The properties of microparticles from RAW 264.7 macrophage cells undergoing in vitro activation or apoptosis

Microparticles (MPs) are small, membrane-bound vesicles that arise from dead and dying cells, and display pro-inflammatory and pro-thrombotic activity. As shown previously, the RAW 264.7 murine macrophage cell line can release MPs following stimulation with LPS or polyinosinic:polycytidylic acid [poly (I:C)], ligands of TLR4 and TLR3 respectively. To determine the relationship of these MPs to those released during apoptosis, the nucleic acid content of MPs from cultures stimulated with LPS or poly (I:C) was compared with the nucleic acid content of MPs from untreated cells or cells induced to undergo apoptosis by treatment with etoposide or staurosporine (STS). As results of these studies showed, MPs from activated, apoptotic and untreated cells had features in common, as demonstrated by binding of the nucleic acid dyes SYTO 13 and propidium iodide; molecular mass of DNA; and binding of monoclonal anti-DNA and anti-nucleosome Abs. While MPs from the different culture conditions all contained ribosomal RNA, ribosomal RNA from MPs from STS-treated cells showed cleavage and degradation. Taken together, these studies indicate that the nucleic acid content of MPs from activated and apoptotic cells have important similarities, suggesting that events during TLR activation may lead to apoptosis and subsequent MP release.