Abstract: Objective To explore the mechanism of immunosuppression induced by ultraviolet.Methods Cultured HaCaT cells were sham irradiated(control)or irradiated with 0.6,1.2,1.8,2.4,3.0,3.6 J/cm² UVA radiation,and respectively.The cell viability was determinated by MTT method.In addition,cultured HaCaT cells were either sham irradiated(control)or exposured to 214 J/cm² UVA radiation.Cells and suspended medium were collected at 0,2,4,12,24,48h post-irradiation respectively.The levels of IL10 mRNA and protein expression were detected by RT-PCR and ELISA respectively.Results Compared with control group,cell viability decreased significantly(P<0.05)in irradiated g roups with 310 or 316 J/cm² UVA radiation.There was no significant difference(P>0.05)between control and irradiated cells with less than 214 J/cm² UVA radiation.Among control and irr adiated cells over a 48 period,IL10 gene was expressed only at 12h and its protein was expressed only at 24h post-irradiation.Conclusion IL10 may not be expressed in HaCaT cells,but UVA can induce the expression of IL10 gene and protein.