The evaluation of the immune status of COVID-19 recovered subjects with persistent abnormal lung CT after one year: A longitudinal cohort study

OBJECTIVES: COVID-19 is an immune-related disease caused by novel Coronavirus SARS-COV-2. Lung lesions persist in some recovered patients, making long-term follow-up monitoring of their health necessary. The mechanism of these abnormalities is still unclear. In this study, the immune status was observed to explore the immune mechanism of persistent lung CT abnormalities in one-year COVID-19 recovered subjects. METHODS: One-year follow-up of 73 recovered patients from COVID-19 confirmed in Taizhou City, Zhejiang Province, was conducted to collect laboratory indicators such as blood immune cells, cytokines, complement series, immunoglobulin, and lung imaging; According to the results of lung CT, 60 patients were divided into normal CT group (n = 40) and abnormal CT group (n = 20). We compared the dynamic changes of immune indexes at three timepoints namely onset (T1), discharge (T2), and 1-year follow-up (T3), and studied the relationship between immune indexes and pulmonary sequelae. RESULTS: Compared with the healthy control, there was no significant difference in immune-related indexes, and immune levels had recovered. Patients with elder age, high BMI, severe patients, and those with underlying diseases (hypertension or diabetes) had a higher CT abnormal rate after recovery. Longitudinal observation showed that immunoglobulin increased first and then decreased, immune cell TBNK decreased in the onset period and increased in the recovery period, cytokine level increased significantly in the onset period and decreased to the normal level in the recovery period, and complement series C1q, C3 and C4 increased at the onset and decreased during the one-year follow-up. Complement C3 remained at a high level in the CT abnormal group (CT normal group vs CT abnormal group; P = 0.036). Correlation analysis showed that C3 negatively correlated restrictive ventilation index (TLC-He (ratio) (r = −0.302, P = 0.017). The above results suggest that complement C3 is a negative factor correlating abnormal pulmonary function 1 year after the recovery. CONCLUSION: After one year recovering from COVID-19, the subjects were with stable immune indicators. High levels of complement C3 were associated with persistent lung abnormalities in COVID-19 recovered subjects.