IGHG3 and rubella: The IgG3 subclass is usually a significant component of virus-induced IgG, typically comprising 12–50 % of circulating virus-specific IgG for measles, rubella, HTLV-1 and hepatitis B in seropositive individuals (Gregorek et al., 2000; Kalvenes et al., 1996; Lal et al., 1993; Toptygina et al., 2005).