Beta Defensins in the Host Defense of Sheep Tongues: Cellular Localization and Possible Roles

In domestic animals, a diverse range of antimicrobial peptides function as natural barriers to microbial invasion. Among these, defensins small, cationic, cysteine-rich, amphipathic peptides represent key elements of the innate immune system in multicellular organisms. The present study aimed to investigate the presence, regional localisation, and cellular distribution of β-defensin 1 (BD1), β-defensin 2 (BD2), β-defensin 3 (BD3), and β-defensin 4 (BD4), members of the defensin family, in the tongues of adult sheep using immunohistochemical techniques. BD1 and BD2 exhibited weak to moderate immunoreactivity, primarily localized to the basal and parabasal layers of the lingual epithelium, whereas BD3 and BD4 displayed strong expression across the entire epithelial layer. All of the defensins examined showed higher expression levels in the epithelial cells of filiform and lenticular papillae. Furthermore, variable expression of BD1, BD2, BD2, and BD4 was detected in stromal cells, skeletal muscle fibres, and vascular structures. In particular, BD3 and BD4 showed a more intense expression in all tongue tissues. These findings indicate that β-defensins are predominantly expressed in the epithelial compartment of the sheep tongue, suggesting their role in providing rapid local defence against microbial pathogens. The increased expression of BD3 and BD4 suggests that they play a more prominent role in immune responses triggered by inflammatory stimuli.