Suppression of superoxide-generating ability during differentiation of monocytes to dendritic cells

Human peripheral monocytes cultured with GM-CSF and IL-4 differentiated to dendritic cells (DCs) and with GM-CSF alone to macrophages. Superoxide-generating ability in such DCs was found to be suppressed whereas that in macrophages remained constant. To examine the reason for the suppression in DCs, we evaluated by immunoblotting the levels of essential components of the superoxide generating system in the cells during the differentiation. In contrast to the levels of cytosolic 47- and 65-kDa components and Rac-p21, which remained constant throughout cultivation, those of the large and the small subunits of cytochrome b558 were found to decrease quickly by day 2 during cultivation of monocytes with GM-CSF and IL-4. DCs obtained after 7 days of cultivation had lost the large subunit almost completely and most of the small subunit. A cell surface epitope of the cytochrome detected by a monoclonal antibody also decreased during the differentiation. On the other hand, these components, including both subunits of cytochrome b558, were maintained in the cells during differentiation of monocytes to macrophages. These results indicate that the decreased levels of cytochrome b558, especially that of the large subunit, is responsible for the low level of superoxide-generating ability of DCs and that the suppression is caused by IL-4.