IMMUNOLABELING OF TYPE-IV COLLAGEN, LAMININ, AND ALPHA-SMOOTH MUSCLE ACTIN CELLS IN THE INTIMA OF NORMAL AND VARICOSE SAPHENOUS VEINS

Smooth muscle cells (SMC) of normal and varicose human saphenous intim a were studied on cryostat sections by immunohistochemistry with alpha -smooth muscle actin (ASMA), type IV collagen, and laminin antibodies and also by transmission electron microscopy. The findings suggest two structurally distinct subtypes of smooth muscle cells with thin and t hicker external lamina. Thin external lamina SMC were characterized by laminin, type IV collagen, weaker external lamina reactivity, and int ense cytoplasmic a-smooth muscle actin immunoreactivity. Ultrastructur ally, they exhibited abundant cytoplasmic microfilaments and thin exte rnal lamina. These cells were found isolated or, more frequently, clus tered in fascicles close to the subendothelium in focal or zonal cushi ons, or in diffuse enlargement of the intima. In contrast, thicker ext ernal lamina smooth muscle cells were intensely immunolabeled for lami nin and collagen IV, showing irregular cytoplasmic ASMA reaction. Sing le or clustered thicker external lamina SMC were seen predominantly in zonal cushions and in intima diffuse enlargement. It is very likely t hat these cells secrete these matrices in a nonpolarized fashion. The thicker external lamina of these SMCs showed a fine granular amorphous aspect sometimes intermingled with microfibrils. These external lamin a were interposed between neighboring cells and exposed to collagen fi brils and elastic fibers. The cells also exhibited rarefaction of the cytoplasmic filaments. Intermediary cells exhibiting both features wer e rarely seen. Thicker external lamina SMC should be discussed in the context of an adaptive/proliferative response leading to dysfunction o f the fibroelastic properties of the vein wall.