Enterovirus type 71 (EV71) causes hand, foot, and mouth disease (HFMD), which is mostly self-limited but may be complicated with a severe to fatal neurological syndrome in some children. Understanding the molecular basis of virus-host interactions might help clarify the largely unknown neuropathogenic mechanisms of EV71. In this study, we showed that human annexin II (Anx2) protein could bind to the EV71 virion via the capsid protein VP1. Either pretreatment of EV71 with soluble recombinant Anx2 or pretreatment of host cells with an anti-Anx2 antibody could result in reduced viral attachment to the cell surface and a reduction of the subsequent virus yield in vitro. HepG2 cells, which do not express Anx2, remained permissive to EV71 infection, though the virus yield was lower than that for a cognate lineage expressing Anx2. Stable transfection of plasmids expressing Anx2 protein into HepG2 cells (HepG2-Anx2 cells) could enhance EV71 infectivity, with an increased virus yield, especially at a low infective dose, and the enhanced infectivity could be reversed by pretreating HepG2-Anx2 cells with an anti-Anx2 antibody. The Anx2-interacting domain was mapped by yeast two-hybrid analysis to VP1 amino acids 40 to 100, a region different from the known receptor binding domain on the surface of the picornavirus virion. Our data suggest that binding of EV71 to Anx2 on the cell surface can enhance viral entry and infectivity, especially at a low infective dose.Enterovirus type 71 (EV71) is a member of the Enterovirus genus of the family Picornaviridae and is one of the causative viral agents of hand, foot, and mouth disease (HFMD) (6,7,14,16,41). HFMD is largely a common self-limited childhood illness but may have complications of severe to fatal neurological symptoms in some children (1,5,6,16,21). In the past decade, the frequency of EV71 outbreaks associated with severe neurological illness appeared to have increased in the Pacific region, most notably in China, where large outbreaks have been occurring annually since 2007 (24, 53). While the epidemiological or virological mechanism underlying this regional focus of severe EV71 infection remains largely unknown, the impact of EV71 infection is a global concern, as evidenced by the increase in virological surveillance and studies of EV71 infection in many regions of the world (29,46,53).EV71 is composed of a single-stranded, positive-polarity RNA molecule surrounded by a nonenveloped, pentameric icosahedral capsid (3, 35), which consists of 60 copies of the four structural proteins VP1 to VP4. While there is no animal model for EV71 infection in humans, intraperitoneal injection of EV71 is lethal to suckling mice. Suckling mice born to mothers previously immunized with VP1 subunit vaccines acquire resistance to lethal EV71 challenge (8, 50), and administration of a VP1-based antigen, either protein or DNA, to mice could elicit a neutralizing antibody against EV71 infection in vitro (8,42,44). The serum collected from EV71-infected individuals during the convalescent pha...
