Sagawa T, Tominaga A, Kodama T, Okada M
Department of Clinical Pathology, Ehime College of Health Science, Japan.
Immunology. 1993 Apr;78(4):650-6.
Platelet cytotoxicity was examined in vitro using various tumour cell lines as target cells. Thrombin-activated platelets as well as unstimulated platelets exerted a cytotoxic effect on some tumour cell lines including K562, KU812, LU99A and KG1, but other tumour cell lines including U937, MIA PaCa-2 and MOLT-4 were completely insensitive to this effect. Electron microscopic examinations showed that unstimulated platelets adhered to target K562 cells but thrombin-activated platelets did not. Morphological changes of K562 cells induced by unstimulated and thrombin-activated platelets were indistinguishable. When platelets and K562 cells were co-cultured in the same vessel but were prevented from coming into direct cell-to-cell contact by means of a membrane barrier, cytotoxicity of unstimulated platelets was completely blocked but that of thrombin-activated platelets was still detectable. However, no cytotoxic activity to K562 cells was detected in the supernatants obtained after stimulation of platelets with either target cells or thrombin for 4 hr. Extracellular Ca2+ ion was not required for the platelet-mediated cytotoxicity. Esterase inhibitors SBTI and TPCK had no effect on the formation of platelet-target cell adhesion but inhibited the cytotoxicity of unstimulated platelets. In contrast, the inhibitors had no effect on the cytotoxic activity of thrombin-activated platelets. These results suggest that direct contact between platelets and target cells is essential for unstimulated platelets but not for thrombin-activated platelets to exert cytotoxicity and that some esterases play a role in the cytotoxic process of unstimulated platelets. They also provide evidence that some cytotoxic effectors are soluble and easily inactivated factors liberated by activated platelets. Our findings indicate that platelets may be one of the cytotoxic effector cells against certain neoplasia.
使用各种肿瘤细胞系作为靶细胞，在体外检测血小板的细胞毒性。凝血酶激活的血小板以及未刺激的血小板对包括K562、KU812、LU99A和KG1在内的一些肿瘤细胞系具有细胞毒性作用，但包括U937、MIA PaCa-2和MOLT-4在内的其他肿瘤细胞系对这种作用完全不敏感。电子显微镜检查显示，未刺激的血小板粘附于靶K562细胞，而凝血酶激活的血小板则不粘附。未刺激和凝血酶激活的血小板诱导的K562细胞形态变化无法区分。当血小板和K562细胞在同一容器中共培养，但通过膜屏障阻止它们直接细胞间接触时，未刺激血小板的细胞毒性被完全阻断，但凝血酶激活血小板的细胞毒性仍可检测到。然而，在用靶细胞或凝血酶刺激血小板4小时后获得的上清液中，未检测到对K562细胞的细胞毒性活性。血小板介导的细胞毒性不需要细胞外Ca2+离子。酯酶抑制剂SBTI和TPCK对血小板-靶细胞粘附的形成没有影响，但抑制未刺激血小板的细胞毒性。相反，这些抑制剂对凝血酶激活血小板的细胞毒性活性没有影响。这些结果表明，血小板与靶细胞之间的直接接触对于未刺激的血小板发挥细胞毒性是必不可少的，但对于凝血酶激活的血小板则不是，并且一些酯酶在未刺激血小板的细胞毒性过程中起作用。它们还提供了证据，表明一些细胞毒性效应物是由活化血小板释放的可溶性且易失活的因子。我们的发现表明，血小板可能是针对某些肿瘤形成的细胞毒性效应细胞之一。
