Rifampicin-dependent antibodies target glycoprotein IIb/IIIa and cause clearance of human platelets in NOD/SCID mice

Shear Forces Induced Platelet Clearance Is a New Mechanism of Thrombocytopenia

BACKGROUND

Thrombocytopenia has been consistently described in patients with extracorporeal membrane oxygenation (ECMO) and associated with poor outcome. However, the prevalence and underlying mechanisms remain largely unknown, and a device-related role of ECMO in thrombocytopenia has been hypothesized. This study aims to investigate the mechanisms underlying thrombocytopenia in ECMO patients.

METHODS

In a prospective cohort of 107 ECMO patients, we investigated platelet count, functions, and glycoprotein shedding. In an ex vivo mock circulatory ECMO loop, we assessed platelet responses and VWF (von Willebrand factor)-GP Ibα (glycoprotein Ibα) interactions at low- and high-flow rates, in the presence or absence of red blood cells. The clearance of human platelets subjected or not to ex vivo perfusion was studied using an in vivo transfusion model in NOD/SCID (nonobese diabetic/severe combined Immunodeficient) mice.

RESULTS

In ECMO patients, we observed a time-dependent decrease in platelet count starting 1 hour after device onset, with a mean drop of 7%, 35%, and 41% at 1, 24, and 48 hours post-ECMO initiation (P=0.00013, P<0.0001, and P<0.0001, respectively), regardless of the type of ECMO. This drop in platelet count was associated with a decrease in platelet GP Ibα expression (before: 47.8±9.1 versus 24 hours post-ECMO: 42.3±8.9 mean fluorescence intensity; P=0.002) and an increase in soluble GP Ibα plasma levels (before: 5.6±3.3 versus 24 hours post-ECMO: 10.8±4.1 µg/mL; P<0.0001). GP Ibα shedding was also observed ex vivo and was unaffected by (1) red blood cells, (2) the coagulation potential, (3) an antibody blocking VWF-GP Ibα interaction, (4) an antibody limiting VWF degradation, and (5) supraphysiological VWF plasma concentrations. In contrast, GP Ibα shedding was dependent on rheological conditions, with a 2.8-fold increase at high- versus low-flow rates. Platelets perfused at high-flow rates before being transfused to immunodeficient mice were eliminated faster in vivo with an accelerated clearance of GP Ibα-negative versus GP Ibα-positive platelets.

CONCLUSIONS

ECMO-associated shear forces induce GP Ibα shedding and thrombocytopenia due to faster clearance of GP Ibα-negative platelets. Inhibiting GP Ibα shedding could represent an approach to reduce thrombocytopenia during ECMO.

A case of severe thrombocytopenia after the first exposure to rifampicin

Severe immune thrombocytopenia is a rare side-effect of rifampicin (RFP) and can be life-threatening. Here, we report the case of a 74-year-old male with tuberculous pleurisy who developed severe thrombocytopenia after first exposure to RFP. Platelet count decreased to 1 × 10³/μL after 7 days of treatment with RFP, isoniazid, ethambutol, and pyrazinamide. After all the drugs were discontinued, the platelet count recovered. As thrombocytopenia did not occur after re-administration of drugs other than RFP, the patient was diagnosed with RFP-induced thrombocytopenia. Clinicians should be aware that RFP can induce acute and severe thrombocytopenia even without previous exposure to this drug.

Rifampicin-Induced Thrombocytopenia: A Case Report and Short Review of the Literature

Thrombocytopenia may be associated with a variety of conditions and risks depending on its severity, ranging from mild epistaxis to life-threating bleeding. Many drugs or herbal remedies can cause thrombocytopenia by either inhibiting platelet production and/or enhancing their destruction from the peripheral blood mediated via an immunological mechanism implicating drug-dependent antibodies. The latter entity is called drug-induced immune thrombocytopenia: a life-threatening, under-recognised condition, which is often a diagnostic challenge. Rifampicin is a widely used, well-tolerated, and effective bactericidal drug. Adverse events, except for gastrointestinal effects, headache, skin rash, and pruritus, are uncommon. The authors herein report on a patient with isolated thrombocytopenia with a recent medical history of brucellosis on rifampicin and doxycycline. Thrombocytopenia was proved to be rifampicin-induced. Also presented is a short review of the literature on this rare subject, which should be of great importance to clinicians.

Differentiation of CD45‑/CD31+ lung side population cells into endothelial and smooth muscle cells in vitro

Side population (SP) cells are a small subpopulation of cells found in many mammalian tissues and organs, identified by their capacity to efflux Hoechst 33342 dye. They are enriched for stem/progenitor cell activity. SP cells isolated from the adult mouse lung can be separated into a CD45⁺ subset (bone marrow-derived) and a CD45⁻ subset that can be subdivided into CD31⁻ and CD31⁺ subpopulations. CD45⁻/CD31⁻ lung SP (LSP) cells are known to be mesenchymal stem cells. However, CD45⁻/CD31⁺ LSP cells are not fully characterized. In the present study, it was found that CD45⁻/CD31⁺ LSP cells were able to form colonies. Based on the expression of vascular endothelial growth factor receptor 2 (VEGFR2), these cells were separated into VEGFR2⁻ and VEGFR2⁺ cells. The CD45⁻/CD31⁺/VEGFR2⁻ LSP cells expressed genes characteristic of smooth muscle and endothelial progenitors, and were able to differentiate into smooth muscle and endothelial cells in vitro. The CD45⁻/CD31⁺/VEGFR2⁺ LSP cells expressed genes characteristic of endothelial progenitors and gave rise to endothelial cells, although not smooth muscle, in vitro. The data demonstrate that CD45⁻/CD31⁺/VEGFR2⁻ LSP cells differentiated into CD45⁻/CD31⁺/VEGFR2⁺ LSP cells and then endothelial cells, indicating that CD45⁻/CD31⁺/VEGFR2⁺ LSP cells are likely to be derived from CD45⁻/CD31⁺/VEGFR2⁻ LSP cells. Taken together, the results suggest that CD45⁻/CD31⁺ LSP cells can be separated into CD45⁻/CD31⁺/VEGFR2⁻ LSP cells, which may be progenitors of endothelial and smooth muscle, whereas CD45⁻/CD31⁺/VEGFR2⁺ LSP cells may serve as late commitment endothelial progenitors in the adult mouse lung.