Immunohistochemical demonstration of bone morphogenetic protein-2 and transforming growth factor-beta in the ossification of the posterior longitudinal ligament of the cervical spine.

To clarify the mechanism of ossification of the posterior longitudinal ligament, immunohistochemical localization of bone morphogenetic protein-2 and transforming growth factor-beta was examined using surgical specimens of ligament tissues from an affected patient. Two polyclonal antibone morphogenetic protein-2 antibodies and an anti-human transforming growth factor-beta antibody were used as primary antibodies. Bone morphogenetic protein-2 and transforming growth factor-beta were present in ossified matrix and chondrocytes of adjacent cartilaginous areas of ossification of the posterior longitudinal ligament. Although immunostaining with antibone morphogenetic protein-2 antibodies also was observed in mesenchymal cells with fibroblastic features in the immediate vicinity of the cartilaginous areas, no staining could be detected with anti-human transforming growth factor-beta antibody in these cells. The presence of these factors were specific for the ossified ligament because no immunostaining was observed after using antibodies in the posterior longitudinal ligament at unossified levels from the same patient. It is suggested that bone morphogenetic protein-2 and transforming growth factor-beta play important roles in the development of ossification of the posterior longitudinal ligament and that bone morphogenetic protein-2 may act as an initiating factor in the development of ossification of the posterior longitudinal ligament by stimulating differentiation of mesenchymal progenitor cells. Transforming growth factor-beta may stimulate bone formation at a later stage of the process of ectopic ossification.