Type IX collagen distribution in human periodontal ligament

The periodontal ligament (PDL) is unique in that it provides significant resistance to compressive loads as well as tensile stresses. Some of this can be attributed to the arrangement of the PDL principal fibers; however, the viscoelastic properties that help the tissue withstand compressive loads are not characteristic of purely tendonous tissues, which contain type I collagen as the major component of the fibrils. Articular cartilage, which is a tissue that undergoes compressive loading, utilizes type II collagen as the predominant fibrillar collagen. Collagen type IX, a member of the FACIT collagen group is covalently bound to type II collagen fibrils in cartilage and other type II-containing tissues. There has also been evidence of type IX collagen being expressed in the healing alveolar bone after tooth extraction. The resistance to compressive loads of the PDL as well as the presence of type IX collagen in the healing extraction socket leads to question whether or not type IX collagen can be founding the human PDL. Objectives: the purpose of this study was to localize the distribution of type IX collagen in the human PDL utilizing immunohistochemistry. Methods: Healthy human premolars that were extracted for orthodontic purposes were fixed in ethanol, decalcified, paraffin embedded and sectioned. Immunostaining was performed using a commercially available á(1)IX monoclonal antibody and a labeled secondary antibody. Immunostaining above background was noted in the PDL. Results: The distribution of the signal was diffuse and similar to that seen in previous work with immunohistochemistry of extraction sockets. Conclusion: Type IX collagen is present pericellularly in the human PDL. This study was supported by the Baylor Oral Health Foundation.