Role of viral hemagglutinin glycosylation in anti-influenza activities of recombinant surfactant protein D

Kevan L Hartshorn,Ronald K Scheule,Clark Pan,Rodney J Moreland,Erika C Crouch,Tesfaldet Tecle,Susan Boucher,Richard Webby,Mitchell R White

doi:10.1186/1465-9921-9-65

Kevan L Hartshorn, Ronald K Scheule + Show 7 more

Open Access

https://doi.org/10.1186/1465-9921-9-65

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Abstract

BackgroundSurfactant protein D (SP-D) plays an important role in innate defense against influenza A viruses (IAVs) and other pathogens.MethodsWe tested antiviral activities of recombinant human SP-D against a panel of IAV strains that vary in glycosylation sites on their hemagglutinin (HA). For these experiments a recombinant version of human SP-D of the Met11, Ala160 genotype was used after it was characterized biochemically and structurally.ResultsOligosaccharides at amino acid 165 on the HA in the H3N2 subtype and 104 in the H1N1 subtype are absent in collectin-resistant strains developed in vitro and are important for mediating antiviral activity of SP-D; however, other glycans on the HA of these viral subtypes also are involved in inhibition by SP-D. H3N2 strains obtained shortly after introduction into the human population were largely resistant to SP-D, despite having the glycan at 165. H3N2 strains have become steadily more sensitive to SP-D over time in the human population, in association with addition of other glycans to the head region of the HA. In contrast, H1N1 strains were most sensitive in the 1970s–1980s and more recent strains have become less sensitive, despite retaining the glycan at 104. Two H5N1 strains were also resistant to inhibition by SP-D. By comparing sites of glycan attachment on sensitive vs. resistant strains, specific glycan sites on the head domain of the HA are implicated as important for inhibition by SP-D. Molecular modeling of the glycan attachment sites on HA and the carbohydrate recognition domain of SPD are consistent with these observations.ConclusionInhibition by SP-D correlates with presence of several glycan attachment sites on the HA. Pandemic and avian strains appear to lack susceptibility to SP-D and this could be a contributory factor to their virulence.

Highlights

Influenza A viruses (IAVs) remain a major cause of morbidity and mortality and have the potential to cause massive mortality if novel pandemic strains emerge through reassortment of human and avian strains or direct adaptation of avian strains to humans [1,2]
The Surfactant protein D (SP-D) contains small amounts of trimers (~3 Sv) together with larger amounts of dodecamers (~6.5 Sv) and high molecular weight multimers (20–35 Sv). These analytical ultracentrifugation (AUC) results were confirmed by atomic force microscopy (AFM), ie., small amounts of trimers can be seen interspersed with dodecamers and higher order multimers (Figure 1B)
Overall our results show that the Met11 form of SP-D has strong antiviral and opsonizing activities

Summary

Introduction

Influenza A viruses (IAVs) remain a major cause of morbidity and mortality and have the potential to cause massive mortality if novel pandemic strains emerge through reassortment of human and avian strains or direct adaptation of avian strains to humans (as appears to have occurred in 1918) [1,2]. It is likely that innate host defense mechanisms play an important role in defense against novel strains associated with antigenic drift or shift. These defense mechanisms may play a greater role in more vulnerable subjects (e.g., those who are immunocompromised in other ways). Mice lacking either SPA or SP-D experience greater viral replication, inflammation and illness in the first several days after infection with IAV strains known to be susceptible to inhibition by these host defense lectins in vitro [4,9,10]. Surfactant protein D (SP-D) plays an important role in innate defense against influenza A viruses (IAVs) and other pathogens

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