2Department of Radiation Oncology, Ege University School of Medicine, İzmir-Turkey DOI : 10.5505/tjo.2018.1726 OBJECTIVE
Total-body-irradiation (TBI) causes significant immunosuppression, but different lymphocyte subsets have various radiosensitivities. Regulatory T (Treg) cells, which are crucial for self-tolerance and are potent suppressors of antitumor immunity are found to be resistant to radiotherapy (RT) compared with T helper (Th) cells and Cytotoxic-T lymphocytes (CTL) in both in-vivo and in-vitro studies, but the data on this subject is relatively scarce. Besides, recent developments in the context of combination of immunotherapy with RT compelled us to revisit the concept of radiation-induced quantitative and functional changes in lymphocyte subsets by flow cytometry using animal models with the aim of transitioning the findings to clinical studies.
METHODS
Twenty-three Swiss albino rats were exposed to TBI at a single fraction of 5 Gy. Immediately prior to irradiation,
at time points of 1 day and 7 and 14 days post-TBI, flow cytometric analyses were performed.
RESULTS
There has been statistically significant decrease in all T lymphocyte subsets at 1, 7 and 14 days post-TBI. The
decrease in Th subset was more pronounced compared to CTL. Baseline CD4+/CD8+ ratio was 0.85 which
significantly decreased to 0.29 1 day post-TBI, then increased steadily in subsequent measurements and
reached near normal. The number of Treg cells markedly declined to 6.5% of baseline value one day after TBI,
and then steadily increased during the follow-up. By the end of 14 days, it reached half of its baseline value.
CONCLUSION
Radiation-induced immunosuppression may be explained not only by the decrease in lymphocyte cell number
but also by the relative increase in Treg cell number because the higher regenerative capacity may present
an additional role.