Background: Detailed understanding of the immune response to SARS-CoV-2, the cause of coronavirus disease 2019 (COVID-19), has been hampered by a lack of quantitative antibody assays. Objective: To develop a quantitative assay for IgG to SARS-CoV-2 proteins that could readily be implemented in clinical and research laboratories. Methods: The biotin-streptavidin technique was used to conjugate SARS-CoV-2 spike receptor-binding-domain (RBD) or nucleocapsid protein to the solid-phase of the ImmunoCAP resin. Plasma and serum samples from patients with COVID-19 (n=51) and samples from donors banked prior to the emergence of COVID-19 (n=109) were used in the assay. SARS-CoV-2 IgG levels were followed longitudinally in a subset of samples and were related to total IgG and IgG to reference antigens using an ImmunoCAP 250 platform. Results: Performance characteristics demonstrated 100% sensitivity and 99% specificity at a cut-off level of 2.5 μg/mL for both SARS-CoV-2 proteins. Among 36 patients evaluated in a post-hospital follow-up clinic, median levels of IgG to spike-RBD and nucleocapsid were 34.7 μg/mL (IQR 18-52) and 24.5 μg/mL (IQR 9-59), respectively. Among 17 patients with longitudinal samples there was a wide variation in the magnitude of IgG responses, but generally the response to spike-RBD and to nucleocapsid occurred in parallel, with peak levels approaching 100 μg/mL, or 1% of total IgG. Conclusions: We have described a quantitative assay to measure IgG to SARS-CoV-2 that could be used in clinical and research laboratories and implemented at scale. The assay can easily be adapted to measure IgG to novel antigens, has good performance characteristics and a read-out in standardized units.

中文翻译：

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使用 ImmunoCAP 定量测量 SARS-CoV-2 蛋白的 IgG

背景：由于缺乏定量抗体检测，对导致 2019 年冠状病毒病 (COVID-19) 的 SARS-CoV-2 的免疫反应的详细了解受到阻碍。目的：开发一种可在临床和研究实验室中轻松实施的 SARS-CoV-2 蛋白 IgG 定量检测方法。方法：生物素-链霉亲和素技术用于将 SARS-CoV-2 刺突受体结合域 (RBD) 或核衣壳蛋白与 ImmunoCAP 树脂的固相结合。检测中使用了来自 COVID-19 患者（n=51）的血浆和血清样本以及来自 COVID-19 出现之前储存的捐赠者的样本（n=109）。在样本子集中纵向跟踪 SARS-CoV-2 IgG 水平，并使用 ImmunoCAP 250 平台与总 IgG 和 IgG 参考抗原相关。结果：性能特征表明，两种 SARS-CoV-2 蛋白在 2.5 μg/mL 的截止水平下具有 100% 的敏感性和 99% 的特异性。在院后随访诊所评估的 36 名患者中，对尖峰 RBD 和核衣壳的 IgG 中位水平分别为 34.7 μg/mL (IQR 18-52) 和 24.5 μg/mL (IQR 9-59)。在 17 名纵向样本患者中，IgG 反应的幅度差异很大，但通常对尖峰 RBD 和核衣壳的反应平行发生，峰值水平接近 100 μg/mL，或总 IgG 的 1%。结论：我们已经描述了一种用于测量 SARS-CoV-2 的 IgG 的定量分析方法，可用于临床和研究实验室并大规模实施。该测定法可以很容易地适用于测量新抗原的 IgG，