We previously reported elevated P-selectin positive (CD62p+) platelet aggregates (pAG) in TTP patients, and showed that TTP plasma promoted formation of pAG when added to normal Wood in vitro [Blood 86:342a, 1995]. The present study further characterizes the pAG Induced by TTP plasma, addressing leukocyte binding to pAG and comparing effects of TTP plasma with those from patients with other disorders: TTP (n-12), ITP (n-18) and thrombosis (THR, n-11). Platelet-poor plasmas (PPP) were incubated with citrated O+ whole blood or platelet-rich plasma (PRP) from normal donors, then labeled with FITC a-CD41 and either PE a-CD62p or a-CD45 (a pan leukocyte marker). Numbers and percentages of pAG generated were assayed by flow cytometry. When PPP from all patient groups was added to whole blood (WBD), the %CD62+ pAG Increased relative to controls [p<0.01 or better) by the following factors: TTP (6.05 ±3.67), ITP (3.02 ±1.34), THR (1.63 ±0.87). Other distinctive features of TTP plasma effects were: (I) highest absolute number of CD62+ pAG, found with both WBD and PRP: (II) highest %CD62+ free platelets. (Ill) The %CD45+ pAG, Indicative of leukocyte binding, was increased 1.90 ±0.96 fold over controls with TTP plasma, vs. 1.50 ±0.24 fold In ITP and 1.14 ± 0.12 fold In THR (all p<0.01 or better). In parallel experiments using conventional Lumiaggregometry, none of the TTP or other patient plasmas induced any aggregation or release. To further define the unknown activator in TTP plasma, it was passed through a Staphylococcal A column to adsorb Immune complex, or was 3X frozen-thawed to test whether the activator would cryo-precipitate. Two of the 3 column-treated plasmas retained full potency. Freezethawing had no effect on the pro-aggragatory potency of TTP plasma. To summarbe: (1) TTP plasma is the most potent In increasing %CD62+ expression and leukocyte binding in pAG. (2) Flow cytometry Is much more sensitive than aggregometiy In detecting pro-aggregatory lactor(s) in TTP plasma. (3) These factor(s) are not removed by Staph. A column or by repeated freezing and thawing in most samples tested.
|Original language||English (US)|
|Journal||Journal of Investigative Medicine|
|State||Published - Jan 1 1996|
ASJC Scopus subject areas
- Biochemistry, Genetics and Molecular Biology(all)