Granulocyte-macrophage colony-stimulating factor regulates cytokine production in cultured macrophages through CD14-dependent and -independent mechanisms

Granulocyte-macrophage colony-stimulating factor (GM-CSF) has multiple effe cts on the antigen phenotype and function of macrophages. In this study we investigated the effect of GM-CSF on cytokine production by macrophages. We found that GM-CSF may modify the tumour necrosis factor-alpha (TNF-alpha) and interleukin-6 (IL-6) response to lipopolysaccharide (LPS) through two d ifferent mechanisms. Relatively early in culture, GM-CSF increases the amou nt of cytokines synthesized by responding cells; this effect appears to be unrelated to modulation of CD14 expression and LPS-binding capacity. After prolonged incubation, GM-CSF up-regulates both CD14 expression and LPS-bind ing capacity, and the frequency of cytokine-producing cells. Release of CD1 4 in the culture supernatant was decreased in the presence of GM-CSF, sugge sting that a reduced shedding was responsible for the effect of GM-CSF on C D14 expression. Enhancement of cytokine production was also observed in GM- CSF-treated macrophages after stimulation by phorbol 12-myristate 13-acetat e (PMA), thus indicating that GM-CSF affects both CD14-dependent and -indep endent cytokine production. Finally, GM-CSF did not modulate the LPS- and P MA-induced production of IL-10 and IL-12. We conclude that GM-CSF may play a role in manipulating the activation-induced expression of pro-inflammator y cytokines by macrophages. Enhanced production of these cytokines could pl ay an important role in the pathogenesis of Gram-negative septic shock synd rome and in defence against infectious agents.