Antigen-binding protein directed against epitope in the CH1 domain of human IgG antibodies

The present disclosure relates to a method for the purification of a human IgG-CH1 domain comprising molecule using an antigen-binding protein that is capable of binding to an epitope that is comprised in the CH1 domain of each of human IgG1, human IgG2, human IgG3 and human IgG4. The disclosure further relates to the antigen-binding proteins that can be used in the method of the disclosure. The frame-work regions of the antigen-binding proteins of the invention preferably correspond to those of antibodies that naturally are devoid of light chains as may e.g. be found in camelids. The disclosure further relates to nucleic acids that encode such antigen-binding proteins, to immunoadsorbent materials that comprise such proteins, and to the uses of such immunoadsorbent materials for the purification of IgG-CH1 domain containing molecules from a variety of species.