Coronavirus disease (COVID-19) is an acute infectious disease caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Human SP-D (surfactant protein D) is known to interact with the spike protein of SARS-CoV, but its immune surveillance against SARS-CoV-2 is not known. The current study aimed to examine the potential of a recombinant fragment of human SP-D (rfhSP-D) as an inhibitor of replication and infection of SARS-CoV-2. The interaction of rfhSP-D with the spike protein of SARS-CoV-2 and human ACE-2 (angiotensin-converting enzyme 2) receptor was predicted via docking analysis. The inhibition of interaction between the spike protein and ACE-2 by rfhSP-D was confirmed using direct and indirect ELISA. The effect of rfhSP-D on replication and infectivity of SARS-CoV-2 from clinical samples was assessed by measuring the expression of RdRp gene of the virus using quantitative PCR. In silico interaction studies indicated that three amino acid residues in the receptor-binding domain of spike protein of SARS-CoV-2 were commonly involved in interacting with rfhSP-D and ACE-2. Studies using clinical samples of SARS-CoV-2–positive cases (asymptomatic, n = 7; symptomatic, n = 8) and negative control samples (n = 15) demonstrated that treatment with 1.67 μM rfhSP-D inhibited viral replication by ∼5.5-fold and was more efficient than remdesivir (100 μM) in Vero cells. An approximately two-fold reduction in viral infectivity was also observed after treatment with 1.67 μM rfhSP-D. These results conclusively demonstrate that the rfhSP-D mediated calcium independent interaction between the receptor-binding domain of the S1 subunit of the SARS-CoV-2 spike protein and human ACE-2, its host cell receptor, and significantly reduced SARS-CoV-2 infection and replication in vitro.

冠状病毒病 (COVID-19) 是由严重急性呼吸系统综合症冠状病毒 2 (SARS-CoV-2) 引起的急性传染病。已知人类 SP-D（表面活性剂蛋白 D）与 SARS-CoV 的刺突蛋白相互作用，但其对 SARS-CoV-2 的免疫监视尚不清楚。目前的研究旨在检查人类 SP-D (rfhSP-D) 重组片段作为 SARS-CoV-2 复制和感染抑制剂的潜力。通过对接分析预测了 rfhSP-D 与 SARS-CoV-2 的刺突蛋白和人 ACE-2（血管紧张素转换酶 2）受体的相互作用。使用直接和间接 ELISA 证实了 rfhSP-D 对刺突蛋白和 ACE-2 之间相互作用的抑制。病毒的RdRp基因使用定量 PCR。计算机相互作用研究表明，SARS-CoV-2 刺突蛋白受体结合域中的三个氨基酸残基通常参与与 rfhSP-D 和 ACE-2 的相互作用。使用 SARS-CoV-2 阳性病例（无症状，n = 7；有症状，n  = 8）和阴性对照样本（n = 15) 证明用 1.67 μM rfhSP-D 处理可将病毒复制抑制约 5.5 倍，并且在 Vero 细胞中比 remdesivir (100 μM) 更有效。在用 1.67 μM rfhSP-D 处理后，还观察到病毒感染性降低了大约两倍。这些结果最终证明 rfhSP-D 介导了 SARS-CoV-2 刺突蛋白 S1 亚基的受体结合域与其宿主细胞受体人 ACE-2 之间的钙非依赖性相互作用，并显着降低了 SARS-CoV- 2体外感染和复制。