Immunolocalization of bone‐resorptive cytokines in rat pulp and periapical lesions following surgical pulp exposure

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Abstract
The bone‐resorptive cytokines interleukin 1 (IL‐1) and tumor necrosis factor (TNF) have been implicated in the pathogenesis of many chronic inflammatory diseases, including pulpitis and apical periodontitis. To further elucidate their role in these disorders, we have identified cells that express IL‐1α and TNFα in infected pulps and in developing rat periapical lesions after surgical pulp exposure. As detected by immunohistochemistry, IL‐1α‐ and TNFα‐positive cells were present as early as 2 days after pulp exposure in both the pulp and periapical region. The numbers of cytokine‐expressing cells increased up to day 4 in the pulp and up to day 30 in the periapex. In contrast, cells expressing IL‐1β and TNFβ the homologous forms of these mediators, were not found in pulp or periapical lesions during this period. Cells expressing IL‐1α and TNFα were identified primarily as macrophages and fibroblasts, with occasional staining of polymorphonuclear leukocytes. Osteoblasts and osteoclasts were also positive, whereas lymphocytes were negative. In general, cytokine‐expressing cells were located proximal to abscesses and the root apex. These findings demonstrate that cells that express bone‐resorptive cytokines IL‐1α and TNFα are present immediately after pulp exposure in this model, which supports the hypothesis that these mediators play a key role in pulpal and periapical pathogenesis, including the concomitant bone destruction. They also indicate that both resident connective tissue cells as well as infiltrating cells express bone‐resorptive cytokines in response to infection in these lesions.