Dysregulation of of phospholipid-specific phagocytosis by B1 B cells in diet-induced obese mice

B1 B cells have received increasing attention recently due to their newly discovered phagocytic and microbicidal capabilities. Several studies have demonstrated that B1 cells can phagocytize polystyrene fluorescent particles, bacteria (Staphylococcus aureus, Escherichia coli), and even apoptotic cells. Nevertheless, little is known about the biological significance of this seemingly redundant function of B1 B cells as compared to that of conventional phagocytes. Here we investigate the unique phosphotidylcholine (PtC)-specific B1 B cell phagocytosis. PtC is a major phospholipid in the biological membrane and a classical antigen recognized by B1 B cell-derived natural antibodies. These antibodies play important roles in immune defense as well as tissue homeostasis. Here we report that B1 cells preferentially phagocytose PtC-coated beads, differing from that of conventional macrophages. We further attest that these beads were truly internalized and subsequently fused with hydrolytic lysosomes indicated by increasing fluorescent intensity of a pH-sensitive dye. Despite the differences in antigen specificity, phagocytosis of both B1 cells and macrophages can be inhibited by the microtubule-inhibitor, Colchicine, in a dose-dependent manner. Most intriguingly, upon chronic high-fat diet (HFD) consumption by the host, B1 cell phagocytosis starts to lose antigen-specificity for PtC. Morphologically, some of these B1 B cells in DIO mice show enlarged cytosol and engulfed more beads, indicating a transition to macrophage-like cells. Our study suggests for the first time that B1 B cells have unique phospholipid-specific phagocytosis capacity, which is affected by diet-induced obesity

Porcine NK cells stimulate proliferation of pseudorabies virus-experienced CD8+ and CD4+ CD8+ T cells

Natural killer (NK) cells belong to the innate immune system and play a central role in the defense against viral infections and cancer development, but also contribute to shaping adaptive immune responses. NK cells are particularly important in the first line defense against herpesviruses, including alphaherpesviruses. In addition to their ability to kill target cells and produce interferon-g, porcine and human NK cell subsets have been reported to display features associated with professional antigen presenting cells (APC), although it is currently unclear whether NK cells may internalize debris of virus-infected cells and whether this APC-like activity of NK cells may stimulate proliferation of antiviral T cells. Here, using the porcine alphaherpesvirus pseudorabies virus (PRV), we show that vaccination of pigs with a live attenuated PRV vaccine strain triggers expression of MHC class II on porcine NK cells, that porcine NK cells can internalize debris from PRV-infected target cells, and that NK cells can stimulate proliferation of CD8(+) and CD4(+) CD8(+) PRV-experienced T cells. These results highlight the potential of targeting these NK cell features in future vaccination strategies

Expression of DC-SIGN and DC-SIGNR on human sinusoidal endothelium: a role for capturing hepatitis C virus particles.

Hepatic sinusoidal endothelial cells are unique among endothelial cells in their ability to internalize and process a diverse range of antigens. DC-SIGNR, a type 2 C-type lectin expressed on liver sinusoids, has been shown to bind with high affinity to hepatitis C virus (HCV) E2 glycoprotein. DC-SIGN is a closely related homologue reported to be expressed only on dendritic cells and a subset of macrophages and has similar binding affinity to HCV E2 glycoprotein. These receptors function as adhesion and antigen presentation molecules. We report distinct patterns of DC-SIGNR and DC-SIGN expression in human liver tissue and show for the first time that both C-type lectins are expressed on sinusoidal endothelial cells. We confirmed that these receptors are functional by demonstrating their ability to bind HCV E2 glycoproteins. Although these lectins on primary sinusoidal cells support HCV E2 binding, they are unable to support HCV entry. These data support a model where DC-SIGN and DC-SIGNR on sinusoidal endothelium provide a mechanism for high affinity binding of circulating HCV within the liver sinusoids allowing subsequent transfer of the virus to underlying hepatocytes, in a manner analogous to DC-SIGN presentation of human immunodeficiency virus on dendritic cells

Kidney surveillance in the spotlight: contrast-induced acute kidney injury illuminated

Acute kidney injury comprises a heterogeneous group of conditions characterized by a sudden decrease in renal function over hours to days. Contrast-induced acute kidney injury (CI-AKI) is caused by radiographic contrast agents used in diagnostic imaging. In the current issue of the JCI, Lau et al. use a mouse model of CI-AKI to study the role of resident and infiltrating phagocytes, recruited leukocytes, and tubular cells in the immune surveillance response to contrast agents. This study has the potential to provide innovative therapies for human CI-AKI

Photoacoustic Detection of Circulating Prostate, Breast and Pancreatic Cancer cells using targeted Gold Nanoparticles: Implications of Green Nanotechnology in Molecular Imaging

