Figure 1.
Radiation-induced immunosuppressive effects in the tumor micromilieu. RT induces recruitment, proliferation and polarization of immunosuppressive cell subtypes including myeloid-derived suppressor cells (MDSCs), M2 tumor-associated macrophages, N2 neutrophils, and regulatory T cells (CD4+CD25+Foxp3+). RT induces increased levels of suppressive factors including nitric oxide synthase (NOS) and reactive nitrogen intermediates (RNI), reactive oxygen species (ROS), cytokines (IL-4, IL-10, TGF-β), matrix metalloproteinases (MMPs), arginase I, collagenase, lipoxygenase (LOX) which in turn leads to the suppression of the T cell activity.