Many studies have been carried out to investigate the histological structure of the trachea in many species of birds. However, the
cellular organization of the trachea in the mallard duck is still unclear. This study was performed on 12 sexually mature maleMallard
duck to demonstrate the cellular organization of the trachea using light and electronmicroscopy. The tracheal epithelium is considered
the first line of defense against airborne pathogens. The mallard trachea was lined by a pseudostratified ciliated columnar epithelium
that contained many morphologically distinct cell types: ciliated, non-ciliated, basal cells that encircled by a population of subepithelial
immune cells, fibroblasts, and telocytes (TCs). Telocytes were first recorded in duck trachea in this study and showed a
wide variety of staining affinity. They presented two long telopodes that made up frequent close contacts with epithelium, tracheal
cartilages, and other neighboring TCs, immune cells, blood capillaries, and nerve fibers. TCs express VEGF and S-100 protein. The
immune cells include mast cells, eosinophils, basophils, lymphocytes, plasma cells, and dendritic reticular cells. The ciliated tracheal
epithelium was interrupted by numerous intraepithelialmucous glands and solitary goblet cells. Thismucociliary apparatus constitutes
the major defense mechanism against inhaled foreign materials. The cellular organization of the duck trachea and its relation to the
immunity was discussed.