Tonsils of the soft palate of young pigs: crypt structure and lymphoepithelium

Tonsils of the soft palate are especially important in pigs as the major pharyngeal mucosal-associated lymphoid tissue and as a portal of entry for microorganisms. They play a key role in initiating immune responses against antigens entering tonsillar crypts from the oropharynx. The aim of this study was to describe the architecture of the tonsillar crypst and the morphology of their epithelial surface.

Tissue taken from the tonsil of the soft palate of freshly-killed pigs was examined using light microscopy, electron microscopy, and three-dimensional reconstruction techniques.

Tonsils of the soft palate in pigs are penetrated by numerous crypts which extend into, and branch extensively within, the lymphoid tissue. Stratified squamous non-keratinised epithelium covering the oropharyngeal surface is continuous with that lining the neck of crypts. Lymphoepithelium covers the tonsillar lymphoid tissue within the crypts. It consists of non-keratinised epithelial cells, M cells, goblet cells and many intraepithelial lymphoid cells. M cells have a variable surface morphology: some are covered by relatively regular and well-formed microvilli; others possess very long undulant microvilli emanating from broad membranous folds.

Variations in M cell surface morphology occur and these may reflect alterations of the apical plasmalemma in response to antigenic stimuli. Further investigation will be required to determine molecular specializations of the apical membrane of M cells which may facilitate interactions with antigenic material.