Human Surfactant Protein D Binds Spike Protein and Acts as an Entry Inhibitor of SARS-CoV-2 Pseudotyped Viral Particles.

Miao-Hsi Hsieh,Taruna Madan,Jiu-Yao Wang,Wen-Shuo Kuo,Valarmathy Murugaiah,Hui-Fang Kao,Nazar Beirag,Uday Kishore,Yu-Chi Chou

doi:10.3389/fimmu.2021.641360

Abstract

Human SP-D is a potent innate immune molecule whose presence at pulmonary mucosal surfaces allows its role in immune surveillance against pathogens. Higher levels of serum SP-D have been reported in the patients with severe acute respiratory syndrome coronavirus (SARS-CoV). Studies have suggested the ability of human SP-D to recognise spike glycoprotein of SARS-CoV; its interaction with HCoV-229E strain leads to viral inhibition in human bronchial epithelial (16HBE) cells. Previous studies have reported that a recombinant fragment of human SP-D (rfhSP-D) composed of 8 Gly-X-Y repeats, neck and CRD region, can act against a range of viral pathogens including influenza A Virus and Respiratory Syncytial Virus in vitro, in vivo and ex vivo. In this context, this study was aimed at examining the likely protective role of rfhSP-D against SARS-CoV-2 infection. rfhSP-D showed a dose-responsive binding to S1 spike protein of SARS-CoV-2 and its receptor binding domain. Importantly, rfhSP-D inhibited interaction of S1 protein with the HEK293T cells overexpressing human angiotensin converting enzyme 2 (hACE2). The protective role of rfhSP-D against SARS-CoV-2 infection as an entry inhibitor was further validated by the use of pseudotyped lentiviral particles expressing SARS-CoV-2 S1 protein; ~0.5 RLU fold reduction in viral entry was seen following treatment with rfhSP-D (10 µg/ml). These results highlight the therapeutic potential of rfhSP-D in SARS-CoV-2 infection and merit pre-clinical studies in animal models.

Highlights

Human surfactant protein D (SP-D), a collagen-containing C-type lectin and a member of the collectin family, is known to be involved in pulmonary surfactant homeostasis and immunity [1]
The first part of this study was aimed at examining the interaction of LPS-free recombinant fragment of human SP-D (rfhSP-D) and hFL-SP-D with spike protein (S1) using direct binding ELISA
It was found that rfhSP-D/hFL-SP-D bound severe acute respiratory syndrome (SARS)-CoV-2 S1 protein in a dose-dependent manner (Figure 1A); this interaction was inhibited by maltose and EDTA (Figure 2A)

Summary

Introduction

Human surfactant protein D (SP-D), a collagen-containing C-type lectin and a member of the collectin family, is known to be involved in pulmonary surfactant homeostasis and immunity [1]. SP-D binds haemagglutinin (HA) and neuraminidase (NA) glycoproteins of IAV, and inhibits hemagglutination at initial stages of the infection [7]. A recombinant fragment of human SP-D (rfhSP-D), composed of homotrimeric neck and CRD region, was shown to bind HA, NA and Matrix 1 (M1) protein of IAV, and act as an entry inhibitor of IAV infection on A549 lung epithelial cells [8]. Interaction between SP-D and HCoV-229E, another coronavirus strain, leads to inhibition of viral infection in human bronchial epithelial (16HBE) cells [13]

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