Prenatal development of palatine tonsil in sheep (Ovis aries)

Abstract Introduction: The palatine tonsil play a key role in initiating immune responses against the antigenic material entering the mouth. Materials and Methods: Tissue pieces of oropharynx for the palatine tonsilwere collected from different prenatal age groups of sheep. These tissue pieces were fixed and processed for routine paraffin embedding technique to get 3-5pm thick sections. The paraffin sections were subjected to routine haematoxylin and eosin and some other special staining methods. Results: In three months foetal age of sheep, the palatine tonsils appeared as diffused lymphocytic infiltration in the propria submucosa overlaid by the mucosa of the oropharynx. The surface epithelium of the mucosa of the oropharynx formed primary crypts. The primary crypts in turn invaginated to form secondary crypts. The collagen fibres from the submucosa appeared to enter at the base of the developing tonsil. In the fourth month of foetus, the tonsillar surface epithelium became thicker and many crypts arose from that of primary crypts. Organized lymphocytic infiltration as isolated units was noticed near or around the secondary crypts. In five months of foetal age, the crypt epithelium was found to be infiltrated with lymphocytes, macrophages, plasma cells and mesenchymal cells. The connective tissue capsule and septa were completely formed. The lymphocytic tissue was characterized by an increased population of lymphocytes in the primary follicles without germinal centres. Conclusion: The results were compared with the literature and the palatine tonsil showed the gradual changes of histoarchitecture from third to fifth month of foetal age.