FCGR2A and acute disseminated encephalomyelitis: The YTE mutation in the IgG4 Fc moiety could reduce the binding to FcγR, and so decrease the risk of ADE effect (Liu et al., 2019; Graham, 2020), and may increase the binding to FcRn, and so enable a longer half-life, and increased distribution to the respiratory system mucosa in comparison with IgG1 antibodies (Dall'Acqua et al., 2006; Guo et al., 2021; Tabrizi et al., 2019; Spiess et al., 2013).