In contrast, CD86 upregulation induced by the TLR4 agonist MPLA was completely dependent on TLR4, while poly I:C stimulation was shown to be TLR4-independent as expected. demonstrated that the phospholipid fraction, not the protein fraction, mediated macrophage activation through a TLR4 dependent process. P2X7activation is known to induce calcium independent phospholipase A2(iPLA2), calcium dependent phospholipase A2(cPLA2), and phospholipase D (PLD) activities, but inhibition of these enzymes did not inhibit MV generation or shedding. However, blocking PLD activity resulted in release of MV incapable of activating recipient macrophages. These data demonstrate a novel mechanism of macrophage activation resulting from exposure to MV from non-primed macrophages, and identifies phospholipids in these MV as the biologically active component. We suggest that phospholipids delivered by MV may be mediators of sterile inflammation in a number of diseases. == Introduction == Released microvesicles (MV) mediate intercellular communication between Nadolol multiple cell types, and affect cytokine secretion, inflammatory processes, and tumor progression (1). MV can be released from intracellular storage sites or shed directly from the cell surface. Release of plasma membrane-derived MV is typically regulated by intracellular Ca2+mediated processes (2,3), or by protein kinase B (4) or protein kinase C (5,6), and may involve engagement of Nadolol a number of cell type specific receptors. Shedding typically involves a Nadolol budding process, in which surface blebs selectively accumulate cellular constituents that are then packaged into MV. In contrast, MV deriving from inside cells include secretory lysosomes (79), characterized by expression of lysosomal proteases and other markers, and exosomes (1,10), which are stored in multivesicular bodies before being released by an active exocytic process. In macrophages and other myeloid cells, engagement of P2X7purinergic receptors triggers the release of MV deriving from both inside the cell (8,11,12) and from the plasma membrane (2,3,1315). Secretion of IL-1 mediated by P2X7was suggested to occur through the release of Nadolol cell surface derived MV many years ago (14), but the content of these MV is still unclear. A more recent study suggests that the majority of IL-1 containing MV may be exosomes as opposed to larger shedding vesicles (11). Members of the IL-1 family, including IL-1, IL-1, and IL-18, are stored as inactive precursors and their release after processing can be MV-mediated (2,3,11,14) but this does not exclude other mechanisms of secretion (1618). In any case, rapid secretion of mature IL-1 requires the NLRP3 inflammasome, which recruits caspase-1, allowing cleavage of the pro-form of the cytokine to its bioactive form (19). Some exosomes from macrophages contain Class II MHC and their exocytosis requires the NLRP3 inflammasome despite being caspase-1 independent (12). Less clear is the requirement for NLRP3 in controlling the P2X7-dependent release of secretory lysosomes (8) although their exocytosis from human monocytes is caspase-1 independent. Macrophages and other cells of the phagocytic lineage bind and internalize MV from Rabbit Polyclonal to VAV1 various sources with diverse effects on their function (10). Human monocytes binding tumor derived MV become activated, expressing increased HLA-DR, reactive oxygen species, and TNF- through a CD44-dependent mechanism (20). In another study, human tumor-derived MV promote differentiation of CD14+ myeloid cells, resulting in an HLA-DR low phenotype lacking CD80 and CD86 expression, Nadolol and secreting TNF-, TGF, and IL-6, with suppressive effects on T cell proliferation (21). Less is known about potential immune stimulatory effects that macrophage-derived P2X7-induced MV may exert, which could involve IL-1. To address this question, we induced MV shedding from non-primed mouse primary macrophages or cell lines through P2X7activation and tested isolated MV for their ability to activate bone marrow derived macrophages (BMDM). We found that MV were able to activate BMDM in a partially TLR4-dependent manner and that the stimulatory component within the MV was found within phospholipid fractions. MV derived phospholipids activated macrophage through TLR4. Furthermore, MV induced activation is independent of observed loaded cargo such as IL-1, TNF-, and HMGB1. == Materials and Methods == == Cell culture and reagents == J774A.1 (TIB-67; ATCC; Manassas, VA), a murine macrophage cell line, and D2SC-1, a murine splenic.