key: cord-0813012-rnq1hfsj
authors: Liu, Bingfeng; Shi, Yaling; Zhang, Wanying; Li, Rong; He, Zhangping; Yang, Xiaofan; Pan, Yuejun; Deng, Xilong; Tan, Mingkai; Zhao, Lingzhai; Zou, Fan; Zhang, Yiwen; Pan, Ting; Zhang, Junsong; Zhang, Xu; Xiao, Fei; Li, Fang; Deng, Kai; Zhang, Hui
title: Recovered COVID-19 patients with recurrent viral RNA exhibit lower levels of anti-RBD antibodies
date: 2020-09-16
journal: Cell Mol Immunol
DOI: 10.1038/s41423-020-00528-0
sha: 210474118925f8567f2ebb7d99675a7a46b587c0
doc_id: 813012
cord_uid: rnq1hfsj

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Plasma samples were collected from these 47 patients with COVID-19 at the time of convalescence and assessed for antibodies against the following SARS-CoV-2 proteins: the spike glycoprotein (S); the receptor-binding domain (RBD); conserved heptad repeats (HR1-HR2) in the S2 domain; and the nucleocapsid (N), membrane (M), and envelope (E) proteins. The concentrations of IgG secreted in response to these SARS-CoV-2 proteins varied in different patients, with detection rates of 100.0% (47/47), 83.0% (39/47), 97.9% (46/47), 100.0% (47/47), 55.3% (26/47), and 21.3% (10/47) for the S, RBD, HR1-HR2, N, M, and E proteins, respectively ( Fig. 1a; Fig. S2 ). The detection rates of IgM to the S, RBD, HR1-HR2, and N proteins were 100.0% (47/47), 95.7% (45/47), 83.0% (39/47), and 100% (47/47), respectively ( Fig. 1b; Fig. S2 ). Notably, significantly higher levels of SARS-CoV-2-specific IgG and IgM developed to the S and N proteins (Fig. 1a, b) .

To evaluate the effect of specific antibodies on RP status, we compared the levels of anti-SARS-CoV-2 IgG to the S, RBD, HR1-HR2, N, and M proteins in these patients during their convalescent period ( Fig. 1c; Fig. S3 ). The results showed that RP patients induced significantly lower levels of anti-RBD IgG than PRN patients (p = 0.013) (Fig. 1c) . As all of these RP patients were in a moderate condition before recovery, the PRN patients were further classified as moderate (28 patients) or severe (11 patients) according to their symptoms before recovery. The levels of anti-RBD IgG in RP patients were still significantly lower than those of either PRN-severe or PRN-moderate patients (p = 0.012 and p = 0.040, respectively; Fig. 1d ). In addition, the patients with severe symptoms within the PRN group were more likely to induce higher levels of anti-RBD IgG (p = 0.012; Fig. 1d ), which is consistent with previous reports. 12 In contrast, there were no significant differences either in IgG to other viral proteins or in IgM between PRN and RP patients (Fig. 1c, e; Figs. S4, S5) , suggesting that the humoral response to RBD rather than to other regions of the S protein or the full-length S protein might have played an important role in preventing viral rebound during recovery.

Furthermore, we observed that the titers of IgG to RBD among these recovered patients positively correlated with the spikebinding antibodies targeting the S, HR1-HR2, and N proteins (r = 0.71, p < 0.0001; r = 0.53, p < 0.0001; and r = 0.33, p = 0.022, respectively) but not with the M or E proteins (Fig. S6a) . Moreover, The Y-axis represents optical density units at OD450 nm, and the X-axis represents reciprocal plasma dilutions. c Normalized OD450 nm values of the anti-SARS-CoV-2 IgG to the RBD, S, HR1-HR2, N, M, and E proteins are compared between PRN and RP patients. The P value was calculated using a two-tailed Mann-Whitney U test or unpaired Student's t test. d Normalized OD450 nm values of the anti-RBD IgG were compared between PRN-severe, PRN-moderate, and RP patients. The P value was calculated using a two-tailed Mann-Whitney U test or unpaired Student's t test. e Normalized OD450 nm values of the anti-RBD IgM were compared between PRN and RP patients. The P value was calculated using a two-tailed Mann-Whitney U test the level of IgM to the RBD protein among these recovered patients also correlated with the S, HR1-HR2, and N proteins (r = 0.67, p < 0.0001; r = 0.56, p < 0.0001; and r = 0.60, p < 0.0001, respectively) (Fig. S6b) . In addition, a positive correlation was also observed between age and IgG level to the RBD, S, HR1-HR2, and N proteins (r = 0.38, P = 0.0077; r = 0.40, P = 0.0055; r = 0.45, P = 0.0017; and r = 0.44, P = 0.0021, respectively; Fig. S7 ), indicating the important role of age in the generation of specific binding antibodies. 13 Because of the lack of clinical characteristics and the unknown significance of RP patients, it is critical to provide comprehensive serological profiling to guide the management of recovered COVID-19 patients after discharge. An important feature of the RP patients was their younger age than that of the PRN patients, and the ages of these recovered patients positively correlated with titers of IgG to the RBD protein. 1, 2, 13 These observations are consistent with the conclusion that the level of IgG to the RBD protein in RP patients is significantly lower than that in the PRN group.

Based on our findings, the anti-RBD IgG level could serve as an indicator of RP status. To minimize the risk of possible viral rebound and retransmission during the current pandemic, close monitoring of anti-RBD IgG levels at viral shedding and a longterm follow-up of patients with lower levels of RBD antibodies is needed. Moreover, the relationship between anti-SARS-CoV-2 IgG titers and RP status suggests that the interplay between the virus and the host immune response in coronavirus infections should be further investigated for the development of more accurate diagnostic technologies and effective vaccines against viral infection.

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The online version of this article (https://doi.org/10.1038/s41423-020-00528-0) contains supplementary material.Competing interests: The authors declare no competing interests.