Expression of adhesion molecules on the microvasculature of the pharyngeal tonsil (adenoid)

We have examined the vasculature of 12 human adenoids and the expression and distribution of four endothelial adhesion molecules, ICAM-1, VCAM-1, P-selectin and E-selectin, in tissue sections using histology, immunocytochemistry and immunoelectron microscopy (IEM). The connective tissue septa and septula contained arterioles, veins and efferent lymphatics. Branches of arterioles supplied lymphoid follicles and divided into sub- and intraepithelial capillary plexuses which drained into interfollicular venules, mostly high endothelial venules (HEV), before joining larger veins. No afferent lymphatics were observed entering the adenoid. Although ICAM-1 was widely distributed in the tissue, it was preferentially expressed on luminal aspects of HEV. E-selectin was found only in a few areas on HEV and subepithelial capillaries, whereas P-selectin was strongly expressed on segments of HEV, adjacent small venules and a few follicular capillaries. IEM showed the localisation of VCAM-1 on the components of the perivascular sheath, but not on the endothelium, of some HEV and capillaries. Its strongest expression was on follicular dendritic cells (FDC). These findings showed that in addition to HEV, lymphocyte-binding molecules are expressed on other segments of adenoid vasculature and their distribution and intensity of expression varies. In the non-inflamed adenoid, the VCAM-1 does not seem to participate in the adhesive mechanism of recirculating lymphocytes to the endothelium which, in this study, lacked the expression of VCAM-1 in all vessels.