COVID-19 patient serum IgG glycosylation differs depending on disease severity and may influence immune receptor binding

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) caused the current global coronavirus disease 2019 (COVID-19) pandemic. SARS-CoV-2 infection typically stimulates production of serum antibodies against various viral antigens (Ags) over time and the antibody level is associated with neutralisation and clearance as immune receptors and effector functions are engaged1. However antibody-Ag complex immune receptor binding has not yet been associated with disease severity and phagocytosis. Serum IgG, IgM and IgA were purified from patient sera with mild, moderate and severe COVID-19 and from pre-pandemic healthy donor sera. Core fucosylation in the severe disease cohort serum IgG was revealed by lectin microarray profiling and HPLC analysis, which was absent in the other cohorts. Serum antibodies were profiled for Ag binding on a recombinant SARS-CoV-2 protein microarray. For serum IgG, there was a significant association between disease severity and binding intensity for the spike protein fragment S1 expressed in HEK (S1 HEK) and Sf21 cells (S1 Sf21) and the nucleocapsid protein (NP) expressed in E. coli (NP Ecoli). NP Ecoli and NP HEK bound most intensely to the immune receptors TLR4 and C1q while S1 HEK and S1 Sf21 bound most intensely to DC-SIGN and C1q, indicating activation of different immune pathways. Serum IgG-Ag immune complexes modulated immune receptor interactions, with most intense binding with FcRI. Lectin microarray profiling indicated that the binding modulation may be related to Ag and IgG glycosylation. Higher binding to CD64 and greater phagocytosis was associated with severe disease IgG.