Ultramicroscopic Examination of the Ovine Tonsillar Epithelia

Abstract

As solid morphological knowledge of ovine tonsillar epithelia might contribute to a better understanding of the pathogenesis of several diseases including prion diseases, the epithelia of all tonsils of 7 one-yearold Texel sheep were examined using scanning and transmission electron microscopy. Major parts of the pharyngeal and tubal tonsils were covered by pseudostratified columnar ciliated epithelia that were interrupted by patches of epithelium containing cells with densely packed microfolds or microvilli, and cells with both microvilli and cilia. Smaller parts were covered by either flattened polygonal cells with densely packed microvilli or microfolds, squamous epithelial cells, or patches of reticular epithelium. The palatine and paraepiglottic tonsils were mainly lined by squamous epithelial cells with apical microplicae or short knobs. Additionally, regions of reticular epithelium containing epithelial cells with apical microvilli were seen. The lingual tonsil was uniformly covered by a keratinized squamous epithelium and devoid of microvillous cells and patches of reticular epithelium. The rostral half of the tonsil of the soft palate was lined by a pseudostratified columnar ciliated epithelium with characteristics of the pharyngeal and tubal tonsils. The epithelium of the caudal part resembled the epithelia of the palatine and paraepiglottic tonsils. Putative M cells, mainly characterized by apical microvilli or microfolds and a close association with lymphoid cells, seem manifestly present on the nasopharyngeal tonsils. The reticular epithelium of the palatine and paraepiglottic tonsils also harbor cells with small apical microvilli. The exact nature of these presumptive M cells should, however, be elucidated in functional studies. Anat Rec,

Histomorphology and Scanning Electron Microscopy of the Lingual Tonsil in Goats

“…The signs of degeneration in the nuclei were more towards the free surface of the epithelium. Casteleyn et al, (2010) also made similar observations in the lingual tonsils of sheep. The presence of keratohyaline granules in the stratum superficiale was reported in the nonkeratinized epithelium of lingual tonsil in horse by Kumar and Timoney (2005b) and in goat by Kumar and Kumar (2005).…”

“…5). Kumar and Kumar (2005) and Casteleyn et al, (2010) made similar observations on the morphology of the tonsils in goats and sheep, respectively. Large numbers of lymphocytes were seen in the propria submucosa (Fig.…”

Examination of the Reticular Epithelium of the Bovine Pharyngeal Tonsil

“…Studies of the ovine pharyngeal tonsil identified a heterogeneous population of microvillus containing cells (i.e. M-cells) (Chen et al, 1991;Casteleyn et al, 2010). Such cells have been variably described as electron dense or electron lucent, flattened, cuboidal or columnar, and covered with microfolds, microvilli, or both microvilli and cilia.…”

“…Terminology of Mv1, Mv2, In, S etc. was adapted from previous examination of the ovine pharyngeal tonsil (Casteleyn et al, 2010) and equine pharyngeal tonsil (Kumar and Timoney, 2001; Table 2). …”

“…Ruminants have less extensive RTALT than other species and the pharyngeal tonsil has been described as the major component of RTALT in cattle and sheep (Anderson et al, 1986;Chen et al, 1989;Schuh and Oliphant, 1992;Liebler-Tenorio and Pabst, 2006). Descriptions of microscopic, ultrastructural, and immunohistochemical features of the ovine and bovine pharyngeal tonsil have added to our understanding of this important tissue (Casteleyn et al, 2010;Breugelmans et al, 2011). Nevertheless, previous studies in the bovine have not focused on reticular epithelium, an active site of antigen uptake and initiation of an immune response.…”