OBJECTIVETo study the cytokeratin 18 and 13 and their gene (CK) expression in post-operation maxillary cyst linings with metaplastic epithelium.

METHODSCK expressions were examined with immunohistochemistry in 46 post-operative maxillary cyst (POMC) which were lined with pseudostriated columnar cells only (13 cases), both kinds of columnar and squamous cells (30 cases) and squamous cells only (3 cases).

RESULTSThe expressions of CK8, CK13 and CK18 were observed in 39, 9 and all of the 43 columnar epithelial linings, respectively. Metaplastic squamous epithelia expressed more CK13 and less CK18 and CK8. Of the 33 metaplastic linings, 24 expressed CK8, 23 CK13 and 26 linings expressed CK18. The expression of CK13- and CK18-mRNA was generally correlated with the protein expression level. By in situ hybridization, CK18-mRNA expression was observed not only in 26 metaplastic linings which were positive for CK18 protein but also in five of the seven metaplastic linings which did not express CK18 protein. In addition, RT-PCR revealed an expression of CK18-mRNA in all metaplastic squamous linings although the expression level was weaker than that in the columnar epithelial linings. The CK13-mRNA was expressed in a fashion inverse to the CK18-mRNA.

CONCLUSIONSThese results indicate that CK18-mRNA is preserved through metaplasia although the protein expression decreases and metaplastic squamous cells differentiate with a decrease of CK18 and an increase of CK13 expression.