Stimulation of P2 receptors causes release of IL-1β–loaded microvesicles from human dendritic cells

Dendritic cells (DCs) are professional antigen-presenting cells that initiate the immune response by activating T lymphocytes. DCs express plasma membrane receptors for extracellular nucleotides named P2 receptors (P2Rs). Stimulation of P2Rs in these cells is known to cause chemotaxis, cytokine release, and cell death and to modulate LPS-dependent differentiation. Here we show that stimulation of the P2X7 receptor subtype (P2X7R) causes fast microvesicle shedding from DC plasma membrane. Vesicle release occurs from both immature and mature DCs; however, only vesicles from mature DCs, due to their previous exposure to LPS, contain IL-1β. Microvesicles, whether from immature or mature DCs, also contain caspase-1 and -3 and cathepsin D. They also express the P2X7R in addition to other P2Rs and known markers of immune cells such as major histocompatibility complex II (MHC II) and CD39. Activation of the P2X7R by extracellular ATP causes IL-1β release from the vesicle lumen. Previous studies demonstrated that high extracellular K+ inhibits IL-1β processing and release; here we show that high ionic strength reduces microvesicle shedding when compared with a low ionic strength medium but strongly increases microvesicle IL-1β loading.