COVID-19 in Tunisia (North Africa): IgG and IgG subclass antibody responses to SARS-CoV-2 according to disease severity

Coronavirus disease 2019 (COVID 19) expresses a wide spectrum of disease severity. We investigated the profile of IgG and IgG subclass antibody responses to SARS CoV 2 in Tunisian patients with COVID 19 according to disease severity (86 patients with severe disease and 63 with mild to moderate disease). Two in house developed ELISA with excellent performance were used to test for antibodies to the nucleocapsid (N) protein and the receptor-binding domain of the spike antigen (S-RBD) of SARS CoV 2. IgG, IgG1 and IgG3 antibodies were significantly higher in patients with severe disease compared to non-severe disease. Antibodies to S-RBD or the N protein were dominated by IgG1 and IgG3 or IgG1/IgG3 and IgG2 subclasses respectively. In patients with severe disease, IgG antibodies' appearance to S RBD was delayed compared to the N protein. IgG subclass imbalance may reflect the pathophysiology of COVID 19 and may herald disease aggravation. This study brings information on the immune responses to SARS CoV 2 in North African patients and completes the picture drawn on COVID 19 in different African populations and worldwide.