title: Platelet Apoptosis in Adult Immune Thrombocytopenia: Insights into the Mechanism of Damage Triggered by Auto-Antibodies.
abstract: Mechanisms leading to decreased platelet count in immune thrombocytopenia (ITP) are heterogeneous. This study describes increased platelet apoptosis involving loss of mitochondrial membrane potential (ΔΨm), caspase 3 activation (aCasp3) and phosphatidylserine (PS) externalization in a cohort of adult ITP patients. Apoptosis was not related to platelet activation, as PAC-1 binding, P-selectin exposure and GPIb-IX internalization were not increased. Besides, ITP platelets were more sensitive to apoptotic stimulus in terms of aCasp3. Incubation of normal platelets with ITP plasma induced loss of ΔΨm, while PS exposure and aCasp3 remained unaltered. The increase in PS exposure observed in ITP platelets could be reproduced in normal platelets incubated with ITP plasma by adding normal CD3+ lymphocytes to the system as effector cells. Addition of leupeptin -a cathepsin B inhibitor- to this system protected platelets from apoptosis. Increased PS exposure was also observed when normal platelets and CD3+ lymphocytes were incubated with purified IgG from ITP patients and was absent when ITP plasma was depleted of auto-antibodies, pointing to the latter as responsible for platelet damage. Apoptosis was present in platelets from all patients carrying anti-GPIIb-IIIa and anti-GPIb auto-antibodies but was absent in the patient with anti-GPIa-IIa auto-antibodies. Platelet damage inversely correlated with platelet count and decreased during treatment with a thrombopoietin receptor agonist. These results point to a key role for auto-antibodies in platelet apoptosis and suggest that antibody-dependent cell cytotoxicity is the mechanism underlying this phenomenon.
authors: Departamento de Hematología Investigación. Instituto de Investigaciones Médicas A. Lanari-IDIM, Universidad de Buenos Aires (UBA), Consejo Nacional de Investigaciones Cientificas y Tecnicas (CONICET), Buenos Aires, Argentina.
authors: Nora P
authors: NP
authors: Goette
authors: Departamento de Hematología Investigación. Instituto de Investigaciones Médicas A. Lanari-IDIM, Universidad de Buenos Aires (UBA), Consejo Nacional de Investigaciones Cientificas y Tecnicas (CONICET), Buenos Aires, Argentina.
authors: Ana C
authors: AC
authors: Glembotsky
authors: Departamento de Hematología Investigación. Instituto de Investigaciones Médicas A. Lanari-IDIM, Universidad de Buenos Aires (UBA), Consejo Nacional de Investigaciones Cientificas y Tecnicas (CONICET), Buenos Aires, Argentina.
authors: Paola R
authors: PR
authors: Lev
authors: Departamento de Hematología Investigación. Instituto de Investigaciones Médicas A. Lanari-IDIM, Universidad de Buenos Aires (UBA), Consejo Nacional de Investigaciones Cientificas y Tecnicas (CONICET), Buenos Aires, Argentina.
authors: Matías
authors: M
authors: Grodzielski
authors: Departamento de Hematología Investigación. Instituto de Investigaciones Médicas A. Lanari-IDIM, Universidad de Buenos Aires (UBA), Consejo Nacional de Investigaciones Cientificas y Tecnicas (CONICET), Buenos Aires, Argentina.
authors: Geraldine
authors: G
authors: Contrufo
authors: Departamento de Hematología, Hospital Ramos Mejía, Buenos Aires, Argentina.
authors: Marta S
authors: MS
authors: Pierdominici
authors: Departamento de Hematología Investigación. Instituto de Investigaciones Médicas A. Lanari-IDIM, Universidad de Buenos Aires (UBA), Consejo Nacional de Investigaciones Cientificas y Tecnicas (CONICET), Buenos Aires, Argentina.
authors: Yesica R
authors: YR
authors: Espasandin
authors: Departamento de Hematología, Centro de Educación Médica e Investigaciones Clínicas "Norberto Quirno" (CEMIC), Buenos Aires, Argentina.
authors: Dardo
authors: D
authors: Riveros
authors: Laboratorio de Citometría de Flujo, Centro de Educación Médica e Investigaciones Clínicas "Norberto Quirno" (CEMIC), Buenos Aires, Argentina.
authors: Alejandro J
authors: AJ
authors: García
authors: Departamento de Hematología Investigación. Instituto de Investigaciones Médicas A. Lanari-IDIM, Universidad de Buenos Aires (UBA), Consejo Nacional de Investigaciones Cientificas y Tecnicas (CONICET), Buenos Aires, Argentina.
authors: Felisa C
authors: FC
authors: Molinas
authors: Departamento de Hematología Investigación. Instituto de Investigaciones Médicas A. Lanari-IDIM, Universidad de Buenos Aires (UBA), Consejo Nacional de Investigaciones Cientificas y Tecnicas (CONICET), Buenos Aires, Argentina.
authors: Paula G
authors: PG
authors: Heller
authors: Departamento de Hematología Investigación. Instituto de Investigaciones Médicas A. Lanari-IDIM, Universidad de Buenos Aires (UBA), Consejo Nacional de Investigaciones Cientificas y Tecnicas (CONICET), Buenos Aires, Argentina.
authors: Rosana F
authors: http://orcid.org/0000-0002-0403-9565
authors: RF
authors: Marta
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001323:Autoantibodies / Q000276:immunology*; D001792:Blood Platelets / Q000187:drug effects / Q000276:immunology / Q000473:pathology*; D017252:CD3 Complex / Q000378:metabolism; D000001:Calcimycin / Q000494:pharmacology; D053148:Caspase 3 / Q000378:metabolism; D006801:Humans; D008214:Lymphocytes / Q000276:immunology / Q000378:metabolism; D008875:Middle Aged; D010718:Phosphatidylserines / Q000378:metabolism; D010949:Plasma; D015539:Platelet Activation; D016553:Purpura, Thrombocytopenic, Idiopathic / Q000097:blood / Q000276:immunology*; D055815:Young Adult
chemical_list: D001323:Autoantibodies; D017252:CD3 Complex; D010718:Phosphatidylserines; D000001:Calcimycin; D053148:Caspase 3