Enhanced Antiviral Activity of Human Surfactant Protein D by Site-Specific Engineering of the Carbohydrate Recognition Domain

Front Immunol. 2019 Oct 22:10:2476. doi: 10.3389/fimmu.2019.02476. eCollection 2019.

Abstract

Innate immunity is critical in the early containment of influenza A virus (IAV) infection and surfactant protein D (SP-D) plays a crucial role in innate defense against IAV in the lungs. Multivalent lectin-mediated interactions of SP-D with IAVs result in viral aggregation, reduced epithelial infection, and enhanced IAV clearance by phagocytic cells. Previous studies showed that porcine SP-D (pSP-D) exhibits distinct antiviral activity against IAV as compared to human SP-D (hSP-D), mainly due to key residues in the lectin domain of pSP-D that contribute to its profound neutralizing activity. These observations provided the basis for the design of a full-length recombinant mutant form of hSP-D, designated as "improved SP-D" (iSP-D). Inspired by pSP-D, the lectin domain of iSP-D has 5 amino acids replaced (Asp324Asn, Asp330Asn, Val251Glu, Lys287Gln, Glu289Lys) and 3 amino acids inserted (326Gly-Ser-Ser). Characterization of iSP-D revealed no major differences in protein assembly and saccharide binding selectivity as compared to hSP-D. However, hemagglutination inhibition measurements showed that iSP-D expressed strongly enhanced activity compared to hSP-D against 31 different IAV strains tested, including (pandemic) IAVs that were resistant for neutralization by hSP-D. Furthermore, iSP-D showed increased viral aggregation and enhanced protection of MDCK cells against infection by IAV. Importantly, prophylactic or therapeutic application of iSP-D decreased weight loss and reduced viral lung titers in a murine model of IAV infection using a clinical isolate of H1N1pdm09 virus. These studies demonstrate the potential of iSP-D as a novel human-based antiviral inhalation drug that may provide immediate protection against or recovery from respiratory (pandemic) IAV infections in humans.

Keywords: antiviral agent; collectin; influenza A virus; innate immunity; lung infection; pandemics; recombinant expression; surfactant protein D.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Binding Sites
  • Carbohydrates* / immunology
  • Disease Resistance / genetics
  • Disease Resistance / immunology
  • Glycosylation
  • Humans
  • Influenza A virus / immunology
  • Influenza, Human / genetics
  • Influenza, Human / immunology
  • Influenza, Human / virology
  • Models, Molecular
  • Molecular Conformation
  • Protein Binding
  • Protein Engineering*
  • Protein Interaction Domains and Motifs* / genetics
  • Pulmonary Surfactant-Associated Protein D / chemistry*
  • Pulmonary Surfactant-Associated Protein D / genetics
  • Pulmonary Surfactant-Associated Protein D / immunology
  • Pulmonary Surfactant-Associated Protein D / metabolism*
  • Recombinant Proteins
  • Structure-Activity Relationship

Substances

  • Carbohydrates
  • Pulmonary Surfactant-Associated Protein D
  • Recombinant Proteins