>90%, by SDS-PAGE under reducing conditions and visualized by silver stain.
<0.10 EU per 1 μg of the protein by the LAL method.
Measured by its ability to inhibit Type-I IFN-mediated anti-viral activity. Symons, J.A. et al. (1995) Cell 81:551. The ED50 for this effect, as measured by inhibition of Recombinant Human IFN‑ alpha 2 (Catalog # 11105-1)
, is 0.3-1.8 ng/mL.
Human embryonic kidney cell, HEK293-derived viral B18R protein
The viral type I IFN receptor, B18R, inhibits the anti-viral activity of Recombinant Human IFN-alpha 2. The ED50 for this effect is 0.3-1.8 ng/mL.
(Soluble interferon alpha/beta receptor B18) is a 60-65 kDa protein
encoded by the Vaccinia virus genome and by the genomes of other
orthopoxviruses. Its function represents one of several mechanisms used
by these viruses to evade the host immune response (1, 2). It is known
as B18R in the Western Reserve (WR) strain of Vaccinia but as B19R in
the Copenhagen strain (3). There is a structurally-unrelated, larger
Vaccinia protein that is also known as B18R (or B16R) that contains
multiple ankyrin-like repeats (4). The soluble interferon receptor B18R,
however, contains three immunoglobulin-like domains and shows homology
to human, mouse, and bovine type I interferon receptors (5). The Wyeth
strain of Vaccinia virus encodes a truncated protein that lacks the
C-terminal Ig-like domain, and B18R is functionally absent in the Lister
strain (6, 7). B18R functions as a decoy receptor for type I
interferons (IFN alpha, beta, omega). It binds to type I interferons
from multiple species and prevents IFN signaling through its receptors
(6-8). B18R binds to the surface of virus infected and uninfected cells
where it retains its capacity to bind and neutralize IFN (6, 8). It
shields those cells from the antiviral effects of type I interferons,
thereby enabling virus replication and pathogenicity (6-8). B18R also
limits the effectiveness of IFN alpha produced following TLR activation
(9), and it limits adaptive T cell responses (3). B18R is a common factor used for increasing the efficiency of RNA reprogramming in induced pluripotent stem cells (IPS cells) (10).
Smith, G.L. et al. (2013) J. Gen. Virol. 94:2367.
Perdiguero, B. and M. Esteban (2009) J. Interferon Cytokine Res. 29:581.
Gomez, C.E. et al. (2012) J. Virol. 86:5026.
Goebel, S.J. et al. (1990) Virology 179:247.
Smith, G.L. and Y.S. Chan (1991) J. Gen. Virol. 72:511.
Alcami, A. et al. (2000) J. Virol. 74:11230.
Symons, J.A. et al. (1995) Cell 81:551.
Colamonici, O.R. et al. (1995) J. Biol. Chem. 270:15974.
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