Abstract
Phagocytic cells serve critical roles in the body’s immune response by recognizing, phagocytosing and destroying foreign particles. A major class of phagocytic cells is composed of monocytes and macrophages. During inflammation there is release of several inflammatory mediators and chemokines, which attract circulating monocytes towards the endothelium. Monocytes firmly adhere to, and actively migrate through, endothelial tight junctions in order to enter tissue, where they then differentiate into macrophages and function to phagocytose apoptotic bodies and damaged cells. Migration of monocytes into tissues through endothelial tight junctions requires shape and volume change. However, the underlying mechanisms involved in monocyte shape and volume change are unclear.|Alteration in ion channels, especially chloride channels, is generally involved in the shape and volume change of circulating cells for successful invasion into tissues. In this work, we examined chloride currents in human blood monocytes and macrophages, and their role in adhesion and migration. Chloride currents were recorded in freshly isolated human blood monocytes and WBC264-9C cells (a macrophage-like cell line) using the whole-cell patch clamp technique. The effects of chloride channel blockers were then examined on chloride currents and on the migration and adhesion of human blood monocytes to vascular endothelial cells.|Whole-cell Cl' currents in human blood monocytes were outwardly rectifying and time-independent. Macrophage cell line Cl' currents were outwardly rectifying and time-dependent. Volume-sensitive chloride channel blockers, NPPB and IAA94, attenuated Cl' currents, as well as inhibited monocyte chemotaxis with similar sensitivity, as measured in a Boyden chemotactic chamber. NPPB, but not IAA94, increased cell volume (as measured by shape change) and decreased TNF-a-induced monocyte adhesion to endothelial cells. Inflammatory cytokines IL-8 and IL-12 increased Cl' currents in monocytes. IFN-y also activated Cl' currents in monocytes, but to a lesser degree than that of IL-8 and IL-12. Interestingly, IFN-y also activated Cl' currents in a macrophage-like cell line.|These results suggest that chloride channels affect monocyte migration, presumably due to changes in cell volume and shape. Inflammatory cytokines can enhance Cl' current to facilitate monocyte migration into tissues as well as to regulate macrophage function.