Endoplasmic reticulum and erythrophagocytosis.

<p>BMDM were incubated with mouse artificially aged erythrocytes (mRBC) for 15 (A) to 30 min (B–G) and were processed either for calnexin fluorescence labeling (A) or G6Pase activity for EM analysis (B–G). In A, engulfed erythrocytes were visualized by phase contrast (upper panel) or by hemoglobin autofluorescence at 520 nm (middle panel). Lower panel in A shows calnexin labeling around one phagosome containing a RBC (arrow and inset). The nuclear membrane (N) and the ER (intracellular staining) are specifically labeled for calnexin. (B) At the ultrastrutural level, some ingested mRBC phagosomes were negative for G6Pase. A dense area located around the membrane of the phagosome was clearly negative for any cellular structure and for G6Pase activity (see inset high magnification). This region likely corresponds to a network of actin filaments surrounding the phagosome and indicates the early nature of this phagosome. In C, some G6Pase positive patches are organized around and close to the membrane of the mRBC-containing phagosome (see inset). In most of mRBC-containing phagosomes, EM sections reveal intense G6Pase labeling that accumulates between the phagosomal membrane and the membrane of the ingested erythrocyte (D to F; see arrows in inset). Some erythrophagosomes present irregular shapes associated with appearance of intra-phagosomal electron-opaque particles that likely correspond to G6Pase precipitates that diffuse throughout the phagosome (F and G; see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0042199#s2" target="_blank">results</a> and <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0042199#s3" target="_blank">discussion</a>). In G (see inset), asterisks indicate vesicular compartments harboring strong G6Pase activity that may illustrate fragmentation of the erythrophagosome. The nuclear envelope (NE) and endoplasmic reticulum (ER) were specifically and strongly labeled.