Expression of macrophage inflammatory protein-3a in human pulpitis

Objective: Severe pulpitis is characterized by marked inflammatory infiltrate such as lymphocytes. However, little is known about the recruitment of these cells to the pulpal lesions. Macrophage inflammatory protein-3 a (MIP-3 a), one of the CC chemokines, is known to attract CC chemokine receptor 6 (CCR6)-expressing T cells, and it may participate in the infiltration of lymphocytes in inflamed pulps. The aim of this study was to investigate the role of MIP-3 a in the pathogenesis of pulpitis. Methods: Inflamed pulpal samples were obtained from extracted human deep-carious third molars that showed spontaneous pain and/or lingering pain in response to cold and/or heat stimulus. These samples were used for RNA isolation and for preparation of formalin-fixed, paraffin-embedded sections. Expression of MIP-3 a mRNA was examined by RT-PCR, while localization of both MIP-3 a and CCR6 was investigated by immunohistochemistry. Asymptomatic pulps from noncarious third molars were used as normal controls. Results: In inflamed pulps, the expression of MIP-3 a mRNA was detected. Moreover, MIP-3 a was immunohistochemically observed in all of the inflamed pulpal samples, and it was mostly distributed in macrophages accumulated in the area adjacent to the caries lesion and microvascular endothelial cells. Furthermore, CCR6 expression was also observed in the infiltrating lymphocytes. In contrast, MIP-3 a was scarcely detected in normal pulps. Conclusion: These findings suggest that MIP-3 a plays an important role in the advancement of pulpal inflammation via the recruitment of CCR6-expressing lymphocytes.