Histochemical profiles of mucins in the tracheal epithelium during the post-hatching period of Japanese quail (Coturnix coturix japonica)

Mucus normally protects the airway epithelium from dehydration and inhaled infectious agents and possibly toxic substances. Two components of mucus, mucin and water play major roles in the elimination of inhaled foreign material. Mucins are large carbohydrates rich glycoprotein. The objective of the present study was to determine the histochemical changes in mucin pattern of the goblet cells and intraepithelial glands of the trachea in quails during the post-hatching period using specific various staining procedures for complex carbohydrates (Periodic acid Schiff Alcian blue-Periodic acid Schiff (pH 2.5), Aldehyde fuchsin-Alcian blue (pH 2.5), High-iron diamine-Alcian blue (pH 2.5), Periodic acid-Phenylhydrazine-Schiff). The intraepithelial alveolar glands were present at hatching and their numbers increased with the advance of age. In quail of all ages, the histochemical reactions revealed that the goblet cells and mucous cells of intraepithelial glands contained the mucins with vicinal diol groups, neutral mucin, sialomucin and sulphomucin. In all ages studied, the tracheal epithelium contained three distinct types of goblet or mucous cells producing neutral-, acid- and mixture of neutral- and acid mucins. In 1 day old, the majority of the goblet cells and gland cells contained neutral mucin or a mixture of neutral- and acid mucins, while the proportion of only acid mucin-producing cells was few. The majority of acidic mucins consisted of sulphomucin. The sialomucin-containing cells were only a few. After day 14, it was seen that the content of sialomucin in the epithelium became more diffuse toward adulthood. In conclusion, the content of mucin of tracheal epithelium was variable depending on the ages during the post-hatching period. These changes in mucin dynamics could affect the protective functions against pathogens and toxins of the tracheal epithelium.