Effects of low dose X-ray irradiation on antigen presentation and IL-12 secretion in human dendritic cells in vitro

Objective To explore the effects of low dose X-ray irradiation on the ability of antigen presentation and IL-12 secretion in human dendritic cells that had been cultured for different time in vitro.Methods The human peripheral blood mononuclear cells ( PBMC ) were collected and differentiated to dendritic cells (DCs) by rhGM-CSF and rhIL-4 treatment in vitro.The DCs were divided into 3 groups,group A:DCs were cultured for 2 d and then irradiated with 0.05,0.1,0.2 and 0.5 Gy X-rays; group B:DCs were cultured for 6 d and then irradiated as above; group C:DCs were cultured without irradiation.At 8 d of cell culture,the DCs were applied to activate T cells and CCK-8 was used to detect MLR ( mixed lymphocyte reaction),and the antigen presentation ability of DCs was evaluated.MTT assay was also used to test the cell-killing effect of the activated T-cells on A549 cells.IL-12 in the culture medium of DCs was detected by ELISA.Results After irradiation with 0.2 and 0.5 Gy X-rays,the antigen presentation ability of DCs was decreased in group A (t =2.79 and 3.71,P ＜ 0.05 ),but significantly increased in group B (t =3.60 and 3.11,P ＜ 0.05).The ability of the T cell activation was detected and the proliferation of A549 cells was slightly inhibited by the DCs in group A (t =2.89 and 2.91,P ＜ 0.05),but was obviously inhibited by the DCs in group B (t =2.91 and 2.82,P ＜0.05).Meanwhile,the level of IL-12 was dramatically decreased in group A (t =4.44 and 6.93,P ＜ 0.05),but was increased in group B (t =3.51 and 4.12,P ＜0.05).Conclusions The abilities of antigen presentation and proliferation inhibition of DCs could be down-regulated by low dose( ＜ 0.5 Gy) of X-ray irradiation at the early stage of DCs,but was up-regulated at the late stage of DCs culture. Key words: X-rays; Dendritic cells; A549 cells; Interleukin-12