A macroscopic salivary gland and a potential organ or simply tubarial sero-mucinous glands?

Are dental professionals aware of the discovery of newly identified salivary glands? Is there a debate about this discovery?

AIM

Writing a letter to the editor.

BACKGROUND

Saliva plays a crucial role in chewing, swallowing, digestion, taste, and oral hygiene. In addition to the three major salivary glands in humans (parotid, submandibular, and sublingual glands), the existence of small salivary glands scattered in the submucosa of the nasopharynx and oropharynx is also known.

MATERIAL AND METHODS

Is it a new organ? This discovery has attracted significant attention from the scientific community but has also raised questions and sparked debates. Should the tubarial glands be classified as major or minor salivary glands, or as a separate organ? For a structure to be classified as an organ, it must have a distinct shape and structure, consist of multiple tissue types, and perform specific functions.

CONCLUSION

As we know, the definition and recognition of an organ must be based on scientific foundations. More research is needed on tubarial glands, and it seems that this discussion will continue for some time. Our purpose in writing this letter is to raise awareness of this issue among dental professionals.

Evidence is not sufficient to declare the tubal gland conglomerates as salivary

The letter to Editor is regarding an article by Pringle et al., 2023 which presents the histological and immunohistochemical characterization of the submucosal seromucous gland conglomerate at the nasopharyngeal end of the auditory tube (AT) and compares the same with the major and minor salivary glands, while trying to substantiate the claims of a previous work by Valstar et al., 2021. Contrary to their findings, a recent article by Kumari et al. 2023 presented the morpho-functional characterization of these glands and suggested against considering them as salivary. They mentioned that AT glands are "taxonomically different from the salivary glands" based on their anatomical location along the respiratory tract, the overlying mucosa lined with respirator yepithelium, and the absence of enzyme salivary amylase. This letter presents data from the already existing literature to emphasise the fact that the evidence given by Pringle et al., 2023 are not sufficient to declare the tubal gland conglomerates as salivary.

Immunohistological profiling confirms salivary gland-like nature of the tubarial glands and suggests closest resemblance to the palatal salivary glands

BACKGROUND AND PURPOSE

High label uptake in 68 Ga-PSMA-11 PET/CT recently identified a bilateral nasopharyngeal structure as a salivary gland (SG)-like additional 'area of interest', to be considered in conditions affecting SGs. These structures were termed 'tubarial glands'. We aimed to further characterize their histological and immunohistochemical position compared to established SGs.

METHODS

Tubarial gland tissue was compared with parotid, submandibular, sublingual, palatal and labial SGs tissue using immunohistological techniques.

RESULTS

Expression of acinar cell-associated aquaporin-5 (AQP5) was detected in tubarial glands, in an apical location associated in control, established SGs with polarized, secretory acinar cells. Keratin14 (KRT14) expression in cells peripheral to AQP5+ clusters also suggested presence of myoepithelial cells. α-amylase, prolactin-induced protein, proline rich protein Haelll subfamily 2, and Muc5B expression suggests mucous acinar cell presence, and presence of muco-serous acinar cells peripheral to putative mucous acinar cells. Expression of adrenergic receptor-β1 by acinar-like cells of the tubarial gland suggests ability to transduce sympathetic neuronal signaling. In terms of ductal architecture, tubarial glands contained large excretory-like ducts (similar to all other SGs), and squamous ducts, comprised of intermingled KRT14+ and KRT7+ cells. These squamous ducts were also observed in palatal, sublingual and labial SGs. No striated or intercalated ducts were observed, similar to palatal SGs.

CONCLUSION

Based on histological and immunohistochemical analyses, the tubarial glands resemble SGs. They most convincingly echo characteristics of the palatal SGs in terms of ductal cells, and both the palatal and labial SGs when considering acinar cells.

Morpho-functional characterization of the submucosal glands at the nasopharyngeal end of the auditory tube in humans

BACKGROUND

The auditory tube (AT), an osteocartilaginous channel, connects the nasopharynx to the middle ear cavity. At the nasopharyngeal opening of the AT, there are dense collections of submucosal glands. In a recent article, Valstar et al. proposed these nasopharyngeal tubal glands conglomerate as salivary glands, which starkly contrasts with their previously known anatomy for being a component of the respiratory tract. This study examines the contesting views regarding the taxonomical categorization of the nasopharyngeal tubal glands.

MATERIALS AND METHODS

The AT glands in context were examined in human cadavers grossly, and microscopically using routine and special (Hematoxylin and Eosin [H&E] and Periodic acid-Schiff [PAS] respectively), as well as immunohistochemical (for alpha-SMA and salivary amylase) staining methods and compared with the major and minor salivary glands and the submucosal glands in the trachea. Further, a biochemical analysis was performed to detect the presence of salivary amylase in the oral and nasopharyngeal secretions of the four living human subjects, representing major salivary glands and tubal glands, respectively.

RESULTS

The submucosal seromucous glands with a surface lining of respiratory epithelium were observed at the nasopharyngeal end of AT. The cells in the tubal glands showed cytoplasmic positivity for alpha-SMA, which indicated the presence of the myoepithelial cells; however, this expression was significantly lower than in the seromucous submucosal glands within the trachea. Salivary alpha-amylase was undetectable in the cadaveric tissue samples. Moreover, the amylase level in the nasopharyngeal swabs was negligible compared to the oral swabs.

CONCLUSION

The anatomical location along the respiratory tract, the presence of respiratory epithelium in the overlying mucosa, their morpho-functional resemblance to the seromucous glands in the trachea, and the absence of salivary amylase strongly indicate that the tubal glands are taxonomically different from the salivary glands. Given the available evidence, their existing recognition as a part of the respiratory tract and an integral component of the AT seems more appropriate.