Objectives:Cyclosporin A (CsA) is the most frequently used immunosuppressor in transplant surgery, but one of the adverse side effects by CsA is gingival overgrowth (GO). The previous reports have demonstrated that GO was effectively treated by azithromycin (AZI), a macrolide antibotic of azalide subclass that suppresses protein synthesis. However, the mechanism by which AZI suppresses CsA-induced gingival overgrowth (CIGO) has not yet been elucidated. In the present study, we examined the inhibitory effect of AZI on CIGO and its mechanism of action as well as the mechanism whereby CsA induces GO. Methods:Human gingival fibroblasts were isolated from the gingival tissues of the healthy subjects and the patients exhibiting GO caused by CsA therapy. Cell proliferation was measured by MTT assay, and mRNA levels and activities of matrix metalloproteinases (MMPs) by reverse transcription polymerases chain reaction (RT-PCR) and zymography, respectively. Differential display - PCR was performed to identify genes, which are differentially expressed as a result of CsA treatment. Results:The CsA treatment resulted in higher proliferation in cells derived from the patient with CIGO compared to those from the healthy subjects. Azithromycin inhibited the cell proliferation of gingival fibroblasts increased by CsA exposure for 5 days. The morphological changes were observed in the gingival cells stimulated with CsA, AZI, and the combination of AZI and CsA. The mRNA level and activity of MMP-2 were inhibited by CsA, but increased by the combination of AZI and CsA. In contrast, the mRNA level of testican 1 was increased by CsA, but inhibited by the combination of AZI and CsA. Conclusions:The induction of MMP-2 by AZI treatment plays an important role for the inhibition of AZI on CIGO. This study was supported by a grant of the Korea Health 21 R&D Project, Ministry of Health & Welfare, Republic of Korea (01-PJ5-PG3_20507-0020)