Gamma irradiation of human dendritic cells influences proliferation and cytokine profile of T cells in autologous mixed lymphocyte reaction

Abstract Dendritic cells (DC) are the most potent antigen‐presenting cells (APC); their ability to induce proliferation of T cells in a mixed lymphocyte reaction (MLR) assay is commonly used for the evaluation of their function. It is a general thought that gamma irradiation of APC does not influence their ability to activate T‐cell proliferation, but the data from several studies are controversial. To further determine the mechanisms involved in DC‐induced T‐cell activation in MLR assay, human DC induced from peripheral blood mononuclear cells (PBMC) were gamma‐irradiated and determine their effects on the proliferation and cytokine profiles of T cells in an autologous MLR. DC were induced from the PBMC of 11 multiple sclerosis (MS) patients with RMPI 640 medium containing recombinant human GM‐CSF (rhGM‐CSF; 800 U/ml) and recombinant human IL‐4 (rhIL‐4; 500 U/ml). DC harvested on day 7 were divided into two equal parts. One part was not irradiated (naive DC); the other was γ‐irradiated at a dose of 30 Gy. Cell surface molecules were analyzed by flow cytometry. T‐cell proliferation was determined using a beta‐scintillation counter. The levels of IL‐2, IL‐4, IL‐6 and IL‐10 in co‐culture supernatants were measured by ELISA. The results indicated that gamma irradiation reduced expression of CD86, CD80 and HLA‐DR molecules on DC, especially CD86 ( P =0.0072). DC, irradiated or non‐irradiated, effectively stimulated autologous T‐cell proliferation. Compared to naive DC, irradiated DC showed a markedly lower capacity to promote T‐cell proliferation ( P =0.0073), and strikingly up‐regulated secretion of IL‐4 ( P =0.0145) and IL‐2 ( P =0.0323) by autologous T cells. No significant differences were noted in IL‐6 and IL‐10 production between T cells co‐cultured with naive DC and irradiated DC ( P >0.05). It is concluded that gamma irradiation of DC not only influences the phenotype of DC but also alters their capacity to stimulate the proliferation and the cytokine profiles of autologous T cells in a MLR.