Lenter M, Uhlig H, Hamann A, Jenö P, Imhof B, Vestweber D
Hans Spemann Laboratory, Max Planck Institute for Immunology, Freiburg, Federal Republic of Germany.
Proc Natl Acad Sci U S A. 1993 Oct 1;90(19):9051-5. doi: 10.1073/pnas.90.19.9051.
We have generated a monoclonal antibody (mAb), 9EG7, against mouse endothelial cells that blocks adhesion of lymphocytes to endothelial cells. Sequencing of four tryptic peptides of the purified antigen revealed its identity with the integrin chain beta 1. The only beta 1 integrin that is known to mediate cell-cell adhesion is alpha 4 beta 1 (VLA-4). This is not the integrin that is functionally defined by the mAb 9EG7 on endothelial cells. First, alpha 4 is not present on the analyzed endothelial cells. Second, mAb 9EG7 does not block the cell-adhesion function of alpha 4 beta 1 on the nonactivated mouse lymphoma L1-2. Thus, the mAb 9EG7 can functionally distinguish between different beta 1 integrins and defines a beta 1 integrin other than alpha 4 beta 1 as a newly discovered cell-cell adhesion molecule. This integrin is most likely alpha 6 beta 1, since an antibody against the alpha 6 chain blocks lymphocyte adhesion to the same degree as the mAb 9EG7, the effect of both antibodies is not additive, and the alpha 6 chain is coprecipitated with beta 1 in 9EG7 immunoprecipitations. Surprisingly, activation of alpha 4 beta 1 on L1-2 cells with phorbol ester or Mn2+ allows blocking of alpha 4 beta 1-mediated adhesion of L1-2 cells to endothelial cells with mAb 9EG7. Furthermore, only the activated alpha 4 beta 1 heterodimer, but not the unactivated complex, is detectable with 9EG7 in immunoprecipitations and by flow cytometry. Thus, mAb 9EG7 defines an epitope on integrin chain beta 1, which is accessible on the alpha 4 beta 1 heterodimer only after activation of this integrin.
我们制备了一种针对小鼠内皮细胞的单克隆抗体（mAb）9EG7，它能阻断淋巴细胞与内皮细胞的黏附。对纯化抗原的四个胰蛋白酶肽段进行测序后发现，其与整合素β1链相同。已知唯一介导细胞间黏附的β1整合素是α4β1（VLA - 4）。但这并非mAb 9EG7在内皮细胞上功能所定义的整合素。首先，所分析的内皮细胞上不存在α4。其次，mAb 9EG7不能阻断α4β1在未活化的小鼠淋巴瘤L1 - 2细胞上的细胞黏附功能。因此，mAb 9EG7在功能上能够区分不同的β1整合素，并将一种不同于α4β1的β1整合素定义为新发现的细胞间黏附分子。这种整合素很可能是α6β1，因为一种针对α6链的抗体与mAb 9EG7阻断淋巴细胞黏附的程度相同，两种抗体的作用并非相加，并且在9EG7免疫沉淀中α6链与β1共沉淀。令人惊讶的是，用佛波酯或Mn2 +激活L1 - 2细胞上的α4β1后，mAb 9EG7能够阻断L1 - 2细胞与内皮细胞之间由α4β1介导的黏附。此外，在免疫沉淀和流式细胞术中，只有活化的α4β1异二聚体，而不是未活化的复合物，能够被9EG7检测到。因此，mAb 9EG7定义了整合素β1链上的一个表位，该表位仅在这种整合素活化后在α4β1异二聚体上才可及。
