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 FCYR LOCUS, AND WHEREIN THE MOUSE IS CAPABLE OF EXPRESSING A FUNCTIONAL FCRY-CHAIN. GENETICALLY MODIFIED MICE ARE DESCRIBED, INCLUDING MICE THAT EXPRESS LOW AFFINITY HUMAN FCYR GENES FROM THE ENDOGENOUS FCYR LOCUS, AND WHEREIN THE MICE COMPRISE A FUNCTIONAL FCRY-CHAIN. GENETICALLY MODIFIED MICE THAT EXPRESS UP TO FIVE LOW AFFINITY HUMAN FCYR GENES ON ACCESSORY CELLS OF THE HOST IMMUNE SYSTEM ARE PROVIDED.
