Peripheral lymph node addressins are expressed on skin endothelial cells

The term "peripheral node addressins" describes a set of several endothelia l adhesion molecules, which collectively bind to L-selectin and react with monoclonal antibody MECA-79. They regulate lymphocyte recirculation through peripheral nodes, Their expression is thought to be restricted to a specia lized vascular segment within the node, called the high endothelial venule. In certain chronic skin diseases, however, postcapillary venules of the sk in may also acquire a high endothelial venule-like morphology, Employing im munohistochemistry on cryostat sections, we found these skin endothelial ce lls - like peripheral node high endothelial venules - to be reactive with m onoclonal antibody MECA-79. Tissue lysates fi om the same specimens were th en analyzed by immunoprecipitation using recombinant human L-selectin Fc-ch imeras followed by immunoblotting using monoclonal antibody MECA-79. In con trast to peripheral node endothelium, which mainly expressed peripheral nod e addressin moieties of molecular sizes 90-110 kDa and 160 kDa, endothelial cells in cutaneous T cell lymphoma skin lesions expressed an additional an d not yet defined 220 kDa peripheral node addressin-like molecule. Most sur prisingly, even in normal skin specimens, we found a distinct subset of end othelial cells located around hair follicles constitutively expressing 90-1 10 kDa peripheral node addressin-like moieties. It is intriguing to specula te that - in analogy to the role of peripheral node addressins in periphera l nodes - the induced expression of peripheral node addressins in chronic T cell mediated skin diseases is responsible for a sustained lymphocyte recr uitment. The constitutive expression of peripheral node addressins on perif ollicular endothelium may serve for a continuo us lymphocyte recirculation through normal skin.