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Obesity associated with a sedentary lifestyle can lead to changes in the immune system balance resulting in the development of inflammatory diseases. The aim of this study was to compare lymphocyte activation mechanisms between overweight children practicing regular circus physical exercises with non-exercised children. The study comprised 60 pubescent children randomly divided into 4 groups: Overweight Children (OWC) (10.67 ± 0.22 years old), Overweight Exercised Children (OWE) (10.00 ± 0.41 years old), Eutrophic Children (EC) (11.00 ± 0.29 years old) and Eutrophic Exercised Children (EE) (10.60 ± 0.29 years old). OWE and EE groups practiced circus activities twice a week, for 4.3 ± 0.5 and 4.4 ± 0.5 months, respectively. Percentage of T regulatory cells (Treg) and the expression of CD95 and CD25 in CD4+ lymphocytes were evaluated by flow cytometry. Lymphocyte proliferation capacity was measured by [14C]-thymidine incorporation and mRNA expression of IL-35, TGF-beta, IL-2 and IL-10 by real-time PCR. Lymphocyte proliferation was higher in OWC and OWE groups compared with the EC (3509 ± 887; 2694 ± 560, and 1768 ± 208 cpm, respectively) and EE (2313 ± 111 cpm) groups. CD95 expression on lymphocytes was augmented in the EC (953.9 ± 101.2) and EE groups (736.7 ± 194.6) compared with the OWC (522.1 ± 125.2) and OWE groups (551.6 ± 144.5). CTLA-4 expression was also lower in the OWC and OWE groups compared with the EC and EE groups. Percentage of Treg, IL-35, and IL-10 mRNA expression were lower in the OWC and OWE groups compared with the EC and EE groups. In conclusion, overweight children present altered immune system balance characterized by elevated lymphocyte proliferation due to a decrease in T regulatory cell percentage. These effects were partially reverted by moderate physical exercise, as demonstrated by decreased lymphocyte proliferation.