Branched oligosaccharide structures on HBV prevent interaction with both DC-SIGN and L-SIGN.

Hepatitis B virus (HBV) is a DNA virus that infects the liver as primary target. Currently, a high affinity receptor for HBV is still unknown. The dendritic cell specific C-type lectin DC-SIGN is involved in pathogen recognition through mannose and fucose containing carbohydrates leading to the induction of an anti-viral immune response. Many glycosylated viruses subvert this immune surveillance function and exploit DC-SIGN as a port of entry and for trans-infection of target cells. The glycosylation pattern on HBV surface antigens (HBsAg) together with the tissue distribution of HBV would allow interaction between HBV and DC-SIGN and its liver-expressed homologue L-SIGN. Therefore, a detailed study to investigate the binding of HBV to DC-SIGN and L-SIGN was performed. For HCV, both DC-SIGN and L-SIGN are known to bind envelope glycoproteins E1 and E2. Soluble DC-SIGN and L-SIGN specifically bound HCV virus-like particles, but no interaction with either HBsAg or HepG2.2.15-derived HBV was detected. Also, neither DC-SIGN nor L-SIGN transfected Raji cells bound HBsAg. In contrast, highly mannosylated HBV, obtained by treating HBV producing HepG2.2.15 cells with the alpha-mannosidase I inhibitor kifunensine, is recognized by DC-SIGN. The alpha-mannosidase I trimming of N-linked oligosaccharide structures thus prevents recognition by DC-SIGN. On the basis of these findings, it is tempting to speculate that HBV exploits mannose trimming as a way to escape recognition by DC-SIGN and thereby subvert a possible immune activation response.

Identification of a novel occlusion derived virus-specific protein in Spodoptera exigua multicapsid nucleopolyhedrovirus.

Understanding the molecular basis of the distinct biological properties of Spodoptera exigua multicapsid nucleopolyhedrovirus (SeMNPV), such as its narrow host range and high virulence, requires detailed information on the temporal expression and subcellular localization of SeMNPV gene products. The expression of two unique SeMNPV ORFs, 116 (Se116) and 117 (Se117), which show 45% amino acid similarity, was analyzed. Se116 and Se117 were expressed both in cultured cells and in larvae of S. exigua as polyadenylated transcripts of 0.80 and 0.75 kb, respectively. These transcripts initiated from ATCA(G/T)T promoter motifs, commonly found for baculovirus early genes. Se116 transcripts were detected with increasing abundance from 8 to 48 h p.i., whereas Se117 transcripts were present from 4 h p.i. and most abundantly at 24 h p.i. Western blot analysis of infected Se301 cells revealed 27- and 23-kDa proteins for Se116 and Se117, respectively. C-terminal GFP-fusion proteins of Se116 and Se117 were primarily localized in the nucleus of Se301 cells. When Se301 cells were infected with SeMNPV, both GFP-fusion proteins were localized in the virogenic stroma of the nucleus. While the function of the Se116 protein is still enigmatic, the Se117 protein appeared to be a structural protein associated with nucleocapsids of occlusion-derived SeMNPV virions but not of budded virus.