The Ovine Tonsilla Lingualis: Scattered Lymphocyte Aggregations Rather Than a Well‐defined Tonsillar Structure

Abstract

Recently, it has been hypothesized that the BSE‐causing agent PrPSc can infect sheep, making these animals a possible source of infection for man. Furthermore, experimental studies in inoculated sheep have demonstrated that PrPSc is not only present in neuronal tissue, but also in lymphoid tissue. Therefore, ovine tonsils are considered as high‐risk material and consequently have to be removed after slaughter. The present study is part of an elaborate project in which anatomical, histological and immunological aspects of ovine tonsils are studied within the framework of BSE/TSE research. The tongues of two sheep of 9‐months‐old were collected immediately after slaughter. The lingual root between the base of the epiglottis and the torus linguae was dissected and the 4.5 cm wide and 8 cm long sample was cut into 24 pieces which were subsequently fixed in 3.5% formaldehyde and embedded in paraffin. From each tissue block, ten 8‐μm‐thick sections with 1000 μm interval were cut and stained with eosin–haematoxylin. Microscopic analysis revealed that lymphocytes are mainly present at the lateral side of the tongue forming numerous small aggregates, while in the more central part the amount of aggregates was lower. In both lateral and central parts, the aggregations were located in an area ranging from 1–2 cm till 6 cm rostral to the epiglottis. These lymphatic clusters were in general smaller than the lymphatic nodules seen in the other pharyngeal lymphoid tissue, and a differentiation into secondary nodules was never observed. The epithelium covering these lymphocyte aggregations was a stratified squamous epithelium without infiltration of lymphocytes. It was concluded that the tonsilla lingualis in sheep consists of scattered lymphocyte aggregations without forming a well‐defined tonsillar organization. Further studies are planned to examine the tongues of more sheep and to determine the presence of dendritic cells, follicular dendritic cells and different B‐ and T‐cell populations.This study was supported by the BOF project grant #011B4101 of Ghent University.