Genetically modified non-human animals and methods and compositions for making and using them are provided, wherein the genetic modification comprises a deletion of the endogenous low affinity Fc³R locus, and wherein the mouse is capable of expressing a functional FcR³-chain. Genetically modified mice are described, including mice that express low affinity human Fc³R genes from the endogenous Fc³R locus, and wherein the mice comprise a functional FcR³-chain. Genetically modified mice that express up to five low affinity human Fc³R genes on accessory cells of the host immune system are provided.
