Oxley S M, Sackstein R
Division of Bone Marrow Transplantation, H. Lee Moffitt Cancer Center, University of South Florida College of Medicine, Tampa.
Blood. 1994 Nov 15;84(10):3299-306.
L-selectin, the peripheral lymph node "homing receptor," is an adhesion protein that mediates lymphocyte binding to lymph node high endothelial venules. Ligands for this protein have been identified only on endothelial cells, and recent murine studies indicate that CD34 on endothelial cells is an L-selectin ligand. To investigate whether CD34 expressed on hematopoietic cells functions as an L-selectin ligand, we used an in vitro binding assay to examine lymphocyte adherence to KG1a, a CD34+ human hematopoietic progenitor cell line. We observed specific L-selectin-mediated adherence of lymphocytes to KG1a: the binding was calcium-dependent, was strictly inhibited by anti-L-selectin antibodies and by carbohydrate ligands of L-selectin, and was abrogated by induction of L-selectin shedding from the lymphocyte membrane by treatment with phorbol esters. However, blocking studies using anti-CD34 antibodies, and experiments using KG1a cells sorted for CD34 expression and COS-7 cells transfected with full-length CD34 cDNA indicate that the ligand on KG1a is not CD34; moreover, RPMI 8402, a CD34+ cell line, does not support lymphocyte adherence in the binding assay. Treatment of KG1a with the enzymes neuraminidase, chymotrypsin, and bromelain abrogated lymphocyte binding to the cells, indicating that the ligand is a glycoprotein. These experiments show that CD34 on hematopoietic cells is not an L-selectin ligand and provide the first evidence of a ligand for L-selectin present on a non-endothelial cell.
L-选择素是外周淋巴结的“归巢受体”，是一种介导淋巴细胞与淋巴结高内皮微静脉结合的黏附蛋白。该蛋白的配体仅在内皮细胞上被鉴定出来，最近的小鼠研究表明内皮细胞上的CD34是一种L-选择素配体。为了研究造血细胞上表达的CD34是否作为L-选择素配体发挥作用，我们使用体外结合试验来检测淋巴细胞对KG1a（一种CD34+人类造血祖细胞系）的黏附。我们观察到淋巴细胞通过L-选择素特异性介导对KG1a的黏附：这种结合依赖于钙，被抗L-选择素抗体和L-选择素的碳水化合物配体严格抑制，并且通过用佛波酯处理诱导淋巴细胞膜上L-选择素的脱落而被消除。然而，使用抗CD34抗体的阻断研究以及使用根据CD34表达分选的KG1a细胞和用全长CD34 cDNA转染的COS-7细胞进行的实验表明，KG1a上的配体不是CD34；此外，RPMI 8402（一种CD34+细胞系）在结合试验中不支持淋巴细胞黏附。用神经氨酸酶、胰凝乳蛋白酶和菠萝蛋白酶处理KG1a消除了淋巴细胞与细胞的结合，表明该配体是一种糖蛋白。这些实验表明造血细胞上的CD34不是L-选择素配体，并提供了非内皮细胞上存在L-选择素配体的首个证据。
