To better understand humoral immunity following SARS-CoV-2 infection, 114 hospitalised COVID-19 patients with antibody monitored over 8 weeks from symptom onset were retrospectively investigated. A total of 445 serum samples were assessed via chemiluminescence immunoassay. Positive rate of virus-specific IgM reached up to over 80% from the second week to the eighth week after symptom onset, then declined quickly to below 30% in the twelfth week. Concentrations of IgG remained high for at least 3 months before subsequently declining. As compared with the non-severe group, serum IgM level from week 3 to week 8 was significantly higher among the patients with severe clinical symptoms (P = 0.012) but not IgG (P = 0.053). Serum IgM level from week 3 to week 8 was correlated with positive virus RNA test (r = 0.201, P = 0.044), albumin level (r = -0.295, P = 0.003), lactic dehydrogenase (LDH) level (r = 0.292, P = 0.003), alkaline phosphatase (ALP) level (r = 0.254, P = 0.010), C-reactive protein (CRP) level (r = 0.281, P = 0.004) during the same course, while serum IgG level was correlated with age (r = 0.207, P = 0.038). This presented results provide insight into duration of SARS-CoV-2 antibodies and interaction between the virus and host systems.
Keywords: COVID-19; Humoral immunity; Illness severity; Immunoglobulin G; Immunoglobulin M; SARS-CoV-2.
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