The present invention relates to antagonists or inhibitors, which bind selectively to selected bone factors, RANKL/OPGbp, OPG, Sclerostin, DKK1, cathepsin K and regulate the interaction between these ligands and their testicular corresponding receptors. In particular, the present invention relates to an antibody or antigen binding domain, fragment or derivative thereof, immunoreactive with one of the listed bone factors peptide for use in the treatment, prevention or alleviation of male infertility or reduced male fertility such as oligospermia or azospermia.
