Biological effects of kojic acid on human monocytes in vitro

Monocytes are mononuclear phagocytes in peripheral blood that can differentiate into macrophages and dendritic cells. Macrophages play a specific role in the inflammatory process and are essential for the innate response. Given the important role of monocytes/macrophages in the immune response, this study aimed to evaluate the activity of kojic acid (KA), a natural product of certain fungal species, on human peripheral blood monocytes in vitro. Purified monocytes isolated from human blood were incubated with KA (50 μg/mL for 48 h) and analyzed by light microscopy, scanning electron microscopy, transmission electron microscopy and flow cytometry. Host cell cytotoxicity was measured by the colorimetric MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay. KA treatment induced morphological alterations in monocytes, such as increased cell size, as well as numerous cellular projections. Furthermore, flow cytometry revealed increased labeling of cell surface EMR1-F4/80 but decreased labeling of CD11b and CD14. KA also promoted increased IL-6 cytokine production but did not cause cytotoxic effects in monocytes. In conclusion, our results show that KA promotes the differentiation of monocytes into macrophages and can act as an immunomodulatory agent.