptor complex, the identity of which remains to be discovered.

Identification, Cloning, and Characterization of a Novel Soluble Receptor That Binds IL-22 and Neutralizes Its Activity

With the use of a partial sequence of the human genome, we identified a gene encoding a novel soluble receptor belonging to the class II cytokine receptor family. This gene is positioned on chromosome 6 in the vicinity of the IFNGR1 gene in a head-to-tail orientation. The gene consists of six exons and encodes a 231-aa protein with a 21-aa leader sequence. The secreted mature protein demonstrates 34% amino acid identity to the extracellular domain of the IL-22R1 chain. Cross-linking experiments demonstrate that the protein binds IL-22 and prevents binding of IL-22 to the functional cell surface IL-22R complex, which consists of two subunits, the IL-22R1 and the IL-10R2c chains. Moreover, this soluble receptor, designated IL-22-binding protein (BP), is capable of neutralizing IL-22 activity. In the presence of the IL-22BP, IL-22 is unable to induce Stat activation in IL-22-responsive human lung carcinoma A549 cells. IL-22BP also blocked induction of the suppressors of cytokine signaling-3 (SOCS-3) gene expression by IL-22 in HepG2 cells. To further evaluate IL-22BP action, we used hamster cells expressing a modified IL-22R complex consisting of the intact IL-10R2c and the chimeric IL-22R1/γR1 receptor in which the IL-22R1 intracellular domain was replaced with the IFN-γR1 intracellular domain. In these cells, IL-22 activates biological activities specific for IFN-γ, such as up-regulation of MHC class I Ag expression. The addition of IL-22BP neutralizes the ability of IL-22 to induce Stat activation and MHC class I Ag expression in these cells. Thus, the soluble receptor designated IL-22BP inhibits IL-22 activity by binding IL-22 and blocking its interaction with the cell surface IL-22R complex.

Cutting Edge: IL-26 Signals through a Novel Receptor Complex Composed of IL-20 Receptor 1 and IL-10 Receptor 2

The receptor for IL-26 (AK155), a cytokine of the IL-10 family, has not previously been defined. We demonstrate that the active receptor complex for IL-26 is a heterodimer composed of two receptor proteins: IL-20R1 and IL-10R2. Signaling through the IL-26R results in activation of STAT1 and STAT3 which can be blocked by neutralizing Abs against IL-20R1 or IL-10R2. IL-10R2 is broadly expressed on a wide variety of tissues, whereas only a limited number of tissues express IL-20R1. Therefore, the ability to respond to IL-26 is restricted by the expression of IL-20R1. IL-10, IL-19, IL-20, IL-22, and IL-24 fail to signal through the combination of IL-10R2 and IL-20R1 proteins, demonstrating that this receptor combination is unique and specific for IL-26.

Tuning sensitivity to IL-4 and IL-13: differential expression of IL-4Rα, IL-13Rα1, and γc regulates relative cytokine sensitivity

Interleukin (IL)-4 and -13 are related cytokines sharing functional receptors. IL-4 signals through the type I (IL-4Rα/common γ-chain [γc]) and the type II (IL-4Rα/-13Rα1) IL-4 receptors, whereas IL-13 utilizes only the type II receptor. In this study, we show that mouse bone marrow–derived macrophages and human and mouse monocytes showed a much greater sensitivity to IL-4 than to IL-13. Lack of functional γc made these cells poorly responsive to IL-4, while retaining full responsiveness to IL-13. In mouse peritoneal macrophages, IL-4 potency exceeds that of IL-13, but lack of γc had only a modest effect on IL-4 signaling. In contrast, IL-13 stimulated greater responses than IL-4 in fibroblasts. Using levels of receptor chain expression and known binding affinities, we modeled the assemblage of functional type I and II receptor complexes. The differential expression of IL-4Rα, IL-13Rα1, and γc accounted for the distinct IL-4–IL-13 sensitivities of the various cell types. These findings provide an explanation for IL-13s principal function as an “effector” cytokine and IL-4s principal role as an “immunoregulatory” cytokine.

Alpha and Lambda Interferon Together Mediate Suppression of CD4 T Cells Induced by Respiratory Syncytial Virus

ABSTRACT The mechanism by which respiratory syncytial virus (RSV) suppresses T-cell proliferation to itself and other antigens is poorly understood. We used monocyte-derived dendritic cells (MDDC) and CD4 T cells and measured [3H]thymidine incorporation to determine the factors responsible for RSV-induced T-cell suppression. These two cell types were sufficient for RSV-induced suppression of T-cell proliferation in response to cytomegalovirus or Staphylococcus enterotoxin B. Suppressive activity was transferable with supernatants from RSV-infected MDDC and was not due to transfer of live virus or RSV F (fusion) protein. Supernatants from RSV-infected MDDC, but not MDDC exposed to UV-killed RSV or mock conditions, contained alpha interferon (IFN-α; median, 43 pg/ml) and IFN-λ (approximately 1 to 20 ng/ml). Neutralization of IFN-α with monoclonal antibody (MAb) against one of its receptor chains, IFNAR2, or of IFN-λ with MAb against either of its receptor chains, IFN-λR1 (interleukin 28R [IL-28R]) or IL-10R2, had a modest effect. In contrast, blocking the two receptors together markedly reduced or completely blocked the RSV-induced suppression of CD4 T-cell proliferation. Defining the mechanism of RSV-induced suppression may guide vaccine design and provide insight into previously uncharacterized human T-cell responses and activities of interferons.

