Histology, immunohistochemistry and ultrastructure of the tonsil of the soft palate of the horse.

This research article explores the unique structure and properties of the tonsil of the soft palate in horses. The study found unusual characteristics not seen in tonsils of other species, including various layers of the epithelium that exhibit different reactions to certain lectins.

Understanding the Structure

The study identified the tonsil of the soft palate as an oval, flat structure centrally located on the oral surface of the soft palate in horses. Unlike tonsils observed in other species, this tonsil displayed several unique structural properties:

• It was covered with a stratified squamous non-keratinized epithelium, a type of tissue not usually associated with tonsils.
• This epithelium was perforated by various holes or small crypts, deep portions of which exhibited a loosely spongiform inter-digitation with lymphoid tissue.
• Crypts and reticulated epithelium, which are commonly seen in the lingual and palatine tonsils, were not observed.

Chemical Reactions and Cellular Composition

The researchers found differences in how various layers of the epithelium reacted to lectins. They also observed a few Langerhans cells distributed among surface epithelial cells. However, some cells typically found in other species’ tonsils, called M cells, were not observed.

• Lymphoid tissue was arranged loosely, with isolated lymphoid follicles in the subepithelial lamina propria mucosae.
• The amount of lymphoid tissue was much less than typically found in the lingual and palatine tonsils.
• The majority of follicular germinal centres lacked a darkly stained corona, a feature usually present in other species’ tonsils.
• Tissue also contained IgA+ cells and macrophages — immune cells responsible for combatting pathogens.

Distribution of Immune Cells and Other Structures

The article also reported that there were more CD4 positive cells than CD8+ lymphocytes, and these cells were mainly found in the parafollicular and inter-follicular areas.

• Large clusters of mucus acini were also present.
• These, along with acidic and neutral mucopolysaccharides, separated the lymphoid tissue from deeply placed striated muscle.
• The researchers observed only a few high endothelial venules (HEVs) in the same parafollicular and inter-follicular areas. These lacked significant numbers of vesiculo vacuolar or other organelles, and there were few lymphocytes attaching to their walls.

This study offers new insights into the unique structural and immuno-histochemical properties of the tonsil of the soft palate in horses, which could potentially lead to advancements in equine health and disease management.