Expression of CD34 and CD146 vascular markers contributes to the immunological function of the human palatine tonsil

The fundamental function of the palatine tonsil is the immune response to airborne and foodborne pathogenic agents. Small blood vessels have an important role in the provision of a special microenvironment in which the immune response occurs. In this study, we investigated the expression of vascular markers CD34 and CD146 and basal lamina marker - type IV collagen - in the small blood vessels of the human palatine tonsil in the context of their role in the immunological function of the tonsil. The tonsils were collected after tonsillectomy from ten patients with chronic tonsillitis, aged 18-28 years. Five-µm-thick paraffin sections were routinely stained with haematoxylin and eosin, while the studied markers (CD34, CD146 and type IV collagen) were detected immunohistochemically using LSAB2/HRP method. CD34 was expressed equally in the capillaries within and below the crypt epithelium, in lymphoid follicles and in high endothelial venules localized para- and interfollicularly. CD146 molecule was expressed on the luminal surface of endothelial cells in the capillaries of the crypt epithelium, while its expression in high endothelial venules was seen on the luminal and lateral surfaces of the cuboidal endothelial cells. In contrast to the basal lamina of intraepithelial capillaries, where collagen IV-immunopositivity is mostly seen as a continuing line, the basal lamina of high endothelial venules was seen as a two- or three-layered structure beneath the cuboidal endothelial cells. The specifics of expression of CD34, CD146, and type IV collagen confirm the morphofunctional specialization of endothelium in crypt epithelium capillaries, and also in endothelium of high endothelial venules, which is directly associated with the role of these vessels in the immune function of the tonsil.