An isolated protein that comprises a heavy chain variable domain sequence and a light chain able domain sequence that can form an antigen binding site that binds to human TWEAK, wherein the protein has one or more of the following properties: (a) the protein competes with P2D10, huP2D10-l, or huP2D10-2 for binding to human TWEAK (b) the protein binds to an epitope on human TWEAK that overlaps with the epitope bound by P2D10, huP2D10-l, or huP2D10-2 (c) the heavy and/or light chain variable domain sequence is encoded by a nucleic acid that hybridizes under high stringency conditions to the complement of a nucleic acid encoding P2D10, huP2D10-l, or huP2D10-2 (d) the heavy and/or light chain variable domain sequence is at least 80% identical to the amino acid sequence of the corresponding variable domain of P2D10, huP2D10-l, orhuP2D10-2 (e) the heavy and light chain variable domain sequence is at least 95% identical in the CDR regions (collectively) to the CDR regions of the heavy and light chain variable domains of P2D10, huP2D10-l, or huP2D10-2 or (f) at least 95% identical in the framework regions (collectively) to the framework regions of the heavy and light chain variable domains of P2D10, huP2D10-l, or huP2D10-2.
