SUPPRESSION OF SUPEROXIDE-GENERATING ABILITY DURING DIFFERENTIATION OF MONOCYTES TO DENDRITIC CELLS

Human peripheral monocytes cultured with GM-CSF and IL-4 differentiate d to dendritic cells (DCs) and with GM-CSF alone to macrophages. Super oxide-generating ability in such DCs was found to be suppressed wherea s that in macrophages remained constant, To examine the reason for the suppression in DCs, we evaluated by immunoblotting the levels of esse ntial components of the superoxide generating system in the cells duri ng the differentiation. In contrast to the levels of cytosolic 47- and 65-kDa components and Rac-p21, which remained constant throughout cul tivation, those of the large and the small subunits of cytochrome b(55 8) were found to decrease quickly by day 2 during cultivation of monoc ytes with GM-CSF and IL-4. DCs obtained after 7 days of cultivation ha d lost the large subunit almost completely and most of the small subun it. 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 b(558), were maintained in the cells during differentiation of monocytes to macroph ages. These results indicate that the decreased levels of cytochrome b (558), especially that of the large subunit, is responsible for the lo w level of superoxide-generating ability of DCs and that the suppressi on is caused by IL-4.