IGHG3 and viral infectious disease: Here, the predominance of IgG3 in SARS-CoV-2 infection may be explained by the fact that generally, IgG3 appears early in viral infections because it is encoded in the most upstream (5ʹ) constant (C) γ region of the immunoglobulin heavy chain gene locus on chromosome 14 and elicits classical complement pathway activation.