[Platelets-morphology, shape changing factor, and platelet agglutinating factor. TTP Research Group].

The morphology of circulating platelets in thrombotic thrombocytopenic purpura (TTP) was studied, and basic mechanism of the characteristic shape abnormality found in TTP was investigated in in vitro condition. The platelet shape was spineless sphere (spherical platelets without pseudopods), and shape change persisted 2 months after remission. This type of platelets were produced by long term of activation of normal resting platelets by several agonists except ADP, and induced by dysfunction of both microtubules and microfilaments. These suggest that the shape change in TTP is not specific, but a good parameter for the activity of TTP. PAF activity by the method of Kelton et al. (1984) was detected in only 1 out of 30 samples from 10 patients. PSCF activity was found in 9 out of 29 samples from 10 patients independently from disease activity. Both activities does not reflect the activity of TTP.