Fibrocellular tissue response after percutaneous transluminal coronary angioplasty. An immunocytochemical analysis of the cellular composition. BACKGROUND. Restenosis after initial, successful percutaneous transluminal coronary angioplasty (PTCA) is due to fibrocellular proliferation. METHODS AND RESULTS. The present study focused on the nature of fibrocellular tissue in humans by use of immunocytochemical techniques. Four hearts (five coronary arteries) were investigated; time lapse between PTCA and death varied between 20 days (two arteries) and 1 year 7 months. Proliferating cells stained positive with smooth muscle cell-specific monoclonal antibodies. Cells from early proliferative lesions (20 days) have a phenotypic expression different from cells in "old" lesions. Proliferating cells stained positive with vimentin but were negative with desmin, irrespective of the lesion's age. CONCLUSIONS. The findings indicate a change in actin isoform expression of smooth muscle cells while adapting to a pathological state. 