The ciliary necklace--a transmission electron microscopic study using tannic acid-containing fixation.

Human respiratory cilia, including those in seven cases of immotile cilia syndrome, were examined by transmission electron microscopy after tannic acid-containing fixation. This fixation method is useful for ultrastructural observation of unit membranes and of the dynein arms and protofilaments of cilia. In addition, intramembrane particles and electron-dense strands were also demonstrated in the neck of the cilia. These structures may correspond to the ciliary necklace, which has been demonstrated by the freeze-etch technique. In high-magnification electron micrographs, the intramembrane particles were 10 nm in diameter and the necklace spacing was about 30 nm in human respiratory cilia. Prior to this study, no reports on ultrastructural abnormalities of the ciliary necklace in humans had appeared, probably because of technical problems with tissue preparation. Therefore tannic acid-containing fixation appears to be useful for ultrastructural observation of the ciliary necklace.