Transendothelial migration of leukocytes is promoted by plasma from a subgroup of immune thrombocytopenic purpura patients with small‐vessel ischemic brain disease

We previously described a subgroup of immune thrombocytopenic purpura (ITP) patients presenting with recurring transient ischemic attack‐like symptoms and progressive cognitive impairment due to small vessel disease (SVD) seen in the brain. They presented minimal bleeding despite thrombocytopenia, and platelet activation was elevated compared to classic ITP. On the hypothesis that the blood–brain barrier (BBB) is compromised in this subgroup, we investigated the effect of plasma from SVD‐ITP patients on the transendothelial migration of leukocytes (TEML). Brain microvascular endothelial cells (BMVEC) were grown to confluence on 6.5‐μm pore filters and plasma from 10 healthy controls, 20 classic ITP, and 5 SVD‐ITP were added and incubated 24 hr. Then 1 × 105 monocytes (U937) were added and the number migrated through the EC monolayer after 6 hr was measured by flow cytometry. The effect on TEML of danazol was also assessed. We found that plasma from SVD‐ITP but not classic ITP induced 10‐fold rise in EC activation marker CD62E and a sevenfold increase in TEML, to 38.5% ± 12.5% of cells migrated, compared to normal controls (5.6% ± 1.2%) or classic ITP (6.1% ± 0.2%), P < 0.001. Preincubation of U937 with endothelial microparticles (EMP) increased TEML by 20.0% ± 6.4% with SVD‐ITP plasma, significantly more than with classic ITP or control plasmas, P = 0.003. Pretreatment of cultures with danazol (100 μg/mL) inhibited TEML by 25% in all wells tested, whether or not EMP were added. In summary, SVD‐ITP plasma activates EC and augments TEML, suggesting plasma‐mediated BBB dysfunction in this syndrome. Danazol modestly but significantly inhibited TEML. Am. J. Hematol., 2008. © 2007 Wiley‐Liss, Inc.