Immunolocalization of osteonectin in avian tibial dyschondroplastic cartilage

Osteonectin is an acidic calcium-binding protein found in cartilage, bone matrix, vascular endothelium, and areas of tissue repair. Using immunocytochemistry, osteonectin has been localized in all zones of the normal avian epiphyseal growth plate with notably high amounts in the hypertrophic zone. In the proximal portion of this zone the staining was intracellular, while in the distal calcifying portion of the hypertrophic zone staining was both intracellular and extracellular. Osteonectin was also detected in the growth plate associated with lesions of chickens with tibial dyschondroplasia (TD). Intense intracellular staining was observed in hypertrophic chondrocytes proximal to the lesion; staining was markedly diminished in the TD lesion; extracellular matrix was devoid of staining. Staining intensity was high along the peripheral edges of the lesion that were undergoing vascularization and resorption. This was the only area in the dysplastic cartilage where staining was observed in the extracellular matrix as well as intracellularly. Similar patterns were viewed in all TD lesions examined, whether they were spontaneous or induced by dietary treatments or genetic selection.