Inducible expression of murine IP-10 mRNA varies with the state of macrophage inflammatory activity

We have examined the expression of inducible inflammatory genes in murine macrophages from different tissues and at different stages of inflammatory activity. Although i.v. administration of IFN-gamma (10,000 U/mouse) strongly induced expression of IP-10 mRNA in the adherent cell population of the spleen, thioglycollate-elicited peritoneal macrophages were essentially unresponsive at the same dose. In contrast, D3 mRNA was expressed in both cell populations. This differential sensitivity of IP-10 mRNA expression was not restricted to stimulation by IFN-gamma as it was also seen when LPS (25 micrograms/mouse) was administered i.v. Expression of JE and KC mRNA, which encode cytokines related to IP-10, were also differentially expressed in elicited peritoneal macrophages from mice injected with LPS. Differential sensitivity was at least partially related to the state of macrophage activation because IP-10 mRNA was highly inducible in resident but not thioglycollate-elicited peritoneal macrophages. The eliciting agent was also an important determinant because proteose-peptone-elicited peritoneal macrophages were nearly as sensitive as splenic macrophages with respect to expression of IP-10 mRNA. IFN-gamma treatment induced IP-10 and D3 mRNA rapidly and transiently with the same time course in the spleen. IP-10 mRNA was not induced by IFN-gamma in TG-elicited macrophages regardless of the time after treatment. This differential expression of IP-10 was a consequence of different concentration requirements for IFN-gamma in the two cell types; thioglycollate-elicited macrophages required five- to 10-fold more IFN-gamma than did resident cells to achieve comparable IP-10 mRNA levels whether the agent was provided in vitro or in vivo. Thus variable sensitivity for induction of IP-10 mRNA was a characteristic of the macrophage itself and was not mediated by other cellular or molecular elements present in the inflammatory peritoneal cavity. The reduced sensitivity to IFN-gamma or LPS for expression of IP-10, JE, and KC mRNA as compared with TNF-alpha or D3 mRNA suggests that this distinct pattern of regulation may be restricted to members of these two related cytokine gene families that exhibit cell-type specific chemoattractant activity.