The soluble murine type I interferon receptor Ifnar-2 is present in serum, is independently regulated, and has both agonistic and antagonistic properties

Abstract

The ability to modify responses to type I interferons (IFNs) could alter processes such as hematopoiesis and immunity, which involve endogenous IFNs and responses to exogenous IFNs. The data presented here support a significant role for a recently identified soluble isoform of the murine type I IFN receptor, muIfnar2a, as an efficient regulator of IFN responses. The messenger RNA (mRNA) transcript encoding muIfnar-2a is generally more abundant than that encoding the transmembrane isoform, muIfnar-2c. Furthermore, the ratio of muIfnar-2a:2c transcripts varied from more than 10:1 in the liver and other organs to less than 1:1 in bone-marrow macrophages, indicating independent regulation of the 2 transcripts encoding receptor isoforms and suggesting that the soluble muIfnar-2a levels are biologically relevant in some organs. Western blot analysis showed that soluble muIfnar-2 was present at high levels in murine serum and other biologic fluids and bound type I IFN. Recombinant muIfnar-2a competitively inhibited the activity of both IFN␣ and ␤ in reporter assays using the L929 cell line and in antiproliferative and antiviral assays using primary cells. Surprisingly, IntroductionThe type I interferons (IFNs) are a family of cytokines produced in physiologic and pathologic conditions. Their biologic activities include inhibition of macrophage and lymphocyte proliferation, differentiation of macrophages, activation of natural killer and dendritic cells, and increased survival of memory T cells in addition to their well-characterized antiviral and antitumor activities. [1][2][3][4][5][6] These activities make type I IFNs important mediators of physiologic processes and disease pathogenesis and useful in the treatment of viral infections, some cancers (particularly those of hematopoietic origin), and other diseases, including multiple sclerosis. 7 In both human and mouse, the type I IFNs include multiple IFN␣ subtypes with about 75% to 99% amino acid identity and a single IFN␤ with about 30% amino acid identity to IFN␣. 8 All type I IFNs have similar biologic activities and compete for binding to a common cell surface receptor. 9 The type I IFN receptor is composed of 2 known subunits: IFNAR-1 10 and IFNAR-2. 11 In humans and mice, there is a single form of IFNAR-1. 12 In contrast, multiple isoforms of human IFNAR-2 have been shown to result from alternative splicing of the same gene producing huIFNAR-2a (encoding a putative soluble isoform), huIFNAR-2b (encoding a putative transmembrane receptor with a truncated cytoplasmic domain), and huIFNAR-2c (encoding a putative full-length transmembrane receptor). 13 HuIFNAR-2c reconstituted IFN signaling in the huIFNAR-2-deficient cell line (U5A), which was otherwise unresponsive to IFN, whereas huIFNAR-2b did not, indicating that the latter was a nonfunctional isoform. 13 We recently cloned the murine orthologue of IFNAR-2 (muIfnar-2) and identified complementary DNAs (cDNAs) encoding full-length muIfnar-2c and soluble muIfnar-2a isoforms. 14 Northern blots showed 2 transcript...

Improved biological and transcriptional activity of monopegylated interferon-α-2a isomers

“…18 Surface expression of full-length IFNR2 is sufficient for binding, but both receptors are required for signal transduction. [19][20][21] Mutational studies suggest that IFNR2 has at least three interferon-a-binding sites, at the A helix (residues 12-15), at the AB loop (residues 26-35) and at the E helix (residues 144-153), 22 whereas the IFNR1-binding site was mapped in the vicinity of K121. 23 The affinity of IFN to IFNR2 (K D B10 nM) is at least 10-fold higher than that to IFNR1 (K D 4100 nM), 24 and it is likely that the rather bulky PEG side chains disturb binding or appropriate positioning of the ligand between its receptors.…”

Higher Serum Levels of Type I Interferon Receptor in Adults with Chronic Hepatitis B Leading to Hepatitis B Surface Antigen Clearance

“…Even though these soluble cytokine receptors have been considered as antagonists for transmembrane forms of the receptors, they also perform as carrier proteins to increase the stability of type I IFNs ligands by keeping them from proteolysis and clearance. In this way, they are agonists for modifying ligand activity in a transsignaling pathway (6,9,25,26). On the other hand, it has been demonstrated that the numbers of pDC are decreased in the IFNI-dependent proapoptotic manner in viral hepatitis (9).…”

“…Likewise, Zhao et al (24) showed that the mRNA and plasma levels of IFNAR1 and IFNAR2c were increased in CHB and liver cirrhosis patients compared with healthy controls. Soluble IF-NAR2 is an important regulator of endogenous and systemically administered of type I IFNs (9,25,26). Interferons-α/β are virus-interfering factors that involved in both immunostimulatory and immunosuppressive properties (27).…”

Interferons as Biomarkers and Effectors: Lessons Learned from Animal Models

“…IFNs are highly conserved across species, highlighting their evolutionary importance in host immune responses against pathogens. Murine IFN−αs have over 70% sequence identity with human IFN−αs [9,10]. However, there is only one IFN−β subtype expressed in both humans and mice [11].…”