December 3, 2012

Macrophages are our little Pac-Man cells that gobble up the nasty pathogens that we may come into contact with. They’re importance is undeniable, and the images of macrophages doing their thing are always fascinating to me. Today’s image is from a paper describing the role of the protein Bcl10 in the process. 

Phagocytosis is the process during which a cell engulfs cellular debris or pathogens. Macrophages employ phagocytosis to rid the body of infectious agents, cellular debris in the lung, and necrotic tissue throughout the body. Phagocytosis requires regulation of actin polymerization and dynamics for the extension and then closure of a phagocytic cup that engulfs the target material. A recent paper describes the role of the NF-κB signaling protein Bcl10 in actin and membrane remodeling in human macrophages. Marion and colleagues found that without Bcl10, phagocytosis begins but then stops with accumulated actin. Bcl10 regulates actin polymerization in cups, which allows the vesicle exocytosis that causes membrane extension of the phagocytic cup. In the images above, macrophages were incubated with red blood cells (red) to track phagocytosis 5 minutes (left column) and 10 minutes (right column) after the start of the assay. Control macrophages (top) are able to phagocytose red blood cells after a few minutes into the assay (arrows point to membrane deformations indicative of phagocytosed particles). Cells lacking Bcl10 (bottom), however, are not able to complete engulfment of the red blood cells, and have shorter and disorganized membrane extensions compared with control cells. 

Marion, S., Mazzolini, J., Herit, F., Bourdoncle, P., Kambou-Pene, N., Hailfinger, S., Sachse, M., Ruland, J., Benmerah, A., Echard, A., Thome, M., & Niedergang, F. (2012). The NF-κB Signaling Protein Bcl10 Regulates Actin Dynamics by Controlling AP1 and OCRL-Bearing Vesicles Developmental Cell, 23 (5), 954-967 DOI: 10.1016/j.devcel.2012.09.021
Copyright ©2012 Elsevier Ltd. All rights reserved.

January 6, 2011

Our immune system has many different types of specialized cells, and macrophages have to be my favorite. One look at our image today, and you’ll see why they are such amazing little workers.

Macrophages are white blood cells that engulf and ingest material as part of the immune response against pathogens. Macrophages have specialized receptors on their surface that identify the target and initiate the pathway leading to engulfment and ingestion. Past models have suggested that these receptors passively find and bind targets, but a recent paper shows that macrophages actively probe the extracellular environment for targets, especially when targets are sparse or moving quickly. In addition, this paper shows that these probing protrusions are actin-rich and are dependent on some known actin regulators. Images above are scanning electron micrographs of macrophages in the presence of beads that are treated to make them targets for macrophages. Protrusions are obvious in control cases (left and middle, arrows), but are absent in cases when actin is depolymerized by a drug called latrunculin B (right).

Flannagan, R., Harrison, R., Yip, C., Jaqaman, K., & Grinstein, S. (2010). Dynamic macrophage "probing" is required for the efficient capture of phagocytic targets originally published in The Journal of Cell Biology, 191 (6), 1205-1218 DOI: 10.1083/jcb.201007056

May 24, 2010

Phagocytosis is the process in which solid material is endocytosed in the cell. Investigators recently worked through the details of the involvement of the actin cytoskeleton, myosin, and actin-binding proteins in efficient phagocytosis. Actin-binding proteins are enriched in concentric rings at the furrow site where the phagosome eventually closes off, and image above shows the actin motors MyoK (green) and myosin II (red) at the furrow of the amoeba Dictyostelium engulfing budding yeast cells.

Reference: Régis Dieckmann, Yosuke von Heyden, Claudia Kistler, Navin Gopaldass, Stéphanie Hausherr, Scott William Crawley, Eva C. Schwarz, Ralph P. Diensthuber, Graham P. Côté, Georgios Tsiavaliaris, and Thierry Soldati. Authors’ Molecular Biology of the Cell paper can be found here.