Genetically modified non-human animals are provided that comprise an immunoglobulin heavy chain locus comprising an unrearranged human heavy chain variable region nucleotide sequence comprising an addition of at least one histidine codon or a substitution of at least one endogenous non-histidine codon with a histidine codon. Compositions and methods for making the genetically modified non-human animals as described herein are provided. Non-human animals capable of expressing an antigen-binding protein characterized by pH-dependent antigen binding, enhanced recyclability and/or enhanced serum half-life are also provided.
