Characteristics and roles of SARS‐CoV‐2 specific antibodies in patients with different severities of COVID‐19

Huang, Zhifeng; Chen, Hao; Xue, Mingshan; Huang, Huimin; Zheng, Peiyan; Luo, Wenting; Liang, Xueqing; Sun, Baoqing; Zhong, Nanshan

BACKGROUND: The diagnosis of COVID‐19 relies mainly on viral nucleic acid detection, but false negatives can lead to missed diagnosis and misdiagnosis. SARS‐CoV‐2‐specific antibody detection is convenient, safe, and highly sensitive. IgM and IgG are commonly used to serologically diagnose COVID‐19; however, the role of IgA is not well known. We aimed to quantify the levels of SARS‐CoV‐2‐specific IgM, IgA, and IgG antibodies, identify changes in them based on COVID‐19 severity, and establish the significance of combined antibody detection. METHODS: COVID‐19 patients, divided into a severe & critical group and a moderate group, and non‐COVID‐19 patients with respiratory disease were included in this study. A chemiluminescence method was used to detect the levels of SARS‐CoV‐2‐specific IgM, IgA, and IgG in the blood samples from the three groups. Epidemiological characteristics, symptoms, blood test results, and other data were recorded for all patients. RESULTS: Compared to the traditional IgM–IgG combined antibodies, IgA–IgG combined antibodies are better for diagnosing COVID‐19. During the disease process, IgA appeared first and disappeared last. All three antibodies had significantly higher levels in COVID‐19 patients than in non‐COVID‐19 patients. IgA and IgG were also higher for severe & critical disease than for moderate disease. All antibodies were at or near low levels at the time of tracheal extubation in critical patients. CONCLUSIONS: Detection of SARS‐CoV‐2‐specific combined IgA–IgG antibodies is advantageous in diagnosing COVID‐19. IgA detection is suitable during early and late stages of the disease. IgA and IgG levels correspond to disease severity.