Nanoscience Poster SessionCirculating tumor cells are hallmarks of metastasis cancer. The presence of circulating tumor cells in blood stream correlates with the severity of disease. Photoacoustic imaging (PA) of tumor cells is an attractive technique for potential applications in diagnostic imaging of circulating tumor cells. However, the sensitivity of photoacoustic imaging of tumor cells depends on their photon absorption characteristics. In this context, gold nanoparticle embedded tumor cells offer significant advantages for diagnostic PA of single cells. As the PA absorptivity is directly proportional to the number of nanoparticles embedded within tumor cells, the propensity of nanoparticles to internalize within tumor cells will dictate the sensitivity for single cell detection. We are developing biocompatible gold nanoparticles to use them as probes as part of our ongoing effort toward the application of X ray CT Imaging, Ultra Sound (US) and photoacoustic imaging of circulating breast, pancreatic and prostate tumor cells. We, herein report our latest results which have shown that epigallocatechin gallate (EGCG)-conjugated gold nanoparticles (EGCG-AuNPs) internalize selectively within cancer cells providing threshold concentrations required for photo acoustic signals. In this presentation, we will describe, our recent results on the synthesis and characterization of EGCG gold nanoparticles, their cellular internalization and photo acoustic imaging of PC-3 prostate cancer cells and PANC-1 pancreatic cancer cells

ELMO1 has an essential role in the internalization of Salmonella Typhimurium into enteric macrophages that impacts disease outcome.

Backgrounds and aims4-6 million people die of enteric infections each year. After invading intestinal epithelial cells, enteric bacteria encounter phagocytes. However, little is known about how phagocytes internalize the bacteria to generate host responses. Previously, we have shown that BAI1 (Brain Angiogenesis Inhibitor 1) binds and internalizes Gram-negative bacteria through an ELMO1 (Engulfment and cell Motility protein 1)/Rac1-dependent mechanism. Here we delineate the role of ELMO1 in host inflammatory responses following enteric infection.MethodsELMO1-depleted murine macrophage cell lines, intestinal macrophages and ELMO1 deficient mice (total or myeloid-cell specific) was infected with Salmonella enterica serovar Typhimurium. The bacterial load, inflammatory cytokines and histopathology was evaluated in the ileum, cecum and spleen. The ELMO1 dependent host cytokines were detected by a cytokine array. ELMO1 mediated Rac1 activity was measured by pulldown assay.ResultsThe cytokine array showed reduced release of pro-inflammatory cytokines, including TNF-α and MCP-1, by ELMO1-depleted macrophages. Inhibition of ELMO1 expression in macrophages decreased Rac1 activation (~6 fold) and reduced internalization of Salmonella. ELMO1-dependent internalization was indispensable for TNF-α and MCP-1. Simultaneous inhibition of ELMO1 and Rac function virtually abrogated TNF-α responses to infection. Further, activation of NF-κB, ERK1/2 and p38 MAP kinases were impaired in ELMO1-depleted cells. Strikingly, bacterial internalization by intestinal macrophages was completely dependent on ELMO1. Salmonella infection of ELMO1-deficient mice resulted in a 90% reduction in bacterial burden and attenuated inflammatory responses in the ileum, spleen and cecum.ConclusionThese findings suggest a novel role for ELMO1 in facilitating intracellular bacterial sensing and the induction of inflammatory responses following infection with Salmonella

Vomocytosis: Too Much Booze, Base, or Calcium?

Macrophages are well known for their phagocytic activity and their role in innate immune responses. Macrophages eat non-self particles, via a variety of mechanisms, and typically break down internalized cargo into small macromolecules. However, some pathogenic agents have the ability to evade this endosomal degradation through a nonlytic exocytosis process termed vomocytosis. This phenomenon has been most often studied for Cryptococcus neoformans, a yeast that causes roughly 180,000 deaths per year, primarily in immunocompromised (e.g., human immunodeficiency virus [HIV]) patients. Existing dogma purports that vomocytosis involves distinctive cellular pathways and intracellular physicochemical cues in the host cell during phagosomal maturation. Moreover, it has been observed that the immunological state of the individual and macrophage phenotype affect vomocytosis outcomes. Here we compile the current knowledge on the factors (with respect to the phagocytic cell) that promote vomocytosis of C. neoformans from macrophages

Steric interactions between mobile ligands facilitate complete wrapping in passive endocytosis

Receptor-mediated endocytosis is an ubiquitous process through which cells internalize biological or synthetic nanoscale objects, including viruses, unicellular parasites, and nanomedical vectors for drug or gene delivery. In passive endocytosis the cell plasma membrane wraps around the "invader" particle driven by ligand-receptor complexation. By means of theory and numerical simulations, here we demonstrate how particles decorated by freely diffusing and non-mutually-interacting (ideal) ligands are significantly more difficult to wrap than those where ligands are either immobile or interact sterically with each other. Our model rationalizes the relationship between uptake mechanism and structural details of the invader, such as ligand size, mobility and ligand/receptor affinity, providing a comprehensive picture of pathogen endocytosis and helping the rational design of efficient drug delivery vectors.Comment: Updated version of the manuscript. Accepted for publication in PR