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Infect Immun, March 1998, p. 932-937, Vol. 66, No. 3
0019-9567/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.

Regulation of Periodontal Ligament Cell Functions by Interleukin-1

Sudha Agarwal,^1,* Charu S. Chandra,² Nicholas P. Piesco,¹ Herman H. Langkamp,¹ Lathe Bowen,² and Coskun Baran³

Division of Oral Biology¹ and Division of Dental Surgical Sciences,² University of Pittsburgh, Pittsburgh, Pennsylvania 15261, and Department of Periodontology, University of Gazi, Ankara, Turkey³

Received 13 May 1997/Returned for modification 7 July 1997/Accepted 16 December 1997

Periodontal ligament (PDL) cells maintain the attachment of the tooth to alveolar bone. These cells reside at a site in which they are challenged frequently by bacterial products and proinflammatory cytokines, such as interleukin-1 (IL-1), during infections. In our initial studies we observed that IL-1 down-regulates the osteoblast-like characteristics of PDL cells in vitro. Therefore, we examined the functional significance of the loss of the PDL cell's osteoblast-like characteristics during inflammation. In this report we show that, during inflammation, IL-1 can modulate the phenotypic characteristics of PDL cells to a more functionally significant lipopolysaccharide (LPS)-responsive phenotype. In a healthy periodontium PDL cells exhibit an osteoblast-like phenotype and are unresponsive to gram-negative bacterial LPS. Treatment of PDL cells with IL-1 inhibits the expression of their osteoblast-like characteristics, as assessed by the failure to express transforming growth factor 1 (TGF-1) and proteins associated with mineralization, such as alkaline phosphatase and osteocalcin. As a consequence of this IL-1-induced phenotypic change, PDL cells become responsive to LPS and synthesize proinflammatory cytokines. The IL-1-induced phenotypic changes in PDL cells were transient, as removal of IL-1 from PDL cell cultures resulted in reacquisition of their osteoblast-like characteristics and lack of LPS responsiveness. The IL-1-induced phenotypic changes occurred at concentrations that are frequently observed in tissue exudates during periodontal inflammation (0.05 to 5 ng/ml). The results suggest that, during inflammation in vivo, IL-1 may modulate PDL cell functions, allowing PDL cells to participate directly in the disease process by assuming LPS responsiveness at the expense of their normal structural properties and functions.

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^* Corresponding author. Mailing address: Division of Oral Biology, 579 Salk Hall, University of Pittsburgh, Pittsburgh, PA 15261-1964. Phone: (412) 648-8951. Fax: (412) 648-8219. E-mail: sagar+{at}pitt.edu.

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