Protective effect of epigallocatechin gallate on the immune function of dendritic cells after ultraviolet B irradiation

Abstract

To investigate the protective effect of epigallocatechin gallate (EGCG) on the immune function of dendritic cells (DCs) after ultraviolet B irradiation (UVB) and its underlying mechanisms. The monocytes were isolated from peripheral blood and cultivated into DCs with cytokines, such as granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin (IL)-4. DCs were harvested after cultivation for 7 days and subjected to irradiation with different dosages of UVB. Then, 200 microg/mL of EGCG was added in certain groups 24 h before irradiation. DCs simply treated with UVB or treated with both UVB and EGCG were co-cultured with lymphocytes, and Mono-nuclear cell direct cytotoxicity (MTT) assay was used to detect the ability of DCs to stimulate proliferation of lymphocytes. Surface markers CD80, CD86, human leukocyte antigen(locus)-DR (HLA-DR), and CD40 were detected using flow cytometry, and the levels of IL-10 and IL-12 secreted from DCs 24 h after cultivation were measured using ELISA. UVB irradiation was able to inhibit the ability of DCs to stimulate the proliferation of lymphocytes and surface expressions of CD80, CD86, HLA-DR, and CD40 on DCs in a dose-dependent manner. The inhibition rate of DCs was improved to some extent after treatment with 200 microg/mL of EGCG. UVB showed no significant influence on the secretion of IL-10 and IL-12 from DCs, while EGCG was able to down-regulate the secretion level of IL-12 and up-regulate that of IL-10. EGCG can antagonize the inhibitory effect on DCs induced by UVB irradiation. This function has some relationship with its protecting effect of the expression of the costimulating molecules on the surface of DCs and the secretion level of IL-10 and IL-12.