[Filamentary granules in human bronchi]

Mucous cells of human bronchial glands contain secretory granules with 5,5-7 nm parallel filaments. In contrast with the glycoproteic-rich mucous granules, filamentary granules exhibit weak reactivity with tannic acid, indicative of proteins. Exocytosis or discharge in glandular lumen are sometimes observed. These original granules may probably represent an additional component of fibrillar matrix in mucus.