Abstract

In this work, the effects of bacterial LPS, TNF-?, and IFN-? on gap junctional communication (dye coupling) and on the expression of connexin43 (immunofluorescence, immunoblotting, and RT-PCR) in monocytes/macrophages were studied. Freshly isolated human monocytes plated at high density and treated either with LPS plus IFN-? or TNF-? plus IFN-? became transiently dye coupled (Lucifer yellow) within 24 h. Cells treated with LPS, TNF-?, or IFN-? alone remained dye uncoupled. In dye-coupled cells, the spread of Lucifer yellow to neighboring cells was reversibly blocked with 18 ?-glycyrrhetinic acid, a gap junction blocker, but it was unaffected by oxidized ATP or probenecid, which block ionotropic ATP-activated channels and organic anion transporters, respectively. Abs against TNF-? significantly reduced the LPS plus IFN-?-induced increase in dye coupling. In dye-coupled monocytes/macrophages, but not in control cells, both connexin43 protein and mRNA were detected, and their levels were higher in cells with an elevated incidence of dye coupling. In dye-coupled cells, the localization of connexin43 immunoreactivity was diffuse at perinuclear regions and thin cell processes. The addition of 18-?-glycyrrhetinic acid induced a profound reduction of monocyte/macrophage transmigration across a blood brain barrier model. It also induced a significant reduction in the secretion of metalloproteinase-2 in cells treated with TNF-? plus IFN-?. We propose that some monocyte/macrophage responses are coordinated by connexin-formed membrane channels expressed transiently at inflammatory sites in which these cells form aggregates.