IMMUNOHISTOCHEMICAL AND ULTRASTRUCTURAL ANALYSIS OF AN EXTRACELLULAR-MATRIX BOUND ANTIGEN PREFERENTIALLY ASSOCIATED WITH MUCOSAL POSTCAPILLARY VENULES

Human lymphoma derived monoclonal antibody (anti 'mucosal vessel assoc iated antigen' [MVAA]) binds to high endothelial venules (HEV) in gut- associated lymphoid tissue, but shows only weak reactivity with HEV in peripheral lymphoid tissues. We have used immunohistochemistry and im munoelectron microscopy to define the precise ultrastructural distribu tion of the molecule, and to determine whether there is any associatio n between this molecule and cellular traffic. We have observed that MV AA is a component of basement membrane which is only expressed by a su bset of blood vessels. Although it is restricted to vessels which supp ort lymphocyte traffic within lymphoid tissue, we did not observe any association between the distribution of MVAA and extravasating lymphoc ytes. MVAA is expressed in the fetal intestine in association with a s ubset of larger vessels. It is therefore not necessarily induced as a consequence of antigenic challenge. It is likely that MVAA has a struc tural role related to its restricted microanatomical distribution; pos sibly the maintenance of integrity of vessel walls which are continuou sly disrupted by the extravasation of lymphocytes.