Swiss Association of the Diagnostic Industry (SVDI), Bern, Switzerland.
Independent Researcher, Bern, Switzerland.
Front Immunol. 2020 Jun 5;11:1120. doi: 10.3389/fimmu.2020.01120. eCollection 2020.
Human coronavirus (HCoV) is one of the most common causes of respiratory tract infections throughout the world. Two phenomena observed so far in the development of the SARS-CoV-2 pandemic deserve further attention. First, the relative absence of clinical signs of infections in children, second, the early appearance of IgG in certain patients. From the point of view of immune system physiology, such an early rise of specific IgG is expected in secondary immune responses when memory to a cross-reactive antigen is present, usually from an earlier infection with a coronavirus. It is actually typical for the immune system to respond, to what it already knows, a phenomenon that has been observed in many infections with closely related viruses and has been termed "original antigenic sin." The question then arises whether such cross-reactive antibodies are protective or not against the new virus. The worst scenario would be when such cross-reactive memory antibodies to related coronaviruses would not only be non-protective but even enhance infection and the clinical course. Such a phenomenon of antibody dependent enhancement (ADE) has already been described in several viral infections. Thus, the development of IgG against SARS-CoV-2 in the course of COVID-19 might not be a simple sign of viral clearance and developing protection against the virus. On the contrary, due to cross-reaction to related coronavirus strains from earlier infections, in certain patients IgG might enhance clinical progression due to ADE. The patient's viral history of coronavirus infection might be crucial to the development of the current infection with SARS-CoV-2. Furthermore, it poses a note of caution when treating COVID-19 patients with convalescent sera.
人冠状病毒（HCoV）是全球呼吸道感染的最常见原因之一。在 SARS-CoV-2 大流行的发展过程中，目前观察到两个现象值得进一步关注。首先，儿童感染的临床症状相对较少，其次，某些患者的 IgG 出现较早。从免疫系统生理学的角度来看，当存在针对交叉反应抗原的记忆时，在二次免疫反应中通常会出现这种早期出现的特异性 IgG，这种交叉反应抗原通常来自先前的冠状病毒感染。实际上，免疫系统对它已经知道的东西做出反应是很典型的，这种现象在许多密切相关病毒的感染中都观察到了，并被称为“原始抗原性错误”。那么，这些交叉反应性抗体是否对新病毒具有保护作用呢？最糟糕的情况是，相关冠状病毒的这种交叉反应性记忆抗体不仅没有保护作用，反而会增强感染和临床病程。这种抗体依赖性增强（ADE）现象已在几种病毒感染中得到描述。因此，在 COVID-19 期间针对 SARS-CoV-2 产生 IgG 可能不仅仅是病毒清除和对病毒产生保护作用的简单标志。相反，由于与先前感染的相关冠状病毒株发生交叉反应，在某些患者中，IgG 可能会因 ADE 而加重临床进展。患者冠状病毒感染的病史可能对当前 SARS-CoV-2 感染的发展至关重要。此外，在使用恢复期血清治疗 COVID-19 患者时应谨慎。
