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 C-type 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.

Surfactant protein D inhibits mite-induced alveolar macrophage and dendritic cell activations through TLR signalling and DC-SIGN expression.

BACKGROUND: Surfactant protein D (SP-D), a secreted pattern recognition molecule associated with pulmonary innate immunity, has been shown to mediate the clearance of pathogens in multiple ways. However, how SP-D interacts with alveolar macrophages (AMs) and dendritic cells (DCs) during allergen exposure remains unclear. OBJECTIVE: This study was performed to characterize the immunomodulatory effects of SP-D on mite allergen (Dermatophagoides pteronyssinus, Der p)-induced inflammatory signalling in AMs and DCs. METHODS: Murine AM, alveolar macrophage cell line derived from BALB/c mice (MH-S cells), and human monocyte-derived dendritic cells (MDDC) were used as model systems. The production of nitric oxide (NO) and TNF-alpha, expression of surface Toll-like receptors (TLRs), and expression of the C-type lectin receptor known as dendritic cell (DC)-specific ICAM-grabbing non-integrin (DC-SIGN) were measured as a function of pretreatment with SP-D and subsequent exposure to Der p. Der p-dependent cellular activations that were modified by SP-D in these model systems were then identified. RESULTS: Pretreatment of MH-S cells with SP-D reduced Der p-dependent production of NO, TNF-alpha, and the downstream activations of IL-1 receptor-associated kinase, mitogen activated protein kinase (MAPK) kinase, and nuclear factor-kappaB. SP-D interacted with CD14 such that CD14 binding to Der p was inhibited and Der p-induced signalling via TLRs was blocked. DC-SIGN expression was suppressed by Der p in MH-S and MDDC; this down-regulation of DC-SIGN expression was prevented by pretreatment with SP-D. CONCLUSIONS: These results indicated that the inhibition of Der p-induced activation of MH-S and MDDC by SP-D is mediated through suppression of the CD14/TLR signalling pathway and maintenance of DC-SIGN expression, which may protect allergen-induced airway inflammation.