Fab fragment antibodies are generated by papain digestion of whole IgG antibodies to remove the entire Fc portion, including the hinge region. These antibodies are monovalent, containing only a single antigen binding site. The molecular weight of Fab fragments is about 50 kDa.-Based on antigen-binding assay, Western blot and/or ELISA, the antibody reacts with the VHH domain of heavy chain (HC) alpaca IgG, subclasses 2 and 3; and with the VHH domain of llama IgG, subclasses 2 and 3. No antibody was detected against non-immunoglobulin serum proteins. The antibody has been tested by ELISA and/or solid-phase adsorbed to ensure minimal cross-reaction with bovine, human, mouse, rabbit, and rat serum proteins, but it may cross-react with immunoglobulins from other species.