Longitudinal Observation of Humoral Immune Response Along with Coagulation and InflammationSpecific Clinical Biomarkers in A COVID-19 Convalescent Donor Cohort |Biomedgrid

In this longitudinal study on convalescent COVID-19 donors, we assessed the humoral response to SARS-CoV-2 and biomarkers of coagulation, fibrinolysis, inflammation, and endothelial function associated with disease severity and prognosis. Plasma donations and donor characteristics were collated for 26 adult convalescent donors over 168 days after initial molecular diagnosis of the infection. Parallel monitoring of live virus neutralization test, surrogate VNT, SARS-CoV-2 specific serology markers, and further biomarkers were evaluated. Neutralizing antibodies were found in all donors with an initial median titre of 510.5 International Unit/milliliter (WHO unit) and decreasing titer (2.7-fold) over the study period. Strong positive correlation was revealed between cellular VNT and sVNT as well as high-throughput anti-S1-RBD-SARS-CoV-2 antibody immunoassays. NAb, anti-spike S1, and anti-S1-RBD antibody levels significantly correlated with disease severity. Prolonged, markedly elevated D-dimer and prothrombin fragment 1+2 levels were assessed in 26.9% of the convalescent donors. Although acute-phase biomarkers and reactants of the complement system and endothelial function were in the normal range in most convalescents, we identified C-reactive protein, C3, and C4 being associated with severity. We observed robust but decreasing NAb progression and anti-S1/S1-RBD antibody levels correlated to disease severity. Donors with long-term symptoms had significant lower anti-S1, anti-S1-RBD, and anti-NC antibody, D-dimer, and Fibrinogen levels and higher SAA levels, compared to donors that fully recovered. While inflammatory biomarkers returned to normal in most convalescents, the persistence of abnormal D-dimer and F1+2 levels need further investigation to probe connection with pathogenesis.