Background

Spike protein domains are being used in various serology-based assays to detect prior exposure to SARS-CoV-2 virus. However, there has been limited comparison of antibody titers against various spike protein antigens among COVID-19 infected patients.

Methods

We compared four spike proteins (RBD, S1, S2 and a stabilized spike trimer (ST)) representing commonly used antigens for their reactivity to human IgG antibodies using indirect ELISA in serum from COVID-19 patients and pre-2020 samples. ST ELISA was also compared against the EUROIMMUN IgG ELISA test. Further, we estimated time appropriate IgG and IgA seropositivity rates in COVID-19 patients using a panel of sera samples collected longitudinally from the day of onset of symptoms (DOS).

Results

Among the four spike antigens tested, the ST demonstrated the highest sensitivity (86.2 %; 95 % CI: 77.8–91.7 %), while all four antigens showed high specificity to COVID-19 sera (94.7–96.8 %). 13.8 % (13/94) of the samples did not show seroconversion in any of the four antigen-based assays. In a double-blinded head-to-head comparison, ST based IgG ELISA displayed a better sensitivity (87.5 %, 95 % CI: 76.4–93.8 %) than the EUROIMMUN IgG ELISA (67.9 %, 95 % CI: 54.8–78.6 %). Further, in ST-based assays, we found 48 % and 50 % seroconversion in the first six days (from DOS) for IgG and IgA antibodies, respectively, which increased to 84 % (IgG) and 85 % (IgA) for samples collected ≥22 days from DOS.

Conclusions

Comparison of spike antigens demonstrates that spike trimer protein is a superior option as an ELISA antigen for COVID-19 serology.

中文翻译：

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SARS-CoV-2 血清学刺突蛋白抗原的评估

 背景

刺突蛋白结构域被用于各种基于血清学的检测中，以检测之前是否接触过 SARS-CoV-2 病毒。然而，针对 COVID-19 感染患者中各种刺突蛋白抗原的抗体滴度的比较有限。

 方法

我们使用间接 ELISA 方法比较了代表常用抗原的四种刺突蛋白（RBD、S1、S2 和稳定的刺突三聚体 (ST)）与人 IgG 抗体的反应性，这些蛋白来自 COVID-19 患者的血清和 2020 年前的样本。 ST ELISA 还与 EUROIMMUN IgG ELISA 测试进行了比较。此外，我们使用从症状出现之日起纵向收集的一组血清样本（DOS）估计了 COVID-19 患者中适当时间的 IgG 和 IgA 血清阳性率。

 结果

在测试的四种刺突抗原中，ST 表现出最高的敏感性（86.2％；95％CI：77.8-91.7％），而所有四种抗原都对 COVID-19 血清表现出高特异性（94.7-96.8％）。 13.8% (13/94) 的样品在四种基于抗原的检测中均未显示血清转化。在双盲头对头比较中，基于 ST 的 IgG ELISA 显示出比 EUROIMMUN IgG ELISA（67.9 %，95 % CI：54.8–78.6 %）更好的灵敏度（87.5 %，95 % CI：76.4–93.8 %） ）。此外，在基于 ST 的检测中，我们发现 IgG 和 IgA 抗体在前六天（从 DOS 开始）分别有 48% 和 50% 的血清转化率，对于收集的样品，血清转化率增加到 84% (IgG) 和 85% (IgA)距 DOS ≥22 天。

 结论

刺突抗原的比较表明，刺突三聚体蛋白是作为 COVID-19 血清学 ELISA 抗原的绝佳选择。