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Affinity-purified antibodies to major components of the extracellular matrix (fibronectin and collagen type I) and basal lamina (laminin) were used in indirect immunofluorescence studies on frozen sections of 12 pancreatic ductal adenocarcinoma of the human and on sections of normal and inflamed pancreatic tissue of the same patients. Laminin-specific immunoreactivity was distributed in close correlation to the grade of differentiation of the tumor tissue. Intact basement membranes, also with some structural irregularities were found only in the highest grade of differentiation where tumor cells grew as tubular structures. With progressive dedifferentiation basal laminae were either absent or the laminin-positive material was focally distributed without spatial association with tumor cells. In all cases of pancreatic tumors a remarkable increase in interstitial connective tissue was observed, as demonstrated by antibodies specific for human collagen type I and for human serum fibronectin. Tumor extracts contained high amounts of collagen type I and V but no significant amount of collagen type I11 as visualized by analytical SDS gel electrophoresis. A similar distribution of collagen types was observed in lymph node and liver metastases, and in tumors xenografted into nude mice. Since previously a close correlation between grading and growth kinetics of primary tumors had been observed, in vitro experiments were performed analyzing the effect of purified extracellular matrix proteins on tumor cell proliferation. In vitro cultivation of two established cell lines of pancreatic carcinoma on collagen type I or on laminin resulted in an arrest of proliferation on laminin substrates, while normal proliferation comparable to growth on regular culture dishes was found using collagen type I and fibronectin as substrates. Fine structural studies demonstrated a higher degree of cell differentiation in the presence of laminin, as compared to collagen type I or fibronectin.