大腸菌O157産生ベロトキシン-1による低ずり応力下惹起血小板凝集亢進作用に関する研究

Abstract

The effect of verotoxin (VT)-1 produced by Escherichia coil O157 on platelets was studied with a laser light-assisted shear-induced platelet aggregometer and with binding assays. VT-1 remarkably enhanced the platelet aggregation under low shear stress, but did not affect it under high shear stress. The minimal concentration of VT-1 required for the enhancement was 0.25 ng/ml, and almost maximal enhancement was achieved at a final concentration of 4 ng/ml. This enhanced platelet aggregation disappear- ed after leukocyte depletion from normal platelet-rich plasma with a specific filter. In contrast, with a standard platelet aggregometer such enhanced platelet aggregation was not detected either in the presence or absence of ADP. ¹²⁵I-Labeled VT-1 did not specifically bind to normal washed platelets depleted of leukocytes, and thin layer chromatographic analysis of neutral glycolipids extracted from normal platelet lysates also demonstrated that leukocyte-depleted platelets lacked VT-1-specific receptor globotriaosylceramide (Gb 3), but pre-filtered ones retained Gb 3. Supernatant from mononuclear cell suspension stimulated with VT-1 enhanced platelet aggregation, but that from polymorphonuclear cell suspension did not. Several cytokines released from monocytes reproduced this enhance- ment in vitro. Further, plasmas from six out of seven patients with hemolytic uremic syndrome (HUS) exhibited the same effect as did the purified VT-1. This effect was almost impaired after treatment of HUS plasmas with Gb 3 in accord with decreased levels of plasma VT-1. Taken together, these results indicate that platelet lacks Gb 3, and VT- 1 appears to modulate platelet aggregation in an indirect fashion, presumably by releasing cytokines or proteins from target tissues.