Plasminogen activators (PA) have been implicated with the degradation of extracellular matrix during the invasive growth of metastasising tumour cells. The significance of PA expression in tumour cells for the in vivo growth of malignant tumours is still a matter of debate. We, therefore, performed immunohistological studies on human colon tumours using
monoclonal antibodies against
urokinase- (
u-PA) and
tissue-type plasminogen activator (t-PA) as well as against
plasminogen activator inhibitors 1 and 2 (PAI-1, PAI-2). Normal colorectal mucosa of seven samples was negative for all four constituents of the PA system. Tumour epithelium of 64
colorectal carcinomas and 10 liver
metastases was consistently negative for both, PA and their inhibitors. However, two of four human colon
carcinoma cell lines weakly expressed
u-PA,
PAI-1 and
PAI-2. Intestinal dendritic or fibroblast-like cells within the tumour tissue strongly expressed
u-PA and, at a lower level, also t-PA,
PAI-1 and
PAI-2. Vascular endothelial cells were weakly positive for all components of the PA system in colon
carcinoma. Our findings indicate that colon
carcinoma cells in their natural environment do not express constituents of the PA system. PA activity, previously found in colon
carcinoma tissue, is most likely derived from interstitial cells.