Abstract: Objective To investigate the effects of melanoma culture supernatants (MCS) on the monocytic interleukin-12 (IL-12) production and on the monocyte-derived dendritic cell (DC) differentiation in vitro.Methods Human peripheral blood monocytes were isolated and the purity of the monocytes was>85%.The concentrated MCS in different amount was added to the IFN-γ(100 pg/mL) and LPS (10 ng/mL) enriched culture media.The IL-12 production by monocytes was determined by the enzymelinked immunosorbent assay(ELISA).The expression of CD14 and CD1a was analyzed by flow cytometry 5 days after the monocytes were co-cultured with MCS.Results The production of monocytic IL-12 was down-regulated by MCS in a dose dependent manner.The amount of IL-12 from monocytes decreased along with an increased dose (25-100μL) of MCS applied in the reaction.It was also observed that the differentiation from CD14 expressing monocytes to CD1a dendritic cells was impaired by MCS.The ability of MCS to inhibit the production of IL-12 by monocytes and to suppress the differentiation of monocytes to dendritic cells in vitro could be disrupted by PD98059,an ERK specific inhibitor.Conclusions MCS appears to inhibit IL-12p40 production by monocytes and inhibit differentiation of monocytes in vitro via secretion of ERK stimulating factor.The inhibitory factors in MCS and their chemical natures need further research.

Key words: Monocytes, Interleukin-12, Antigens,CD14, Antigens,CD1, M14 melanoma culture supernatant