Respiratory syncytial virus (RSV) is the most frequent cause of lower respiratory disease in infants, but no
vaccine or effective
therapy is available. The initiation of
RSV infection of immortalized cells is largely dependent on cell surface
heparan sulfate (HS), a receptor for the RSV attachment (G)
glycoprotein in immortalized cells. However, RSV infects the ciliated cells in primary well differentiated human airway epithelial (HAE) cultures via the apical surface, but HS is not detectable on this surface. Here we show that soluble HS inhibits
infection of immortalized cells, but not HAE cultures, confirming that HS is not the receptor on HAE cultures. Conversely, a "non-neutralizing"
monoclonal antibody against the
G protein that does not block
RSV infection of immortalized cells, does inhibit
infection of HAE cultures. This antibody was previously shown to block the interaction between the
G protein and the
chemokine receptor CX3CR1 and we have mapped the binding site for this antibody to the CX3C motif and its surrounding region in the
G protein. We show that CX3CR1 is present on the apical surface of ciliated cells in HAE cultures and especially on the cilia.
RSV infection of HAE cultures is reduced by an antibody against CX3CR1 and by mutations in the
G protein CX3C motif. Additionally, mice lacking CX3CR1 are less susceptible to
RSV infection. These findings demonstrate that RSV uses CX3CR1 as a cellular receptor on HAE cultures and highlight the importance of using a physiologically relevant model to study virus entry and antibody neutralization.