Different pathogens may induce variable IgG subclassresponses.[15] Viral infections induce an antibody responsepredominantly consisting of IgG1 and IgG3 while bacterialinfections are associated with the induction of IgG2 and IgG4subclasses.[16] An apparent deficiency of IgG2 has been reportedin patients infected with the H1N1 virus and this correlatedwith worsened outcome.[17] A study from Australia[11] also foundevidence of an IgG2 subclass deficiency in patients with severeH1N1 infections and the IgG2 deficiency was considered to bethe underling risk factor for severity. This evidence concerns the gene IGHG3 and viral infectious disease.