en Original Research: Basic Science in Medicine Original Research: Basic Science in Medicine The aim of this study was to evaluate the immune system and lymphocyte function in 41 Iranian β-thalassemic patients and 50 controls, ages ranging from 2 to 18 years. The patients consisted of 20 splenectomized and 21 non-splenectomized patients. They were treated with Desferal, and had received repeated blood transfusion. Laboratory investigations included measurement of total T lymphocytes, active T lymphocytes, B-Iymphocytes and function of lymphocytes treated with PHA. In this study we observed a significant reduction of active T lymphocytes and total T lymphocytes in the patient group compared to controls (p<0.005 & p<0.001), but there was no significant difference between splenectomized and non-splenectomized patients. Also in both groups, lymphocyte function was reduced against PHA (phytohemagglutinin) compared with the controls, and the numbers of B cells were increased. These results lead to the conclusion that the deficient immune system in β-thalassemia causes infectious diseases, which finally leads to death. Therefore, stimulation of the immune system as well as clinical treatment may prevent infectious disease in patients with β- thalassemia. Thalassemic patient, Immune system, Cytomegalovirus, Blood transfusion. 169 172 http://mjiri.iums.ac.ir/browse.php?a_code=A-10-298-205&slc_lang=en&sid=1 T ZANDIEH TZ7892000@Yahoo.com 20031947532846003969 20031947532846003969 Yes From the Iranian Blood Transfusion Service, Tehran F TARABADI 20031947532846003970 20031947532846003970 No From the Iranian Blood Transfusion Service, Tehran A TABATABAIYAN 20031947532846003971 20031947532846003971 No From the Iranian Blood Transfusion Service, Tehran M IZADYAR 20031947532846003972 20031947532846003972 No the Department of Hematology, Pediatric Medical Center, Tehran University of Medical Sciences, Tehran, I.R. Iran.