p53 is a well-known tumor suppressor. However, the regulatory mechanism(s) for p53 expression in B lymphoma cells, and the possible role of p53 in the development of the radioresistance in tumor cells are largely unknown. A human B lymphoma cell line, Karpas1106 (k1106), was used as a model of radioresistance. Apoptosis of k1106 cells was determined using flow cytometry. Expression of p53 was assessed using real time RT-PCR and western blotting. The results showed that irradiation at 8 Gy induced apoptosis in up to 40% of k1106 cells. At the same time, the irradiation markedly increased IL-6 production of the k1106 cells. When k1106 cells were cocultured with regulatory T cells (Tregs) and irradiated, the rate of apoptotic k1106 cells was significantly reduced, indicating an acquired resistance to irradiation. IL-6 derived from the irradiation-treated k1106 cells induced IL-17 expression in Tregs. The IL-17(+)Foxp3(+) T cells suppressed p53 expression in k1106 cells. Collectively, irradiated k1106 cells induce the expression of IL-17 in Tregs, which interferes with the expression of p53 protein in k1106 cells and thereby represses irradiation-triggered apoptosis in k1106 cells.