Time‐ and dose‐dependent changes of intracellular cytokine and cytokine receptor profile of Ewing tumour subpopulations under the influence of ionizing radiation

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Abstract
Purpose: Cytokines and their corresponding cell surface receptors are involved in intercellular signalling pathways and in the radioresistance of normal and malignant cells. The aim was the characterization of the expression of intracellular cytokines, their receptors and apoptosis‐associated markers under the influence of radiation. Materials and methods: Two Ewing tumours were characterized in vitro before and 4, 24 and 72 h after radiation with 5 and 10 Gy, and in vivo 4, 6 and 15 days after radiation with 5 and 30 Gy by five parameter flow cytometry. Direct fluorescence‐conjugated antibodies directed against intracellular cytokines (interferon‐gamma, tumour necrosis factor [TNF]‐alpha, interleukin 1) and their receptors (CD119, CD120a, CD121a) were used. Annexin V and 7‐amino‐actinomycin D were used to identify radiation‐induced apoptosis. Results: Inter‐ and intra‐individual heterogeneities were identified by the expression of cytokine receptors and the intracellular cytokine profile before radiation. Time‐ and dose‐dependent up‐regulation of the cytokines TNF‐alpha and interleukin 1 were found in vitro. In vivo, an up‐regulation of CD120a and CD121a was detectable on tumour cell subpopulations. For interferon‐gamma and CD119, no changes were seen. Conclusions: The observed radiation‐induced changes of cytokine and receptor profile are an indication for complex intercellular interactions in view of radioresistance‐associated mechanisms between cell populations within one individual tumour. The observed heterogeneous response on radiation might have therapeutic implications for an individualized therapy based on combined radiation and cytokine modulation, defined by flow cytometric characterization of markers potentially informative for radioresistance.

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