M cells and associated lymphoid tissue of the equine nasopharyngeal tonsil

• Published in: Equine veterinary journal 2001-05, Vol.33 (3), p.224-230
• Main Authors: KUMAR, P., TIMONEY, J. F., SHEORAN, A. S.
• Format: Article
• Language: English
• Subjects: Animals; Female; follicle associated epithelium; horse; Horses - anatomy & histology; Immunity, Mucosal - physiology; Immunohistochemistry; Lymphoid Tissue - anatomy & histology; Lymphoid Tissue - ultrastructure; M cells; Male; Microscopy, Electron, Scanning - veterinary; Microscopy, Electron, Scanning Transmission - veterinary; Microvilli - ultrastructure; nasopharyngeal tonsil; Nasopharynx - anatomy & histology; Nasopharynx - ultrastructure; Palatine Tonsil - anatomy & histology; Palatine Tonsil - ultrastructure
• ISSN: 0425-1644; 2042-3306
• DOI: 10.2746/042516401776249697

Summary The aim of this study was to characterise the morphological and histochemical features of equine nasopharyngeal tonsillar tissue. Nasal and oropharyngeal tonsillar tissue has been described as the gatekeeper to mucosal immunity because of its strategic location at the entrance to the respiratory and alimentary tracts. A combination of light, scanning and transmission electron microscopy has revealed the presence of follicle‐associated epithelium (FAE) overlying lymphoid tissue of the equine nasopharyngeal tonsil caudal to the pharyngeal opening of the guttural pouch. Membranous microvillus (M) cells were identified in the FAE on the basis of short microvilli, an intimate association with lymphocytes, cytoplasmic vimentin filaments and epitopes on the apical surface reactive with lectin GS I‐B4 specific for α‐linked galactose. CD4‐positive lymphocytes were scattered throughout the lamina propria mucosae as well as forming dense aggregates in the subepithelial part. The central follicular area was heavily populated with B lymphocytes and the dome and parafollicular areas contained both CD4‐ and CD8‐positive lymphocytes. CD8‐positive lymphocytes were also present in the epithelium and, together with B lymphocytes, in small numbers in the lamina propria mucosae. These observations indicate that the nasopharyngeal tonsil is potentially an important mucosal immune induction site in the horse and an appropriate target forintranasally administered vaccines.