Occludin, the final essential factor for HCV entry?

Evaluation of: Ploss A, Evans MJ, Gaysinskaya VA et al: Human occludin is a hepatitis C virus entry factor required for infection of mouse cells. Nature 457(7231), 882-886 (2009). Hepatitis C is a major health problem, with 3% of the world's population infected. The causative agent of the disease is the HCV, This virus has a very narrow host specificity, infecting only humans and chimpanzees, thus, precluding the use of a small animal model, Entry of the virus into target cells depends on several receptors/cellular entry factors, such as CD81, scavenger receptor class B type I and claudin-1. Despite normal expression levels of all identified entry factors, some cells are resistant to HCV infection, suggesting that one or more factors still remain unknown. The recent article by Ploss and colleagues identifies occludin as an additional entry factor for HCV, thereby, finally completing identification of the set of factors necessary to allow entry of HCV into nonhuman cells.