Tehran University of Medical Sciences Iranian Journal of Allergy, Asthma and Immunology 1735-1502 13 2 2014 04 15 85 92 EN Nargess Arandi Department of Immunology, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran Abbas Mirshafiey Department of Immunology, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran Mahmood Jeddi-Tehrani Monoclonal Antibody Research Center, Avicenna Research Institute, ACECR, Tehran, Iran Mohammadreza Shaghaghi Research Center for Immunodeficiency, Pediatrics Center of Excellence, Children’s Medical Center, Tehran University of Medical Sciences, Tehran, Iran Bamdad Sadeghi Research Center for Immunodeficiency, Pediatrics Center of Excellence, Children’s Medical Center, Tehran University of Medical Sciences, Tehran, Iran Hassan Abolhassani Research Center for Immunodeficiency, Pediatrics Center of Excellence, Children’s Medical Center, Tehran University of Medical Sciences, Tehran, Iran Ramazan Ali Sharifian Clinic of Hematology and Oncology, Vali-Asr Hospital, Faculty of Medicine, Tehran University of Medical Sciences, Tehran, Iran Mohammad Saeid Rahiminejad Division of Pediatric Hematology Oncology, Children's Medical Center, Tehran University of Medical Sciences, Tehran, Iran Asghar Aghamohammadi Research Center for Immunodeficiency, Pediatrics Center of Excellence, Children’s Medical Center, Tehran University of Medical Sciences, Tehran, Iran 2015 10 16 Immune thrombocytopenic  purpura (ITP) is an autoimmune bleeding disorder characterized by production  of auto-antibodies against platelet antigens. It is obvious that regulatory T cells (Tregs) have a major role in controlling immune homeostasis and preventing autoimmunity. To investigate the frequency and functions of Tregs, twenty ITP patients and twenty age- and sex- matched healthy controls were recruited. The peripheral blood mononuclear cells were isolated and the proportion of Tregs was defined by flow cytometry method. The expression of immune-regulatory markers, cytotoxic T-lymphocyte associated antigen-4 (CTLA-4) and glucocorticoid induced tumor necrosis  factor  receptor  (GITR)  were  also  assessed by  quantitative  Real-time polymerase chain reaction TaqMan method. For evaluation of Treg function, Tregs were enriched and their ability to inhibit proliferation of T cells was measured and levels of immune-regulatory cytokines IL-10 and Transforming growth factor beta (TGF-β) were also measured.Results showed that the frequency of Tregs  and  the  mean  fluorescence  intensity  of  forkhead  box  P3  (FOXP3)  protein  significantly decreased in ITP patients compared to those in healthy controls. In addition, there was a significant reduction  in relative expression of both  CTLA-4 and GITR  mRNA  in ITP  patients (p=0.02 and p=0.006, respectively). The suppressive function of Tregs also diminished in ITP patients compared to controls. Both  IL-10 and TGF-β  cytokines were produced  in lower amounts  in ITP  patients than controls. It  could  be  concluded  that  alteration  in  Treg  frequency and  functional  characteristics might  be responsible for loss of self-tolerance and subsequently destructive immune responses observed in ITP patients. https://ijaai.tums.ac.ir/index.php/ijaai/article/view/472 https://ijaai.tums.ac.ir/index.php/ijaai/article/download/472/365