IL-10 inhibits granulocyte-macrophage colony-stimulating factor-dependent human monocyte survival at the early stage of the culture and inhibits the generation of macrophages

We previously demonstrated that IL-10 alone does not stimulate growth and d ifferentiation of human monocytes, but enhances those of monocytes stimulat ed with M-CSF. We studied here the effect of IL-10 on human monocytes stimu lated with GM-CSF. Monocytes stimulated with GM-CSF alone survived and deve loped into macrophages. Monocytes cultured with GM-CSF plus IL-10, however, died through apoptosis. IL-10 decreased expression of bcl-2, bcl-x(L), and mcl-1- but not box mRNA in monocytes stimulated with GM-CSF. IL-10 did not change the expression of mRNA of both GM-CSFR alpha -chain and beta -chain , but inhibited tyrosine phosphorylation of STAT5 and extracellular signal- regulated kinases 1 and 2 in the monocytes. The inhibitory effect of IL-10 was restricted to treatment 48 h after stimulation with GM-CSF. Addition of IL-10 after that time induced neither apoptosis nor a decrease in expressi on of bcl-2, bcl-x(L), and mcl-1 mRNA. IL-10, however, inhibited LPS-induce d TNF-alpha production even in these cells, indicating that the cells still possessed responsiveness to IL-10. Monocytes pretreated for >48 h with GM- CSF became resistant to GM-CSF withdrawal, and the cells could survive with out GM-CSF. These results indicate that IL-10 selectively inhibits GM-CSF-d ependent monocyte survival by inhibiting the signaling events induced by GM -CSF, but the timing of addition of IL-10 is critical, and IL-10 had to be added within 48 h after stimulation with GM-CSF to achieve the inhibitory e ffect. These results taken together with our previous results indicate that IL-10 plays a pivotal role in monocyte survival and development into macro phages in concert with M-CSF and GM-CSF.