Vaccinia virus (VACV) was used as a surrogate of Variola virus (genus Orthopoxvirus), the causative agent of
smallpox, to study
orthopoxvirus infection via the respiratory airway. Lung
surfactant, a physiological barrier to
infection encountered by the virus, is predominantly composed of
phospholipids whose role during
orthopoxvirus infection has not been investigated. An attenuated Lister strain, derived from the traditional
smallpox vaccine and the Western Reserve (WR) strain, lethal for mice infected by the respiratory route, were examined for their ability to bind various
surfactant phospholipids. Dipalmitoyl
phosphatidylglycerol (
DPPG) was found to interact with both VACV strains.
DPPG incorporated in small unilamellar vesicle (SUV-
DPPG) inhibited VACV cell
infection, unlike other
phospholipids tested. Both pre-incubation of virus with SUV-
DPPG and pretreatment of the cell with SUV-
DPPG inhibited cell
infection. This specific
DPPG effect was shown to be concentration and time dependent and to prevent the first step of the viral cycle, i.e. virus cell attachment. Cryo-electron microscopy highlighted the interaction between the virus and SUV-
DPPG. In the presence of the
phospholipid, virus particles displayed a hedgehog-like appearance due to the attachment of
lipid vesicles. Mice infected intranasally with VACV-WR pre-incubated with SUV-
DPPG survived a lethal
infection. These data suggest that
DPPG in lung
surfactant could reduce the amount of orthopoxvirus particles able to infect pneumocytes at the beginning of a respiratory
poxvirus infection. The knowledge acquired during this study of virus-
DPPG interactions may be used to develop novel chemotherapeutic strategies for
smallpox.