Expression of inducible nitric oxide synthase in T lymphocytes and macrophages in vessels with advanced atherosclerosis.

While endothelial nitric oxide synthase is expressed in the endothelial cells of normal and atherosclerotic vessels, there are few reports about inducible nitric oxide synthase (iNOS) in atheroma. We investigated the expression of iNOS and its relation to inflammatory cells in atheroma. New Zealand White rabbits received a 1% cholesterol diet for 9 weeks (atherogenic diet) or a 1% cholesterol diet for 9 weeks then a normal diet for 36 weeks (reversible diet). The aortas were examined by immunohistochemical staining for anti-iNOS antibody, as well as antibodies for macrophages, T lymphocytes, and muscle actin. No iNOS was detected in normal aortas, intimal thickening, or fatty streaks. Although iNOS was detected in advanced plaques, it was not seen in smooth muscle-derived cells or endothelial cells, but was found in some macrophage-derived cells and in T lymphocytes. In regressive atherosclerotic aortas, iNOS was detected only in advanced plaques and not in macrophage-derived cells, but in T lymphocytes. These findings suggest that T lymphocytes and some macrophages induce iNOS through cytokine production in atheroma.