GLOBAL VASCULAR EXPRESSION OF MURINE CD34, A SIALOMUCIN-LIKE ENDOTHELIAL LIGAND FOR L-SELECTIN

Extravasation of leukocytes into organized lymphoid tissues and into s ites of inflammation is critical to immune surveillance. Leukocyte mig ration to peripheral lymph nodes (PLN), mesenteric lymph nodes (MLN) a nd Peyer's patches (PP) depends on L-selectin, which recognizes carboh ydrate-bearing, sialomucin-like endothelial cell surface glycoproteins . Two of these ligands have been identified at the molecular level. On e is the potentially soluble mucin, GlyCAM 1, which is almost exclusiv ely produced by high endothelial venules (HEV) of PLN and MLN. The sec ond HEV ligand for L-selectin is the membrane-bound sialomucin CD34. H istorically, this molecule has been successfully used to purify human pluripotent bone marrow stem cells, and limited data suggest that huma n CD34 is present on the vascular endothelium of several organs. Here we describe a comprehensive analysis of the vascular expression of CD3 4 in murine tissues using a highly specific antimurine CD34 polyclonal antibody. CD34 was detected on vessels in all organs examined and was expressed during pancreatic and skin inflammatory episodes. A subset of HEV-like vessels in the inflamed pancreas of nonobese diabetic (NOD ) mice are positive for both CD34 and GlyCAM 1, and bind to an L-selec tin/immunoglobulin G (IgG) chimeric probe. Finally, we found that CD34 is present on vessels of deafferentiated PLN, despite the fact that t hese vessels are no longer able to interact with L-selectin or support lymphocyte binding in vitro or trafficking in vivo. Our data suggest that the regulation of posttranslational carbohydrate modifications of CD34 is critical in determining its capability to act as an L-selecti n ligand. Based on its ubiquitous expression, we propose that an appro priately glycosylated form of vascular CD34 may act as a ligand for L- selectin-mediated leukocyte trafficking to both lymphoid and nonlympho id sites. (C) 1994 by The American Society of Hematology.