Previous studies of the intrapulmonary conducting airways of sheep and rabbit have demonstrated marked diversity in the epithelial populations lining them. Because studies of trachea and centriacinar regions of macaque monkeys suggested that primates may be even more diverse, the present study was designed to characterize the epithelial population throughout the airway tree of one primate species, the rhesus monkey. Trachea and intrapulmonary airways of the right cranial and middle lobes of glutaraldehyde/paraformaldehyde-infused lungs of five adult rhesus monkeys were microdissected following the axial pathway. Each branch was assigned a binary number indicating its specific location within the tree. The trachea and six generations of intrapulmonary airway from the right cranial lobe were evaluated for ultrastructure and quantitative histology as were those of the right middle lobe for quantitative carbohydrate histochemistry. Four cell types were identified throughout the tree: ciliated, mucous goblet, small mucous granule, and basal. The tallest epithelium lined the trachea; the shortest, the respiratory bronchiole. The most cells per unit length of basement membrane were in proximal intrapulmonary bronchi; the least, in the respiratory bronchiole. The nonciliated bronchiolar epithelial or Clara cell was restricted to respiratory bronchioles. Sulfomucins were present in the vast majority of surface goblet cells in the trachea and proximal bronchi. In proximal bronchi, neutral glycoconjugates predominated in glands and acidic glycoconjugates in surface epithelium. In terminal and respiratory bronchioles the ratio of acidic glycoconjugate to neutral glycoconjugate equaled that in proximal bronchi, although glands were not present. Sulfomucins were minimal in terminal airways. We conclude that the characteristics of the epithelial lining of the mammalian tracheobronchial airway tree are very species-specific. The lining of the rhesus monkey does not have the diversity in cell types in different airway generations observed in sheep and rabbit. Also, the populations lining these airways in the rhesus are very different from either the sheep or rabbit in number, proportions of different cell types, glycoconjugate content, and distribution of specific cell types.

Experimentally applied irritants and chronic respiratory diseases appear to alter the amount and composition of secretory cell product in surface epithelium and submucosal glands of pulmonary airways. Previous methods used to quantify these changes have been very time-consuming or have not measured the same components of the airway wall. The present study describes a rapid, reproducible, and standardized automated method for quantifying secretory products. The tracheas from eight macaque monkeys were fixed with glutaraldehyde-paraformaldehyde, embedded in glycol methacrylate, serially sectioned at 2 microns, and histochemically stained to demonstrate neutral, sialylated, and sulfated mucosubstances in the cartilaginous, intercartilaginous, and membranous regions of both proximal and distal trachea. Volume densities were determined using an image analyzer and are expressed as volume of stained mucosubstance per unit surface area of epithelial basal lamina. Comparison of the automated method to manual point counting and evaluation of internal variance showed that the automated method had a twelve-fold increase in efficiency with no significant differences in measurements. After weighting the values of each region according to their anatomical contribution, the total secretory product (TSP) for the entire trachea was determined. Periodate-reactive acid material predominated (73%) in luminal surface epithelium, and neutral material predominated (78%) in submucosal glands. Surface epithelium contained 66% of the TSP. The greater contribution by surface epithelium and predominance of acid mucins there resulted in a TSP from the trachea that consisted of 59% acid material (most of which was sulfated) and 41% neutral material. The method proved to be a valid, reproducible, and rapid technique for evaluating variability in abundance of mucosubstances within airway epithelium.

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