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

ABSTRACT

：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.