Ciliated smooth muscle cells in atherosclerotic lesions of human aorta.

One or two rudimentary cilia were observed by electron microscopy in smooth muscle cells (SMCs) of fatty dots and streaks, but not in normal intima of human aorta. Similar organelles are known to occur in many cell types and various species, but to the best of the author's knowledge, have never been found in the SMCs of arterial or other tissues of man in health and disease; recently, they were reported to be present in the SMCs of experimental atherosclerosis in rabbits. The rudimentary cilia observed in this study had a "9 + 0" axoneme (microtubular complex) and differed also in other aspects from the classical cilia. Semiserial sections of SMCs containing a diplosome disclosed that on several occasions both of its constituent centrioles gave rise to rudimentary cilia. SMCs containing cilia or their basal bodies were observed more often in the human than in experimental atherosclerotic lesions. Whereas the function and significance of the rudimentary cilia remain largely unknown, the current theory proposes that a sudden transformation from a mitotic replicative to a nonmitotic structured tissue "diverts" centrioles to the formation of these unusual organelles. It is conceivable that rudimentary cilia could serve as morphological indicators of aborted mitosis in human atherosclerotic lesions.