Iranian J Parasitol: Vol. 6, No.2, 2011, pp.9-16 leukocytes, and make them incapable of eliminating the parasite. This process is more prominent in the earlier stages of infec- tion, in which the concentration of leuko- cytes are not high enough to resist the para- site (18). In conclusion, the results of this study repre- sent apoptosis as an important mechanism by which E. granulosus overwhelms host defenses. Further investigations with larger sample size are needed to confirm this find- ing. Acknowledgements This study was conducted and financially supported by Mashhad University of Medical Sciences (MUMS). This article is derived from the master's thesis of the last author (Thesis No. A-247). We should appreciate scientific aids from dear Dr. Ali Akbar Shamsian and Mr. Gholamreza Farnoosh, as well Dr. Esmaeeli for statistical consults. In addition, we should thank all staff of Ghaem Hospital Mycoparasitology lab and Bu-Ali Research center Immunobiochemistry Lab for their co- operation. The authors declare that there is no conflict of interests. References 1. Sadjjadi SM. Present situation of echinococcosis in the Middle East and Arabic North Africa. Parasitol Int. 2006; 55 Suppl: S197-202. 2. Rokni MB. The present status of human helminthic diseases in Iran. Ann Trop Med Parasitol. 2008; 102(4): 283 - 95. 3. Siracusano A, Riganò R, Ortona E, Profumo E, Margutti P, Buttari B, Delunardo F, Teggi A. Immunomodu- latory mechanisms during Echinococcus 15 granulosus infection. Exp Parasitol. 2008; 119(4): 483 - 9. 4. Lorenzo C, Last JA, González-Sapienza GG. The immunogenicity of Ech- inococcus granulosus antigen 5 is determined by its post-translational mod- ifications. Parasitology. 2005; 131(5): 669 - 77. 5. Mamuti W, Sako Y, Nakao M, Xiao N, Nakaya K, Ishikawa Y, Yamasaki H, Lightowlers MW, Ito A. Recent advances in characterization of Echinococcus antigen B. Parasitol Int. 2006; 55 Suppl: S57-62. 6. Liu D, Rickard MD, Lightowlers MW. A strategy for production of monoclonal antibodies to Echinococcus granulosus antigen 5 and antigen B. Int J Parasitol. 1992; 22(7): 1013 - 6. 7. Cabrera G, Cabregos ME, Morassutti AL, Cabezon C, Orellana J, Hellman U, Zaha A, Galanti N. DNA Damage, RAD9 and Fertility/Infertility of Echinococcus granulosus Hydatid Cysts. Journal of Cellular Physiology. 2008; 216:498–506. 8. Paredes R, Jimenez V, Cabrera G, Iraguen D, Galanti N. Apoptosis as a possible mechanism of infertility in Echinococcus granulosus hydatid cysts. J Cell Biochem. 2007; 100: 1200- 9. 9. Riganò R, Profumo E, Bruschi F, Carulli G, Azzarà A, Ioppolo S, Buttari B, Ortona E, Margutti P, Teggi A, Siracusano A. Modulation of human immune response by Echinococcus granulosus antigen B and its possible role in evading host defenses. Infect Immun. 2001; 69(1): 288 - 96. 10. Macintyre AR, Dixon JB. Echinococcus granulosus: regulation of leukocyte growth by living protoscoleces from horses, sheep, and cattle.Exp Parasitol. 2001; 99(4): 198 - 205. 11. Macintyre AR, Dixon JB, Bleakley JS, Green JR. Echinococcus granulosus: assays for hydatid immunoregulatory