Jakubowski A, Rosa M D, Bixler S, Lobb R, Burkly L C
Biogen, Inc., Cambridge, MA 02142, USA.
Cell Adhes Commun. 1995 May;3(2):131-42. doi: 10.3109/15419069509081282.
The Very Late Antigen-4 receptor (VLA-4) (alpha 4 beta 1) is constitutively expressed on leukocytes and plays a role in cell trafficking, activation and development through its interaction with two alternative ligands, Vascular Cell Adhesion Molecule (VCAM-1) and fibronectin (FN). VLA-4-dependent cell adhesion is augmented by various stimuli, such as divalent cations, certain beta 1-specific monoclonal antibodies (mAbs) and cell activation. However, the steps of the adhesive process which they affect are currently undefined. In order to investigate whether or not these stimuli affect the primary step, VLA-4/ligand binding, we employed a recombinant VCAM-IgG fusion protein (VCAM-Ig) as a soluble ligand for VLA-4. Using this soluble ligand, we have directly demonstrated that the VLA-4 receptor can exist in at least three different affinity states on the cell surface. Two distinct high affinity states are induced on normal peripheral blood T cells, one by the anti-beta 1 mAb TS2/16, and one of 15-20 fold higher affinity by the divalent cation Mn2+. Interestingly, activation through the T cell receptor (TcR), through CD31 or by the Macrophage Inflammatory Protein-1 beta chemokine (MIP-1 beta) do not detectably increase VLA-4 affinity although they do augment VLA-4 dependent cell adhesion in vitro. Thus, VCAM-Ig binding defines high affinity VLA-4 receptors, revealing unique effects of the TS2/16 mAb and Mn2+ cations in vitro, and distinguishes VLA-4/VCAM interactions from subsequent steps in cell adhesion.
极迟抗原-4受体（VLA-4）（α4β1）在白细胞上组成性表达，并通过与两种替代配体——血管细胞黏附分子（VCAM-1）和纤连蛋白（FN）相互作用，在细胞迁移、激活和发育中发挥作用。VLA-4依赖性细胞黏附可被多种刺激增强，如二价阳离子、某些β1特异性单克隆抗体（mAb）和细胞激活。然而，它们所影响的黏附过程步骤目前尚不清楚。为了研究这些刺激是否影响第一步，即VLA-4/配体结合，我们使用重组VCAM-IgG融合蛋白（VCAM-Ig）作为VLA-4的可溶性配体。使用这种可溶性配体，我们直接证明了VLA-4受体在细胞表面至少可以以三种不同的亲和力状态存在。在正常外周血T细胞上诱导出两种不同的高亲和力状态，一种由抗β1 mAb TS2/16诱导，另一种由二价阳离子Mn2+诱导，其亲和力高15 - 20倍。有趣的是，通过T细胞受体（TcR）、通过CD31或巨噬细胞炎性蛋白-1β趋化因子（MIP-1β）激活，虽然在体外确实增强了VLA-4依赖性细胞黏附，但并未检测到VLA-4亲和力增加。因此，VCAM-Ig结合定义了高亲和力VLA-4受体，揭示了TS2/16 mAb和Mn2+阳离子在体外独特的作用，并将VLA-4/VCAM相互作用与细胞黏附的后续步骤区分开来。
