Histology and ultrastructure of the equine lingual tonsil. I. Crypt epithelium and associated structures.

The research examines the microscopic and ultra-microscopic characteristics of the lingual tonsil in horses. The study reveals an intricate structure, potentially involved in initiating and maintaining immune responses, and several unique features, such as the absence of certain types of cells and the presence of specific binding patterns, which might be beneficial for future scientific research.

Overview of the Research

The researchers studied the morphology of the equine lingual tonsil in five young horses at both the microscopic and ultra-microscopic scale. The tonsil is located on the root of the horse’s tongue and is covered in a variant of stratified squamous non-keratinized epithelium – a type of skin cell – which changes shape due to the infiltration of lymphoid cells (immune cells). The tonsil’s structure includes numerous folds and crypts and an irregular surface with rounded elevations.

Structure and Cellular Composition

• The outer surface of the tonsil is covered by a stratified squamous non-keratinized epithelium which is heavily infiltrated by lymphoid cells, creating a “reticular epithelium” within the crypts of the tonsil.
• The study shows that the tonsil’s epithelium, the outer layer of the skin cell, resembles Hassall’s corpuscle – a structure typically found in the thymus, another important organ of the immune system.
• Despite exhaustive scanning, the researchers did not identify any microvillus cells, also known as M cells, which are vital for the absorption of nutrients in many organisms.

Role in Immune Response

The modification of epithelium into reticular epithelium seems to indicate a potential function of the equine lingual tonsil in initiating and maintaining immune responses against infectious agents and antigens. Aggregations of these immune cells form lymphoid follicles to combat foreign substances.

Lectin Binding Patterns and Absence of Vimentin Filaments

• The research identified unique lectin binding patterns on the stratum superficiale (top layer) of the reticular epithelium. These patterns could serve as markers for future embryological and microbiological analyses.
• No vimentin filaments were detected in the studied tissue samples, thus reaffirming the absence of M cells.

Mucus Glandular Acini and Cell Organelles

In the creation of the tissue, mucus glandular acini deep within the lamina propria mucosae – the deepest layer of the tonsil – were found to contain glycogen and various types of mucopolysaccharides. This finding, combined with the observation that the outer epithelial surface has an abundance of cell organelles, further enhances the complexity and capacity of the lingual tonsil.

Conclusion

The study aids in contributing to the scientific understanding of the lingual tonsil’s function and structure in equine species. This anatomical and cellular knowledge could pave the way for future studies related to the lingual tonsil’s role in immunology, veterinary medicine, and comparative anatomy.