Regulation of IL-1 and TNF-α expression during the differentiation of bone marrow derived macrophage

Macrophage differentiation is accompanied by the acquisition of both Ag presentation and tumoricidal activities. In this set of experiments, the expression of IL-1 by bone marrow-derived macrophage (BMDM) was found to be highly regulated, with both the expression of IL-1 mRNA and mIL-1 appearing only at discrete stages of activation. The accumulation of IL-1α (membrane) mRNA was induced by endotoxin but not IFN-γ or CSF-1. mIL-1 was detected by D10.G4.1 T cells on BMDM only after 7 days of in vitro differentiation. Secreted IL-1β was detected by day 3 of culture, with enhanced production observed after activation with endotoxin. IL-1β mRNA was found to be constitutively expressed in BMDM as early as day 3 of culture. The expression of IL-1β mRNA was up-regulated by endotoxin after 30 min of exposure with maximal expression occurring after 2 to 6 h of exposure. Constitutive expression of IL-1α mRNA was not detected but 1 h of endotoxin exposure resulted in the appearance of IL-1α transcripts. As with IL-1β, TNF-α mRNA was also constitutively expressed during a wide time period of differentiation; however, in contrast, to IL-1β, TNF-α mRNA expression was up-regulated by both endotoxin and IFN-γ. The expression of TNF-α macrophage by BMDM coincided with the acquisition of tumoricidal activity. An examination of the mRNA sequences encoding the proto-oncogenes c-myc and c-fms demonstrated the expression of c-myc only on day 3, whereas c-fms was constitutively expressed throughout the culture period. Endotoxin stimulation of BMDM resulted in a transitory increase in c-myc expression only at day 3 of culture, whereas endotoxin had no effect on c-fms expression until 7 days of culture at which time expression declined. In contrast, the expression of transferrin receptor mRNA transcripts, which were also constitutively expressed throughout the entire culture period, were not affected by stimulation with either endotoxin or IFN-γ. These results indicate BMDM expression of the affector molecules IL-1α and β and the effector molecule TNF-α are regulated separately during unique 'differentiation-specific' phases of development.