Characterization of anti-viral immunity in recovered individuals infected by SARS-CoV-2

Chen Dong; Ling Ni; Fang Ye; Meng-Li Chen; Yu Feng; Yong-Qiang Deng; Hui Zhao; Peng Wei; Jiwan Ge; Xiaoli Li; Lin Sun; Pengzhi Wang; Peng Liang; Han Guo; Xinquan Wang; Cheng-Feng Qin; Fang Chen

Using sera from patients and healthy donors, IgG and IgM against SARS-CoV-2 NP, main protease and S-RBD antigens were analyzed. There was no significant antibody response to main protease in sera from several patients (data not shown), suggesting that it may not serve as an antigen for humoral immunity. We thus focused on NP and S-RBD. The serum from a patient and human AB serum were titrated in order to determine optimal dilutions (data not shown). Dilution of 1:50 was used for IgM and 1:150 for IgG. NP-and S-RBD-specific IgM and IgG antibodies were both detected in the sera of newly discharged patients, compared with healthy donor groups ( Figure 1A ). Anti-SARS-CoV-2 IgG antibodies were also more obviously observed than IgM in the follow-up patients (#7-12), when compared with healthy donors ( Figure 1A ). Taken together, these findings indicate that COVID-19 patients mounted IgG and IgM responses to SARS-CoV-2 proteins, especially NP and S-RBD, and also suggest that infected patients could maintain their IgG levels, at least for two weeks.