M cells and associated lymphoid tissue of the equine nasopharyngeal tonsil.

The research article investigates the detailed structure and function of the equine nasopharyngeal tonsil tissue, suggesting its importance as a site for immune response and a potential target for vaccine administration in horses.

Study Objective and Methodology

• The study aimed to describe the morphological and histochemical attributes of the nasopharyngeal tonsillar tissue in horses. This tissue has been linked to the activation of the immune response in the respiratory and alimentary tracts.
• The researchers utilized various techniques including light, scanning, and transmission electron microscopy to investigate the follicle-associated epithelium (FAE) over the nasopharyngeal tonsil, located after the pharyngeal opening of the guttural pouch.

Findings on M (Membranous Microvillus) Cells

• M cells were identified in the FAE based on their short microvilli, connection with lymphocytes, and cytoplasmic vimentin filaments. These M cells also showed reactivity with lectin GS I-B4 that is specific for alpha-linked galactose.

Observations on Lymphocytes

• The presence of CD4-positive lymphocytes was noted scattered throughout the lamina propria mucosae and in dense aggregates in the subepithelial parts.
• The central follicular area was densely populated with B lymphocytes. CD4- and CD8-positive lymphocytes were found in both the dome and parafollicular areas.
• CD8-positive lymphocytes were detected in the epithelium and, in small amounts, in the lamina propria mucosae along with the B lymphocytes.

Implications for Vaccine Development

• The findings suggest that the nasopharyngeal tonsil could be a significant site for inducing an immune response in horses. This indication makes it a potential target for administering vaccines intranasally.