Abstract
Vaccinia virus (VACV) was used as a surrogate of variola virus (VARV) (genus Orthopoxvirus), the causative agent of smallpox, to study Orthopoxvirus infection. VARV is principally transmitted between humans by aerosol droplets. Once inhaled, VARV first infects the respiratory tract where it could encounter surfactant components, such as soluble pattern recognition receptors. Surfactant protein D (SP-D), constitutively present in the lining fluids of the respiratory tract, plays important roles in innate host defense against virus infection. We investigated the role of SP-D in VACV infection and studied the A27 viral protein involvement in the interaction with SP-D. Interaction between SP-D and VACV caused viral inhibition in a lung cell model. Interaction of SP-D with VACV was mediated by the A27 viral protein. Binding required Ca2+ and interactions were blocked in the presence of excess of SP-D saccharide ligands. A27, which lacks glycosylation, directly interacted with SP-D. The interaction between SP-D and the viral particle was also observed using electron microscopy. Infection of mice lacking SP-D (SP-D-/-) resulted in increased mortality compared to SP-D+/+ mice. Altogether, our data show that SP-D participates in host defense against the vaccinia virus infection and that the interaction occurs with the viral surface protein A27.
Highlights
Vaccinia virus (VACV) is the prototype for the Poxviridae family and the Orthopoxvirus genus which includes variola virus (VARV), the etiological agent of smallpox
Proteins bound to the membranes were detected using a specific anti-surfactant protein antibody and enhanced chemiluminescence
Nonspecific signal was comparable to the signals observed with human alveolar proteinosis surfactant protein A (AP-surfactant proteins (SP)-A) and human recombinant surfactant protein A (RhSP-A)
Summary
Vaccinia virus (VACV) is the prototype for the Poxviridae family and the Orthopoxvirus genus which includes variola virus (VARV), the etiological agent of smallpox. IAV expressing the HA of pandemic viruses were associated with significant pathology of the lower respiratory tract and showed a low binding activity for SP-D while virus expressing HA of a seasonal strain induced only mild disease and exhibited strong in vitro binding to SP-D [29, 34]. These studies established that the innate immune activity of SP-D is principally mediated through interaction with viral membrane glycoproteins. Scheme adapted from [50]
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