Differential responses of human monocytes and macrophages to IL-4 and IL-13.

The primary interleukin‐4 (IL‐4) receptor complex on monocytes (type I IL‐4 receptor) includes the 140‐kDa α chain (IL‐4Rα) and the IL‐2 receptor γ chain, γc, which heterodimerize for intracellular signaling, resulting in suppression of lipopolysaccharide (LPS)‐inducible inflammatory mediator production. The activity of IL‐13 on human monocytes is very similar to that of IL‐4 because the predominant signaling chain (IL‐4Rα) is common to both receptors. In fact, IL‐4Rα with IL‐13Rα1 is designated both as an IL‐13 receptor and the type II IL‐4 receptor. When the anti‐inflammatory activities of IL‐4 and IL‐13 were investigated on synovial fluid macrophages and compared with the responses by monocytes isolated from the patients at the same time as joint drainage, the response profiles differed with some responses similar in the two cell populations, others reduced on the inflammatory cells. Similar differences were recorded in the response profiles to IL‐4 and IL‐13 by monocytes and monocytes cultured for 7 days in macrophage colony‐stimulating factor (M‐CSF) or granulocyte‐macrophage CSF (GM‐CSF) (monocyte‐derived macrophages, MDMac). MDMac have reduced γc mRNA levels and reduced expression of the functional 64‐kDa γc. There was a similar loss of IL‐13Rα1 mRNA on monocyte differentiation. In turn, there was a significant reduction in the ability of IL‐4 and IL‐13 to activate STAT6. These findings suggest that different functional responses to IL‐4 and IL‐13 by human monocytes and macrophages may result from reduced expression of γc and IL‐13Rα1. J. Leukoc. Biol. 66: 575–578; 1999.

Regulation of the Dephosphorylation of Stat6 PARTICIPATION OF TYR-713 IN THE INTERLEUKIN-4 RECEPTOR α, THE TYROSINE PHOSPHATASE SHP-1, AND THE PROTEASOME

Signal transducer and activator of transcription 6 (Stat6) plays an important role in interleukin (IL)-4-induced responses. To analyze the regulation of Stat6 phosphorylation, cells were cultured in the continuous presence of IL-4 or after a pulse and washout. In the continual presence of IL-4, Stat6 remained phosphorylated for an extended period. After IL-4 removal and inhibition of the Janus family kinase, tyrosine-phosphorylated Stat6 decayed at a rate dependent upon the length of IL-4 stimulation. The decay of tyrosine-phosphorylated Stat6 was similar in the presence or absence of either cycloheximide or actinomycin D. In the absence of functional Src homology-containing phosphatase-1 (SHP-1), the early loss of tyrosine-phosphorylated Stat6 was substantially reduced. Furthermore, the rate of loss of tyrosine-phosphorylated Stat6 in cells expressing a mutation of the human IL-4 receptor α in the immunoreceptor tyrosine-based inhibitory motif sequence (Y5F) was dramatically decreased compared with wild-type cells. The early rate of decay was similar in the presence or absence of MG132, an inhibitor of the proteasome, but the later rate of decay was decreased 5-fold. These results suggest that the loss of tyrosine phosphorylation of Stat6 is regulated by the action of SHP-1 and the proteasome but is not dependent on new protein synthesis.

INHIBITION OF IL-4-INDUCIBLE GENE EXPRESSION IN HUMAN MONOCYTES BY TYPE I AND TYPE II INTERFERONS

The Th2‐type cytokines, interleukin‐4 (IL‐4) and interleukin‐13 (IL‐13), induce expression of a distinct subset of genes in human monocytes, including Fc∊RIIb (CD23), 15‐lipoxygenase, IL‐1 receptor antagonist (IL‐1ra), and type I and type II IL‐1 receptors (IL‐1R). Type I interferons (IFN‐α and IFN‐β) and type Ii interferon (IFN‐γ) inhibit induction of these genes by IL‐4 and IL‐13. However, the mechanism by which IFNs mediate this inhibition has not been defined. In this overview, we discuss the role of the transcription factor, STAT6 (signal transducer and activator of transcription‐6) in mediating IL‐4‐ and IL‐13‐induced gene expression in monocytes. We also discuss our recent findings that type I and type II IFNs suppress IL‐4/IL‐13‐inducible gene expression by inhibiting tyrosine phosphorylation and nuclear translocation of STAT6. The ability of type I and type II IFNs to inhibit IL‐4/IL‐13‐induced STAT6 activity is dose‐and time‐dependent, and is not unique to monocytes because IFNs induce the same effects in fibroblasts. Inhibition of STAT6 activity is not evident unless cells are preincubated with IFN for at least 1 h before IL‐4 stimulation. Furthermore, inhibition can be blocked by actinomycin D, indicating a requirement for de novo transcription. We propose a model in which stimulation of monocytes by IFN activates de novo synthesis of an inhibitory factor, possibly one or more members of the SOCS/SSI/CIS gene family, capable of suppressing activation of STAT6 by IL‐4 and IL‐13. Because STAT6 activation plays an essential role in IL‐4/IL‐13‐induced gene expression, the ability of IFN‐β and IFN‐γ to inhibit STAT6 activity provides an explanation for how IFNs can suppress IL‐4/IL‐13‐inducible gene expression. J. Leukoc. Biol. 65: 307–312; 1999.