PNAd

PNAd, short for Peripheral Node Addressin, is a group of endothelial ligands that decorate high endothelial venules (HEVs) in peripheral lymph nodes and some inflamed or tertiary lymphoid tissues. They mediate the trafficking of naive lymphocytes by binding to L-selectin (CD62L) on these cells, promoting rolling and entry into lymphoid tissue. This mechanism is a key component of lymphocyte recirculation and immune surveillance.

The PNAd family comprises several mucin-like glycoproteins that present sulfated and fucosylated carbohydrate epitopes recognized by L-selectin. The principal components include GlyCAM-1 and CD34, which carry the characteristic PNAd carbohydrate motifs. The MECA-79 monoclonal antibody recognizes a shared PNAd carbohydrate epitope and is widely used to identify and study HEVs in tissue sections, serving as a histological marker of functional HEVs.

Localization and regulation of PNAd are tissue- and condition-dependent. In healthy individuals, PNAd expression is largely restricted to HEVs of peripheral lymph nodes, supporting routine lymphocyte homing. During development, PNAd expression emerges as lymphoid organs form, and in inflammatory states, PNAd-like ligands can be ectopically expressed on HEVs in nonlymphoid tissues, contributing to the formation of tertiary lymphoid structures and altered leukocyte recruitment.

Clinical and research relevance centers on understanding lymphocyte trafficking and inflammatory disease. PNAd and its interaction with L-selectin are targets of interest for modulating immune cell entry, with MECA-79-based detection aiding histopathological assessment of lymphoid vasculature. See also L-selectin, high endothelial venules, GlyCAM-1, and CD34.