Keratin is a major class of epithelial intermediate filaments, and comprises a group at least 20 different multigene derived proteins. It is expressed in different epithelia with specific combinations. Polyclonal and monoclonal antibodies to cytokeratin(CK) polypeptides were used to study the expression in normal, squamous metaplasia, reserve cell hyperplasia, and neoplastic epithelium of the respiratory tract. All cases were performed of immunohistochemical stain for panel of monoclonal cytokerain antibodies. Also, some cases were examined by electron and immunoelectron microscopy. The squamous papillomas were positive for CK 1, 5/6, 8, 10 and 17. Dysplastic cells were positive for CK 1, 13, 14, and 19. Well differentaited squamous cell carcinomas were reactive for CK 1, 5/6, 13, 14 and 17. Poorly differentiated squamous cell carcinomas were reactive for CK 5/6, 8, 10 and 19. Small cell carcinomas were negative for all keratin subtypes. Adenocarcinomas are reactive for CK 7, 8, 18 and 19. CK 20 is exceptionally negative in all cases. Immunoelectron microscopic examination shows localized gold particles in intermediate filaments and tonofilaments of normal or tumor cells. In conclusion, keratin subtypes of well differentiated squamous cell carcinoma is similar to those of metaplastic cells of the bronchial epithelium and dysplastic cells, while keratin subtypes of poorly differentiated squamous cell carcinoma resembles those of hyperplastic reserve cells and squamous papilloma. It is thought that the application af cykokeratin panel can indicate the degree of differentiation of tumors and distinguish the main subtypes of lung cancer. In addition,immunoelectron microscopic examination is helpful to lo- calization of keratin filaments and diagnosis of epithelial tumors.
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