Pulido R, Elices M J, Campanero M R, Osborn L, Schiffer S, García-Pardo A, Lobb R, Hemler M E, Sánchez-Madrid F
Sección de Inmunología, Hospital de la Princesa, Universidad Autónoma de Madrid, Spain.
J Biol Chem. 1991 Jun 5;266(16):10241-5.
The human integrin VLA (very late activation antigens)-4 (CD49d/CD29), the leukocyte receptor for both the CS-1 region of plasma fibronectin (Fn) and the vascular cell surface adhesion molecule-1 (VCAM-1), also mediates homotypic aggregation upon triggering with specific anti-VLA-4 monoclonal antibody (mAb). Epitope mapping of this integrin on the human B-cell line Ramos, performed with a wide panel of anti-VLA-4 mAb by both cross-competitive cell binding and protease sensitivity assays, revealed the existence of three topographically distinct epitopes on the alpha 4 chain, referred to as epitopes A-C. By testing this panel of anti-VLA-4 mAb for inhibition of cell binding to both a 38-kDa Fn fragment containing CS-1 and to VCAM-1, as well as for induction and inhibition of VLA-4 mediated homotypic cell adhesion, we have found overlapping but different functional properties associated with each epitope. Anti-alpha 4 mAb recognizing epitope B inhibited cell attachment to both Fn and VCAM-1, whereas mAb against epitope A did not block VCAM-1 binding and only partially inhibited binding to Fn. In contrast, mAb directed to epitope C did not affect cell adhesion to either of the two VLA-4 ligands. All mAb directed to site A, as well as a subgroup of mAb recognizing epitope B (called B2), were able to induce cell aggregation, but this effect was not exerted by mAb specific to site C and by a subgroup against epitope B (called B1). Moreover, although anti-epitope C and anti-epitope B1 mAb did not trigger aggregation, those mAb blocked aggregation induced by anti-epitope A or B2 mAb. In addition, anti-epitope A mAb blocked B2-induced aggregation, and conversely, anti-epitope B2 mAb blocked A-induced aggregation. Further evidence for multiple VLA-4 functions is that anti-Fn and anti-VCAM-1 antibodies inhibited binding to Fn or to VCAM-1, respectively, but did not affect VLA-4-mediated aggregation. In summary, we have demonstrated that there are at least three different VLA-4-mediated adhesion functions, we have defined three distinct VLA-4 epitopes, and we have correlated these epitopes with the different functions of VLA-4.
人整合素VLA（极迟活化抗原）-4（CD49d/CD29）是血浆纤连蛋白（Fn）的CS-1区域和血管细胞表面黏附分子-1（VCAM-1）的白细胞受体，在用特异性抗VLA-4单克隆抗体（mAb）触发后也介导同型聚集。通过交叉竞争细胞结合和蛋白酶敏感性测定，用大量抗VLA-4 mAb对人B细胞系Ramos上的这种整合素进行表位作图，揭示了α4链上存在三个拓扑学上不同的表位，称为表位A-C。通过测试该抗VLA-4 mAb组对细胞与含有CS-1的38-kDa Fn片段和VCAM-1结合的抑制作用，以及对VLA-4介导的同型细胞黏附的诱导和抑制作用，我们发现每个表位都具有重叠但不同的功能特性。识别表位B的抗α4 mAb抑制细胞与Fn和VCAM-1的附着，而针对表位A的mAb不阻断VCAM-1结合，仅部分抑制与Fn的结合。相反，针对表位C的mAb不影响细胞与两种VLA-4配体中任何一种的黏附。所有针对位点A的mAb以及识别表位B的一个亚组mAb（称为B2）都能够诱导细胞聚集，但位点C特异性的mAb和针对表位B的一个亚组mAb（称为B1）则没有这种作用。此外，尽管抗表位C和抗表位B1 mAb不会触发聚集，但这些mAb会阻断抗表位A或B2 mAb诱导的聚集。此外，抗表位A mAb阻断B2诱导的聚集，反之，抗表位B2 mAb阻断A诱导的聚集。多个VLA-4功能的进一步证据是，抗Fn和抗VCAM-1抗体分别抑制与Fn或VCAM-1的结合，但不影响VLA-4介导的聚集。总之，我们已经证明至少存在三种不同的VLA-4介导的黏附功能，我们定义了三个不同的VLA-4表位，并将这些表位与VLA-4的不同功能相关联。
