Immunocytochemical demonstration of collagen types I and IV in cells isolated from malignant mesothelioma and in lung cancer cell lines

Malignant mesotheliomas often constitute a difficult diagnostic problem. A possible marker for a mesenchymal origin of the tumor is the type of collagen produced. A study was therefore made of the immunocytochemical reactivity of collagen type I, as an indicator of mesenchymal origin, and of collagen type IV, which is normally found in basement membranes of epithelial tissues. The reaction patterns of cells isolated and cultured from four patients with malignant mesothelioma were compared in this way with those of 3 lung cancer cell lines and exfoliated benign mesothelial cells. The reactivity of normal pleura was also studied. The normal pleura contained both type I and type IV collagen, the latter in a thin rim corresponding to the basal lamina underlying the superficial cells. The malignant mesothelioma cells showed coexpression of both type I and type IV collagen, while in the carcinomas only the collagen type IV epitope could be detected. The reactivity of the malignant cells was mainly intracellular, but in 3 of the mesothelioma cell lines the type IV epitope was also seen as extracellular deposits. No significant reactivity was obtained with antibodies against type IV collagen in benign mesothelial cells. Such coexpression has not been described for other tumors and this determination may therefore improve the diagnostic arsenal in cases of malignant mesothelioma.