van Kooyk Y, Weder P, Hogervorst F, Verhoeven A J, van Seventer G, te Velde A A, Borst J, Keizer G D, Figdor C G
Division of Immunology, The Netherlands Cancer Institute, Amsterdam.
J Cell Biol. 1991 Jan;112(2):345-54. doi: 10.1083/jcb.112.2.345.
The leukocyte function-associated molecule-1 (LFA-1) plays a key role in cell adhesion processes between cells of the immune system. We investigated the mechanism that may regulate LFA-1-ligand interactions, which result in cell-cell adhesion. To this end we employed an intriguing anti-LFA-1 alpha mAb (NKI-L16), capable of inducing rather than inhibiting cell adhesion. Aggregation induced by NKI-L16 or Fab fragments thereof is not the result of signals transmitted through LFA-1. The antibody was found to recognize a unique Ca2(+)-dependent activation epitope of LFA-1, which is essentially absent on resting lymphocytes, but becomes induced upon in vitro culture. Expression of this epitope correlates well with the capacity of cells to rapidly aggregate upon stimulation by PMA or through the TCR/CD3 complex, indicating that expression of the NKI-L16 epitope is essential for LFA-1 to mediate adhesion. However, expression of the NKI-L16 epitope in itself is not sufficient for cell binding since cloned T lymphocytes express the NKI-L16 epitope constitutively at high levels, but do not aggregate spontaneously. Based on these observations we propose the existence of three distinct forms of LFA-1: (a) an inactive form, which does not, or only partially exposes the NKI-L16 epitope, found on resting cells; (b) an intermediate, NKI-L16+ form, expressed by mature or previously activated cells; and (c) an active (NKI-L16+) form of LFA-1, capable of high affinity ligand binding, obtained after specific triggering of a lymphocyte through the TCR/CD3 complex, by PMA, or by binding of NKI-L16 antibodies.
白细胞功能相关分子-1（LFA-1）在免疫系统细胞间的细胞黏附过程中起关键作用。我们研究了可能调节LFA-1-配体相互作用（从而导致细胞间黏附）的机制。为此，我们采用了一种有趣的抗LFA-1α单克隆抗体（NKI-L16），它能够诱导而非抑制细胞黏附。由NKI-L16或其Fab片段诱导的聚集并非通过LFA-1传递信号的结果。发现该抗体识别LFA-1一个独特的Ca2(+)依赖性激活表位，静止淋巴细胞上基本不存在该表位，但在体外培养时会被诱导产生。该表位的表达与细胞在受到佛波酯（PMA）刺激或通过TCR/CD3复合物刺激后快速聚集的能力密切相关，表明NKI-L16表位的表达对于LFA-1介导黏附至关重要。然而，NKI-L16表位本身的表达不足以实现细胞结合，因为克隆的T淋巴细胞持续高水平组成性表达NKI-L16表位，但不会自发聚集。基于这些观察结果，我们提出存在三种不同形式的LFA-1：（a）一种无活性形式，在静止细胞上不存在或仅部分暴露NKI-L16表位；（b）一种中间的NKI-L16+形式，由成熟或先前激活的细胞表达；（c）一种活性（NKI-L16+）形式的LFA-1，能够进行高亲和力配体结合，在淋巴细胞通过TCR/CD3复合物、PMA或NKI-L16抗体结合而受到特异性触发后获得。
