Iranian J Parasitol: Vol. 6, No.2, 2011, pp.9-16 Iranian J Parasitol Open access Journal at http:// ijpa.tums.ac.ir Iranian Society of Parasitology http:// isp.tums.ac.ir Tehran University of Medical Sciences Publication http:// tums.ac.ir Original Article Apoptosis of Human Lymphocytes after Exposure to Hydatid Fluid M Mokhtari Amirmajdi1, M Sankian 2, *I Eftekharzadeh Mashhadi 1, A Varasteh 2, F Vahedi 2, A Sadrizadeh 3, A Spotin 1 1Department of Mycoparasitology, Faculty of Medicine, Mashhad University of Medical Sciences, Mashhad, Iran 2Immunobiochemistry Laboratory, Immunology Research Center, Bu-Ali research Institute, School of Medicine, Mashhad University of Medical Sciences, Mashhad, Iran 3Department of Thoracic surgery, Faculty of Medicine, Mashhad University of Medical Sciences, Mashhad, Iran (Received 15 Nov 2010; accepted 05 May 2011) ABSTRACT Background: Modulation of the immune response is an important strategy by which establish- ment and growth of hydatid cyst in the internal organs of human is warranted. Induction of apop- tosis in the lymphocytes might be a considerable component. This study was designed to evaluate apoptotic impact of hydatid fluid (HF) on human lymphocytes. Methods: Human lymphocytes were treated with hydatid fluid. After 6 hours of exposure, cas- pase-3 activity, the central enzyme of apoptosis cascade, was measured by fluorometric assay in the HF-treated lymphocytes and control cells. In addition, the expression of Bax (a pro-apoptotic protein) and Bcl-2 (an anti-apoptotic protein) mRNA was assessed by RT-PCR after 12 hours of exposure. Results: Both the ratio of Bax/Bcl-2 mRNA expression and Caspase-3 activity were higher in the HF-treated lymphocytes relative to the control group. Conclusion: Apoptosis could be as a possible mechanism by which Echinococcus granulosus overwhelms host defenses. Keywords: Hydatidosis, Fertile/Infertile Hydatid Cysts, Apoptosis *Corresponding author: Email: Iman.Eftekharzadeh.m@gmail.com 9