Non-human animals comprising a human or humanized IL-4 and/or IL-4Rα nucleic acid sequence are provided. Non-human animals that comprise a replacement of the endogenous IL-4 gene and/or IL-4Rα gene with a human IL-4 gene and/or IL-4Rα gene in whole or in part, and methods for making and using the non-human animals, are described. Non-human animals comprising a human or humanized IL-4 gene under control of non-human IL-4 regulatory elements is also provided, including non-human animals that have a replacement of non-human IL-4-encoding sequence with human IL-4-encoding sequence at an endogenous non-human IL-4 locus. Non-human animals comprising a human or humanized IL-4Rα gene under control of non-human IL-4Rα regulatory elements is also provided, including non-human animals that have a replacement of non-human IL-4Rα-encoding sequence with human or humanized IL-4Rα-encoding sequence at an endogenous non-human C IL-4Rα locus. Non-human animals comprising human or humanized IL-4 gene and/or IL-4Rα sequences, wherein the non-human animals are rodents, e.g., mice or rats, are provided.
