Radiation causes a loss of regulatory T cells in the skin, which leads to an increase in CD4⁺ T cell proliferation.

<p>(A) ICR mice were exposed to 0, 1, or 2 Gy of gamma radiation, skin was obtained prior to and 2, 7, or 14 days later, and poly(A) RNA was isolated. Copies of CD3 and FoxP3 mRNA were quantitated and normalized to copies of GAPDH mRNA. Data are expressed as % of unirradiated. Ten mice per group were analyzed and data are presented as mean +/− SEM. (B) Cells were obtained from the skin of pre-irradiation or gamma irradiated (2 Gy) mice at the indicated times post irradiation. Cells were analyzed for regulatory T cells (CD4⁺, CD25⁺, FoxP3⁺). (C) Skin cells were depleted with CD25 beads or not, labeled with CFSE, and stimulated with plate bound anti-CD3. The number of cells that proliferated was calculated, as described <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0100800#pone.0100800-Suchin1" target="_blank">[19]</a>. Five mice per time point were analyzed and data are presented as mean +/− SEM. Statistical significance compared to pretreatment was determined by Student’s t-test, * = p<0.05. For 4C, a significant increase in skin cell proliferation compared to pretreatment was observed at 4 and 7 days post-radiation, as noted by a *.