The effects of differentiating agents on IL-1 beta production in cultured human monocytes

Human monocytes aged in medium exhibit a decrease in LPS-induced IL-1 beta production in comparison with fresh cells. The objective of these experiments was to evaluate the effects of differentiation for 1 or 6 days in IFN-gamma, 1,25-(OH)2-vitamin D3, granulocyte-macrophage CSF, or in various combinations of these agents on both steady state IL-1 beta mRNA levels and protein production in LPS-stimulated monocytes. Monocytes preincubated in IFN-gamma for 1 day, then cultured for 24 h with LPS, exhibited similar kinetics of IL-1 beta mRNA production, but a higher peak mRNA level at 8 h after LPS stimulation, in comparison with cells cultured in medium before LPS stimulation. An increase in IL-1 beta protein production with variable secretion was noted in monocytes preincubated in IFN-gamma before stimulation with LPS. Monocytes preincubated for 1 day in 1,25-(OH)2-D3 alone or in both IFN-gamma and 1,25-(OH)2-D3 exhibited similar kinetics and peak expression of LPS-induced IL-1 beta mRNA levels as cells cultured in medium. However, monocytes preincubated for 1 day in both agents displayed a 50% or greater restoration in LPS-induced IL-1 beta synthesis and secretion in comparison with fresh cells. Granulocyte-macrophage-CSF did not augment the effects of the other differentiating agents on IL-1 beta production. Monocytes cultured over 6 days in differentiating agents failed to exhibit any restoration in LPS-induced IL-1 beta production. These in vitro-derived macrophages exhibited very low levels of both IL-1 beta mRNA and protein production under any culture condition. These results suggest that the effects of differentiating agents on LPS-induced IL-1 beta production may in part be related to the state of maturation of the monocyte. Furthermore, a repression in IL-1 beta transcription that is not reversed by exposure to differentiating agents may be acquired by monocytes as they mature into macrophages in vitro.