Assessment of the Antiviral Properties of Recombinant Porcine SP-D against Various Influenza A Viruses In Vitro

The emergence of influenza viruses resistant to existing classes of antiviral drugs raises concern and there is a need for novel
antiviral agents that could be used therapeutically or prophylacticaly. Surfactant protein D (SP-D) belongs to the family of Ctype
lectins which are important effector molecules of the innate immune system with activity against bacteria and viruses,
including influenza viruses. In the present study we evaluated the potential of recombinant porcine SP-D as an antiviral
agent against influenza A viruses (IAVs) in vitro. To determine the range of antiviral activity, thirty IAVs of the subtypes H1N1,
H3N2 and H5N1 that originated from birds, pigs and humans were selected and tested for their sensitivity to recombinant
SP-D. Using these viruses it was shown by hemagglutination inhibition assay, that recombinant porcine SP-D was more
potent than recombinant human SP-D and that especially higher order oligomeric forms of SP-D had the strongest antiviral
activity. Porcine SP-D was active against a broad range of IAV strains and neutralized a variety of H1N1 and H3N2 IAVs,
including 2009 pandemic H1N1 viruses. Using tissue sections of ferret and human trachea, we demonstrated that
recombinant porcine SP-D prevented attachment of human seasonal H1N1 and H3N2 virus to receptors on epithelial cells of
the upper respiratory tract. It was concluded that recombinant porcine SP-D holds promise as a novel antiviral agent against
influenza and further development and evaluation in vivo seems warranted.