In order to correctly evaluate radiation effects on Treg suppression, it should be determined how irradiation impacts those phenotypical markers on Treg cells that are directly linked to their suppressor activity. Unfortunately the number of studies in this field is very limited and it is very difficult to drawa solid conclusion. As detailed in the first part of this review the level of Treg activation and its cytokine profile highly influence Treg suppressive capacity. Although CTLA4 is not a classical Treg activation marker, its presence or upregulation on Treg cells is necessary for Treg suppression. Available data in the literature regarding radiation-induced changes in CTLA4 levels on Tregs are notmany and quite contradictory. Baba et al. did not notice any changes in CTLA4 expression in C57Bl/6 mice after total-body irradiation with 5 Gy, but the paper does not give methodological details how the measurements
were performed [72]. Balogh et al. showed that cell surface expression of CTLA4 moderately increased on the splenic Tregs of mice irradiated with 2 Gy [67].