Toxicol Ind Health. 2010 Mar 26. [Epub ahead of print]Affects of ionizing radiation on T-cell population lymphocyte: A risk factor of irritable bowel syndrome.Mr SS, Lv K, Vb B.National Medical Academy for Post Graduate Education, Kiev, Ukraine.Irritable bowel syndrome is observed mostly in Ukrainian children and may be related to adverse health effects as a result of the Chernobyl disaster. The aim of this study was to determine status of T-cell population lymphocytes in children with clinical symptom of irritable bowel syndrome. The test population consisted of 95 participants: 75 rural patients aged 4 to 18 who lived in a contaminated area exposed to natural environmental radiation with clinical symptom of irritable bowel syndrome (categorized in three groups) and 20 healthy urban participants from Kiev aged 5 to 15 as control group. Internal radiation activity has been measured by gamma-ray spectrometry. Peripheral blood leukocytes were analyzed for T-lymphocytes subset such as T-lymphocytes (CD3(+)), T-helper (CD4(+)) and T-cytotoxic (CD8(+)) and then CD4/CD8 ratio was calculated. Percentage of CD3(+) and CD4(+) in all study groups decreased significantly in comparison to control group (p < 0.001). Percentage of CD8(+) increased significantly in all study groups in comparison to control group (p < 0.05). The CD4/CD8 ratio decreased significantly all study groups in comparison to control group (p < 0.001). Cellular immune status of study groups that are residing in a contaminated area has changed. Our data have demonstrated that this change may be related to a higher incidence of children with irritable bowel syndrome.