Different radiosensitivity of CD4(+)CD25(+) regulatory T cells and effector T cells to low dose gamma irradiation in vitro.
OBJECTIVE
To determine the radiosensitivity difference of human Cluster of Differentiation (CD)4(+)CD25(+) regulatory T cells (Treg) and effector T cells to low dose gamma ray and elucidate the underlying mechanisms in vitro.


METHODS
Blood samples were collected from five health subjects and five patients with advanced hepatocellular carcinoma (HCC). Treg and CD4(+)CD25⁻ T cells were selected using magnetic microbeads. The proliferative profiles, cytokine secretion, and differential expressions of apoptosis-related proteins in Treg and CD4(+)CD25⁻ T cells were compared using [³H]-thymidine incorporation, Luminex assay and flow cytometry when treated with various low doses of γ-ray.


RESULTS
A dose-dependent reduction of proliferation in response to irradiation which paralleled the induction of apoptosis existed in Treg and CD4(+)CD25⁻ T cells. Treg were more radiosensitive to low-dose irradiation (0.94 Gray [Gy]) than effector T cells. The interferon-γ (IFNγ) was significantly upregulated and interleukin 10 (IL-10) was significantly downregulated in irradiated Treg. An enhanced immune response to low dose gamma ray existed in the peripheral blood in patients with advanced HCC. Higher levels of active caspase-3, CD95, B cell lymphoma 2 (Bcl-2)-associated X protein (Bax) expression were observed in Treg compared to CD4(+)CD25⁻ T cells. In addition, gamma irradiation activated CD4(+)CD25⁻ T cells to express CD25.


CONCLUSIONS
These studies revealed that Treg were more radiosensitive than CD4(+)CD25⁻ T cells to low dose irradiation. Higher expressions of apoptosis-related proteins such as caspase-3, CD95 and Bax were observed in Treg when compared to CD4(+)CD25⁻ T cells. Our results suggest that treatment with low doses of gamma irradiation may be a viable strategy to enhance immune response in patients with advanced HCC.
Section of Hepatobiliary Diseases, Department of Medicine, University of Florida, Gainesville, FL 32610-0214, USA. caom@medicine.ufl.edu
Mengde
M
Cao
Roniel
R
Cabrera
Yiling
Y
Xu
Chen
C
Liu
David
D
Nelson
D000368:Aged; D017209:Apoptosis / Q000528:radiation effects; D006528:Carcinoma, Hepatocellular / Q000276:immunology / Q000473:pathology / Q000532:radiotherapy; D053148:Caspase 3 / Q000378:metabolism; D049109:Cell Proliferation / Q000528:radiation effects; D004307:Dose-Response Relationship, Radiation; D005260:Female; D005720:Gamma Rays / Q000627:therapeutic use*; D006801:Humans; D066298:In Vitro Techniques; D007371:Interferon-gamma / Q000096:biosynthesis; D016753:Interleukin-10 / Q000096:biosynthesis; D008113:Liver Neoplasms / Q000276:immunology / Q000473:pathology / Q000532:radiotherapy; D008297:Male; D008875:Middle Aged; D011836:Radiation Tolerance / Q000276:immunology; D016176:T-Lymphocyte Subsets / Q000276:immunology* / Q000378:metabolism / Q000473:pathology / Q000528:radiation effects*; D050378:T-Lymphocytes, Regulatory / Q000276:immunology* / Q000378:metabolism / Q000473:pathology / Q000528:radiation effects*; D051028:bcl-2-Associated X Protein / Q000378:metabolism; D019014:fas Receptor / Q000378:metabolism
C494826:BAX protein, human; C491901:FAS protein, human; C508609:IL10 protein, human; D051028:bcl-2-Associated X Protein; D019014:fas Receptor; D016753:Interleukin-10; D007371:Interferon-gamma; C505407:CASP3 protein, human; D053148:Caspase 3