Biochem. Soc. Symp. 70, 107–114 (Printed in Great Britain) © 2003 Biochemical Society 107 9 Use of anti-neoepitope antibodies for the analysis of degradative events in cartilage and the molecular basis for neoepitope specificity John S. Mort*† 1 , Carl R. Flannery‡ 2 , Joe Makkerh* 3 , Joanne C. Krupa* and Eunice R. Lee*† *Shriners Hospital for Children, Montreal, Quebec, Canada, †Department of Surgery, McGill University, Montreal, Quebec, Canada, and ‡Connective Tissue Biology Laboratory, Cardiff School of Biosciences, University of Cardiff, Cardiff, Wales, U.K. Abstract Degradation of the cartilage proteoglycan, aggrecan, is an essential aspect of normal growth and development, and of joint pathology. The roles of different proteolytic enzymes in this process can be determined from the sites of cleavage in the aggrecan core protein, which generates novel termini (neoepitopes). Antibodies specific for the different neoepitopes generated by such cleavage events provide powerful tools with which to analyse these processes. The same approach can be used to differentiate the processed, active forms of proteases from their inactive pro-forms. Since the proteolytic pro- cessing of these enzymes requires the removal of the inhibitory pro-region, it also results in the generation of N-terminal neoepitopes. Using the newborn rat long bone as a model system, it was shown that the active form of ADAMTS-4 [ADAM (a disintegrin and metalloproteinase) with throm- bospondin motifs-4], but not ADAMTS-5, co-localizes with the aggrecan cleavage neoepitopes known to be produced by this metalloproteinase. Thus, 1 To whom correspondence should be addressed: Joint Diseases Laboratory, Shriners Hospital for Children, 1529 Cedar Avenue, Montreal, Quebec, Canada H3G 1A6 (e- mail jmort@shriners.mcgill.ca). 2 Present address: Wyeth Research, 200 Cambridge Park Drive, Cambridge, MA, U.S.A. 3 Present address: Montreal Neurological Institute, McGill University, Montreal, Quebec, Canada.