The known IgG FcRs primarily mediate inflammation by interacting with IgG1, even though IgG2 isotypes tend to be more pathogenic. Nimmerjahn et al. (2005) have just identified a novel Fc gamma R that binds IgG2 but not IgG1, potentially explaining differences in biological activity that are seen with various IgG isotypes (Nimmerjahn et al., 2005).