Human parvovirus B19 VP2 empty capsids bind to human villous trophoblast cells in vitro via the globoside receptor.

BACKGROUND Pregnant women acutely infected with human parvovirus B19 (B19) may transmit the virus to the developing fetus. The mechanism whereby the virus interacts with the placenta is unknown. It is known that globoside receptor is required for successful infection of the target cells, which are the highly undifferentiated, actively dividing colony and burst-form units of the erythroid series. Globoside is present on trophoblast cells which have intimate contact with maternal blood, and may therefore serve as a potential route for B19 transmission into the fetal compartment. OBJECTIVES The purpose of this study was to determine whether B19 VP2 capsids could bind to villous trophoblast cells in vitro and whether globoside was involved. METHODS Binding of B19 VP2 empty capsid to first-trimester villous trophoblast cells was assessed by multiple approaches, including ICC using either biotinylated B19 VP2 empty capsid or unlabeled B19 VP2 empty capsid. Quantification of viral binding involved I125-labeled B19 VP2 empty capsid. Competition studies included excess unlabeled empty capsids or pretreatment with globoside-specific IgM antibody. RESULTS Linear binding of B19 VP2 capsid to purified villous trophoblast cells in vitro was clearly demonstrated (R2= 0.9524). Competition studies revealed specificity of I125-labeled B19 VP2 capsid binding to villous trophoblast cells when pretreatment with either 60-fold excess unlabeled B19 capsid or globoside-specific IgM antibody took place. The results illustrated B19's ability to bind in a specific manner to globoside-containing villous trophoblast cells. CONCLUSION We speculate that the globoside present on trophoblast cells may play a role in viral binding in vivo, which may facilitate B19 transmission across the maternal-fetal interface.