Abstract: The present disclosure relates to methods for reducing the oxidation level of cysteine residues in recombinant polypeptides such as anti-IL-17 antibodies during cell culture (e.g., a preparation of secukinumab antibodies) that have been recombinantly produced by mammalian cells. Also provided are purified preparations of recombinant polypeptides such as anti-IL-17 antibodies or antigen binding fragments thereof produced by such methods, e.g, purified preparations of secukinumab. Also provided are purified preparations of recombinant polypeptides produced by such methods wherein the level of active recombinant polypeptide in the preparation is high.