Coronaviruses share conservative spike protein (S) on their enveloped membrane surface, where S1 subunit recognizes and binds the cellular receptor, and the S2 subunit mediates membrane fusion. This similarity raises the question: does coronaviral infection by one create protection to others? Convalescent SARS-CoV-2 (COVID-19) sera were tested for cross reactivity with peptides from Middle East respiratory syndrome coronavirus (MERS-CoV) which shares 74% homology. Our results showed significant cross-reactivity with a peptide of the heptad repeat 2 (HR2) domain of the MERS-CoV spike protein. Sera samples of 47 validated seropositive convalescent COVID-19 patients and 40 sera samples of control patients, collected in pre-COVID time were used to establish cross-bind reactivity with the MERS-CoV peptide. Significantly stronger binding (p < 0.0001) was observed for IgG antibodies in convalescent COVID-19 patients compared to the control group. In ELISA, MERS-CoV peptide helps to discriminate post-COVID-19 populations and non-infected ones by the presence of antibodies in blood samples. This suggests that polyclonal antibodies established during SARS-CoV-2 infection can recognize and probably decrease severity of MERS-CoV and other coronaviral infections. The high homology of the spike protein domain also suggests that the opposite effect can be true: coronaviral infections produce cross-reactive antibodies effective against SARS-CoV-2. The collected data prove that despite the core HR2 region is hidden in the native viral conformation, its exposure during cell entry makes it highly immunogenic. Since inhibitory peptides to this region were previously described, this opens new possibilities in fighting coronaviral infections and developing vaccines effective even after possible viral mutations.

冠状病毒在其包膜膜表面共享保守的刺突蛋白 (S)，其中 S1 亚基识别并结合细胞受体，而 S2 亚基介导膜融合。这种相似性提出了一个问题：一个人感染冠状病毒是否会对其他人产生保护作用？恢复期 SARS-CoV-2 (COVID-19) 血清与来自中东呼吸综合征冠状病毒 (MERS-CoV) 的肽的交叉反应性进行了测试，该肽具有 74% 的同源性。我们的结果显示与 MERS-CoV 刺突蛋白的七肽重复 2 (HR2) 结构域的肽具有显着的交叉反应性。在 COVID-19 之前收集的 47 名经验证的血清阳性恢复期 COVID-19 患者的血清样本和 40 名对照患者的血清样本用于建立与 MERS-CoV 肽的交叉结合反应性。显着更强的结合力（p 与对照组相比，在康复期 COVID-19 患者中观察到 IgG 抗体 < 0.0001）。在 ELISA 中，MERS-CoV 肽有助于通过血液样本中抗体的存在来区分 COVID-19 后人群和未感染人群。这表明在 SARS-CoV-2 感染期间建立的多克隆抗体可以识别并可能降低 MERS-CoV 和其他冠状病毒感染的严重程度。刺突蛋白结构域的高度同源性也表明相反的效果可能是真实的：冠状病毒感染会产生对 SARS-CoV-2 有效的交叉反应性抗体。收集的数据证明，尽管核心 HR2 区域隐藏在天然病毒构象中，但它在细胞进入过程中的暴露使其具有高度免疫原性。由于先前描述了该区域的抑制肽，