Abstract: Objective: To investigate the effects of bacteria motif,namely CpG oligodeoxynucleotide(CpG-ODN) on morphology and melanogenesis production of and prostaglandin E₂(PGE₂) in melanocytes.Methods: The cultured B16 melanoma cells and melan-α melanocytes in vitro were treated with the CpG-ODN.The B16 cell viability,tyrosinase activity,melanin content and the level of PGE₂ in the culture supernatants was measured by MTT assay,oxidation of L-dopa,NaOH assay and ELISA assay respectively.In addition,the morphological changes of melan-α cells were observed after the CpG-ODN was added.Results: The CpG-ODN at the concentration of 5 μg/ml promoted the proliferation of B16 cells,10 μg/ml with little effects,and 15 μg/ml with depressant effects on the cell proliferation after drugs intervention for 24 h.After 48 h treating,the cell proliferation rates in various groups became stable and were similar to each other,without significant difference between groups at different concentrations of CpG-ODN(P>0.05).The tyrosinase activity and melanin synthesis were promoted by 10 μg/ml CpG-ODN,whose effects resembled that of 25 nmol/ml α-MSH(P>0.05).In addition,10 μg/ml CpG-ODN increased the level of PGE₂ in the culture supernatants,but no statistical significance compared with the control group(P>0.05).It supposed that due to lagging of detection time.The cytodendrites of melan-α cells treated with 10 μg/ml CpG-ODN for 24 h were elongated and enriched,we could see the second and even tertiary dendrites appearing.Conclusions: The optimal concentration of CpG-ODN for stimulating mouse melanocytes is 10 μg/ml,and its effects are in a time-dependent manner.This study is a primary research about CpG-ODN stimulating normal human melanocytes.