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Purpose This study addresses the sensitivity of different peripheral CD4+ T-lymphocyte subsets to irradiation (IR) and identifies potential targets for the prevention or treatment of radiation-induced toxicity. Methods This study was performed on peripheral blood mononuclear cells or sorted peripheral memory lymphocytes of CCR6+ mucosa-homing Th17/CCR6negTh and regulatory T subtypes of healthy volunteers. Cells were irradiated with a 2 Gy with or without pharmacologic inhibitors of different signaling pathways. Senescence of irradiated cells was assessed by resistance to apoptosis and determination of various senescence-associated biomarkers (senescence associated b-galactosidase activity, p16Ink4a-, p21Cdkn1a-, gH2A.X-, H2A.J expression). Cytokine production was measured in supernatants of irradiated cells by Luminex technology. Results Not all CD4+ memory T lymphocyte subsets were equally radiosensitive. High sensitivity of CCR6+Th17 lymphocytes to IR-induced senescence was shown by expression of the histone variant H2A.J, higher SA-b-Gal activity, and upregulation of p16Ink4a and p21Cdkn1a expression. Lower Annexin V staining and cleaved caspase-3, and higher expression of antiapoptotic genes Bcl-2 and Bcl-xL LF, showed that CCR6+Th17 lymphocytes were more resistant to IR-induced apoptosis than CCR6neg memory Th and regulatory T lymphocytes. After a 2 Gy IR, both CCR6+Th17 and CCR6neg cells acquired a moderate senescence-associated secretory phenotype, but only CCR6+Th17 cells secreted interleukin 8 (IL-8) and vascular endothelial growth factor-A (VEGF-A). Pharmacologic targeting of reactive oxygen species (ROS), mitogen-activated protein kinases (MAPKs), and mammalian target of rapamycin (mTOR) signaling pathways prevented the expression of senescent markers and IL-8 and VEGF-A expression by CCR6+Th17 cells after IR. Conclusions This study suggests that IR induces senescence of CCR6+Th17 lymphocytes associated with secretion of IL-8 and VEGF-A that may be detrimental to the irradiated tissue. ROS-MAPKs signaling pathways are candidate targets to prevent this CCR6+Th17-dependent radiation-induced potential toxicity. Finally, the ratio of circulating H2A.J+ senescent CCR6+ Th17/CD4+ T lymphocytes may be a candidate marker of individual intrinsic radiosensitivity.

Ionizing radiation-exposure induces a variety of cellular reactions, such as senescence and apoptosis. Senescence is a permanent arrest state of the cell division, which can be beneficial or detrimental for normal tissue via an inflammatory response and senescence-associated secretion phenotype. Damage to healthy cells and their microenvironment is considered as an important source of early and late complications with an increased risk of morbidity in patients after radiotherapy (RT). In addition, the benefit/risk ratio may depend on the radiation technique/dose used for cancer eradication and the irradiated volume of healthy tissues. For radiation-induced fibrosis risk, the knowledge of mechanisms and potential prevention has become a crucial point to determining radiation parameters and patients' intrinsic radiosensitivity. This review summarizes our understanding of ionizing radiation-induced senescent cell in fibrogenesis. This mechanism may provide new insights for therapeutic modalities for better risk/benefit ratios after RT in the new era of personalized treatments.

Introduction La fumee de cigarette, source de stress oxydant, majore la severite de diverses maladies inflammatoires chroniques par des mecanismes peu connus. Le role pathogene des lymphocytes T CD4+ (LTCD4+) producteurs d’IL17 (Th17) dans est etabli dans ces maladies, dont la bronchopneumopathie chronique obstructive (BPCO), maladie respiratoire inflammatoire chronique dont le principal agent etiologique est le tabagisme. Dans la BPCO, les cellules pulmonaires presentent une senescence prematuree, associee a une inflammation plus importante et a la severite de la maladie. Methodes Les LTCD4+ peripheriques Th17, Th1/Th2 = non-Th17 et Treg de sujets sains sont isoles, puis traites avec du condensat de fumee de cigarette (CFC). L’induction de senescence est evaluee en immunofluorescence par l’expression du marqueur de senescence p16. L’effet des especes reactives de l’oxygene (ERO) est evalue apres traitement par l’anti-oxydant, NAC. La production d’ERO est mesuree par cytometrie en flux par la capacite d’oxydation de la sonde H2DCF-DA. La reponse anti-oxydante est evaluee en RQ-PCR par l’expression des enzymes anti-oxydantes. Resultats L’exposition au CFC induit une expression de p16 plus importante dans les Th17 que dans les autres LTCD4+. Le traitement par NAC previent l’expression de p16, indiquant le role potentiel des ERO contenues dans le CFC. Les Th17 produisent plus d’ERO que les autres LTCD4+ apres exposition au CFC, mais aussi en condition basale. Les resultats de RQ-PCR montrent une moindre expression des enzymes anti-oxydantes (Gpx2, TrxR, HO-1) dans les Th17 par rapport aux Treg, et une expression plus importante d’IL4I1, une mono-amineoxydase productrice d’H2O2. Conclusions Nos resultats indiquent que senescence et susceptibilite a l’agression oxydative pourraient etre liees dans les LTCD4+, et que les Th17 pourraient avoir une plus grande susceptibilite a la senescence induite par le CFC en rapport avec un taux d’ERO plus important par rapport aux autres LTCD4+. Nous analyserons ensuite le secretome inflammatoire des Th17 associe a l’augmentation de p16 apres exposition au CFC, puis nous determinerons si les particularites observees au niveau du secretome et/ou de la reponse oxydative des Th17 chez les sujets sains sont majorees chez les patients BPCO.