Kinetics of IgM and IgG antibody specific to SARS-CoV-2 nucleocapsid and spike proteins

：Objective To study the kinetics of IgM and IgG antibodies based on nucleocapsid（N） and spike（S） protein of SARS-Co V2-in COVID-19 patients. Methods Immunofluorescent kits were used to detect N and S protein specific IgM and IgG antibodies from Jan.21 to Feb.11, 2020 for the 60 hospitalized COVID-19 patients（48 mild, 12 severe cases） with a total of 290 plasma samples collected 9 weeks after the onset of the disease. Results The level of antibodies specific for S protein varied significantly with the course of disease（Ig M from 27.32 to 110.10 TU/ml, IgG from 56.85 to 135.00 TU/ml）, but not for N protein.Higher level of Ig M/Ig G antibodies specific to S protein was observed during the 2-7 week than that to N protein.The seropositive rate of antibodies gradually increased during the early stage of disease.IgM/IgG antibodies specific to N protein changed from 12.50% at the first week to peak level（51.72% and 86.21% respectively） at the 4 th week and those for S protein from 25.00% and 14.58% to 100.00%, and then declined.The seropositive rate of Ig M antibody specific to S protein was higher than that for N protein during 2-8 th week and that for Ig G antibody at 2, 3, 4, 6 and 7 th week.The seropositive rate of Ig G antibody specific to N protein in severe patients at the third week was higher than that in mild patients（100.00% vs 59.52%,χ2=9.67, P=0.001 9）, and the same as to Ig G antibody for S protein at the second week after disease onset（80.00% vs 46.58%, χ2=5.57, P=0.018 2）. Conclusions SARS-Co V2-S protein can induc stronger antibody response than N protein, and the antibody level was related to the severity of the disease.

Kinetic Characteristics of Neutralizing Antibody Responses Vary among Patients with COVID-19.

OBJECTIVE: The coronavirus disease 2019 (COVID-19) pandemic continues to present a major challenge to public health. Vaccine development requires an understanding of the kinetics of neutralizing antibody (NAb) responses to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). METHODS: In total, 605 serum samples from 125 COVID-19 patients (from January 1 to March 14, 2020) varying in age, sex, severity of symptoms, and presence of underlying diseases were collected, and antibody titers were measured using a micro-neutralization assay with wild-type SARS-CoV-2. RESULTS: NAbs were detectable approximately 10 days post-onset (dpo) of symptoms and peaked at approximately 20 dpo. The NAb levels were slightly higher in young males and severe cases, while no significant difference was observed for the other classifications. In follow-up cases, the NAb titer had increased or stabilized in 18 cases, whereas it had decreased in 26 cases, and in one case NAbs were undetectable at the end of our observation. Although a decreasing trend in NAb titer was observed in many cases, the NAb level was generally still protective. CONCLUSION: We demonstrated that NAb levels vary among all categories of COVID-19 patients. Long-term studies are needed to determine the longevity and protective efficiency of NAbs induced by SARS-CoV-2.

Kinetics of SARS-CoV-2 antibodies in COVID-19 patients and relationship with severity of disease

Objective To study the kinetics of SARS-CoV-2 antibodies in COVID-19 patients and the correlation with disease severity. Methods A total of 290 plasma samples were collected from 60 hospitalized patients including 48 mild cases and 12 severe cases within 63 days after disease onset in Guangzhou Eighth People′s Hospital affiliated to Guangzhou Medical University during January 21 to April 11, 2020.SARS-CoV-2 specific antibodies were determined by four commercial colloidal gold serologic reagents validated by National Medical Products Administration in China. Results The seropositive rate ranged from 19.23% to 34.62% by four assays within one week after disease onset, and rapidly increased within the following two weeks.The seropositive rates were 52.27% to 68.18% and 83.05% to 98.31%, respectively.IgM antibody peaked within the fourth week and maintained high level for 1 to 2 weeks, and decreased significantly until the 9 th week.But no obvious decreasing trend of the seropositive rate of IgG antibody was observed during two months after disease onset.The seropositive rates of antibodies between mild and severe cases showed no statistical difference.Four assays demonstrated a sensitivity of 78.33%to 91.67%in 60 COVID-19 patients.The difference was statistically significant between the highest and the lowest values（χ2=4.183,P=0.041）． Conclusions The colloidal gold serologic reagents show good sensitivity during the late stage of disease but not at the early stage.There is no correlation between seropositive and disease severity.The sensitivity of different reagents is different